Management of Supraventricular Tachycardias

118 question(s) with answers and explanations.

Question 1

A 42-year-old woman presents to the emergency department with sudden-onset palpitations and lightheadedness. Her blood pressure is 110/70 mmHg, and her heart rate is 170 beats per minute. A 12-lead electrocardiogram (ECG) demonstrates a regular rhythm with a QRS duration of 135 ms. Which of the following principles regarding the classification and presentation of her tachycardia is correct?

• ○ This rhythm is classified as a narrow QRS tachycardia because supraventricular rhythms fundamentally have a short conduction time.
• ○ The arrhythmia cannot be a supraventricular tachycardia (SVT) because the QRS duration exceeds 120 ms.
• ✓ This is classified as a wide QRS tachycardia, though a supraventricular tachycardia (SVT) may still present with this QRS duration.
• ○ This tachycardia is exclusively caused by abnormal automaticity arising within the native pacemaker cells of the atrioventricular node.

Explanation. A wide QRS tachycardia is defined by a QRS duration greater than 120 ms, and supraventricular tachycardias (SVTs) can clinically present as either narrow or wide QRS tachycardias.

Question 2

A 42-year-old female with a structurally normal heart is undergoing an electrophysiology study for recurrent episodes of narrow-complex tachycardia. Intracardiac mapping and pacing maneuvers demonstrate that the tachycardia is initiated by oscillations in the membrane potential occurring during the repolarization phase, specifically identified as early after-depolarizations. What is the fundamental electrophysiologic classification of this patient's arrhythmia?

• ✓ A non-re-entrant arrhythmia resulting from triggered activity
• ○ A re-entrant arrhythmia resulting from abnormal wavefront propagation
• ○ A non-re-entrant arrhythmia resulting from enhanced automaticity
• ○ A re-entrant arrhythmia dependent on the syncytial nature of myocardial tissue

Explanation. Early or delayed after-depolarizations are changes in the membrane potential that lead to arrhythmias characterized as triggered activity. Arrhythmias driven by triggered activity, along with those resulting from enhanced automaticity, are fundamentally classified as non-re-entrant mechanisms.

Question 3

A 35-year-old woman with no past medical history presents to the emergency department complaining of sudden-onset, rapid palpitations. An electrocardiogram (ECG) confirms a paroxysmal supraventricular tachycardia (SVT). She is diagnosed with lone paroxysmal SVT. Compared to SVT patients who have underlying cardiovascular disease, which of the following clinical characteristics is most likely to be observed in this patient?

• ✓ An earlier onset of symptoms and a faster SVT rate.
• ○ A later onset of symptoms and a slower SVT rate.
• ○ An older age at presentation and a slower SVT rate.
• ○ A later onset of symptoms and an initial presentation more commonly in an outpatient clinic.

Explanation. Patients with lone paroxysmal SVT, compared to those with underlying cardiovascular disease, tend to be younger, have a faster SVT rate, experience an earlier onset of symptoms, and are more likely to have their condition first documented in the emergency department.

Question 4

A 24-year-old male presents to the cardiology clinic with recurrent episodes of sudden-onset, rapid palpitations. A resting 12-lead electrocardiogram (ECG) reveals a short PR interval and a delta wave. He is referred for an electrophysiology study and potential catheter ablation for presumed atrioventricular reentrant tachycardia (AVRT). During a discussion regarding the epidemiology of his condition, which of the following characteristics best describes the demographic and age-related trends of AVRT?

• ✓ AVRT occurs predominantly in men, and its proportional frequency among supraventricular tachycardias (SVT) decreases with advancing age.
• ○ AVRT occurs predominantly in women, and its proportional frequency among supraventricular tachycardias (SVT) increases with advancing age.
• ○ AVRT occurs predominantly in men, and its proportional frequency among supraventricular tachycardias (SVT) increases with advancing age.
• ○ AVRT occurs predominantly in women, and its proportional frequency among supraventricular tachycardias (SVT) decreases with advancing age.

Explanation. Epidemiological data demonstrates that atrioventricular reentrant tachycardia (AVRT) predominantly affects men compared to women (in a roughly 55:45 ratio), and the overall proportion of patients who present with AVRT decreases as patient age increases.

Question 5

A 24-year-old woman is evaluated in the cardiology clinic following a successful radiofrequency catheter ablation for atrioventricular nodal re-entrant tachycardia (AVNRT). She had been previously managed with antiarrhythmic drugs but opted for ablation due to breakthrough symptoms. She inquires about the long-term success of the procedure and any demographic-specific risks. Which of the following statements is most accurate regarding her clinical course and prognosis?

• ✓ Recurrence rates following AVNRT ablation are higher in young women.
• ○ Women are less likely than men to be prescribed antiarrhythmic drugs prior to ablation for supraventricular tachycardia.
• ○ Women experience significantly less improvement in health-related quality of life after ablation compared to men.
• ○ The incidence of atrial flutter in women is more than 2.5 times higher than in men.

Explanation. Recurrence rates following atrioventricular nodal re-entrant tachycardia (AVNRT) ablation are higher in young women.

Question 6

A 34-year-old woman presents to the outpatient cardiology clinic with complaints of episodic, rapid palpitations that begin and terminate abruptly. She notes that these episodes first started when she was 14 years old and have occurred intermittently ever since. During a recent episode, a 12-lead electrocardiogram (ECG) demonstrated a regular narrow-complex tachycardia. Based on the chronicity and age of onset of her symptoms, what is the most likely primary electrophysiologic mechanism of her arrhythmia?

• ✓ A re-entrant mechanism
• ○ Enhanced automaticity within the atrial myocardium
• ○ Triggered activity from delayed afterdepolarizations
• ○ Rapid electrical firing from pulmonary vein foci

Explanation. An onset of supraventricular tachycardia symptoms in the teenage years or younger that continues into adulthood strongly points towards a re-entrant mechanism, as these individuals are less likely to have atrial tachycardia or atrial fibrillation.

Question 7

A 28-year-old female presents to the cardiology clinic reporting recurrent episodes of sudden-onset rapid heart rate. She mentions that during the episodes, she experiences a prominent "pounding in her neck" and has even noticed her shirt flapping in rhythm with her heartbeat. She previously attributed these episodes to panic attacks. The episodes typically last for 30 to 45 minutes before resolving abruptly. Based on this clinical presentation, what is the most likely cause of her symptoms?

• ○ Atrial tachycardia
• ✓ Atrioventricular nodal re-entrant tachycardia
• ○ Sinus tachycardia
• ○ Postural orthostatic tachycardia syndrome

Explanation. Clear descriptions of pounding in the neck (the so-called 'frog sign') or 'shirt flapping' point to the possible competing influences of atrial and ventricular contraction on the tricuspid valve, which makes atrioventricular nodal re-entrant tachycardia (AVNRT) the most likely cause of the patient's symptoms.

Question 8

A 34-year-old woman presents to the cardiology clinic reporting recurrent episodes of rapid palpitations over the past six months. She has not yet been able to have an electrocardiogram (ECG) recorded during an episode. She describes the palpitations as starting and stopping completely out of the blue, often triggered when she bends over to tie her shoes or pick up her child. She states that her heartbeat feels very fast but completely regular during the episodes. Recently, she discovered that chugging a large glass of ice-cold water sometimes abruptly stops the palpitations. Based on her clinical history, what is the most likely underlying mechanism of her arrhythmia?

• ✓ Re-entrant mechanism
• ○ Enhanced automaticity
• ○ Triggered activity
• ○ Parasystole

Explanation. In patients presenting with palpitations without electrocardiographic documentation, a sudden mode of onset and termination, an association with positional changes, the perception of a regular rhythm, and termination by vagal maneuvers or cold water ingestion are classic historical features that strongly point to a re-entrant mechanism for the arrhythmia.

Question 9

A 24-year-old male presents to the cardiology clinic complaining of sporadic, self-terminating episodes of rapid heartbeat associated with lightheadedness, typically occurring during physical exertion. His baseline 12-lead resting electrocardiogram (ECG) demonstrates a PR interval of 110 ms and a slurred upstroke of the QRS complex, consistent with apparent pre-excitation. His baseline echocardiogram is unremarkable. Which of the following tests would be particularly useful to further evaluate his condition?

• ✓ A tolerance exercise test
• ○ An implantable loop recorder
• ○ Myocardial perfusion imaging
• ○ 24-hour ambulatory ECG monitoring

Explanation. A tolerance exercise test is particularly useful in the evaluation of patients who demonstrate apparent pre-excitation on their baseline electrocardiogram, as well as in cases involving catecholamine-dependent arrhythmias.

Question 10

A 32-year-old woman with a history of sudden-onset, regular palpitations undergoes ambulatory electrocardiogram (ECG) monitoring. The recording captures the initiation of a regular narrow-complex tachycardia. The event is triggered by a premature atrial beat that is immediately followed by a sudden, marked prolongation of the PR interval just prior to the onset of the tachycardia. Which of the following is the most likely diagnosis?

• ✓ Typical atrioventricular nodal reentrant tachycardia (AVNRT)
• ○ Automatic focal atrial tachycardia
• ○ Atypical atrioventricular nodal reentrant tachycardia (AVNRT)
• ○ High septal ventricular tachycardia

Explanation. The initiation of tachycardia by an atrial ectopic beat followed by a sudden, marked prolongation of the PR interval is a characteristic hallmark of typical atrioventricular nodal reentrant tachycardia (AVNRT), differentiating it from other causes such as atrial tachycardia which do not depend on marked PR prolongation.

Question 11

A 28-year-old woman with a history of recurrent palpitations presents with a narrow-complex supraventricular tachycardia (SVT). She is referred for an electrophysiology study. During the induced tachycardia, continuous intracardiac recordings demonstrate spontaneous minor fluctuations in the cycle length (CL). Detailed analysis reveals that a change in the ventricular CL consistently precedes a change in the subsequent atrial CL. Based on these findings, which of the following is the most likely mechanism of the tachycardia?

• ✓ Typical atrioventricular nodal re-entrant tachycardia (AVNRT) or atrioventricular reciprocating tachycardia (AVRT)
• ○ Focal atrial tachycardia (AT) or atypical atrioventricular nodal re-entrant tachycardia (AVNRT)
• ○ Multifocal atrial tachycardia (MAT)
• ○ Atrial flutter with variable atrioventricular (AV) conduction

Explanation. During a supraventricular tachycardia, analyzing the sequence of cycle length variations helps differentiate the underlying electrophysiological mechanism. A spontaneous change in the ventricular cycle length that precedes a change in the subsequent atrial cycle length indicates that the variation originates within the atrioventricular node or the ventricle prior to affecting retrograde conduction, which characterizes and favors a diagnosis of typical atrioventricular nodal re-entrant tachycardia (AVNRT) or atrioventricular reciprocating tachycardia (AVRT).

Question 12

A 42-year-old woman presents to the emergency department with sudden-onset palpitations. A 12-lead surface electrocardiogram (ECG) demonstrates a regular narrow-complex tachycardia at 165 beats per minute. Initial evaluation of the P/QRS relationship suggests a long-RP tachycardia. However, a subsequent electrophysiology study confirms the diagnosis of typical atrioventricular nodal re-entrant tachycardia (AVNRT), which typically presents as a short-RP tachycardia. Which of the following surface ECG findings most likely simulated the appearance of a long-RP tachycardia in this patient?

• ✓ Prominent U waves
• ○ T wave alternans
• ○ Rate-dependent right bundle branch block
• ○ Non-specific ST-segment depression

Explanation. Rarely, the recording of prominent U waves during typical atrioventricular nodal re-entrant tachycardia (AVNRT) may simulate a long-RP tachycardia on the surface ECG, which can lead to an initial misinterpretation of the tachycardia mechanism.

Question 13

A 62-year-old male presents to the emergency department complaining of sudden-onset palpitations. An electrocardiogram (ECG) demonstrates a narrow complex tachycardia with a ventricular rate of 150 beats per minute. Closer inspection of the baseline reveals an atrial activity rate of 300 beats per minute, consistent with atrial flutter with 2:1 conduction. An intravenous antiarrhythmic medication is administered to target the atrial arrhythmia; however, no atrioventricular (AV) nodal blocking agent is given. Shortly after administration, the patient's atrial rate decreases to 220 beats per minute, but his ventricular rate paradoxically increases to 220 beats per minute. Which of the following best explains this observed increase in the ventricular rate?

• ✓ Lowering the atrial rate facilitated 1:1 atrioventricular conduction due to the absence of concurrent AV nodal blockade.
• ○ The antiarrhythmic medication triggered a focal atrial tachycardia arising close to the sinus node.
• ○ The medication altered the P wave morphology, causing a shift to a sinus nodal re-entrant tachycardia.
• ○ The antiarrhythmic medication caused a direct positive dromotropic effect on the His-Purkinje system.

Explanation. In the setting of an organized atrial tachyarrhythmia such as atrial flutter, the use of an antiarrhythmic medication that lowers the atrial rate allows the atrioventricular (AV) node more time to recover between impulses. This slowing of the atrial rate permits the AV node to conduct every impulse (a 1:1 conduction ratio), which paradoxically results in a significantly higher ventricular rate when there is an absence of concurrent AV nodal blockade.

Question 14

A 40-year-old woman presents to the emergency department with sudden-onset palpitations. Her electrocardiogram (ECG) reveals a regular narrow-complex tachycardia at 165 beats per minute. Relatively delayed retrograde conduction allows for the identification of retrograde P waves. Which of the following ECG findings has the greatest sensitivity and specificity for diagnosing typical atrioventricular nodal re-entrant tachycardia (AVNRT) in this patient?

• ○ A pseudo r wave in lead V1
• ✓ A pseudo r wave in lead aVR
• ○ A pseudo S wave in the anterior leads
• ○ A difference in RP intervals in leads V1 and III of 10 ms

Explanation. A pseudo r wave in lead aVR has greater sensitivity and specificity than a pseudo r wave in lead V1 for the diagnosis of typical atrioventricular nodal re-entrant tachycardia.

Question 15

A 42-year-old woman presents to the emergency department complaining of sudden-onset palpitations. An electrocardiogram (ECG) reveals a regular narrow QRS tachycardia at 165 beats per minute. Carotid sinus massage is attempted, resulting in transient atrioventricular (AV) block. The continuous ECG recording during the block reveals independent and dissociated P waves that continue at the rapid tachycardia rate, while the ventricular rate temporarily slows. Based on this electrophysiologic finding, which of the following arrhythmias is definitively ruled out?

• ✓ Atrioventricular re-entrant tachycardia (AVRT)
• ○ Focal atrial tachycardia (AT)
• ○ Atrial flutter
• ○ Atrioventricular nodal re-entrant tachycardia (AVNRT)

Explanation. The occurrence of atrioventricular (AV) block or dissociation during a narrow QRS tachycardia definitively rules out atrioventricular re-entrant tachycardia (AVRT) because both the atria and the ventricles are obligate, integral components of the anatomical re-entry circuit.

Question 16

A 35-year-old woman presents to the emergency department with sudden-onset palpitations and lightheadedness. Her electrocardiogram (ECG) shows a regular narrow-complex tachycardia at 170 beats per minute, but the relationship of P waves to QRS complexes is unclear. Vagal maneuvers are attempted without effect. Following a rapid intravenous bolus of adenosine, the tachycardia abruptly terminates. The rhythm strip demonstrates that the arrhythmia ends with a P wave following the last QRS complex before normal sinus rhythm resumes. Which of the following is the most likely diagnosis?

• ✓ Atrioventricular re-entrant tachycardia (AVRT) or typical atrioventricular nodal re-entrant tachycardia (AVNRT)
• ○ Focal atrial tachycardia (AT)
• ○ Macro-re-entrant atrial tachycardia (MRAT)
• ○ Atypical atrioventricular nodal re-entrant tachycardia (AVNRT)

Explanation. Termination of the arrhythmia with a P wave after the last QRS complex following adenosine administration is most common in atrioventricular re-entrant tachycardia (AVRT) and typical atrioventricular nodal re-entrant tachycardia (AVNRT). In contrast, termination with a QRS complex is often seen in atrial tachycardia and possibly in atypical AVNRT. Macro-re-entrant atrial tachycardias are generally not interrupted by adenosine.

