Pericardial Effusion & Cardiac tamponade

Pericardial diseases: effusion and tamponade

A long series of conditions can affect the pericardium (pericardium). The most common of these are acute pericarditis (perimyocarditis), constrictive pericarditis, pericardial effusion and tamponade. Less common are cysts and tumors of the pericardium, as well as congenital malformations leading to an incomplete or absent pericardium. In case of suspicion of pericardial disease, it is important to conduct a careful investigation as several conditions may affect hemodynamics and the underlying cause is often serious (e. g. malignancy, amyloidosis).

In case of suspicion of pericardial disease, in the first place, an echocardiographic examination is done. With echocardiography, good conditions are obtained for visualizing the pericardium, its surroundings, the myocardium and valves. ECG is recorded in all patients with suspected pericardial disease. In addition to echocardiography, ECG and clinical examination, blood tests and other radiological examinations are most often required, in particular computed tomography (DT) and/or magnetic resonance imaging (MRI).

Anatomy of the pericardium

The pericardium consists of a parietal layer and a visceral layer. The parietal layer is 2 mm thick, rich in connective tissue and envelops the entire heart and the departures of the larger vessels. The visceral layer consists of mesothelian cells, collagen and elastin and is fused with the myocardium. At the departures of the larger vessels, the visceral layer is folded back to cover the inside of the parietal layer. Between the visceral and parietal layers there is the pericardial cavity (pericardial sac) containing pericardial fluid. This fluid is produced by the mesothelian cells and consists of 25-50 mL serous fluid.

Function of the pericardium

The pericardium is considered to have several functions, despite the fact that it can be removed without affecting cardiac function or hemodynamics. The following functions are attributed to the pericardium:

• The pericardium serves as a barrier to infections.
• The pericardium reduces friction between the ventricles and surrounding structures of the mediastinum. Friction is reduced because the fluid in the pericardial sac (pericardial fluid) reduces friction between the ventricles and surrounding structures.
• The pericardium provides some fixation of the heart in the mediastinum. The heart is fixed to the larger vessels and diaphragm, which stabilizes the position of the heart.
• The parietal layer limits the volume filling of the chambers. At normal filling volumes, the pericardium is very indulging and thus allows rapid ventricular filling. If the dilatation of the ventricles becomes pronounced, then the pericardium becomes inelastic and rigid, which limits the dilatation. It allows the pericardium to limit the filling of the chambers when the volumes become too large. Thus, the pericardium is considered to contribute to the fact that the ventricles are not overfilled in acute volume loads.

Pericardial Effusion: fluid in the pericardial space

Normally, the pericardial sac contains 25 to 50 ml of liquid. This volume is so small that the pericardial space is usually not visible on ultrasound (alternatively, a few millimeters of pericardial space can be seen). If the amount of fluid in the pericardial cavity exceeds 50 mL, there is an effusion, which is considered pathological. The effusion, as a rule, is ecolucent (ecofatical), but, depending on the etiology, may be more or less echogenic. It is important to estimate the volume, echogenicity and location of the effusion.

Regarding the location, an effusion may be general (circumferential) or localized to a specific area. The effusion itself may consist of serous fluid (transudate), protein-rich fluid (exudate) to pure blood (exudate).

Often pericardial effusion is detected randomly (for example, in CT, MRI, echocardiography). In other cases, the effusion is detected under more dramatic circumstances, as is the case, for example, in acute pericarditis or tamponade. Note that pericardial effusion is not mandatory in acute pericarditis.

Causes of pericardial effusion

A variety of cardiac conditions and systemic diseases can cause pericardial depletion. Despite careful investigation, a significant proportion of all effusions remain classified as idiopathic, which means that the etiology is unknown. Malignancy is a common cause of pericardial depletion.

TABLE 1. Causes of pericardial effusion

Clinical characteristics in pericardial effusion

Pericardial deffusion can be anything from asymptomatic to immediately fatal. There is a strong correlation between the extent of pericardial effusion and hemodynamic consequences. Cardiac tamponade (tamponade) means that the effusion is so pronounced that the heart flows around in the fluid. In the case of tamponade, as a rule, there are hemodynamic consequences that affect the pumping function and which can lead to hypotension and asystole.

