Effects of timolol and propranolol on inducible sustained ventricular tachyarrhythmias in dogs with subacute myocardial infarction.

Timolol and propranolol reduce the incidence of cardiac death after myocardial infarction (MI). To explore possible mechanisms of this reduction in mortality, the antiarrhythmic effects of these 2 beta blockers were compared in a dog model of inducible sustained ventricular tachycardia (VT) or fibrillation (VF) 4 to 6 days after experimental closed-chest MI. Dogs with inducible VT or VF underwent drug studies with timolol and propranolol; the sequence of drug administration was randomized. Timolol doses were 0.1, 0.3, and 1.0 mg/kg; propranolol doses were 1.0, 3.0 and 10.0 mg/kg. Timolol and propranolol were equally effective in abolishing inducible VT or VF: 77% of instances of inducible VT or VF responded to 1 or both beta blockers. The VF threshold was significantly elevated by both timolol and propranolol; the elevation in the VF threshold was significantly greater in "responders," i.e., dogs in whom VT was prevented by beta blockade (15 +/- 9 vs 8 +/- 9 mA, p less than 0.05). The ventricular effective refractory period was prolonged by both drugs; again, more so in the responders than in the nonresponders (16 +/- 9 vs 8 +/- 14 mA, p less than 0.05). The QTc interval was not significantly affected by either beta blocker. Among the responders, no difference was detected between timolol and propranolol in the extent to which the effective refractory period was prolonged or the VF threshold elevated. However, the highest dose of propranolol decreased the mean blood pressure significantly more than the comparable dose of timolol. In conclusion, timolol and propranolol are equally effective in abolishing inducible VT or VF in the dog after subacute MI.(ABSTRACT TRUNCATED AT 250 WORDS)