Question 17

A 62-year-old man presents to the emergency department with palpitations and lightheadedness. An electrocardiogram (ECG) demonstrates a regular wide QRS tachycardia at 175 beats per minute. Blood pressure is 110/70 mmHg. The physician evaluates the differential diagnosis, which includes ventricular tachycardia (VT) and supraventricular tachycardia (SVT) with aberrancy. Based on standard clinical principles for evaluating a wide complex tachycardia, what should be the default presumed diagnosis, and if this arrhythmia is actually SVT with phase 3 aberrancy, what is the most likely bundle branch block morphology and its underlying physiological mechanism?

• ✓ Default diagnosis: VT. Morphology: Right bundle branch block (RBBB), due to the longer refractory period of the right bundle branch.
• ○ Default diagnosis: VT. Morphology: Left bundle branch block (LBBB), due to the use-dependent slowing of conduction in the His-Purkinje tissue.
• ○ Default diagnosis: SVT. Morphology: Right bundle branch block (RBBB), due to the shorter refractory period of the right bundle branch.
• ○ Default diagnosis: SVT. Morphology: Left bundle branch block (LBBB), due to pre-existing antegrade conduction over an accessory pathway.

Explanation. The default diagnosis for any wide QRS tachycardia must be ventricular tachycardia (VT) until proven otherwise, because misdiagnosing VT and administering medications typically utilized for supraventricular tachycardia (SVT) can be clinically harmful. When an SVT conducts with aberration due to the development of a rate-dependent (phase 3) block, it most commonly exhibits a right bundle branch block (RBBB) pattern. This occurs physiologically because the right bundle branch inherently possesses a longer refractory period, making it more susceptible to conduction block at rapid heart rates.

Question 18

A 72-year-old female presents to the emergency department with palpitations and mild shortness of breath. Her electrocardiogram (ECG) reveals a wide QRS complex tachycardia at a rate of 160 beats per minute. The P waves are obscured by the wide QRS and T waves on the standard leads. A modified chest lead placement (Lewis lead) is applied, which reveals an atrial rate of 80 beats per minute completely independent of the ventricular rhythm. Additionally, occasional narrower QRS complexes are seen occurring slightly earlier than the next expected wide complex. What is the most likely diagnosis?

• ✓ Ventricular tachycardia
• ○ Atrioventricular nodal reentrant tachycardia with aberrant conduction
• ○ Atrial flutter with 2:1 atrioventricular conduction
• ○ Antidromic atrioventricular reentrant tachycardia

Explanation. The presence of atrioventricular (AV) dissociation, demonstrated by an independent atrial rate that is slower than the ventricular rate, along with capture or fusion beats (occasional narrower QRS complexes occurring early), are key diagnostic features of ventricular tachycardia.

Question 19

A 65-year-old man with a history of a prior myocardial infarction presents to the emergency department with palpitations and mild dyspnea. He is hemodynamically stable. A 12-lead electrocardiogram (ECG) demonstrates a regular, wide-complex tachycardia at a rate of 170 beats per minute. Which of the following electrocardiographic features would be most diagnostic of ventricular tachycardia (VT) over supraventricular tachycardia (SVT) with aberrancy in this patient?

• ○ A frontal plane QRS axis of -30 degrees
• ○ Positive QRS complexes in all precordial leads from V1 to V6
• ✓ Negative QRS complexes in all precordial leads from V1 to V6
• ○ A QRS duration of 150 ms with a left bundle branch block (LBBB) morphology

Explanation. The presence of negative chest lead concordance, meaning all QRS complexes are completely negative in leads V1 through V6, is almost completely diagnostic of ventricular tachycardia with a specificity greater than 90 percent.

Question 20

A 38-year-old male presents to the emergency department complaining of sudden-onset palpitations. His heart rate is 165 beats per minute, and his blood pressure is 115/75 mmHg. A 12-lead electrocardiogram (ECG) reveals a wide complex tachycardia with a right bundle branch block (RBBB) and left anterior hemiblock morphology. The treating physician is attempting to differentiate between fascicular ventricular tachycardia (VT) and supraventricular tachycardia (SVT) with bifascicular block. Which of the following specific ECG features most strongly suggests that this rhythm is an SVT with bifascicular block?

• ✓ QRS duration greater than 140 ms
• ○ An R:S ratio of less than 1 in lead V6
• ○ A double-peaked R wave in lead V1 with a taller left peak
• ○ A monophasic R wave in lead V1

Explanation. Differentiating fascicular ventricular tachycardia from supraventricular tachycardia with bifascicular block (right bundle branch block and left anterior hemiblock) is highly challenging. In this specific morphological context, an electrocardiographic QRS duration greater than 140 ms, alongside an overall negative QRS complex in lead aVR and an R:S ratio greater than 1 in lead V6, uniquely indicates a supraventricular tachycardia rather than a fascicular ventricular tachycardia.

Question 21

A 62-year-old male with a history of ischemic heart disease presents to the emergency department complaining of sudden-onset palpitations. His heart rate is 170 beats per minute, and his blood pressure is 110/70 mmHg. A 12-lead electrocardiogram (ECG) demonstrates a wide QRS complex tachycardia with a left bundle branch block (LBBB) morphology. When differentiating between ventricular tachycardia (VT) and supraventricular tachycardia (SVT) with aberrant conduction, which of the following findings in lead V6 most strongly supports a diagnosis of VT?

• ✓ The presence of any Q or QS wave
• ○ A narrow, monophasic R wave
• ○ An R/S ratio greater than 1
• ○ The absence of any Q wave

Explanation. In true LBBB resulting from aberrant conduction, no Q wave is present in the lateral precordial leads. Consequently, the presence of any Q or QS wave in lead V6 favors ventricular tachycardia, indicating that the ventricular activation wavefront is moving away from the left ventricular apical site.

Question 22

A 32-year-old male presents to the emergency department complaining of sudden-onset palpitations. A 12-lead electrocardiogram (ECG) reveals a regular, wide QRS complex tachycardia at 190 beats per minute. The treating physician attempts to apply standard morphological criteria to differentiate the rhythm. The arrhythmia is noted to be extremely difficult to distinguish from a ventricular tachycardia (VT) because its ventricular activation directly mimics a VT originating at the insertion site of an accessory pathway in the ventricular myocardium. Which of the following arrhythmias is most likely present?

• ✓ Antidromic atrioventricular re-entrant tachycardia (AVRT)
• ○ Orthodromic atrioventricular re-entrant tachycardia (AVRT) with a pre-existing bundle branch block
• ○ Typical atrioventricular nodal re-entrant tachycardia (AVNRT) with aberrant conduction
• ○ Atrial flutter with 2:1 conduction and rate-related aberrancy

Explanation. In antidromic atrioventricular re-entrant tachycardia (AVRT), antegrade conduction occurs down an accessory pathway directly into the ventricular myocardium. This creates a QRS morphology that is fundamentally similar to a ventricular tachycardia originating at that precise insertion point, making the morphological differentiation between antidromic AVRT and ventricular tachycardia extremely difficult.

Question 23

A 34-year-old man with no known structural heart disease presents to the emergency department with palpitations. A 12-lead electrocardiogram (ECG) demonstrates a regular, wide QRS tachycardia. The attending physician attempts to use conventional ECG algorithms to differentiate ventricular tachycardia (VT) from supraventricular tachycardia (SVT) with aberrancy, but the morphological criteria are equivocal. Subsequent electrophysiology study confirms an idiopathic VT. Conventional ECG criteria are known to have reduced sensitivity for distinguishing VT from SVT with aberrancy when the VT originates from which of the following specific anatomic regions?

• ○ Right ventricular anterior free wall
• ✓ Septal Purkinje network and septal outflow tract
• ○ Left ventricular lateral wall
• ○ Left ventricular apical region

Explanation. Conventional electrocardiogram (ECG) criteria have reduced sensitivity to distinguish ventricular tachycardia (VT) from supraventricular tachycardia (SVT) with aberrancy in patients with idiopathic VT. This limitation is most pronounced in VTs originating from septal sites, particularly Purkinje sites and the septal outflow tract regions, often necessitating an electrophysiology study for definitive diagnosis.

Question 24

A 24-year-old man presents to the emergency department with acute onset of severe palpitations, chest fluttering, and lightheadedness. His electrocardiogram demonstrates an irregular, wide QRS complex tachycardia with a ventricular rate of 220 beats per minute. Analysis of the rhythm strip shows beat-to-beat variation in the QRS morphology and varying widths of the delta wave. Which of the following best explains the mechanism behind the changing QRS morphology in this patient?

• ○ Intermittent rate-related bundle branch block alternating with normal His-Purkinje conduction
• ✓ Varying degrees of fusion due to activation over both the accessory pathway and the atrioventricular node
• ○ Progressive fatigue of the accessory pathway leading to intermittent antegrade block
• ○ Fluctuating vagal tone causing intermittent delay in the atrioventricular node without affecting the accessory pathway

Explanation. Pre-excited atrial fibrillation typically manifests with an irregular rhythm, a rapid ventricular rate, and a varying QRS morphology. This changing QRS morphology results from varying degrees of electrical fusion due to simultaneous ventricular activation over both the accessory pathway and the atrioventricular node, which directly causes the observed variation in the width of the delta wave.

Question 25

A 34-year-old man presents to the emergency department complaining of a rapid, fluttering heartbeat that started abruptly 30 minutes ago while he was resting. He is hemodynamically stable, awake, and alert, with a blood pressure of 122/78 mmHg and a heart rate of 170 bpm. His 12-lead electrocardiogram (ECG) demonstrates a regular, narrow QRS complex supraventricular tachycardia. The physician decides to initiate non-pharmacologic treatment using the Valsalva maneuver. Based on the expected efficacy of this intervention, in which of the following specific patient profiles is the Valsalva maneuver generally shown to be most effective?

• ✓ Adults with atrioventricular re-entrant tachycardia (AVRT)
• ○ Adults with atrioventricular nodal re-entrant tachycardia (AVNRT)
• ○ Children with atrioventricular re-entrant tachycardia (AVRT)
• ○ Children with atrioventricular nodal re-entrant tachycardia (AVNRT)

Explanation. The Valsalva maneuver stimulates receptors that cause reflex activation of the vagus nerve, resulting in acetylcholine release which slows electrical conduction through the atrioventricular node. When utilized as a first-line treatment to terminate narrow QRS supraventricular tachycardia, this maneuver has generally been shown to be most effective in adult patients, and specifically in those with atrioventricular re-entrant tachycardia (AVRT) rather than atrioventricular nodal re-entrant tachycardia (AVNRT).

Question 26

A 38-year-old woman presents to the emergency department with sudden-onset palpitations. Her electrocardiogram (ECG) demonstrates a regular, narrow-complex tachycardia at 180 beats per minute. She is hemodynamically stable. The physician decides to attempt a vagal maneuver using a standardized approach by having her blow into a 10 mL syringe with sufficient force to move the plunger. Which of the following describes the most effective positioning sequence for performing this modified maneuver to maximize conversion success?

• ✓ The patient performs the strain while semi-recumbent, followed immediately by supine repositioning and a passive leg raise.
• ○ The patient performs the strain while supine, followed immediately by sitting upright and taking a deep breath.
• ○ The patient performs the strain while seated, followed immediately by standing and performing active leg flexion.
• ○ The patient performs the strain while in the Trendelenburg position, followed immediately by sitting upright.

Explanation. The modified approach to the Valsalva maneuver significantly enhances arrhythmia conversion success rates. This technique requires the Valsalva strain to be completed in a semi-recumbent position, followed immediately by supine repositioning and a passive leg raise.

Question 27

A 34-year-old male presents to the emergency department with sudden-onset palpitations. An electrocardiogram (ECG) reveals a regular narrow-complex tachycardia at 170 beats per minute. Vagal maneuvers are attempted but fail to terminate the arrhythmia. The physician orders a medication that is known to be metabolized via enzymatic deamination to inactive inosine in seconds. Which of the following represents the most appropriate administration technique and dosing schedule for this medication?

• ✓ 6 mg via rapid intravenous bolus into an antecubital vein with an immediate saline flush, followed by 12 mg after 1 minute if unsuccessful.
• ○ 6 mg via slow intravenous push into a distal forearm vein to minimize flushing, followed by 12 mg after 3 minutes if unsuccessful.
• ○ 12 mg via rapid intravenous bolus into an antecubital vein with an immediate saline flush, followed by 18 mg after 5 minutes if unsuccessful.
• ○ 6 mg via rapid intravenous bolus into a distal hand vein with an immediate saline flush, followed by 6 mg after 1 minute if unsuccessful.

Explanation. Adenosine requires injection as a rapid bolus accompanied by an immediate saline flush to achieve efficient rhythm correction. Large, centrally located veins, such as the antecubital vein, deliver more effective drug concentrations to the heart than smaller distal veins. The appropriate incremental dosing sequence starts with 6 mg in adults, followed by 12 mg. Because the drug has a very short plasma half-life of seconds due to enzymatic deamination, repeat administration is safe within 1 minute of the last dose.

Question 28

A 32-year-old male with a history of Wolff-Parkinson-White syndrome presents to the emergency department with palpitations. An electrocardiogram (ECG) demonstrates a regular, narrow-complex tachycardia, which is diagnosed as an orthodromic atrioventricular reciprocating tachycardia (AVRT). Vagal maneuvers are ineffective, and a rapid intravenous bolus of adenosine is administered. The tachycardia terminates, but the patient immediately develops atrial fibrillation (AF). Which of the following mechanisms best explains the development of AF following the administration of this medication?

• ✓ Direct pulmonary vein triggering or increasing heterogeneity of atrial repolarization
• ○ Reflex sympathetic activation secondary to profound systemic vasodilation
• ○ Paradoxical enhancement of sinoatrial node automaticity
• ○ Homogeneous shortening of the effective refractory period across the atrial myocardium

Explanation. Adenosine administration can precipitate atrial fibrillation through direct triggering of ectopic activity from the pulmonary veins or by increasing the heterogeneity of repolarization within the atrial tissue.

Question 29

A 32-year-old female presents to the emergency department complaining of sudden-onset palpitations. Her heart rate is 175 beats per minute, and her electrocardiogram (ECG) shows a regular, narrow-complex tachycardia consistent with supraventricular tachycardia (SVT). Her blood pressure is 115/75 mmHg. Vagal maneuvers fail to terminate the arrhythmia. Her medical history is significant for severe asthma requiring frequent hospitalizations and oral corticosteroids. Which of the following is the most appropriate pharmacological choice for the acute termination of her arrhythmia?

• ✓ Intravenous verapamil
• ○ Intravenous adenosine
• ○ Intravenous adenosine triphosphate
• ○ Inhaled adenosine

Explanation. Intravenous verapamil is the most appropriate choice for the acute termination of supraventricular tachycardia in a patient with severe asthma. Although intravenous adenosine is generally safe and only rarely associated with clinically important bronchoconstriction, isolated reports of bronchoconstriction dictate that verapamil is a more appropriate alternative specifically in patients with severe asthma.

Question 30

A 60-year-old man presents to the emergency department with palpitations. His heart rate is 165 bpm, and his blood pressure is 115/75 mmHg. A 12-lead electrocardiogram (ECG) reveals a regular narrow-complex tachycardia, consistent with supraventricular tachycardia (SVT). His medical history is significant for ischemic cardiomyopathy with a recent echocardiogram showing a left ventricular ejection fraction (LVEF) of 35%. He is currently euvolemic, breathing comfortably on room air, and has no signs of clinical heart failure decompensation. Which of the following intravenous medications should be explicitly avoided in the acute management of this patient's arrhythmia?

