Electrical alternans: a sign, not a diagnosis.

Electrical alternans is an electrocardiographic phenomenon defined as an alternating amplitude or axis of the QRS complexes in any or all leads. It is most commonly associated with a large pericardial effusion and impending threat of cardiac tamponade; however, a literature review showed that this electrocardiographic finding can be seen in a variety of other clinical scenarios with varying etiologies and prognoses. Several electrocardiogram examples are presented with a brief review of the potential mechanisms and clinical significance and demonstrate that electrical alternans is more correctly considered an electrocardiographic sign, rather than a diagnosis, with a broad differential for potential etiologies. For some causes, the clinical significance is well known, but for others, further research is needed.