Effect of sotalol on human atrial action potential duration and refractoriness: cycle length dependency of class III activity

Using intracardiac electrophysiological techniques the effects of sotalol hydrochloride were studied in the right atrium in eight patients with paroxysmal supraventricular atrial arrhythmias. Atrial action potential duration was recorded from two well separated standard sites via endocardial contact electrodes before and for 30 minutes after intravenous sotalol (1 mg X kg-1). Atrial effective refractory period and vulnerability to atrial arrhythmia initiation were assessed by premature extrastimulation. All patients developed a prolonged action potential duration (mean +6%, p less than 0.01 in high atrial site; +8%, p less than 0.01 in low atrial site), with similar increases in atrial effective refractory period (mean +9%, p less than 0.01). The small regional difference in action potential duration detected between these well separated recording sites was minimally decreased, indicating no tendency towards increased regional inhomogeneity of repolarisation. The relatively refractory zone as denoted by the gap between atrial effective refractory period and action potential duration was slightly reduced, and transient repetitive atrial depolarisations, initially provoked by extrastimuli in two patients, were abolished. The relation between atrial interval and duration, investigated using two modes of paced cycle length modification, showed that a gradual reduction in pacing cycle length was more potent in shortening action potential duration than was isolated premature extrastimulation. Sotalol was significantly more effective in opposing shortening of the action potential duration caused by progressive cycle length reduction than that caused by isolated extrastimulation. The class III antiarrhythmic activity of sotalol, confirmed in the atrium, is dependent on cycle length and mode of cycle length alteration. Under study conditions, there was no tendency to increase atrial vulnerability or regional non-uniformity of repolarisation.