Which echocardiographic sign is most specific for cardiac tamponade?

The echocardiographic sign that is most specific for cardiac tamponade is left atrial collapse. In cases of cardiac tamponade, the accumulation of fluid in the pericardial space exerts pressure on the heart, particularly during diastole when the heart chambers fill with blood. This intrapericardial pressure can lead to compression of the left atrium, especially during ventricular filling when the pressure dynamics change significantly.

The left atrium is more likely to collapse due to its position and the pressure differential created by the excess fluid surrounding the heart. This collapse can often be visualized on echocardiography as a transient loss of the normal volume of the left atrium, particularly during inspiration. It is a highly specific indicator of cardiac tamponade, as it occurs in the context of an elevated pericardial pressure above that of the left atrial pressure.

Other signs such as right atrial collapse can occur as well, but they are not as specific for cardiac tamponade compared to left atrial collapse. Right ventricular wall inversion and left ventricular wall inversion can be seen in various conditions, including other types of volume overloads or infiltrative processes, making them less specific indicators for this particular diagnosis.