Infra-His bundle origin of bidirectional tachycardia.

A case of bidirectional tachycardia is presented in a patient with cardiomyopathy, pulmonary emboli, and digitalis toxicity. The arrhythmia has usually been considered ventricular in origin. A supraventricular origin has also been suggested. Simultaneous recordings of standard electrocardiographic leads and His bundle potentials demonstrated that the abnormal rhythm originated in the left ventricle and indeed was a bidirecti;nal ventricular tachycardia. Enhanced phase 4 depolarization in the divisions of the left bundle branch is advanced as a theoretic underlying mechanism in some instances of this arrhythmia.