• ✓ Intravenous diltiazem
• ○ Intravenous esmolol
• ○ Intravenous metoprolol
• ○ Intravenous digoxin

Explanation. Intravenous non-dihydropyridine calcium channel blockers, such as diltiazem and verapamil, should be avoided in patients presenting with supraventricular tachycardia who have heart failure with a reduced left ventricular ejection fraction (<40%). Beta-blockers (such as esmolol and metoprolol) are contraindicated in decompensated heart failure, but they maintain an excellent safety profile in hemodynamically stable and compensated patients.

Question 31

A 68-year-old male is brought to the emergency department reporting severe palpitations and chest pain that started 45 minutes ago. On physical examination, he is extensively diaphoretic, lethargic, and demonstrates acutely altered mental status. His vital signs show a blood pressure of 82/50 mmHg and a heart rate of 175 beats per minute. A 12-lead electrocardiogram (ECG) reveals a persistent wide QRS tachycardia. What is the most appropriate initial management for this patient?

• ○ Administer intravenous adenosine rapidly
• ✓ Perform immediate synchronized direct current (DC) cardioversion
• ○ Attempt carotid sinus massage or other vagal manoeuvres
• ○ Administer intravenous amiodarone over 10 minutes

Explanation. Synchronized cardioversion is the recommended acute management for any persistent wide QRS tachycardia that results in haemodynamic instability, which manifests as hypotension, acutely altered mental status, chest pain, acute heart failure symptoms, or signs of shock.

Question 32

A 62-year-old man presents to the emergency department with a 1-hour history of palpitations. His blood pressure is 125/80 mmHg, heart rate is 165 beats per minute, and he is fully alert. A prior echocardiogram showed a left ventricular (LV) ejection fraction of 45%. A 12-lead electrocardiogram (ECG) demonstrates a regular wide QRS-complex tachycardia of unknown etiology. The decision is made to pursue pharmacological termination. Which of the following intravenous medications is associated with the highest proportion of tachycardia termination within 40 minutes and the fewest major cardiac adverse events in this clinical scenario?

• ✓ Intravenous procainamide
• ○ Intravenous amiodarone
• ○ Intravenous verapamil
• ○ Intravenous adenosine

Explanation. In patients presenting with a well-tolerated wide QRS-complex tachycardia of unknown etiology, with or without a reduced left ventricular ejection fraction, intravenous procainamide is associated with fewer major cardiac adverse events and a higher proportion of tachycardia termination within 40 minutes compared with amiodarone.

Question 33

A 28-year-old male with a known history of pre-excitation presents to the emergency department with severe palpitations, dizziness, and confusion. Vital signs reveal a blood pressure of 75/40 mmHg and a heart rate of 210 b.p.m. His 12-lead electrocardiogram (ECG) shows a wide QRS-complex irregular tachycardia. What is the most appropriate acute treatment for this patient?

• ✓ Electrical cardioversion
• ○ Intravenous amiodarone
• ○ Intravenous adenosine
• ○ Intravenous beta-blocker

Explanation. Electrical cardioversion is the acute treatment of choice in irregular pre-excited tachycardias associated with haemodynamic instability.

Question 34

A 26-year-old female presents to the cardiology clinic complaining of persistent palpitations even when resting. She reports no significant past medical history and does not use any medications or illicit substances. Her vital signs reveal a resting heart rate of 115 beats per minute (b.p.m.) and a blood pressure of 110/70 mmHg. A 12-lead electrocardiogram (ECG) shows sinus tachycardia. Comprehensive laboratory workup, including thyroid function tests and a complete blood count, is normal. A 24-hour Holter monitor reveals an average heart rate of 108 b.p.m. with sinus rhythm throughout. She is diagnosed with inappropriate sinus tachycardia (IST). What should the physician advise the patient regarding the long-term prognosis of her condition?

• ✓ The condition is generally benign and has not been associated with tachycardia-induced cardiomyopathy.
• ○ The condition is progressive and frequently leads to tachycardia-induced cardiomyopathy if left untreated.
• ○ She is at high risk for developing sick sinus syndrome and will likely require pacemaker implantation.
• ○ The condition carries a high risk of ventricular arrhythmias due to underlying neurohormonal dysregulation.

Explanation. Inappropriate sinus tachycardia is generally considered to have a benign prognosis and the arrhythmia has not been associated with the development of tachycardia-induced cardiomyopathy.

Question 35

A 32-year-old female presents to the cardiology clinic with a 6-month history of bothersome palpitations, mild dyspnoea, and significant exercise intolerance. Her past medical history is unremarkable, and she takes no medications. Physical examination, echocardiography, and laboratory tests including thyroid function are all within normal limits. Her resting electrocardiogram (ECG) shows normal sinus rhythm at 105 beats per minute (b.p.m.). A 24-hour Holter monitor is performed to evaluate her symptoms. Which of the following Holter monitor findings is most characteristic of inappropriate sinus tachycardia (IST)?

• ✓ A mean heart rate >90 b.p.m. with an exaggerated heart rate response >100 b.p.m. during waking hours
• ○ A mean heart rate >100 b.p.m. over 24 hours with frequent episodes of sudden onset and offset of tachycardia
• ○ A mean heart rate >80 b.p.m. with a blunted heart rate response to minimal exertion
• ○ A sustained increase in heart rate of >30 b.p.m. occurring exclusively upon standing from a supine position

Explanation. The diagnosis of inappropriate sinus tachycardia (IST) is a diagnosis of exclusion that typically presents with palpitations, dyspnoea, and exercise intolerance. Characteristically, 24-hour Holter monitoring in patients with IST demonstrates a mean heart rate >90 b.p.m. with an exaggerated heart rate response >100 b.p.m. during waking hours.

Question 36

A 32-year-old female with no structural heart disease complains of chronic, disabling palpitations. Her resting heart rate is consistently between 105 and 115 beats per minute (bpm). A 24-hour Holter monitor demonstrates an average heart rate of 110 bpm, entirely in sinus rhythm, without other arrhythmias. Her thyroid function and blood counts are normal. She has already attempted rigorous volume expansion, exercise training, and complete avoidance of cardiac stimulants, but her symptoms persist. The physician considers starting ivabradine for inappropriate sinus tachycardia. What is the most appropriate strategy regarding the initiation of this medication?

• ○ Prescribe ivabradine as monotherapy to prevent the excessive hypotension frequently seen with non-dihydropyridine calcium channel blockers.
• ✓ Co-administer ivabradine with a beta-blocker to counteract a potential reflex increase in sympathetic activity to the heart.
• ○ Avoid ivabradine entirely and proceed directly to radiofrequency ablation of the sinoatrial node.
• ○ Recommend a strict fluid restriction protocol before initiating ivabradine to maximize the drug's efficacy.

Explanation. Blockade of the 'pacemaker current' (If) by ivabradine can perturb the feedback loop underlying baroreceptor control of autonomic balance, potentially leading to increased sympathetic activity to the heart. To mitigate this effect and potentially achieve greater symptom reduction than with either drug alone, ivabradine should preferably be co-administered with a beta-blocker when treating inappropriate sinus tachycardia.

Question 37

A 16-year-old female presents to the cardiology clinic complaining of frequent dizziness, palpitations, and lightheadedness that occur primarily when she stands up from a seated or supine position. These symptoms have been present for the past six months and significantly interfere with her ability to attend school. To evaluate for Postural Orthostatic Tachycardia Syndrome (POTS), a standing test is performed. Which of the following hemodynamic responses would establish the diagnosis of POTS in this specific patient?

• ✓ An increase in heart rate of >40 beats per minute when standing, without a >20 mmHg decrease in systolic blood pressure.
• ○ An increase in heart rate of >30 beats per minute when standing, without a >20 mmHg decrease in systolic blood pressure.
• ○ An increase in heart rate of >30 beats per minute when standing, accompanied by a >20 mmHg decrease in systolic blood pressure.
• ○ An increase in heart rate of >40 beats per minute when standing, accompanied by a >20 mmHg decrease in systolic blood pressure.

Explanation. Postural Orthostatic Tachycardia Syndrome (POTS) is clinically defined by an increase in heart rate of >40 beats per minute when standing for >30 seconds in individuals aged 12 to 19 years, strictly in the absence of orthostatic hypotension (which is defined as a >20 mmHg drop in systolic blood pressure).

Question 38

A 24-year-old woman presents with debilitating palpitations, lightheadedness, and fatigue that occur primarily when she stands up from a seated or supine position. These symptoms have been present for 8 months. During a 10-minute active stand test, her heart rate increases from 72 beats per minute (bpm) to 118 bpm without a significant change in blood pressure. Workup including complete blood count, thyroid function tests, and plasma free metanephrines is unremarkable. She is not taking any medications. In addition to recommending increased fluid and salt intake and the use of compression garments, which of the following exercise strategies is most appropriate as an initial intervention?

• ✓ Supervised aerobic reconditioning restricted initially to non-upright exercises like swimming or rowing.
• ○ Unsupervised, progressive upright aerobic exercise such as brisk walking and jogging.
• ○ Vigorous resistance training focusing predominantly on the upper body and core musculature.
• ○ Complete avoidance of exercise to prevent exacerbation of orthostatic tachycardia and fatigue.

Explanation. Initial management for postural orthostatic tachycardia syndrome (POTS) involves non-pharmacological treatments. Patients should engage in a regular, graduated, and supervised exercise program featuring aerobic reconditioning and thigh resistance training. To minimize orthostatic stress on the heart, exercise should initially be restricted to non-upright activities, such as using a rowing machine or swimming.

Question 39

A 26-year-old female with a history of Postural Orthostatic Tachycardia Syndrome (POTS) presents for follow-up. She continues to experience bothersome palpitations and lightheadedness upon standing, despite adhering to lifestyle modifications, including increasing her water intake to 3 liters per day and dietary salt intake to 12 grams per day. Her physician decides to initiate pharmacological therapy to improve her symptoms. Which of the following is the most appropriate treatment strategy for this patient?

• ○ High-dose selective beta-blocker to maximize heart rate reduction
• ✓ Low-dose non-selective beta-blocker
• ○ Long-acting propranolol to improve long-term quality of life
• ○ Midodrine administered three times daily, including a dose at bedtime

Explanation. Low-dose non-selective beta-blockers acutely lower standing heart rate and improve symptoms in patients with Postural Orthostatic Tachycardia Syndrome. Non-selective agents are preferred because they provide the additional benefit of blocking epinephrine-mediated beta-2-vasodilation.

Question 40

A 42-year-old man presents with palpitations, shortness of breath, and rare episodes of presyncope. Electrocardiography (ECG) reveals an organized atrial rhythm at 130 beats per minute spreading in a centrifugal pattern over both atria, with dynamic recurrent interruptions and reinitiations. During an electrophysiology study, the arrhythmia is mapped to the pulmonary veins. Where is the arrhythmogenic focus most likely located?

• ✓ At the ostium of the vein or within 1 cm of the designated ostium
• ○ Further distally, approximately 2 to 4 cm into the pulmonary vein
• ○ Deep within the coronary sinus musculature
• ○ At the mid-segment of the superior vena cava

Explanation. In patients with pulmonary vein-related focal atrial tachycardia, the arrhythmogenic focus is characteristically located directly at the ostium of the vein or within 1 cm of the designated ostium.

Question 41

A 42-year-old woman with a structurally normal heart and no history of cardiac surgery presents to the emergency department with sudden-onset palpitations. A 12-lead electrocardiogram (ECG) reveals a regular narrow complex tachycardia. Administration of intravenous adenosine produces transient atrioventricular (AV) block, unmasking monomorphic P waves with a stable cycle length and discrete isoelectric intervals. The P waves are observed to be negative in leads I and aVL, and positive in lead V1. Based on these surface ECG findings, which of the following is the most likely anatomic origin of this patient's arrhythmia?

• ✓ Left atrium
• ○ Lateral right atrium
• ○ Crista terminalis
• ○ Tricuspid valve annulus

Explanation. A negative P wave in leads I and aVL on the surface electrocardiogram indicates a left atrial origin for the focal arrhythmia. Additionally, a positive P wave in lead V1 is characteristic of either a left atrial or septal right atrial origin, fully supporting the left atrium as the anatomical source of the tachycardia when combined with the limb lead findings.

Question 42

A 58-year-old female presents to the emergency department with palpitations, lightheadedness, and mild hypotension. Her electrocardiogram (ECG) reveals a narrow complex tachycardia at 155 bpm with an abnormal P-wave axis, consistent with a focal atrial tachycardia (AT). She is diagnosed with an incessant form of focal AT driven by enhanced automaticity. A synchronized direct current (DC) cardioversion is performed, which briefly restores sinus rhythm for three beats before the focal AT immediately reinitiates. Which of the following is the most appropriate consideration regarding the ongoing acute therapy for this patient's arrhythmia?

• ✓ Repeating the DC cardioversion is unlikely to be appropriate due to the continuous reinitiation of the arrhythmia.
• ○ Intravenous adenosine is the definitive therapy to permanently suppress the enhanced automaticity.
• ○ Intravenous amiodarone should be prioritized due to its proven efficacy for rate control in critically ill patients.
• ○ Intravenous calcium channel blockers are contraindicated for attempting to slow the ventricular rate in focal AT.

Explanation. In incessant forms of focal atrial tachycardia driven by enhanced automaticity, the underlying arrhythmogenic focus remains continuously active. While a shock can successfully terminate the tachycardia momentarily, the enhanced automaticity causes the arrhythmia to reliably reinitiate, meaning that repeating direct current cardioversion is inappropriate and unlikely to yield sustained rhythm control.

Question 43

A 42-year-old man presents with progressive fatigue and shortness of breath over the past month. An electrocardiogram confirms an incessant focal atrial tachycardia (AT). Transthoracic echocardiography reveals a newly reduced left ventricular ejection fraction of 35% with global hypokinesis, consistent with tachycardia-induced cardiomyopathy. Which of the following is the most appropriate management for this patient's arrhythmia?

• ✓ Catheter ablation targeting the earliest atrial activation site
• ○ Intravenous diltiazem to achieve strict ventricular rate control
• ○ Intravenous flecainide to pharmacologically restore sinus rhythm
• ○ Macro-re-entrant circuit ablation targeting the cavotricuspid isthmus

Explanation. Catheter ablation is the treatment of choice for recurrent or incessant focal atrial tachycardia, particularly when it leads to tachycardia-induced cardiomyopathy. Focal ATs display a centrifugal activation pattern spreading throughout the atria, and their mapping and ablation rely on identifying and targeting the site of earliest activation.

Question 44

A 62-year-old man with heart failure and a reduced left ventricular ejection fraction of 35% presents with highly symptomatic, recurrent focal atrial tachycardia (AT). A decision is made to initiate chronic medical therapy to suppress the arrhythmia. Based on his impaired left ventricular function, which of the following medications is theoretically an attractive option for this patient, despite its long-term use being limited by side effects?

• ✓ Amiodarone
• ○ Flecainide
• ○ Verapamil
• ○ Ivabradine

Explanation. Amiodarone is theoretically an attractive pharmacological option for managing focal atrial tachycardia in patients who have impaired left ventricular function, although its long-term utility is often limited by a significant side effect profile.

Question 45

A 72-year-old woman with a history of severe chronic obstructive pulmonary disease presents to the emergency department with worsened dyspnea and palpitations. She is currently taking inhaled bronchodilators and theophylline. Her heart rate is 115 beats per minute and her pulse is irregularly irregular. A 12-lead electrocardiogram (ECG) reveals a rapid, irregular rhythm with variable PP, PR, and RR intervals, alongside at least three distinct P-wave morphologies. Which of the following ECG features best distinguishes this patient's arrhythmia from atrial fibrillation?

