Effects of SUN-1165, N-(2,6-dimethylphenyl)-8-pyrrolizidine acetamide hydrochloride hemihydrate, a new class I antiarrhythmic drug, on ventricular arrhythmias, intraventricular conduction, and the refractory period in canine myocardial infarction.

Effects of SUN-1165, a class I antiarrhythmic drug, on ventricular arrhythmias, intraventricular conduction, and the effective refractory period (ERP) were examined in a canine model of myocardial infarction and compared with those of lidocaine. The antiarrhythmic effects were examined on the arrhythmias developed 24 h after left anterior descending coronary artery (LAD) ligation and ventricular premature stimulation-induced arrhythmias 5-7 days after LAD ligation. Effects on intraventricular conduction and ERP were also examined in animals 5-7 days after LAD ligation. The intraventricular conduction time (CT) was determined by excitation induced by a ventricular stimulation at various coupling intervals from 200 to 1,000 ms. SUN-1165 (1 and 3 mg/kg) showed a marked reduction in the frequency of ventricular ectopic beats 24 h after LAD ligation and was more potent than lidocaine. SUN-1165 (1 and 3 mg/kg) prolonged CT in the infarcted zones over a wide range of the coupling intervals and produced block of severely delayed conduction. In contrast, lidocaine prolonged CT only at short coupling intervals. Ventricular premature stimulation produced ventricular arrhythmias, which were prevented by pretreatment with SUN-1165 (3 mg/kg). ERP was prolonged by SUN-1165 (3 mg/kg). In conclusion, SUN-1165 showed antiarrhythmic effects in a canine model of myocardial infarction. A selective depression of delayed conduction in the infarcted zone and a prolongation of ERP probably contribute to this antiarrhythmic effect.