Verapamil in idiopathic ventricular tachycardia of right bundle branch block morphology: observations during electrophysiologic and exercise testing.

Electrophysiologic studies before and after administration of verapamil were performed in three young patients with recurrent sustained ventricular tachycardia (VT) of right bundle branch block morphology. VT was not provoked by maximal treadmill testing in any patient. Electrophysiologic findings at induction of VT suggested reentry in the first patient and triggered automaticity in the second. Findings were inconclusive in the third patient. Intravenous verapamil terminated the VT in all the three cases. Oral verapamil prevented laboratory induction of sustained VT in the latter two patients. However, VT could be provoked during exercise in both while on oral verapamil therapy. These findings suggest that different mechanisms may underlie ventricular tachycardia dependent upon slow-response tissue; the role of oral verapamil in the treatment of such VT needs further investigation.