• ✓ A distinct isoelectric period between visible P waves
• ○ The presence of highly variable RR intervals
• ○ An atrial rate exceeding 100 beats per minute
• ○ The presence of narrow QRS complexes

Explanation. Multifocal atrial tachycardia is characterized by a rapid, irregular rhythm where there is a distinct isoelectric period between visible P waves, serving as a key distinguishing feature from atrial fibrillation.

Question 46

A 68-year-old man is admitted to the intensive care unit with acute respiratory decompensation secondary to a severe chronic obstructive pulmonary disease (COPD) exacerbation. On telemetry, he is noted to have a narrow-complex, irregular tachycardia at 128 beats per minute. A 12-lead electrocardiogram (ECG) reveals discrete P waves of three distinct morphologies with varying PR intervals and an isoelectric baseline between P waves. Echocardiography demonstrates a normal left ventricular ejection fraction. He has no history of sinus node dysfunction or atrioventricular (AV) block. Treatment of his underlying respiratory condition is underway, but his heart rate remains persistently elevated and he is symptomatic. Which of the following is the most appropriate pharmacological agent to administer for rate control in this patient?

• ✓ Verapamil
• ○ Metoprolol
• ○ Amiodarone
• ○ Flecainide

Explanation. In the management of multifocal atrial tachycardia, slowing conduction at the atrioventricular nodal level is utilized to control the ventricular rate when treating the underlying condition is insufficient. Verapamil is an effective pharmacological agent for this purpose in patients who do not have ventricular dysfunction, sinus node dysfunction, or atrioventricular block, and it serves as a suitable rate-controlling agent when concurrent respiratory decompensation restricts the use of other atrioventricular nodal blocking medications.

Question 47

A 68-year-old man presents to the emergency department complaining of palpitations and mild shortness of breath. An electrocardiogram (ECG) reveals a narrow QRS complex tachycardia with a regular atrial activation rate of 300 beats per minute. Negative saw-tooth waves are clearly visible in leads II, III, and aVF, with positive waves in lead V1. Which of the following best describes the regional sequence of atrial activation in this patient's arrhythmia?

• ✓ Downward in the right atrial free wall, through the cavotricuspid isthmus, and ascending in the right septum.
• ○ Ascending in the right atrial free wall, through the cavotricuspid isthmus, and downward in the right septum.
• ○ Downward in the left atrial free wall, through the mitral isthmus, and ascending in the left septum.
• ○ Circumferential activation originating from a focal source in the pulmonary veins and passively activating the right atrium.

Explanation. The patient's ECG showing a regular atrial activation rate of 300 beats per minute with negative saw-tooth waves in the inferior leads and positive waves in V1 is classic for typical common (counter-clockwise) atrial flutter. The underlying mechanism is a cavotricuspid isthmus-dependent macro-re-entry circuit around the tricuspid annulus. In this common counter-clockwise circuit, electrical activation goes downward in the right atrial free wall, passes through the cavotricuspid isthmus at the inferior boundary, and ascends in the right septum.

Question 48

A 68-year-old man with a history of recurrent paroxysmal atrial fibrillation (AF) is started on flecainide, a class IC antiarrhythmic drug. Two weeks later, he presents to the emergency department complaining of severe palpitations and lightheadedness. His 12-lead electrocardiogram (ECG) demonstrates a regular, wide QRS complex tachycardia at a rate of 190 beats per minute. Which of the following represents the most likely underlying mechanism for this patient's presentation?

• ✓ Typical atrial flutter with 1:1 atrioventricular (AV) conduction and drug-induced ventricular activation changes
• ○ Atypical atrial flutter with rapid 2:1 atrioventricular (AV) conduction
• ○ Orthodromic atrioventricular reentrant tachycardia (AVRT) utilizing a concealed accessory pathway
• ○ Atrioventricular nodal reentrant tachycardia (AVNRT) with rate-dependent bundle branch block

Explanation. Treatment of atrial fibrillation with class IC antiarrhythmic drugs can organize the rhythm into typical atrial flutter and concurrently reduce the flutter rate to less than 200 beats per minute. This slowed atrial rate facilitates 1:1 atrioventricular (AV) conduction, while the drug's effect on ventricular activation broadens the QRS complex, ultimately presenting as a regular wide QRS tachycardia.

Question 49

A 65-year-old man presents to the emergency department complaining of palpitations and mild shortness of breath for the past 4 hours. His heart rate is 150 beats per minute, blood pressure is 115/75 mmHg, and oxygen saturation is 96% on room air. An electrocardiogram (ECG) reveals a regular narrow complex tachycardia without clearly discernible P waves or flutter waves. The physician suspects atrial flutter with 2:1 atrioventricular (AV) block and decides to administer intravenous adenosine to clarify the diagnosis. Which of the following is the most important consideration regarding the use of adenosine in this patient?

• ○ It is highly effective for converting atrial flutter to sinus rhythm but requires pretreatment with amiodarone.
• ✓ It may cause a rebound increase in AV conduction to 1:1 or precipitate atrial fibrillation, requiring resuscitation equipment to be readily available.
• ○ It is strictly contraindicated because it may induce torsades des pointes due to profound QTc prolongation.
• ○ It should be followed by intravenous verapamil to ensure sustained maintenance of sinus rhythm.

Explanation. Intravenous adenosine may be used to increase the degree of atrioventricular block and reveal the typical electrocardiographic pattern of atrial flutter when the diagnosis is not initially obvious. However, adenosine can produce a rebound increase in AV conduction to 1:1 and may also precipitate atrial fibrillation. Therefore, it should only be used if deemed necessary for diagnosis and when resuscitation equipment is immediately available.

Question 50

A 68-year-old male with a history of heart failure with reduced ejection fraction (HFrEF) presents to the hospital with acute-onset palpitations and shortness of breath. An electrocardiogram (ECG) confirms a macro-re-entrant atrial tachycardia (MRAT). The patient is hemodynamically stable but remains highly symptomatic despite initial rate-controlling measures. Which of the following represents a Class I intervention for restoring normal sinus rhythm in this patient?

• ✓ Low-energy synchronized cardioversion
• ○ Invasive high-rate atrial pacing
• ○ Non-invasive high-rate atrial pacing
• ○ Outpatient initiation of oral dofetilide

Explanation. Low-energy synchronized cardioversion is an established Class I intervention for restoring sinus rhythm in patients presenting with macro-re-entrant atrial tachycardia.

Question 51

A 65-year-old man presents to the emergency department with palpitations and mild shortness of breath. His electrocardiogram (ECG) reveals atrial flutter with a ventricular rate of 130 beats per minute. He is hemodynamically stable. If the medical team decides to administer a Class IC antiarrhythmic drug, what is a crucial prerequisite to ensure patient safety?

• ✓ Concurrent administration of an atrioventricular (AV) nodal blocking agent
• ○ Prior administration of intravenous amiodarone to augment rhythm conversion
• ○ Pre-treatment with procainamide to prevent paradoxical QTc prolongation
• ○ Placement of a temporary transvenous pacemaker to prevent post-conversion bradycardia

Explanation. Class IC antiarrhythmic drugs carry the risk of slowing the atrial flutter rate, which can paradoxically allow the atrioventricular node to conduct every atrial impulse. This can lead to dangerous 1:1 atrioventricular conduction with a rapid and potentially life-threatening ventricular response. Therefore, Class IC agents must not be used in the absence of AV-blocking agents.

Question 52

A 68-year-old male with a history of paroxysmal atrial fibrillation (AF) without structural heart disease is currently managed with flecainide and metoprolol. He presents to the cardiology clinic complaining of persistent palpitations and mild exertional dyspnea over the past 3 days. A 12-lead electrocardiogram (ECG) reveals typical cavotricuspid isthmus (CTI)-dependent atrial flutter with 2:1 atrioventricular conduction. Which of the following is the most appropriate management strategy to optimize his long-term rhythm control?

• ○ Discontinue flecainide and initiate oral amiodarone therapy.
• ✓ Perform cavotricuspid isthmus (CTI) catheter ablation and continue flecainide.
• ○ Discontinue flecainide and transition the patient to sotalol.
• ○ Add oral diltiazem for stricter rate control and continue flecainide.

Explanation. When typical cavotricuspid isthmus-dependent atrial flutter ensues during antiarrhythmic drug therapy (such as a Class IC agent like flecainide) for the management of atrial fibrillation, CTI ablation is an effective and appropriate choice. Performing the ablation eliminates the atrial flutter circuit and ensures that the antiarrhythmic drug can be safely continued to maintain sinus rhythm and control recurrent atrial fibrillation.

Question 53

A 65-year-old man presents with palpitations that started 3 days ago. An electrocardiogram (ECG) reveals typical atrial flutter with a ventricular rate of 110 bpm. He has no prior history of atrial flutter or atrial fibrillation (AF). A decision is made to perform electrical cardioversion. Based on the current understanding of stroke risk in atrial flutter, which of the following is the most appropriate consideration regarding his management?

• ○ Proceed with immediate cardioversion without anticoagulation, as atrial flutter carries no significant thrombo-embolic risk compared to AF.
• ✓ Anticoagulation is recommended prior to cardioversion, similar to the approach used for AF, since the flutter has lasted for >48 hours.
• ○ Withhold anticoagulation because the value of the CHA2DS2-VASc score in predicting stroke in atrial flutter has been firmly established to be negligible.
• ○ Left atrial appendage thrombi are more common in atrial flutter than AF, requiring a prolonged anticoagulation period of 8 weeks prior to cardioversion.

Explanation. Although the thrombo-embolic risk of atrial flutter is generally lower than that of atrial fibrillation, it remains clinically significant. Thromboprophylaxis and anticoagulation are recommended in a similar manner to atrial fibrillation, and these recommendations strictly extend to the acute setting for cardioversion when the atrial flutter has lasted for greater than 48 hours.

Question 54

A 68-year-old female with a history of hypertension and paroxysmal atrial fibrillation presents with persistent palpitations. A 12-lead electrocardiogram (ECG) reveals a macro-re-entrant atrial tachycardia with flutter waves that strongly mimic a typical cavotricuspid isthmus (CTI)-dependent flutter pattern. However, an electrophysiology study is performed, and activation mapping and entrainment pacing reveal that the tachycardia circuit is decidedly not dependent on the CTI. Which of the following circuits is most likely responsible for this specific presentation?

• ○ Lower-loop re-entry around the inferior vena cava
• ○ Figure-of-eight double-loop re-entry around the inferior vena cava and tricuspid annulus
• ✓ Upper-loop re-entry
• ○ A typical circuit developing in an extensively ablated atrium

Explanation. Upper-loop re-entry is a macro-re-entrant atrial tachycardia circuit that may produce an electrocardiogram pattern mimicking typical atrial flutter, even though the circuit itself is not dependent on the cavotricuspid isthmus. True atypical flutter (non-CTI-dependent) with a typical electrocardiographic appearance can be attributed to this type of upper-loop re-entry once CTI-dependence is definitively ruled out during an electrophysiology study.

Question 55

A 35-year-old male with a history of complex congenital heart disease and prior surgical atriotomy presents with rapid palpitations and mild dyspnea. His electrocardiogram (ECG) demonstrates a pattern mimicking common atrial flutter. Subsequent electrophysiology mapping identifies a figure-of-eight double-loop macro-re-entrant atrial tachycardia (MRAT) sustained around right atrial free wall scars. Which of the following is the most highly indicated therapeutic intervention for this patient's arrhythmia?

• ✓ Catheter ablation at an experienced center
• ○ Long-term rate control with oral verapamil
• ○ Long-term rate control with an oral beta-blocker
• ○ Empiric surgical maze procedure

Explanation. Catheter ablation performed in an experienced center is the primary, strongly indicated therapeutic intervention for right atrium macro-re-entrant atrial tachycardia (MRAT) occurring secondary to prior complex congenital heart disease surgery and atriotomy scars.

Question 56

A 65-year-old female with a history of surgical atrial septal defect repair via a longitudinal atriotomy presents with highly symptomatic, persistent atypical atrial flutter (macro-re-entrant atrial tachycardia). Her ventricular rate is 115 bpm despite treatment with maximum tolerated doses of metoprolol. She has a history of mild heart failure with preserved ejection fraction. What is the most effective treatment for her arrhythmia?

• ○ Addition of diltiazem for stricter rate control
• ○ Initiation of amiodarone for pharmacological rhythm control
• ✓ Radiofrequency ablation of critical isthmuses at an experienced center
• ○ Atrioventricular node ablation and permanent pacemaker implantation

Explanation. Radiofrequency ablation of critical isthmuses is the most effective treatment for macro-re-entrant atrial tachycardias, which frequently arise around scars from previous medical interventions such as longitudinal atriotomies.

Question 57

A 68-year-old man with a history of persistent atrial fibrillation (AF) underwent extensive left atrial ablation, including circumferential antral pulmonary vein isolation and linear ablation, one year ago. He now presents with recurrent palpitations. A 12-lead electrocardiogram (ECG) demonstrates a regular, organized atrial tachycardia (AT). The electrophysiologist is analyzing the surface ECG to help differentiate the mechanism of the tachycardia prior to an electrophysiology study. Which of the following findings would most likely distinguish a small re-entrant circuit from a macro-re-entrant atrial tachycardia (MRAT) in this patient?

• ✓ A shorter P-wave duration on the surface ECG
• ○ A longer P-wave duration on the surface ECG
• ○ Negative P-wave polarity in at least one precordial lead
• ○ Positive P-wave polarity in all precordial leads

Explanation. An atrial tachycardia caused by a small re-entrant circuit after an atrial fibrillation ablation typically generates a shorter P-wave duration compared to a macro-re-entrant mechanism, which allows for clinical differentiation based on the surface electrocardiogram.

Question 58

A 64-year-old woman presents to the cardiology clinic complaining of continuous palpitations for the past week. She underwent a radiofrequency catheter ablation procedure for persistent atrial fibrillation 6 weeks ago. Her blood pressure is 125/80 mmHg, and her heart rate is 118 beats per minute. An electrocardiogram (ECG) reveals an organized, regular atrial tachycardia, which is suspected to be a peri-mitral flutter. She is hemodynamically stable. What is the most appropriate next step in the management of this patient's arrhythmia?

• ○ Perform immediate re-do catheter ablation to create a stable line of block at the mitral isthmus.
• ✓ Initiate rate-controlling agents and/or antiarrhythmic drugs and delay re-intervention for at least 3 months from the initial procedure.
• ○ Refer the patient for an urgent surgical ablation procedure.
• ○ Perform an electrophysiology study focused on targeting the right and left inferior extensions of the atrioventricular node.

Explanation. Following an initial ablation procedure, organized atrial tachycardias such as peri-mitral flutter or circuits around the pulmonary veins can frequently occur. Intervention to treat these tachycardias should be delayed, if possible, for at least 3 months after the initial procedure. This delay is recommended because some of these tachycardias are transient in nature and will resolve on their own as part of the maturation process of the deployed ablation lesions. Consequently, initial management with rate control and/or the use of antiarrhythmic drugs is the favored approach.

Question 59

A 48-year-old man is evaluated for recurrent sudden-onset palpitations. An electrocardiogram (ECG) during an episode reveals a narrow complex tachycardia at 170 beats per minute. During the episode, brief periods of atrioventricular (AV) dissociation are noted, yet the tachycardia continues uninterrupted. Which of the following best explains the persistence of this specific arrhythmia despite the presence of AV dissociation?

• ✓ Neither the atria nor the ventricles are necessary components of the re-entry circuit.
• ○ An extranodal accessory pathway maintains the circuit through retrograde conduction.
• ○ The tachycardia is driven by enhanced automaticity in the His-Purkinje system.
• ○ The arrhythmia relies on a macro-reentrant circuit localized strictly within the right atrium.

Explanation. In atrioventricular nodal re-entrant tachycardia, the re-entry circuit is localized to the AV node and its atrionodal inputs. Because the circuit does not strictly require the participation of the atrial or ventricular myocardium to sustain itself, the tachycardia can persist uninterrupted even if AV dissociation or AV conduction block is present.

