Electrical alternans on an ECG is commonly associated with which condition?

Electrical alternans on an ECG is a phenomenon characterized by a variation in the amplitude or axis of the QRS complexes in a regularly alternating pattern. This finding is most commonly associated with pericardial effusion, particularly when it leads to cardiac tamponade. In cardiac tamponade, the accumulation of fluid in the pericardial sac exerts pressure on the heart, which can impede its ability to fully expand and contract. As the heart moves within the fluid-filled pericardial space during diastole and systole, the changing positions of the heart lead to variations in electrical activation captured on the EKG, manifesting as electrical alternans.

This distinctive finding—alongside clinical signs such as hypotension, jugular venous distension, and muffled heart sounds—can help clinicians quickly recognize and manage cardiac tamponade, which can be a life-threatening condition. In contrast, while other heart conditions like myocardial infarction or atrial fibrillation can have their own specific ECG changes, they typically do not present with the classic pattern of electrical alternans. Congestive heart failure can lead to various ECG changes as well, but does not usually produce the alternating QRS amplitude seen in tamponade.