Echocardiographic manifestations of tense pericardial effusion.

Echocardiography has emerged as a sensitive study in the evaluation of pericardial effusion. The specificity of echocardiographic signs in cardiac tamponade remains undefined, however. Two such signs, early diastolic collapse of the right ventricular free wall and late diastolic collapse of the right atrial wall, were observed in two patients without clinical evidence of cardiac tamponade. Increased intrapericardial pressure was documented in each patient. Accumulation of pericardial fluid under high pressure results in a reversal of the instantaneous transmural pressure gradients in early and late diastole, causing collapse of the right ventricular and the right atrial wall, respectively; however, such a tense pericardial effusion may not cause hemodynamic embarrassment severe enough to yield clinical signs of cardiac tamponade.