Echocardiographic findings in pericardial effusion

Echocardiography makes it possible to assess hemodynamic consequences of the effusion, as well as assess its location and volume. Regarding the volume of effusion, a rough estimate is made according to Table 2 (measurements are made at the end of diastole).

Table 2. Grading of pericardial effusion

In most cases, the effusion is circumferential, which means that it envelops the entire heart. If the effusion is seen only in certain places, then it is localized, which is more unusual.

Spot ecotate structures in the effusion indicate that it contains coagulated blood. Blood in the pericardium is called hemopericardium and is usually seen after heart surgery, trauma and invasive interventions. Spontaneous hemopericardium is seen in acute myocardial infarction and aortic dissection. Hemopericard has greater hemodynamic consequences because the blood coagulates and solidifies, which compresses the ventricles and prevents their filling.

Cardiac tamponade and electrical alternans

In the case of massive effusions, the ultrasound image shows a heart flowing around the effusion. Because the heart flows around the pericardial sac, the distance between the heart and the chest electrodes varies, which leads to varying QRS amplitudes in the chest leads. This ECG finding is called electric alternance.

If a massive effusion leads to increased pressure in the pericardial sac, then the filling of the ventricles is aggravated, which leads to acute and potentially life-threatening heart failure. This is called cardiac tamponade (tamponade). Effusions that have developed rapidly tend to have greater hemodynamic effects. A relatively small effusion that has increased rapidly may have a greater haemodynamic effect than a large effusion that has developed slowly. Therefore, it is important to try to determine how quickly the effusion occurred.

In case of suspicion of an acute effusion etiology (ventricular rupture, aortic dissection, trauma), treatment should be carried out promptly as the effusion is likely to have haemodynamic consequences which can be expected to increase. This is due to the fact that acute effusions can not be compensated by widening the pericardium. As mentioned above, the pericardium limits the dilatation of the ventricles, as a result of which an acute effusion leads to a rapid rise in pressure in the pericardial sac. However, if the effusion develops slowly (systemic diseases, malignancy, etc.), the pericardium may be stretched gradually, allowing larger effusions (sometimes >2 litres) to occur without haemodynamic consequences.

In the case of tamponade, ventricles and atria may collapse if the pressure in the pericardium exceeds the pressure in the corresponding cardiac space. The lowest pressure is present in the right atrium, which is why the right atrium also collapses first with tamponade. Collapse is defined as the bulging of the right atrial wall during diastole. At higher pressure in the pericardium, even the right ventricle can collapse during diastole.

Collapse of the left atrium occurs. Collapse of the left ventricle is rare because the pressure in the left ventricle is high compared to the pressure in the pericardium. However, trauma and iatrogenic causes of tamponade can lead to such high pericardial pressure that the left ventricle collapses.

In tamponade, the filling of the ventricles and atria deteriorates, which causes the inferior vena cava to widen and does not coincide normally during inspiration or sniffing.

Respiratory variations in blood pressure: pulsus paradoxus

In the case of tamponade, systolic blood pressure may vary more than 10 mmHg during the respiratory cycle. The pressure falls during inhalation and this is called pulsus paradoxus. The explanation is that the filling of the right ventricle increases during inhalation and the septum can bulge into the left ventricle, which thus fills with less blood, thereby reducing stroke volume and blood pressure. During the exhalation, the reverse occurs and systolic pressure rises.

Pulsus paradoxus means that blood pressure varies >10 mm during the respiratory cycle. Blood pressure drops during inhalation and rises during exhalation.

In the case of pulsus paradoxus, echocardiography shows that the septum position varies during inhalation and exhalation. During the inhalation, the septum moves into the left ventricle and vice versa during the exhalation.

The septum position during inhalation and exhalation affects the passive blood flow from the left atrium to the left ventricle, which is represented by the E wave on the pulsed Doppler (see Assessment of Diastolic Function). When inhaled, the septum bulges into the left ventricle, which complicates the filling, and then the E wave velocity decreases. On exhalation, the reverse occurs. If the speed of the E wave varies > 30% during the respiratory cycle, it strongly indicates that the effusion has haemodynamic effects.

Pulsed wave doppler in the tricispidal valve shows reverse ratios compared to the mitral valve; the E wave velocity rises during inhalation and decreases on exhalation.