Infra-His Bundle Origin of Bidirectional Tachycardia

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Abstract
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 bidirectional 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.