Recurrent sustained ventricular tachycardia. 1. Mechanisms.

The mechanism of recurrent sustained ventricular tachycardia (VT) was evaluated in 21 patients. Re-entry as the mechanism for VT was suggested by a) the reproducible initiation (19) and termination (15) of the arrhythmia by programmed stimulation. The rate, ventricle of origin, and stimulation site determined the method of termination. One VPD was usually required with VT rates less than 175/min and/or ventricle of origin ipsilateral to the stimulation site, while two VPDs were usually required for VT with faster rates originating in a contralateral ventricle. The proximal His-Purkinje system (HPS) was not required for initiation or maintenance of VT. Evidence localizing the site of re-entry to a small portion of the ventricles included: a) ventricular capture by ventricular premature depolarizations (VPDs) or pacing (VP) without terminating VT (5), b) sinus capture following VPDs and/or supraventricular fusions without terminating VT (12), and c) atrial pacing normalizing the QRS and H-V intervals without terminating VT (5).