Question 60

A 42-year-old woman presents to the emergency department with sudden onset palpitations. Her 12-lead electrocardiogram (ECG) shows a regular narrow complex tachycardia at 150 beats per minute. P waves are clearly visible before the QRS complexes, with an RP interval greater than the PR interval. The P waves are negative in leads II, III, and aVF, and positive in lead V1. She is taken to the electrophysiology laboratory, where a diagnosis of atypical atrioventricular nodal re-entrant tachycardia (AVNRT) is suspected. If this is the fast-slow variant of atypical AVNRT, which of the following electrophysiological findings is expected?

• ✓ His-atrial interval >70 ms, atrial-His/His-atrial ratio <1, and atrial-His interval <200 ms
• ○ His-atrial interval >70 ms, atrial-His/His-atrial ratio >1, and atrial-His interval >200 ms
• ○ Ventriculoatrial interval <60 ms, atrial-His/His-atrial ratio >1, and atrial-His interval <200 ms
• ○ His-atrial interval <70 ms, ventriculoatrial interval <60 ms, and atrial-His interval <200 ms

Explanation. The fast-slow variant of atypical atrioventricular nodal re-entrant tachycardia (AVNRT) is characterized electrophysiologically by a His-atrial interval >70 ms, a ventriculoatrial interval >60 ms, an atrial-His/His-atrial ratio <1, and an atrial-His interval <200 ms.

Question 61

A 42-year-old female presents to the emergency department with sudden-onset palpitations that began while she was at rest. She is hemodynamically stable, and a 12-lead electrocardiogram (ECG) reveals a regular narrow-complex tachycardia at 170 beats per minute. The attending physician is evaluating the ECG to differentiate between atrioventricular nodal reentrant tachycardia (AVNRT), atrial tachycardia (AT), and atrioventricular reentrant tachycardia (AVRT). Which of the following specific ECG criteria best supports a diagnosis of AVNRT over the other two arrhythmias?

• ✓ A pseudo R deflection in lead V1 and a pseudo S wave in the inferior leads
• ○ An initial P wave morphology that is identical to the subsequent retrograde P waves
• ○ The presence of pronounced RR-interval variation without QRS alternans
• ○ Tachycardia-related ST-segment elevation in the lateral leads

Explanation. A pseudo R deflection in lead V1 and a pseudo S wave in the inferior leads, along with a notch in lead aVL and a pseudo R in aVR, are specific, albeit modestly sensitive, ECG criteria that point toward a diagnosis of AVNRT as opposed to AT or AVRT.

Question 62

A 42-year-old female presents to the electrophysiology laboratory for evaluation of recurrent, highly symptomatic narrow-complex tachycardia. During the study, a sustained tachycardia is induced. Intracardiac recordings demonstrate that the onset of atrial activation appears just after the QRS complex, maintaining an Atrio-His to His-Atrial (AH/HA) ratio >1. The ventriculoatrial (VA) interval, measured from the onset of ventricular activation on the surface electrocardiogram (ECG) to the earliest deflection of atrial activation in the His bundle electrogram, is found to be 45 ms. Earliest retrograde atrial activation is recorded at the His bundle electrogram. Which of the following is the most likely diagnosis?

• ✓ Typical (slow-fast) atrioventricular nodal re-entrant tachycardia (AVNRT)
• ○ Atypical atrioventricular nodal re-entrant tachycardia (AVNRT)
• ○ Orthodromic atrioventricular re-entrant tachycardia (AVRT)
• ○ Focal atrial tachycardia (AT)

Explanation. In the slow-fast form of typical atrioventricular nodal re-entrant tachycardia (AVNRT), the onset of atrial activation appears before, at the onset of, or just after the QRS complex, which maintains an AH/HA ratio >1. Additionally, the defining ventriculoatrial (VA) interval, measured from the onset of ventricular activation on the surface ECG to the earliest deflection of the atrial activation in the His bundle electrogram, is ≤60 ms.

Question 63

A 28-year-old professional athlete undergoes an electrophysiology (EP) study for recurrent, poorly tolerated narrow-complex tachycardia. During the induced tachycardia, intracardiac recordings demonstrate an Atrio-His (AH) interval of 220 ms and a His-Atrial (HA) interval of 160 ms. The Ventriculo-Atrial (VA) interval, measured from the onset of ventricular activation on the surface electrocardiogram (ECG) to the earliest deflection of atrial activation in the His bundle electrogram, is 75 ms. Earliest retrograde atrial activation is noted at the coronary sinus ostium. How is this arrhythmia classified and what is the practical implication of distinguishing it from other atypical variants?

• ✓ It is classified as a 'slow-slow' form of atrioventricular nodal reentrant tachycardia (AVNRT), and distinguishing it from the 'fast-slow' form carries no practical significance.
• ○ It is classified as a 'fast-slow' form of AVNRT, indicating that retrograde conduction is slower than antegrade conduction.
• ○ It is classified as a 'slow-slow' form of AVNRT, which requires a distinct ablation strategy targeting the left atrium compared to the 'fast-slow' form.
• ○ It is classified as a 'fast-slow' form of AVNRT, and differentiating it from the 'slow-slow' form is critical for localizing eccentric atrial activation.

Explanation. The electrophysiological findings of an Atrio-His (AH) interval >200 ms, an AH/HA ratio >1 (220/160), and a Ventriculo-Atrial (VA) interval >60 ms, with earliest retrograde atrial activation at the coronary sinus ostium, are characteristic of the 'slow-slow' form of atypical atrioventricular nodal reentrant tachycardia (AVNRT). This mechanism suggests that two slow pathways are utilized for both anterograde and retrograde activation. In clinical practice, the distinction between the 'fast-slow' and 'slow-slow' forms of atypical AVNRT is of no practical significance.

Question 64

A 42-year-old female undergoes an electrophysiology study for recurrent paroxysmal palpitations. During the study, a sustained narrow-complex tachycardia is induced, and diagnostic maneuvers confirm atrioventricular nodal reentrant tachycardia (AVNRT). The electrophysiologist intends to classify the AVNRT as typical or atypical. However, the His bundle electrogram is not reliably recorded during the tachycardia. Which of the following intervals should be utilized to classify the arrhythmia?

• ✓ The ventriculoatrial (VA) interval measured on the His bundle recording electrode
• ○ The atrial-His (AH) interval measured on the high right atrial electrode
• ○ The His-ventricular (HV) interval measured on the right ventricular apex electrode
• ○ The surface electrocardiogram PR interval

Explanation. When a His bundle electrogram is not reliably recorded, atrioventricular nodal reentrant tachycardia (AVNRT) is conventionally classified as typical or atypical according to the ventriculoatrial (VA) interval measured on the His bundle recording electrode.

Question 65

A 32-year-old female with no structural heart disease presents to the electrophysiology laboratory for catheter ablation of recurrent, highly symptomatic typical atrioventricular nodal reentrant tachycardia (AVNRT). A combined anatomical and mapping approach is planned for slow-pathway modification. To minimize the risk of iatrogenic atrioventricular (AV) block to near zero, the electrophysiologist should appropriately deliver ablation lesions to which of the following structures?

• ✓ The inferior nodal extension at the inferior part of the triangle of Koch
• ○ The roof of the coronary sinus
• ○ The mid-septal region of the right atrium
• ○ The fast pathway at the superior apex of the triangle of Koch

Explanation. In the catheter ablation of atrioventricular nodal reentrant tachycardia (AVNRT), modifying the slow pathway by delivering ablation lesions to the inferior nodal extension at the inferior part of the triangle of Koch achieves a high procedural success rate while minimizing the risk of atrioventricular block.

Question 66

A 68-year-old male presents with frequent, highly symptomatic episodes of atrioventricular nodal reentrant tachycardia (AVNRT) that have been refractory to medical therapy. His baseline electrocardiogram (ECG) during sinus rhythm reveals a PR interval of 250 ms. An electrophysiology study and slow-pathway ablation are planned. Based on his baseline clinical findings, what is the most important procedural consideration for this patient?

• ○ Advanced age is a contraindication for slow-pathway ablation, so an alternative definitive therapy must be selected.
• ✓ He has an increased risk for late atrioventricular (AV) block, and extensive slow-pathway ablation should be avoided.
• ○ He is at high risk for developing permanent, refractory inappropriate sinus tachycardia following slow-pathway ablation.
• ○ Cryoablation should be utilized because it carries a significantly lower recurrence rate than radiofrequency ablation.

Explanation. The pre-existence of first-degree heart block prior to the procedure carries a higher risk for the subsequent development of late atrioventricular (AV) block. Under such conditions, the avoidance of extensive slow-pathway ablation is preferable to minimize this risk.

Question 67

A 28-year-old woman presents to the cardiology clinic complaining of occasional palpitations. She describes brief, regular, rapid heartbeats that last for less than two minutes and occur approximately once every 8 to 10 months. She denies any associated lightheadedness, chest pain, shortness of breath, or syncope, and states the episodes are minimally bothersome. An episode was recently captured on a wearable rhythm monitor, which confirmed atrioventricular nodal re-entrant tachycardia (AVNRT). Her baseline electrocardiogram (ECG) and echocardiogram are unremarkable. She asks about her long-term treatment options. Which of the following is the most appropriate management approach for this patient?

• ✓ Clinical follow-up without the need for ablation or long-term pharmacological therapy.
• ○ Initiation of a daily oral beta-blocker to prevent future recurrences.
• ○ Chronic administration of a Class Ic antiarrhythmic drug such as flecainide.
• ○ Immediate referral for an electrophysiology study and catheter ablation.

Explanation. Patients with minimal symptoms and short-lived, infrequent episodes of atrioventricular nodal re-entrant tachycardia (AVNRT) can be safely managed with clinical follow-up alone, without the need for ablation or long-term pharmacological therapy, as approximately one-half of these individuals may become entirely asymptomatic over time.

Question 68

A 4-month-old infant is in the pediatric intensive care unit 12 hours after open-heart surgery for a congenital heart defect. The continuous cardiac monitor reveals a sudden onset of tachycardia at 210 beats per minute. A 12-lead electrocardiogram (ECG) shows a narrow QRS tachycardia with atrioventricular (AV) dissociation. A diagnosis of post-operative junctional ectopic tachycardia (JET) is established. Which of the following is the drug of choice for the management of this patient's arrhythmia?

• ✓ Intravenous amiodarone
• ○ Intravenous verapamil
• ○ Intravenous propranolol
• ○ Oral ivabradine

Explanation. Intravenous amiodarone is the drug of choice for the treatment and prevention of early post-operative junctional ectopic tachycardia (JET) in children following open-heart surgery. This non-re-entrant arrhythmia arises from abnormal automaticity at the AV node or proximal His bundle and is classically characterized on an ECG by a narrow QRS tachycardia with AV dissociation or a short RP interval.

Question 69

A 45-year-old male presents with palpitations and progressive dyspnea. An initial electrocardiogram (ECG) was read at an outside facility as atrial fibrillation (AF) due to an irregular narrow-complex rhythm. His echocardiogram reveals a left ventricular ejection fraction of 35%, suggestive of tachycardia-induced cardiomyopathy. Careful review of telemetry demonstrates ventricular pauses with a consistent atrioventricular (AV) relationship immediately following each pause, representing a 'linking' phenomenon. An electrophysiology study confirms non-re-entrant AV nodal tachycardia caused by simultaneous multiple nodal pathway conduction (double-fire pathology). Which of the following is the most appropriate targeted intervention for this patient's arrhythmia?

• ✓ Slow-pathway ablation
• ○ Pulmonary vein isolation
• ○ Selective catheter ablation at the site of earliest retrograde atrial activation
• ○ Administration of oral flecainide or propafenone

Explanation. Non-re-entrant atrioventricular (AV) nodal tachycardia caused by simultaneous multiple nodal pathway conduction (dual AV nodal tachycardia) is an uncommon arrhythmia that often presents with repetitive retrograde concealment or 'linking' phenomena, characterized by ventricular pauses with a consistent AV relationship after the pause. These tachycardias can lead to tachycardia-induced cardiomyopathy and appropriately respond to slow-pathway ablation.

Question 70

A 22-year-old male with recurrent, sudden-onset palpitations undergoes an electrophysiology study for a suspected atrioventricular re-entrant tachycardia (AVRT). The baseline electrocardiogram (ECG) reveals a delta wave consistent with a left-sided accessory pathway. The electrophysiologist begins mapping the mitral annulus to locate the precise insertion site. Due to the specific anatomical characteristics of the mitral apparatus, where is this patient's left-sided accessory pathway most likely located?

• ✓ At the attachment of the mural (posterior) leaflet
• ○ At the attachment of the anterior leaflet
• ○ In the superoparaseptal area near the His bundle
• ○ Along the septal aspect of the tricuspid annulus

Explanation. Left-sided accessory pathways are usually limited to the region of the mitral annulus at the attachment of the mural (posterior) leaflet because ventricular muscle is anatomically lacking in the proximity of the anterior leaflet of the mitral valve.

Question 71

A 32-year-old man undergoes an electrophysiological study for recurrent palpitations. During the study, the induced arrhythmia is diagnosed as an atrioventricular re-entrant tachycardia (AVRT) utilizing a 'concealed' accessory pathway. Which of the following electrophysiological properties is characteristic of this specific type of pathway?

• ✓ It conducts impulses exclusively in the retrograde direction.
• ○ It conducts impulses exclusively in the antegrade direction.
• ○ It produces a distinct delta wave on the resting 12-lead electrocardiogram (ECG).
• ○ It depends primarily on a slow calcium current for impulse propagation.

Explanation. Accessory pathways that are classified as "concealed" possess the specific electrophysiological characteristic of exclusively conducting impulses in the retrograde direction.

Question 72

A 28-year-old female with a history of recurrent tachyarrhythmias presents to the cardiology clinic for follow-up. Her resting electrocardiogram (ECG) during sinus rhythm reveals a PR interval of 100 ms, a slurred upstroke of the QRS complex (delta wave), and a QRS duration of 130 ms. Echocardiography demonstrates a structurally normal heart. Which of the following statements regarding her electrocardiographic findings and natural history is most accurate?

• ✓ The pre-excitation pattern observed on her surface ECG can be intermittent and may even disappear permanently over time.
• ○ The degree of pre-excitation on her ECG is determined exclusively by the anatomic location of her accessory pathway.
• ○ Her presentation is highly indicative of an underlying mutation in the PRKAG2 gene or an associated multi-system disease.
• ○ The characteristic wide QRS complex is primarily caused by an intrinsic delay in atrioventricular node conduction.

Explanation. In patients with overt pre-excitation, the pattern seen on the surface electrocardiogram can be intermittent and may disappear permanently in a minority of cases (less than 35%) over time.

Question 73

A 28-year-old woman presents to the emergency department with sudden-onset palpitations. Her electrocardiogram (ECG) initially shows a regular narrow-complex tachycardia at 190 beats per minute with a constant RP interval. Shortly after, the tachycardia continues but the QRS morphology transiently changes, displaying a functional left bundle branch block (LBBB). Assuming the arrhythmia is orthodromic atrioventricular re-entrant tachycardia (AVRT), what is the most likely anatomical location of the re-entrant circuit's retrograde limb?

• ✓ Left-sided accessory pathway
• ○ Right-sided accessory pathway
• ○ Slow atrioventricular nodal pathway
• ○ Fast atrioventricular nodal pathway

Explanation. In orthodromic atrioventricular re-entrant tachycardia, the accessory pathway serves as the retrograde limb of the re-entrant circuit. The development of a functional bundle branch block during the tachycardia is usually associated with an accessory pathway located ipsilateral to the blocked bundle, particularly in young patients. Therefore, the presence of a left bundle branch block indicates a left-sided accessory pathway.

