Cardiac tamponade is a syndrome caused by accumulation of fluid in the pericardial space, resulting in reduced ventricular filling and subsequent hemodynamic compromise. This condition is a medical emergency and its complications include pulmonary edema, shock and death. The pericardium is composed of two layers, the serous layer and the fibrinous layer. The pericardial space normally contains 25-50 ml of fluid.
Three stages of hemodynamic change have been described in cardiac tamponade:
Phase I – The pericardial fluid accumulates and causes increased stiffness of the ventricle, requiring a higher filling pressure. The left and the right ventricular filling pressure are higher than the intrapericardial pressure.
Phase II – The fluid accumulates further and the pericardial pressure increases above the ventricular filling pressure, resulting in reduced cardiac output.
Phase III – The pericardial and left ventricular pressures equilibrate, which causes a further decrease in the cardiac output.
The underlying process for cardiac tamponade is a marked reduction in diastolic filling. This happens when transmural distending pressures become insufficient to overcome increased intrapericardial pressures. The initial response to maintain output is tachycardia. The increased intrapericardial pressure compresses the heart. This impairs systemic venous pressure and results in right atrial and ventricular collapse. Blood accumulates in the venous system, resulting in reduced venous return and cardiac output.
The most common cause for tamponade is malignancy. Uremia, pericarditis, infection diseases and anticoagulation can also cause tamponade. Symptoms vary with the acuteness and cause of tamponade, but typical symptoms include dyspnea, tachycardia, and tachypnea. Cold and clammy extremities are also observed. Some patients may complain of dizziness, drowsiness or palpitations. Dyspnea, tachycardia and elevated jugular venous pressure are noted on physical exam. The Beck triad, which comprises of increased jugular venous pressure, hypotension and diminished heart sounds, is usually observed in patients with acute cardiac tamponade. Pulsus paradoxus (a drop in blood pressure of at least 10 mm Hg on inspiration) is a variable finding. Chest x-rays have unreliable diagnostic value. If no significant pericardial effusion is present, the cardiac silhouette may appear normal The SVC, the azygous vein or both may be dilated. In general, echocardiography is not considered a reliable technique to visualize the pericardium.
Definitive treatment for tamponade is surgery. Pericardiotomy leads to rapid hemodynamic and symptomatic improvements. Diuretics can be used in the early stage of tamponade but must be used cautiously because a drop in intravascular volume can precipitate a drop in cardiac output.