Pericardial effusion and electrical alternans: echocardiographic assessment.

Clinical diagnosis of pericardial effusion is often difficult, and assessment of the effects of effusion on cardiac hemodynamics is often imprecise. Electrical alternans is a reasonably specific ECG indicator of the presence of a large effusion and imminent or actual cardiac tamponade. If echocardiography verifies the presennce of pericardial fluid and shows abnormal cardiac motion, a diagnosis of cardiac tamponade can be made without further, more invasive, studies.