Question 74

A 26-year-old male with known Wolff-Parkinson-White (WPW) syndrome presents to the emergency department with an abrupt onset of palpitations and lightheadedness. His electrocardiogram (ECG) reveals a wide-complex tachycardia with fully pre-excited QRS complexes. P waves are difficult to assess but appear to be inscribed within the ST-T segment. He is diagnosed with antidromic atrioventricular reentrant tachycardia (AVRT). If this patient undergoes an electrophysiology study, which of the following is detected in 30% to 60% of patients with this specific spontaneous arrhythmia?

• ✓ Multiple accessory pathways, either manifest or concealed
• ○ Anterograde conduction occurring exclusively through the atrioventricular node
• ○ A bystander accessory pathway that is not a critical part of the re-entry circuit
• ○ Underlying structural heart disease causing atrial dilation

Explanation. In patients presenting with spontaneous antidromic atrioventricular reentrant tachycardia, multiple accessory pathways (which can be manifest or concealed) are detected in 30% to 60% of cases and may or may not act as the retrograde limb during the arrhythmia.

Question 75

A 22-year-old man presents to the cardiology clinic due to recurrent, poorly tolerated episodes of palpitations. A 12-lead electrocardiogram (ECG) recorded during an episode in the emergency department demonstrates a regular, narrow-complex tachycardia at 180 beats per minute. His resting 12-lead ECG in sinus rhythm is completely normal, showing a PR interval of 150 ms and a QRS duration of 80 ms without any evidence of pre-excitation. An electrophysiology study is performed, which induces orthodromic atrioventricular re-entrant tachycardia (AVRT) mediated by an accessory pathway that conducts only in the retrograde direction. Which of the following is true regarding this patient's condition?

• ✓ The management of this patient's arrhythmia is primarily related to symptom relief without significant prognostic relevance.
• ○ The concealed accessory pathway is most likely localized along the right free wall of the heart.
• ○ This condition is associated with a markedly increased risk of sudden cardiac death.
• ○ This type of accessory pathway exhibits a strong male sex predilection in the general population.

Explanation. The management of atrioventricular re-entrant tachycardia (AVRT) due to a concealed accessory pathway is related to symptom relief, as these pathways do not carry an increased risk of sudden cardiac death and lack significant prognostic relevance in most cases.

Question 76

A 22-year-old man presents with progressive fatigue, shortness of breath on exertion, and palpitations. An echocardiogram demonstrates a left ventricular ejection fraction of 35% with global hypokinesis. A 12-lead electrocardiogram reveals an incessant narrow-complex tachycardia at 135 beats per minute. The electrocardiogram demonstrates a long RP interval with deeply inverted P waves in leads II, III, and aVF. Based on these findings, which of the following describes the most likely underlying electrophysiologic mechanism and the strongly recommended management?

• ✓ An atrioventricular reciprocating tachycardia using a concealed posteroseptal accessory pathway with retrograde decremental conduction; radiofrequency catheter ablation.
• ○ An atrioventricular reciprocating tachycardia using an atriofascicular accessory pathway connecting the right atrium to the right bundle branch; initiation of amiodarone.
• ○ An automatic focal atrial tachycardia originating near the coronary sinus ostium; continuous beta-blocker therapy.
• ○ A junctional ectopic tachycardia with 1:1 retrograde conduction; radiofrequency catheter ablation of the atrioventricular node.

Explanation. The clinical presentation of an incessant long RP tachycardia with deeply inverted retrograde P waves in the inferior leads (II, III, and aVF) resulting in impaired left ventricular function is characteristic of permanent junctional reciprocating tachycardia (PJRT). The underlying mechanism of PJRT is an atrioventricular reciprocating tachycardia utilizing a concealed accessory pathway, typically located in the posteroseptal region, that exhibits retrograde decremental (slow) conduction properties. The incessant nature of the tachycardia frequently leads to tachycardia-induced cardiomyopathy. Radiofrequency catheter ablation is strongly recommended as the definitive treatment in symptomatic patients or those with impaired left ventricular ejection fraction, as the cardiomyopathy typically resolves following successful ablation.

Question 77

A 26-year-old male undergoes an electrophysiology study for recurrent supraventricular tachycardia (SVT). The baseline electrocardiogram shows a normal QRS complex without pre-excitation. During the study, an atriofascicular (atypical) accessory pathway is suspected. Which of the following findings during programmed atrial pacing at progressively shorter cycle lengths would be most characteristic of this type of pathway?

• ✓ An increase in the atrioventricular (AV) interval along with shortening of the His-ventricular (HV) interval, leading to manifest pre-excitation
• ○ A decrease in the atrioventricular (AV) interval along with lengthening of the His-ventricular (HV) interval, leading to manifest pre-excitation
• ○ A constant atrioventricular (AV) interval and His-ventricular (HV) interval with sudden loss of pre-excitation
• ○ His bundle activation consistently preceding the right bundle electrogram during anterograde pre-excitation

Explanation. Atypical (atriofascicular) pathways typically contain accessory nodal tissue with decremental conduction properties. During programmed atrial pacing at shorter cycle lengths, this decremental property results in an increase in the atrioventricular (AV) interval. Concurrently, the His-ventricular (HV) interval shortens as the ventricles become activated primarily via the accessory pathway, leading to obvious manifest pre-excitation.

Question 78

A 24-year-old male presents to the emergency department complaining of sudden-onset palpitations and lightheadedness. His blood pressure is 115/75 mmHg. An electrocardiogram (ECG) shows a regular, wide QRS complex tachycardia. Following a thorough electrophysiological evaluation, the arrhythmia is diagnosed as an antidromic atrioventricular reentrant tachycardia (AVRT). Which of the following medications is most appropriate for acute pharmacological management of this tachycardia?

• ✓ Procainamide
• ○ Verapamil
• ○ Metoprolol
• ○ Diltiazem

Explanation. Antidromic atrioventricular reentrant tachycardia (AVRT) is associated with malignant Wolff-Parkinson-White (WPW) syndrome due to a very fast-conducting accessory pathway. Therefore, pharmacological therapy should be preferentially directed at the accessory pathway using drugs such as procainamide, ibutilide, propafenone, or flecainide.

Question 79

A 27-year-old male with a known history of Wolff-Parkinson-White syndrome presents to the emergency department with sudden-onset palpitations. His blood pressure is 115/75 mmHg. An electrocardiogram reveals an irregularly irregular, wide-complex tachycardia with rapid ventricular rates and varying QRS morphologies, consistent with pre-excited atrial fibrillation. Which of the following intravenous medications is contraindicated for the management of this patient's arrhythmia?

• ○ Intravenous procainamide
• ✓ Intravenous diltiazem
• ○ Intravenous ibutilide
• ○ Intravenous flecainide

Explanation. Intravenous diltiazem is an atrioventricular node-modulating agent and should be avoided in pre-excited atrial fibrillation because it can preferentially direct conduction of electrical impulses via the accessory pathway due to its shorter refractory period, thereby contributing to a risk of ventricular fibrillation.

Question 80

A 62-year-old male presents to the emergency department complaining of severe palpitations and lightheadedness. An electrocardiogram (ECG) reveals an irregularly irregular rhythm with wide, varying QRS complexes and a rapid ventricular rate of 200 beats per minute, consistent with pre-excited atrial fibrillation (AF). His past medical history is significant for a prior myocardial infarction and ischemic cardiomyopathy. The medical team is evaluating pharmacological treatment options for acute management. Based on the patient's history, which of the following medications is specifically contraindicated?

• ✓ Intravenous (i.v.) flecainide
• ○ Intravenous (i.v.) procainamide
• ○ Intravenous (i.v.) amiodarone
• ○ Intravenous (i.v.) ibutilide

Explanation. Intravenous flecainide is contraindicated in patients with ischemic or structural heart disease, which this patient has given his prior myocardial infarction and ischemic cardiomyopathy.

Question 81

A 24-year-old male with a history of recurrent symptomatic palpitations presents for an electrophysiology study and possible catheter ablation. His baseline 12-lead electrocardiogram (ECG) demonstrates a short PR interval, a positive delta wave in leads aVF and aVL, and a narrow positive delta wave in lead V1 accompanied by a prominently negative QRS complex. Based on these findings, the patient is at highest risk for which of the following specific procedural complications during targeted ablation?

• ✓ Complete atrioventricular block
• ○ Right phrenic nerve palsy
• ○ Coronary sinus dissection
• ○ Aortic valve leaflet injury

Explanation. The baseline electrocardiogram findings of a positive delta wave in leads aVF and aVL, combined with a narrow positive delta wave in lead V1 and a prominently negative QRS complex, indicate the presence of a septal accessory pathway located close to the atrioventricular node. Attempted ablation of septal accessory pathways carries a specific, notable risk of complete atrioventricular block due to the anatomical proximity of the pathway to the normal conduction system.

Question 82

A 24-year-old woman with highly symptomatic, recurrent Wolff-Parkinson-White syndrome undergoes an electrophysiology study. Mapping confirms a para-Hisian septal accessory pathway mediating her atrioventricular reciprocating tachycardia (AVRT). The electrophysiologist elects to proceed with catheter ablation using cryoenergy instead of radiofrequency energy. Which of the following best describes the expected comparative outcomes of choosing cryoenergy for this patient's ablation?

• ✓ A lower incidence of atrioventricular (AV) block, but a significantly higher rate of pathway recurrence.
• ○ A higher incidence of atrioventricular (AV) block, but a significantly lower rate of pathway recurrence.
• ○ Reduced radiation and procedure times, with an identical risk of pathway recurrence.
• ○ A lower incidence of atrioventricular (AV) block, and a completely eliminated overall mortality risk.

Explanation. When targeting septal accessory pathways, the application of cryoenergy is associated with a lower incidence of atrioventricular (AV) block compared to the use of radiofrequency energy. However, the recurrence rate of previously blocked pathways is significantly higher when cryoenergy is applied.

Question 83

A 32-year-old female presents with recurrent episodes of palpitations. Diagnostic evaluation confirms symptomatic antidromic atrioventricular reentrant tachycardia (AVRT) with ventricular pre-excitation. She strongly declines catheter ablation at this time. Echocardiography and stress testing reveal a normal ejection fraction and no evidence of structural or ischemic heart disease. Which of the following is the most appropriate pharmacological therapy to manage this patient's condition?

• ✓ A class IC antiarrhythmic drug (e.g., flecainide)
• ○ A non-dihydropyridine calcium channel blocker (e.g., verapamil)
• ○ A beta-blocker (e.g., metoprolol)
• ○ A cardiac glycoside (e.g., digoxin)

Explanation. In patients with pre-excitation and symptomatic antidromic atrioventricular reentrant tachycardia (AVRT) where ablation is not feasible or desirable, and structural or ischemic heart disease has been excluded, class IC antiarrhythmic drugs are the appropriate therapeutic choice because they act primarily on the accessory pathway to prevent recurrent tachycardia.

Question 84

A 68-year-old man presents to the clinic to discuss the findings of a recent 12-lead electrocardiogram (ECG) performed before a minor elective surgery. The ECG shows a short PR interval and a delta wave, consistent with ventricular pre-excitation. He is currently asymptomatic and has no history of palpitations or syncope. During counseling regarding his long-term prognosis, you note that patients with pre-excitation have an increased risk of developing atrial fibrillation (AF) and heart failure (HF), and that his age (>65 years) places him at a higher risk of death. Which of the following accessory pathway locations is most strongly associated with driving the increased risk of AF and HF in this population?

• ✓ Right anteroseptal
• ○ Left lateral
• ○ Right posteroseptal
• ○ Left anterolateral

Explanation. In individuals with pre-excitation, the greater risk of developing incident atrial fibrillation and heart failure is specifically driven by the presence of a right anteroseptal accessory pathway.

Question 85

A 22-year-old male presents for cardiovascular evaluation prior to participating in competitive sports. His baseline 12-lead electrocardiogram (ECG) reveals a PR interval of 100 ms and a prominent delta wave, consistent with ventricular pre-excitation. He is completely asymptomatic. A 24-hour ambulatory Holter monitor is obtained and demonstrates intermittent loss of the delta wave and normalization of the PR interval during normal sinus rhythm at rest. Which of the following best describes the clinical significance of this Holter monitor finding regarding his risk for sudden cardiac death?

• ✓ It is an imperfect marker of low risk, as a significant proportion of such patients still have an accessory pathway effective refractory period of 250 ms or less.
• ○ It is a highly reliable marker of low risk and definitively excludes the capability of the accessory pathway to allow rapid conduction to the ventricles.
• ○ It is a high-risk feature that indicates the presence of multiple accessory pathways and necessitates immediate radiofrequency ablation.
• ○ It confirms an increased risk for sudden cardiac death because the intermittent loss of the delta wave triggers the onset of atrial fibrillation.

Explanation. Intermittent loss of pre-excitation on a resting electrocardiogram or ambulatory monitoring was historically accepted as a credible risk-stratification tool for identifying accessory pathways with longer effective refractory periods. However, more than one-fifth of patients with intermittent pre-excitation actually have an accessory pathway effective refractory period of less than 250 ms, meaning it is an imperfect marker of a low-risk accessory pathway and does not reliably exclude the capacity for rapid antegrade conduction to the ventricles.

Question 86

A 24-year-old male presents for a routine check-up. An electrocardiogram (ECG) reveals a short PR interval and a delta wave, consistent with ventricular pre-excitation. He has never experienced palpitations, syncope, or dizziness. He asks about the potential benefits of prophylactic catheter ablation compared to simply observing his condition. Based on randomized controlled trial data regarding patients with asymptomatic pre-excitation, what is the most accurate information to provide regarding catheter ablation versus clinical follow-up over a 5-year period?

• ✓ Catheter ablation significantly reduces the frequency of arrhythmic events compared to clinical follow-up.
• ○ Catheter ablation has similar rates of arrhythmic events compared to clinical follow-up, but reduces overall mortality.
• ○ Clinical follow-up without treatment is superior as it avoids a high risk of complete atrioventricular block.
• ○ Catheter ablation is associated with a higher rate of ventricular fibrillation due to ablation scar formation.

Explanation. In patients with asymptomatic pre-excitation, prophylactic catheter ablation significantly reduces the frequency of arrhythmic events over 5 years compared to clinical follow-up without treatment.

Question 87

A 25-year-old professional soccer player is found to have a short PR interval and a delta wave on a routine screening electrocardiogram (ECG), consistent with asymptomatic pre-excitation. He reports no history of palpitations, presyncope, or syncope. Given his status as a competitive athlete, an invasive electrophysiology study (EPS) is performed to guide management. Which of the following findings during the EPS identifies this patient as having a high-risk accessory pathway (AP) for which catheter ablation should be performed?

• ✓ An accessory pathway effective refractory period (AP ERP) of 230 ms
• ○ A shortest pre-excited RR interval (SPERRI) of 280 ms
• ○ The presence of a single, isolated left lateral accessory pathway
• ○ Failure to induce an AP-mediated tachycardia during isoproterenol infusion

Explanation. An accessory pathway effective refractory period (AP ERP) of less than 250 ms during an electrophysiology study indicates a high-risk accessory pathway, which warrants subsequent catheter ablation in a competitive athlete with asymptomatic pre-excitation.

Question 88

A 25-year-old asymptomatic man undergoes risk stratification for an incidentally discovered Wolff-Parkinson-White (WPW) pattern on electrocardiogram. An electrophysiological study identifies a 'low-risk' accessory pathway located in the anteroseptal region. He requests catheter ablation to eliminate any potential future risks. Which of the following is the most important consideration that may preclude performing catheter ablation in this specific asymptomatic patient?

• ✓ Ablation of anteroseptal accessory pathways carries a risk of atrioventricular block.
• ○ The presence of a 'low-risk' pathway guarantees he will never experience life-threatening events.
• ○ Electrophysiological studies are highly accurate in predicting the absence of rapidly conducted pre-excited atrial fibrillation.
• ○ Catheter ablation in the anteroseptal region is strongly associated with the development of left ventricular electrical asynchrony.

