Does disopyramide infusion reproduce marked repolarization abnormalities and early afterdepolarizations in patients with a history of Class IA induced torsades de pointes?
Early afterdepolarizations likely play an important role in the genesis of long QT and torsades de pointes, though acute marked repolarization abnormalities could not be fully reproduced by disopyramide infusion in the chronic period.
Early afterdepolarizations (EADs) have been linked to the mechanism of torsades de pointes in long QT syndrome. The purpose of this study was to investigate the role of EADs in Class IA induced torsades de pointes. We studied nine patients with Class IA induced torsades de pointes at the time this arrhythmia was present (acute period, n = 7) and after Class IA therapy was discontinued (chronic period, n = 6). ECGs and 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, QTc interval was markedly prolonged (655 +/- 32 ms1/2), and EAD-like activity was recorded in all patients. QTc interval returned to normal (428 +/- 45 ms1/2) and EAD-like activity disappeared after discontinuation of IA drug. Although, in the chronic period, disopyramide infusion prolonged QTc interval from 428 +/- 48 ms1/2 to 479 +/- 31 ms1/2 and induced EAD in three of six patients, the degree was not as marked as observed in the acute period. EADs may play an important role in the genesis of long QT and torsades de pointes. Disopyramide infusion in the chronic period could not reproduce marked repolarization abnormalities and torsades de pointes.
Kurita et al. (Sat,) studied this question.