A comparison of the long-term effects of sotalol and atenolol on QT interval and arrhythmias after myocardial infarction

In order to dissociate the Class III effects of sotalol on QT interval and arrhythmias from those of chronic beta-receptor blockade, we compared the effects of sotalol 160 mg b.d. and atenolol 50 mg b.d. in a double-blind crossover study of 103 patients followed for one year after discharge following acute myocardial infarction. Sotalol caused a highly significant lengthening of the absolute and corrected QT (QTc) interval over atenolol which was apparent by day 6 and persisted unchanged throughout the follow-up period. The increase in QT interval averaged 43 ms (9%). Sotalol blunted the increase in ventricular premature beat frequency on ambulatory monitoring which occurred with atenolol, although direct comparison of arrhythmia frequency between the groups receiving atenolol and sotalol revealed no significant difference. Marked lengthening of QTc interval (greater than 500 ms) was observed on 29 occasions in patients receiving sotalol, most commonly at day 6, but no episodes of polymorphic ventricular tachycardia were recorded. The Class III action of sotalol persists over and above any response to beta-blockade during a one-year follow-up period. In a population with a low incidence of spontaneous arrhythmias, however, there was only a modest difference in antiarrhythmic efficacy between atenolol and sotalol. Episodes of marked lengthening of QT interval induced by sotalol in the absence of other adverse factors need not be arrhythmogenic.