Explanation. Ablation of accessory pathways located in the anteroseptal or mid-septal regions is associated with a risk of atrioventricular block, which is a significant consideration that may preclude ablation in a patient who is currently asymptomatic.

Question 89

A 15-year-old male is referred to a pediatric electrophysiologist after a routine electrocardiogram (ECG) performed for sports clearance demonstrates a short PR interval and a delta wave. He is completely asymptomatic and has no history of syncope, palpitations, or tachycardia. An electrophysiology study (EPS) is performed, which shows no high-risk characteristics of the accessory pathway. When discussing the potential for catheter ablation with the patient and his family, which of the following is the most appropriate approach to management?

• ✓ The decision to proceed with catheter ablation should be based on the experience of the electrophysiologist and the preferences of the patient.
• ○ Catheter ablation should be strongly discouraged as the risk of complications universally outweighs the benefits in asymptomatic adolescents.
• ○ Catheter ablation should be uniformly mandated since it is the only effective treatment to prevent the future onset of supraventricular tachycardia.
• ○ The patient should be initiated on prophylactic class Ic antiarrhythmic drugs to prevent the development of symptomatic arrhythmias.

Explanation. For patients with asymptomatic pre-excitation who do not exhibit high-risk characteristics at an electrophysiology study, the decision to pursue catheter ablation depends on the experience and expertise of the electrophysiologist performing the procedure, as well as the preferences and values of the patient.

Question 90

A 29-year-old man with a history of surgically repaired congenital heart disease presents to the cardiology clinic reporting recurrent episodes of rapid palpitations and presyncope. A 14-day Holter monitor demonstrates multiple episodes of sustained supraventricular tachycardia (SVT). In addition to causing symptoms, SVT is an established risk factor for sudden cardiac death in specific adult congenital heart disease (ACHD) populations. In which of the following underlying conditions is the presence of SVT most strongly associated with an increased risk of sudden cardiac death?

• ○ Ostium secundum atrial septal defect
• ✓ Tetralogy of Fallot
• ○ Small to moderate perimembranous ventricular septal defect
• ○ Isolated mild pulmonary valve stenosis

Explanation. Supraventricular tachycardias are recognized as important risk factors for sudden cardiac death in specific adult congenital heart disease populations. This heightened risk particularly affects patients with tetralogy of Fallot, obstructive lesions of the systemic ventricle, a systemic right ventricle, and those who have undergone a Fontan operation.

Question 91

A 35-year-old male with a history of transposition of the great arteries who underwent a childhood atrial switch operation presents to the clinic. He has an implantable cardioverter-defibrillator (ICD) and has recently experienced multiple appropriate shocks for ventricular fibrillation. The initiation of a beta-blocker is considered to reduce the incidence of these events. Which of the following underlying conditions is most critical to evaluate for before starting this therapy, as it may cause the patient to be intolerant of the medication?

• ✓ Chronotropic incompetence
• ○ Prolonged QT interval
• ○ Hypokalemia
• ○ Accelerated atrioventricular nodal conduction

Explanation. Beta-blockers can reduce the incidence of ventricular fibrillation and appropriate implantable cardioverter-defibrillator shocks in patients with transposition of the great arteries following an atrial switch operation; however, care must be taken prior to initiation because these patients frequently suffer from underlying chronotropic incompetence and may be unable to tolerate beta-blockade.

Question 92

A 35-year-old male with Adult Congenital Heart Disease (ACHD) presents with recurrent, highly symptomatic atrial arrhythmias. His care team is discussing rhythm control strategies. While amiodarone is perceived to have a lower pro-arrhythmic risk in this population, there are significant concerns regarding its potential to cause severe thyroid disorders and other life-changing complications with prolonged use. Given these considerations, what is the most appropriate primary management strategy for this patient's arrhythmia?

• ✓ First-line catheter ablation attempt
• ○ Long-term use of amiodarone with routine thyroid function monitoring
• ○ Empiric radioactive iodine ablation followed by long-term amiodarone
• ○ Long-term use of amiodarone combined with a beta-blocker

Explanation. In patients with Adult Congenital Heart Disease (ACHD), the long-term use of amiodarone should be severely limited due to its common association with thyroid disorders and other potentially life-changing complications. These significant adverse effects strongly support the use of catheter ablation attempts as the first-line management strategy wherever possible.

Question 93

A 38-year-old male with a history of surgically repaired congenital heart disease presents to the emergency department with palpitations. An electrocardiogram confirms a regular narrow-complex supraventricular tachycardia (SVT). His blood pressure is 112/74 mmHg, and he exhibits no clinical signs of acute decompensated heart failure. However, a recent echocardiogram documents a left ventricular ejection fraction of 30%, indicating heart failure with reduced ejection fraction (HFrEF). The clinical team is evaluating pharmacological options to manage his arrhythmia. Which of the following medications is contraindicated for this patient?

• ✓ Intravenous diltiazem
• ○ Intravenous metoprolol
• ○ Intravenous amiodarone
• ○ Intravenous digoxin

Explanation. Intravenous diltiazem is contraindicated in the management of supraventricular tachycardia in patients who have underlying heart failure with reduced ejection fraction (HFrEF) or hypotension.

Question 94

A 38-year-old female with adult congenital heart disease (ACHD) and previous complex cardiac surgeries presents with symptomatic, recurrent supraventricular tachycardia (SVT). She is scheduled to undergo a reoperative cardiac surgery for valve replacement. Her electrophysiologist and surgeon are discussing the management of her SVT. Based on the considerations for SVT in patients with ACHD, which of the following is the most appropriate approach or counseling point regarding her arrhythmia management?

• ✓ Pre-operative catheter ablation or concomitant arrhythmia surgery should be considered to potentially improve her functional class and reduce chronic antiarrhythmic medication requirements.
• ○ Catheter ablation in the setting of ACHD is associated with higher overall success rates compared to the general population due to well-defined surgical scars.
• ○ If her SVT is found to be a cavotricuspid isthmus (CTI)-related arrhythmia, she should be counseled that catheter ablation has a low acute success rate but excellent long-term freedom from recurrence.
• ○ Her SVT is most likely typical and unrelated to fibrotic atrial tissue, allowing for ablation to be routinely performed at standard non-specialist centers.

Explanation. Pre-operative catheter ablation or concomitant arrhythmia surgery should be considered in patients with adult congenital heart disease undergoing cardiac surgery, as its incorporation can result in improved functional class and potentially decreased requirements for chronic antiarrhythmic medication.

Question 95

A 42-year-old woman is evaluated for exertional dyspnea and palpitations. Transthoracic echocardiography reveals a large secundum atrial septal defect (ASD) with evidence of right ventricular volume overload. An electrocardiogram (ECG) demonstrates atrial flutter. An electrophysiology study confirms a cavotricuspid isthmus (CTI)-dependent right atrial macroreentrant tachycardia. The patient is being considered for closure of the ASD. Which of the following is the most appropriate approach regarding the management of her arrhythmia?

• ✓ Perform catheter ablation of the cavotricuspid isthmus prior to ASD closure.
• ○ Perform ASD closure first, as the reduction in right heart volume overload will independently abolish the arrhythmia.
• ○ Manage the arrhythmia exclusively with rate-controlling medications due to the high post-ablation recurrence rates.
• ○ Perform ASD closure and reassess for catheter ablation only if the arrhythmia persists for more than 6 months.

Explanation. Closure of an existing atrial septal defect in isolation is generally insufficient to abolish an existing atrial tachycardia, and catheter ablation should be considered before defect closure.

Question 96

A 26-year-old male with Ebstein's anomaly presents with progressive exercise intolerance and severe tricuspid regurgitation. He is currently scheduled for surgical repair of his tricuspid valve. He reports a history of intermittent episodes of rapid heart palpitations, though a 12-lead electrocardiogram (ECG) in the clinic reveals normal sinus rhythm. Which of the following is the most appropriate electrophysiological management step prior to his planned surgical intervention?

• ✓ Routine pre-operative electrophysiological study (EPS)
• ○ Ambulatory electrocardiogram (Holter) monitoring for 48 hours, reserving EPS only if sustained arrhythmias are documented
• ○ Intraoperative empiric ablation of the cavotricuspid isthmus
• ○ Initiation of prophylactic oral amiodarone therapy

Explanation. In patients with Ebstein's anomaly undergoing surgical repair, routine pre-operative electrophysiological study (EPS) is indicated because the diagnostic and therapeutic yield in this population is highly significant. Patients with Ebstein's anomaly frequently possess right-sided accessory pathways (APs), and having more than one AP is common. These pathways can independently increase the risk of hemodynamic compromise and sudden cardiac death. Performing a routine pre-operative EPS allows for the precise mapping and high-success catheter ablation of these potential arrhythmia targets prior to surgical intervention.

Question 97

A 32-year-old male with a history of repaired tetralogy of Fallot presents with frequent episodes of palpitations and mild exertional dyspnea. An electrocardiogram (ECG) during an episode documents a new-onset supraventricular tachycardia (SVT). He is hemodynamically stable, and the arrhythmia is acutely terminated in the emergency department. Which of the following is the most appropriate approach for the long-term management of this patient's arrhythmia?

• ○ Initiate lifelong therapy with a class III antiarrhythmic drug to maintain sinus rhythm.
• ✓ Recommend catheter ablation as a first-line option and evaluate for severe pulmonary valve regurgitation.
• ○ Reassure the patient and monitor, as supraventricular arrhythmias are benign in this population.
• ○ Refer the patient for a primary prevention implantable cardioverter-defibrillator (ICD) before further imaging.

Explanation. In patients with tetralogy of Fallot, supraventricular tachycardias are associated with a higher risk of sudden cardiac death. Catheter ablation has a high procedural success rate and is recommended as a first-line option. Furthermore, the presence of new-onset atrial arrhythmias necessitates a thorough evaluation to exclude addressable hemodynamic lesions, such as severe pulmonary valve regurgitation, which may be amenable to surgical or interventional therapy to indirectly reduce the arrhythmia burden.

Question 98

A 6-year-old boy presents to the cardiology clinic after a recent emergency department visit for sudden-onset palpitations. An electrocardiogram (ECG) during the episode confirmed atrioventricular re-entrant tachycardia (AVRT) due to Wolff-Parkinson-White (WPW) syndrome. This was his first documented episode of tachycardia. His parents are highly anxious and ask whether he is likely to outgrow this condition as he gets older. What is the most accurate prognostic information to provide?

• ✓ Because the tachycardia is present after the age of 5, it is expected to persist in >75% of patients.
• ○ The condition is highly likely to resolve spontaneously within the next year due to ongoing maturation of the cardiac structures.
• ○ There is a 90% chance the tachycardia will permanently resolve, as the accessory pathway will likely disappear.
• ○ The tachycardia will resolve in the majority of cases, but will inevitably recur in late childhood in 30 to 50% of patients.

Explanation. In pediatric patients, the natural history of atrioventricular re-entrant tachycardia (AVRT) due to Wolff-Parkinson-White (WPW) syndrome is significantly influenced by the age of onset. If the tachycardia is present after the age of 5, it is known to persist in >75% of patients.

Question 99

A 6-month-old infant is brought to the pediatric emergency department due to progressive irritability, poor feeding, and a flat growth curve over the past month. On physical examination, the infant is lethargic with pale, mottled skin, diminished peripheral pulses, and a capillary refill time of 5 seconds. The heart rate is persistently recorded around 160 beats per minute. Bedside echocardiography reveals severe left ventricular systolic dysfunction consistent with tachycardia-induced cardiomyopathy (TCM) and cardiogenic shock. An electrocardiogram (ECG) demonstrates an incessant, relatively slow narrow-complex tachycardia. Which of the following is the most likely underlying arrhythmia causing this patient's clinical presentation?

• ✓ Permanent junctional reciprocating tachycardia (PJRT)
• ○ Atrioventricular nodal reentrant tachycardia (AVNRT)
• ○ Atrial fibrillation
• ○ Orthodromic atrioventricular reciprocating tachycardia (AVRT) involving a manifest accessory pathway

Explanation. In small children, supraventricular tachycardia (SVT) may present with indirect signs such as irritability, failure to thrive, and flat growth curves rather than specific palpitations. These patients may develop tachycardia-induced cardiomyopathy (TCM) and present in cardiogenic shock due to an incessant SVT. This severe clinical presentation most frequently occurs in the setting of relatively slow SVTs, particularly permanent junctional reciprocating tachycardia (PJRT) and focal atrial tachycardia (AT).

Question 100

A 3-month-old infant presents to the emergency department with a regular, narrow-complex tachycardia at 240 beats per minute. The patient is currently hemodynamically stable, but ice applied to the face (a vagal maneuver) fails to restore sinus rhythm. The treating physician is considering pharmacological intervention to terminate the arrhythmia. Which of the following antiarrhythmic medications should generally be avoided in this small patient due to the high risk of precipitating severe hypotension?

• ○ Adenosine
• ○ Amiodarone
• ✓ Verapamil
• ○ Esmolol

Explanation. Verapamil must be avoided whenever possible or administered with extreme caution to small pediatric patients because it can provoke severe and potentially life-threatening hypotension.

Question 101

A 14-month-old infant presents with recurrent, medically refractory supraventricular tachycardia. The pediatric electrophysiology team is discussing potential catheter ablation but recommends attempting to delay the procedure until the child is over 2 years of age, if clinically possible. Which of the following best describes the primary pathophysiological basis for avoiding radiofrequency ablation in this specific age group?

• ✓ Radiofrequency lesions in immature myocardium are associated with late lesion enlargement and fibrous tissue invasion of normal myocardium.
• ○ Immature myocardium resists acute lesion formation, leading to a high rate of immediate tachycardia recurrence.
• ○ The use of minimum 5 French catheters in this age group universally causes acute transmural ventricular rupture.
• ○ Radiofrequency energy selectively accelerates the apoptosis of the specialized atrioventricular conduction system in infants.

Explanation. Radiofrequency lesion formation in immature myocardium is associated with late lesion enlargement and fibrous tissue invasion of normal myocardium, making it prudent to avoid radiofrequency ablation in the first 2 years of life if at all possible.

Question 102

A 29-year-old pregnant woman at 28 weeks of gestation is referred to the fetal cardiology clinic after an obstetric ultrasound reveals a rapid fetal heart rate. Fetal echocardiography confirms a sustained fetal supraventricular tachycardia (SVT). Which of the following is the most appropriate management strategy for this condition?

• ✓ Administer maternal therapy with medications such as digoxin, flecainide, or sotalol and monitor both the mother and fetus closely.
• ○ Withhold pharmacological therapy and monitor the fetus with weekly echocardiography until signs of hydrops fetalis develop.
• ○ Perform a direct fetal intramuscular or umbilical vein injection of adenosine to terminate the arrhythmia.
• ○ Prescribe maternal amiodarone and follow the fetal response using daily fetal electrocardiograms (ECG).

Explanation. Sustained fetal tachycardia mandates treatment to prevent fetal death due to hydrops. Protocols for treating fetal supraventricular tachycardia rely on administering drugs such as digoxin, flecainide, and sotalol (alone or in combination) directly to the mother. Because a fraction of these medications reaches the fetus to provide the therapeutic effect, close follow-up is necessary to monitor for secondary adverse effects that can manifest in both the mother and the fetus.

Question 103

A 45-year-old pregnant woman is referred to the cardiology clinic for the evaluation of palpitations. In considering the differential diagnosis and pre-test probability of various arrhythmias, which of the following accurately reflects the epidemiological trends of arrhythmias during pregnancy?

• ○ The prevalence of supraventricular tachycardia (SVT) increases significantly with advancing maternal age.
• ✓ The frequency of arrhythmias is greater in older pregnant women, largely due to a higher prevalence of atrial fibrillation (AF) and ventricular tachycardia (VT).
• ○ Atrial flutter is the most common arrhythmia associated with pregnancy-related hospitalizations overall.
• ○ Women with congenital heart disease are primarily at an increased risk for ventricular fibrillation (VF) during pregnancy compared to those without congenital defects.

