Increased dispersion of repolarization time determined by monophasic action potentials in two patients with familial idiopathic ventricular fibrillation.

Abstract

The role of increased dispersion of repolarization in the genesis of torsades de pointes in patients with long QT syndrome has been clarified, but its role in the genesis of idiopathic ventricular fibrillation (VF) is not yet known. To investigate the pathogenesis of VF, we recorded monophasic action potentials (MAPs) from two siblings (48- and 36-year-old males) with familial idiopathic VF. The elder brother (patient 1) showed a late r' wave in lead V1 and ST segment elevation in leads V1 through V3. The younger brother (patient 2) had late r' waves and ST segment elevation in leads II, III, and aVF, and the configurations were very similar to those of patient 1. MAPs were recorded from several sites in the right ventricular (RV) and left ventricular (LV) endocardium during constant right atrial pacing. The repolarization time (RT) was defined as the sum of the activation time (AT) and action potential duration (APD) at 90% repolarization. In patient 1, marked prolongation of the AT (140 msec) and the RT (380 msec) was recorded in the RV septum of the outflow tract, and the RT dispersion was markedly increased (125 msec). In contrast, patient 2 showed prolongation of the AT (80 msec) and RT (310 msec), and fractionated electrograms in the RV floor of the inflow tract. The RT dispersion was also increased (80 msec). VF and nonsustained polymorphic ventricular tachycardia were induced by double premature stimulation in patients 1 and 2, respectively. Chronic amiodarone therapy decreased the RT dispersion and suppressed the induction of ventricular tachyarrhythmias in patient 2, although late r' waves and slight ST segment elevation were unmasked in leads V1 and V2. Our data suggest that the increased dispersion of the RT, which was due mainly to a localized conduction delay in the RV, created an arrhythmogenic substrate in the two patients with familial idiopathic VF.