Action of sotalol on potential reentrant pathways and ventricular tachyarrhythmias in conscious dogs in the late postmyocardial infarction phase.

Abstract

Sotalol is a .beta.-adrenergic blocker that also prolongs action potential duration and myocardial refractoriness over the short term (class III effect). Its short-term antiarrhythmic effects were compared with those of metoprolol, which has neither short-term class III nor membrane-stabilizing action, on reentrant ventricular arrhythmias produced by programmed stimulation in 17 conscious dogs 3 to 8 days after myocardial infarction. Ventricular arrhythmias were prevented or significantly slowed by sotalol in 11 of 19 studies (58%) compared with in 1 of 14 (7%) studies with metoprolol. Sotalol prolonged refractoriness in the infarct zone, measured from an implanted composite electrode, by 41 .+-. 45% (mean .+-. SD, P < 0.01), which was significantly greater than the increases it produced in effective refractory period of the normal ventricle (14.0 .+-. 5.5%) or QT interval (12.5 .+-. 7.8%). Metoprolol had no effect on infarct-zone refractoriness. Sotalol differentially increases refractoriness in potential reentry circuits in ischemic myocardium. Its antiarrhythmic effect in this model is not due to .beta.-blockade and is presumably related to prolongation of action potential duration.