Explanation. The frequency of any arrhythmia is greater in pregnant women aged 41-50 years compared to those aged 18-30 years. This increase is primarily driven by a higher prevalence of atrial fibrillation (AF) and ventricular tachycardia (VT) in the older age group, whereas the prevalence of supraventricular tachycardia (SVT) remains relatively stable over time.

Question 104

A 26-year-old female with a known history of highly symptomatic paroxysmal supraventricular tachycardia (SVT) presents for preconception counseling. She has experienced multiple prolonged episodes of SVT with palpitations and lightheadedness, occasionally requiring emergency department visits. She wishes to minimize potential risks to her future child and asks about the best strategy to manage her arrhythmia as she plans to become pregnant. Which of the following is the most appropriate recommendation for managing her tachyarrhythmia?

• ✓ Recommend catheter ablation prior to pregnancy.
• ○ Plan for catheter ablation during the second trimester to avoid first-trimester teratogenic risks.
• ○ Initiate prophylactic amiodarone therapy prior to conception to ensure complete suppression.
• ○ Discontinue all medical therapy and reassure her that SVT during pregnancy does not affect the foetus.

Explanation. In patients with a known history of symptomatic tachyarrhythmia, catheter ablation should be considered before pregnancy when possible. This proactive approach eliminates the arrhythmia and avoids both the potential haemodynamic effects of tachycardia on the foetus and the side effects of antiarrhythmic medical treatments during pregnancy, labour, delivery, and lactation.

Question 105

A 29-year-old female at 28 weeks of gestation presents to the emergency department with sudden-onset palpitations and shortness of breath. Her blood pressure is 110/70 mmHg. An electrocardiogram (ECG) reveals a regular narrow-complex tachycardia at 175 beats per minute, consistent with supraventricular tachycardia (SVT). Carotid sinus massage and the Valsalva maneuver are performed but fail to restore sinus rhythm. What is the most appropriate next step in the pharmacological management of this patient's arrhythmia?

• ✓ Intravenous adenosine
• ○ Intravenous amiodarone
• ○ Intravenous verapamil
• ○ Oral metoprolol

Explanation. Adenosine is the first-line pharmacological agent for the acute treatment of supraventricular tachycardia (SVT) during the second and third trimesters of pregnancy when non-invasive maneuvers fail to terminate the arrhythmia.

Question 106

A 32-year-old pregnant woman in her first trimester is evaluated for the management of chronic hypertension. The cardiologist is reviewing the safety profile of various antihypertensive medications, including alpha/beta-adrenergic blockers. Based on findings from the EUROmediCAT study, the use of alpha/beta-adrenergic blockers during the first trimester has been specifically associated with an increased risk of which of the following fetal abnormalities?

• ✓ Multicystic renal dysplasia
• ○ Ebstein anomaly
• ○ Neural tube defects
• ○ Cleft lip and palate

Explanation. The EUROmediCAT study reported an association between the use of alpha/beta-adrenergic blockers in the first trimester and the development of multicystic renal dysplasia.

Question 107

A 31-year-old female at 32 weeks of gestation presents to the emergency department with severe palpitations, lightheadedness, and dyspnea. Her blood pressure is 78/45 mmHg, and her heart rate is 210 beats per minute. An electrocardiogram (ECG) reveals a regular, narrow-complex supraventricular tachycardia (SVT). Which of the following is the most appropriate initial management for this patient?

• ✓ Synchronized electrical cardioversion followed by routine monitoring of the fetal heart rate.
• ○ Intravenous (i.v.) diltiazem administration to achieve rapid rate control.
• ○ Intravenous (i.v.) verapamil administration as a first-line pharmacological agent.
• ○ Intravenous (i.v.) ibutilide administration to restore normal sinus rhythm.

Explanation. Electrical cardioversion is the first choice of therapy when arrhythmias are hemodynamically unstable. It is considered safe in all phases of pregnancy as it does not compromise fetal blood flow and carries a low risk of inducing fetal arrhythmias or initiating pre-term labor. Following the procedure, the fetal heart rate should be routinely controlled.

Question 108

A 27-year-old pregnant woman at 9 weeks of gestation presents with recurrent atrioventricular reentrant tachycardia (AVRT). The episodes are poorly tolerated and have become refractory to maximally tolerated medical therapy. The multidisciplinary team determines that catheter ablation is indicated. Her hemodynamic status between episodes is stable enough to allow for optimal timing of the procedure. What is the most appropriate strategy for the timing and technique of catheter ablation in this patient?

• ✓ Postpone the procedure to the second trimester and utilize non-fluoroscopic electroanatomical mapping.
• ○ Postpone the procedure to the third trimester and utilize minimal-dose fluoroscopy with abdominal shielding.
• ○ Perform the procedure immediately in the first trimester utilizing non-fluoroscopic electroanatomical mapping.
• ○ Perform the procedure immediately in the first trimester utilizing minimal-dose fluoroscopy with abdominal shielding.

Explanation. Catheter ablation in pregnant patients with drug-refractory and poorly tolerated tachycardia should be postponed to the second trimester whenever possible, and the procedure should be performed at an experienced center utilizing non-fluoroscopic electroanatomical mapping and catheter navigation systems to eliminate radiation exposure.

Question 109

A 48-year-old male presents with new-onset dyspnea on exertion and fatigue. His pulse is irregular at 135 beats per minute. An electrocardiogram confirms atrial fibrillation with a rapid ventricular response. An echocardiogram demonstrates global hypokinesis with a left ventricular ejection fraction of 28%. The treating cardiologist suspects tachycardiomyopathy (TCM) as the primary cause of his heart failure, but wishes to differentiate it from an underlying irreversible dilated cardiomyopathy. Which of the following diagnostic findings would be most characteristic of pure tachycardiomyopathy in this patient?

• ○ A left ventricular end-diastolic diameter of 72 mm
• ✓ A left ventricular end-systolic diameter of 46 mm
• ○ Evidence of intrinsic structural changes on cardiac magnetic resonance (CMR) imaging
• ○ An increasing N-terminal pro-B-type natriuretic peptide (NT-proBNP) level following successful rate control

Explanation. In tachycardiomyopathy, typical left ventricular dimensions are less dilated than in irreversible dilated cardiomyopathy. Characteristic findings include a left ventricular ejection fraction <30%, a left ventricular end-diastolic diameter <65 mm, and a left ventricular end-systolic diameter <50 mm.

Question 110

A 12-year-old boy presents to the emergency department with progressive dyspnea on exertion, orthopnea, and generalized weakness over the past three weeks. Echocardiography reveals a dilated left ventricle with a reduced ejection fraction of 32%. Continuous telemetry monitoring demonstrates an incessant arrhythmia, and the clinical team suspects tachycardia-induced cardiomyopathy (TCM). Given the patient's age demographic, which of the following is the most common arrhythmic etiology for this presentation?

• ✓ Focal atrial tachycardia (AT)
• ○ Permanent junctional reciprocating tachycardia (PJRT)
• ○ Rapid atrial fibrillation (AF)
• ○ Idiopathic ventricular tachycardia (VT)

Explanation. In pediatric patients under the age of 18 years, focal atrial tachycardia is the most common arrhythmic etiology that leads to the development of tachycardia-induced cardiomyopathy.

Question 111

A 52-year-old man presents with progressive dyspnea and fatigue over the past several months. Electrocardiogram reveals an incessant supraventricular tachycardia (SVT) with a ventricular rate of 135 beats per minute. An echocardiogram shows a dilated left ventricle with an ejection fraction of 30%. He is diagnosed with tachycardiomyopathy (TCM) and is started on a beta-blocker and an angiotensin-converting enzyme inhibitor. During an electrophysiology study, the SVT focus is mapped but is deemed impossible to ablate directly due to an unacceptably high risk of collateral damage. What is the most appropriate next step in the interventional management of this patient?

• ✓ Atrioventricular (AV) nodal ablation with biventricular or His-bundle pacing
• ○ Implantation of an implantable cardioverter-defibrillator (ICD) and initiation of sotalol
• ○ Surgical pulmonary vein isolation and left atrial appendage occlusion
• ○ Long-term oral amiodarone monotherapy without further interventional procedures

Explanation. In cases of tachycardiomyopathy driven by a supraventricular tachycardia where the primary arrhythmia cannot be safely or effectively ablated, performing an atrioventricular nodal ablation alongside the implantation of a biventricular or His-bundle pacemaker is the appropriate intervention to ensure strict rate control and promote left ventricular functional recovery.

Question 112

A 21-year-old asymptomatic male competitive cyclist is referred after a routine screening electrocardiogram (ECG) reveals a short PR interval and a delta wave, indicative of ventricular pre-excitation (Wolff-Parkinson-White pattern). He has never experienced palpitations, presyncope, or syncope. An exercise stress test is performed, which demonstrates persistence of the delta wave at maximal exertion. He wishes to continue participating in competitive cycling. What is the most appropriate next step in his management?

• ✓ Perform invasive risk stratification with an electrophysiology study
• ○ Clear the patient for competitive sports without further testing since he is asymptomatic
• ○ Prescribe an antiarrhythmic medication such as flecainide and clear him for sports
• ○ Restrict the patient from all competitive sports permanently to prevent sudden cardiac death

Explanation. In asymptomatic athletes with ventricular pre-excitation, invasive risk stratification is necessary to assess the potential for fast antegrade conduction over the accessory pathway. This evaluation identifies patients with high-risk features who require catheter ablation, whereas those stratified as low risk are allowed to practice competitive sports.

Question 113

A 26-year-old elite long-distance runner presents for evaluation of episodic palpitations. An electrocardiogram (ECG) recorded during a recent episode demonstrated a narrow-complex, regular tachycardia, and he was diagnosed with paroxysmal atrioventricular nodal re-entrant tachycardia (AVNRT). A comprehensive echocardiogram shows a structurally normal heart. He wishes to continue competitive racing but is concerned about interventions that might hinder his athletic performance. Which of the following is the most appropriate management strategy for this athlete?

• ○ Prescribe a sodium channel blocker to prevent arrhythmia recurrence during sports.
• ○ Prescribe a beta-blocker to control heart rate during episodes.
• ✓ Recommend catheter ablation of the arrhythmia.
• ○ Provide clearance for competitive sports without any intervention, as AVNRT is not associated with sudden cardiac death.

Explanation. Catheter ablation is the recommended management strategy for all athletes with a history of paroxysmal supraventricular tachycardia (SVT), because sympathetic stimulation during sports activity can lead to very high heart rates and subsequent haemodynamic impairment, even in patients with structurally normal hearts.

Question 114

A 52-year-old male driver is brought to the emergency department after a single-vehicle motor vehicle accident. Witnesses report the car slowly drifted off the road into a guardrail. The patient was initially unresponsive but regained consciousness and was subsequently found to have had an episode of atrial fibrillation with rapid ventricular response resulting in syncope. When reviewing the epidemiology of such events, what is the estimated frequency of sudden driver incapacitation as a cause of all motor vehicle accidents, and what proportion of these specific incapacitation events are related to cardiac causes?

• ✓ 1 to 3% of all motor vehicle accidents; of these incapacitations, 5 to 10% are related to cardiac causes.
• ○ 5 to 10% of all motor vehicle accidents; of these incapacitations, 1 to 3% are related to cardiac causes.
• ○ 10 to 15% of all motor vehicle accidents; of these incapacitations, greater than 50% are related to cardiac causes.
• ○ Less than 1% of all motor vehicle accidents; of these incapacitations, less than 2% are related to cardiac causes.

Explanation. The proportion of all motor vehicle accidents established as being due to a driver's sudden incapacitation is small, representing approximately 1% to 3% of all accidents. Of these specific sudden incapacitation events, 5% to 10% are related to cardiac causes, which may occur with or without syncope.

Question 115

A 64-year-old man presents to the cardiology clinic with a 2-week history of continuous palpitations. He underwent a catheter ablation procedure for atrial fibrillation (AF) exactly 6 weeks ago. A 12-lead electrocardiogram (ECG) today demonstrates a regular focal atrial tachycardia (AT) with a ventricular rate of 115 beats per minute. He is hemodynamically stable but bothered by the symptoms. He asks if he can undergo a repeat ablation procedure next week to eliminate this new arrhythmia. What is the most appropriate approach regarding repeat catheter ablation for this patient?

• ✓ Defer the repeat ablation procedure for at least 3 months after the initial AF ablation.
• ○ Proceed with repeat catheter ablation within the next week to target the nodal extensions.
• ○ Refer the patient immediately to a specialized center for surgical atrial ablation.
• ○ Perform immediate catheter ablation targeting the anatomical area of the right septum.

Explanation. In patients presenting with post-atrial fibrillation (AF) ablation atrial tachycardias (ATs), whether focal or macro-re-entrant, the repeat ablation procedure should be deferred for at least 3 months after the initial AF ablation, when possible.

Question 116

A 20-year-old male collegiate basketball player is evaluated during a routine pre-participation sports physical. He denies any history of palpitations, lightheadedness, syncope, or chest pain. His physical examination is unremarkable. A routine 12-lead electrocardiogram (ECG) reveals a PR interval of 110 ms, a widened QRS complex, and a slurred upstroke of the QRS complex (delta wave), consistent with asymptomatic pre-excitation. What is the most appropriate next step in the management of this patient?

• ○ Reassurance and routine clinical follow-up without further testing
• ○ Empiric prescription of flecainide to prevent future arrhythmias
• ✓ Invasive assessment with an electrophysiology study (EPS)
• ○ Immediate empiric catheter ablation without prior pathway risk-stratification

Explanation. Invasive assessment with an electrophysiology study (EPS) is indicated to accurately evaluate the accessory pathway characteristics and risk stratify patients with asymptomatic pre-excitation who engage in competitive athletics or have high-risk occupations.

Question 117

A 72-year-old female presents to the cardiology clinic due to frequent, highly symptomatic palpitations. Holter monitoring documents multiple prolonged episodes of supraventricular tachycardia (SVT). She has undergone two previous electrophysiology studies with attempted radiofrequency ablation, but the SVT could not be successfully ablated due to complex anatomy. She remains highly symptomatic despite maximally tolerated therapy with multiple antiarrhythmic medications. Which of the following is the most appropriate next interventional step for managing this patient's arrhythmia?

• ✓ Atrioventricular (AV) nodal ablation with subsequent biventricular or His-bundle pacing
• ○ Atrioventricular (AV) nodal ablation with standard right ventricular apical pacing
• ○ Surgical isolation of the pulmonary veins and atrial appendages
• ○ Implantation of a dual-chamber implantable cardioverter-defibrillator (ICD)

Explanation. In situations where a supraventricular tachycardia is highly symptomatic, refractory to medical therapy, and cannot be successfully ablated directly, an 'ablate and pace' strategy consisting of atrioventricular nodal ablation coupled with biventricular or His-bundle pacing is indicated to control the heart rate and symptoms while maintaining ventricular synchrony.

Question 118

A 45-year-old woman presents to the emergency department with palpitations and lightheadedness. Her heart rate is 145 beats per minute, blood pressure is 95/60 mmHg, and temperature is 39.5°C (103.1°F). An electrocardiogram (ECG) demonstrates a narrow QRS-complex tachycardia. Laboratory testing reveals a significantly elevated white blood cell count, and urinalysis suggests a severe urinary tract infection. She has no prior history of arrhythmias and no established electrophysiologic diagnosis. What is the recommended first step in the acute management of her tachycardia?

• ○ Administration of intravenous adenosine
• ○ Immediate synchronized electrical cardioversion
• ✓ Treatment of the underlying condition
• ○ Administration of an intravenous non-dihydropyridine calcium channel blocker

Explanation. In the acute management of a narrow QRS tachycardia in the absence of an established diagnosis, addressing the underlying condition causing or exacerbating the arrhythmia is the recommended first step whenever feasible.