Transient left bundle branch block: an unusual electrocardiogram in acute pulmonary embolism.

Pulmonary embolism may result in permanent or transient electrocardiographic abnormalities. New onset left bundle branch block (LBBB) is usually associated with myocardial ischemia. However, nonischemic mechanisms are also known to account for some cases of LBBB. Tachycardia, a common finding in pulmonary embolism, is one such mechanism. This is illustrated by our case, and possible mechanisms for tachycardia-dependent LBBB are discussed. It is important to recognize and interpret the conditions that precipitate it, thereby avoiding inappropriate interventions.