Torsades de pointes: electrophysiologic studies in patients without transient pharmacologic or metabolic abnormalities.

Electrophysiologic studies were performed in 21 patients who had torsades de pointes. This ventricular tachyarrhythmia, characterized by rapid (200-250 beats/min) and irregular paroxysms and progressively varying QRS amplitude and polarity, occurred in the absence of electrolyte disturbance, antiarrhythmic drug therapy or acute ischemia. The QTc interval was prolonged in seven of 21 patients. Electrophysiologic study included ventricular pacing with the introduction of one to three extrastimuli and rapid ventricular pacing. The effect of i.v. procainamide or quinidine in these patients was also studied. Torsades de pointes was inducible n 19 of 21 patients. Induced episodes closely resembled spontaneous episodes. Torsades de pointes spontaneously progressed to ventricular tachycardia with a uniform morphology in three patients and to ventricular fibrillation in four. In eight patients, procainamide or quinidine converted torsades de pointes into typical reentrant ventricular tachycardia. Our data suggest that torsades de pointes in this setting may be a rapid reentrant ventricular tachycardia closely related to recurrent sustained ventricular tachycardia and a precursor to ventricular fibrillation and sudden death.