ECG Test – Mixed Conditions

Welcome to the first ECG quiz. This quiz includes ECGs recorded at 25 mm/s and 50 mm/s. The paper speed has no significance for the interpretation and you should practice ECG interpretation on both 25 mm/s and 50 mm/s. Click on the ECG to enlarge/zoom.

6 question(s) with answers and explanations.

Question 1

A male 25 year-old student at Oxford University is seeing his primary care physician due to palpitations. The palpitations occurs intermittently, but they tend to intensify during stressful periods, such as exam periods. The patient experiences palpitations with sudden onset and occassionally the sensation that the heart skips a beat. Clinical examination reveals nothing suspicious and the patient has not experienced any symptoms during the last week. What does the ECG show?

Paper speed is 50 mm/s. Heart rate is approximately 65 beats per minute.

Figure 1.

• ○ Atrial fibrillation
• ○ Sinus rhythm
• ✓ Sinus arrhythmia

Explanation. The ECG is normal but there is sinus arrhythmia and short QT interval. A new ECG should be recorded within a few days to reassess whether the QT interval is still short.   Detailed interpretation Rate: The rhythm is slightly irregular, which means that the heart rate of 65 beats per minute is an approximation. However, the rate is around 60 beats per minute which is absolutely normal. Rhythm: The rhythm is slightly irregular, because the intervals between the R-waves (or any other waves) varies from beat to beat. For example, the distance between the third and fourth R-wave is shorter than the distance between the fourth and fifth R-wave. P-waves and PR intervals: The P-wave is positive in all leads, and notably in lead II. The PR interval is normal (it slightly shorter than 2 large boxes, which means that it is shorter than 200 ms and therefore normal). QRS complex: The electrical axis is normal because the QRS complex is positive in leads I and II. The R-wave progression is normal in leads V1–V6, because there is a successive increase in R-wave amplitude from V1–V5. There are no pathological Q-waves, which means that there are no signs of previous myocardial infarction. The R-wave amplitudes appear to be normal (not too high or too low). T-wave: All T-waves are positive except from in lead V1. However, an isolated T-wave inversion in V1 is a normal finding. It is considered normal because it is concordant with the direction of the QRS complex (which is also negative in V1) and the T-wave in V2 is positive, making any negative T-wave in V1 non-significant. The T-wave amplitudes appear to be normal. U-wave: not seen. QT interval: Appears a bit short, being roughly 3.5 large boxes wide, i.e 350 milliseconds. This is shorter than normal and may be associated with short QT syndrome which causes ventricular tachycardia. Summary: irregular heart rate with normal P-waves indicates sinus arrhythmia, which is normal in young individuals. The short QT interval may be associated with arrhythmias but another ECG must be recorded to confirm this, because short QT interval is extremely rare.

Question 2

A 70 years-old male was admitted to the ER (emergency room) due to chest pain and discomfort in his left arm. These symptoms debuted a few hours earlier. Physical examination did not reveal anything unusual. The ECG shows a heart rate of 69  beats per minute. The PR interval is 180 ms (normal). The QRS duration is 84 ms (normal). The QTc (corrected QT) interval is 437 ms (normal) and the electrical axis is 30 degrees (normal). Note that the ECG paper speed is 50 mm per second and the leads are presented using the Cabrera format, which is the recommended format. As always, you start by viewing lead II, where you note a positive P-wave. Because the heart rate is 69 per minute, and the P-wave is positive in lead II, you conclude that the rhythm is sinus rhythm, which is correct. You also note that the most positive QRS amplitude is noted in lead –aVR, which is consistent with an electrical axis of 30 degrees (lead –aVR is located at 30 degrees in the coordinate system). Finally you also note that the QRS complex is positive in lead I and lead II, which means that the electrical axis is normal. But the question is, why does this patient experience chest pain? Chest leads Limb leads

• ○ Completely normal ECG
• ○ Mostly normal findings, but flat T-waves
• ○ Mostly normal findings, but poor R-wave progression
• ✓ Mostly normal findings, but flat T-waves, poor R-wave progression and intraventricular conduction defect

Explanation. This ECG is abnormal. Although there are ST segment elevations (e.g V2, V3, V4), they are not significant, meaning that they do not suggest acute myocardial infarction. Moreover, there are no reciprocal ST segment depressions, which further corroborates that the elevations are not caused by acute myoardial infarction. There are Q-waves in several leads, but neither do they fulfill criteria for pathological Q-waves (i.e the Q-waves are considered normal, beacuse they are small). However, the R-wave progression is abnormal and the QRS complexes are slightly fragmented in the chest leads. This is most likely due to an nonspecific intraventricular conduction defect (in some instances these ECG changes may be seen after myocardial infarction). Nevertheless, there are no significant ST segment deviations which is why the ECG does not suggest ongoing myocardial ischemia. On the other hand, there are flat T-waves, and such T-waves may indicate previous ischemia (such T-waves are referred to as postischemic T-wave inversion). To sum up, the ECG does not suggest that there is ongoing ischemia, but there are some minor abnormalities which should be noted.

