In recent clinical trials, class III
anti-arrhythmic drugs were found to reduce arrhythmic deaths in patients after
myocardial infarction. The purpose of this study was to assess the electrophysiologic properties and
anti-arrhythmic efficacy for inducible sustained
ventricular tachycardias (VTs) of the pure class III agent
nifekalant hydrochloride (MS-551) in comparison with those of
procainamide. Programmed ventricular stimulation of up to three extra stimuli was performed for induction of VTs. Effective refractory period (ERP) of the ischemic zone and normal zone was also measured before and after
nifekalant.
Nifekalant and
procainamide suppressed sustained VT induction in four of 15 patients and in six of 15 patients, respectively (p = NS). Sinus cycle length, PR interval, and QRS duration were not changed, but QT and QTc intervals were significantly increased with
nifekalant (p < 0.01). Ventricular ERP also increased, whereas there were no significant differences in the increase of ERP between the ischemic and normal zones. The suppression of VT induction did not correlate with the changes in QT, QTc, and ERP after
nifekalant administration. There were no significant differences in induced VT cycle length at baseline study between responders and nonresponders to
nifekalant. Reverse use dependence was not apparent on review of electrophysiologic parameters. Neither proarrhythmic events nor hemodynamic disturbances occurred after
nifekalant administration. It was concluded that
nifekalant could be used safely and showed comparable effectiveness to
procainamide for the suppression of VT induction.