EARLY AFTERDEPOLARIZATIONLIKE ACTIVITY IN PATIENTS WITH CLASS IA INDUCED LONG QT SYNDROME AND TORSADES-DE-POINTES

Early after depolarizations (EADs) have been linked to the mechanism o f torsades de pointes in long QT syndrome. The purpose of this study w as to investigate the role of EADs in Class IA induced torsades de poi ntes. We studied nine patients with Class IA induced torsades de point es at the time this arrhythmia was present (acute period, n = 7) and a fter Class IA therapy was discontinued (chronic period, n = 6). ECGs a nd monophasic action potentials were recorded in both periods. In the chronic period, electrophysiological studies were performed before and after disopyramide infusion. In the acute period, QT(c) interval was markedly prolonged (655 +/- 32 ms(1/2)), and EAD-like activity was rec orded in all patients. QT(c) interval returned to normal (428 +/- 45 m s(1/2)) and EAD-like activity disappeared after discontinuation of IA drug. Although, in the chronic period, disopyramide infusion prolonged QT(c) interval from 428 +/- 48 ms(1/2) to 479 +/- 31 ms(1/2) and indu ced EAD in three of six patients, the degree was not as marked as obse rved in the acute period. EADs may play an important role in the genes is of long QT and torsades de pointes. Disopyramide infusion in the ch ronic period could not reproduce marked repolarization abnormalities a nd torsades de pointes.