Question 3

Are there any signs of myocardial infarction? Pay attention to lead III in particular. The paper speed is 50 mm/s. Chest leads Limb leads

• ○ The large Q-wave in lead III indicates previous infarction
• ✓ The large Q-wave in lead III is a normal finding

Explanation. There is a large and pathological Q-wave in lead III. That Q-wave is wider and deeper than normal, so it is by definition a pathological Q-waves. However, there is no pathological Q-wave in lead aVF. Recall that pathological waveforms (e.g pathological Q-waves) must be present in at least 2 anatomically contiguous leads (explained below) in order to be clinically significant. Moreover, the size of the Q-wave in lead III varies from one heart beat to the next. Such Q-waves, i.e large Q-waves in lead III which varies in depth from beat to beat, are referred to as respiratory Q-waves and they are considered as normal variants. The reason why they are referred to as respiratory Q-waves is beacuse their amplitude varies with breathing (the position of the heart in the chest varies slightly during the respiratory cycle). ### Explanation: Contiguous ECG leads Contiguous leads view the same anatomical aspect of the heart. For example, leads V3 and V4 (which are contiguous leads) both view the anterior aspect of the left ventricle. Lead III and lead aVL, however, are not contiguous because they view different aspects of the heart; lead III views the inferior wall, and lead aVL views the lateral wall. The traditional way of presenting the ECG leads does not help in determining which leads that are anatomically contiguous. Consider this traditional ECG strip: Figure 1. Traditional presentation of the leads in the 12-lead ECG. Only the chest leads (V1 to V6) are presented in their anatomical order, but the limb leads (I, II, III, aVF, aVL and aVR) are not presented in their anatomical order. Consider the following ECG strip, which uses the Cabrera format of presenting the leads: Figure 19. The Cabrera format and inverted aVR. The Cabrera format facilitates interpretation of the waveforms beacuse the ECG leads are placed in their anatomical order. For example, leads II, aVF and III – which all view the inferior wall – are placed next to one another. Also note that using the Cabrera format means that lead aVR is inverted (flipped 180 degrees) so that it fills a gap in the coordinate system, as shown here: Figure 2. The coordinate system presenting the limb leads in the frontal plane.

Question 4

Why does this 39-year old male experience palpitations intermittently? Note that paper speed is 50 mm/s (1 large box = 100 ms; 1 small box = 20 ms). Limb leads Chest leads

• ○ This ECG is completely normal
• ○ Abnormal ECG due to ST segment depressions and ST segment elevations
• ✓ Abnormal due to pre-excitation

Explanation. The main abnormalities are as follows: - Short PR interval (<120 ms) - Wide QRS complex - Delta waves These three findings are diagnostic of pre-excitation. Hence, his palpitations are part of the Wolff-Parkinson-White (WPW) syndrome. The ST segment depressions and elevations are due to the pre-excitation! Whenever there is pre-excitation, a part of the ventricular myocardium will be activated abnormally, and therefore the repolarization will also be abnormal. Thus, the ST-T changes are secondary to abnormal activation of the ventricles. Read more about pre-excitation here.

Question 5

This 75-year old lady has an abnormal ECG. Two days earlier she experienced chest discomfort and shortness of breath. Define the abnormalitites on the ECG. Paper speed is 50 mm/s.

• ○ No sign of previous infarction, but there are age related conduction defects.
• ○ There are indications of previous myocardial infarction.
• ✓ There are indications of previous infarction as well as recent ischemia.

Explanation. Rhythm cannot be assessed because only one heart beat per ECG lead is presented (this is a signal averaged ECG, meaning that the ECG displays the average of multiple beats). However, the waveforms can be assessed as usual. The most important abnormalities are as follows: - QS complex in lead V1 and V2. A QS complex is defined as a completely negative QRS complex. This is abnormal. - A Q-wave should not be visible in V3, which it is here. - Thus, there are 3 pathological Q-waves (V1, V2, V3) which fulfills the criteria for previous myocardial infarction. (Note: crieria for previous myocardial infarction states that at least 2 leads must display pathological Q-waves). - There are T-wave inversions in several leads and some leads display flat T-waves. These T-waves could be due to previous episodes with myocardial ischemia, given that the patient has experienced chest discomfort earlier.

Question 6

A 71-year old male is admitted to the emegency room (ER) due to palpitations and chest discomfort. What is the correct diagnosis? Note that the paper speed is 50 mm/s. Limb leads Chest leads

• ○ Sinus tachycardia with ST segment depressions due to ischemia.
• ✓ Atrial fibrillation with ST segment depressions which may be due to either myocardial ischemia or the tachycardia itself.
• ○ Atrial fibrillation

Explanation. Tachyarrhythmias frequently cause ST segment depressions, which tend to be most pronounced in leads V3–V6. Such ST depressions (caused by tachycardia) typically displays a downsloping or horizontal ST segment. However, the presence of tachycardia does not rule out myocardial ischemia. It is mandatory to (1) analyze cardiac biomarkers (preferrably troponins) and (2) evaluate whether the ST segment depression resolves when the heart rate returns to normal. The latter is important because tachycardia-induced ST depression typically resolves within minutes after heart rate normalizes.