[Electrophysiologic effects of calcium channel blocking agents on the sinus node function in anesthetized dogs...

The electrophysiologic effects of calcium channel blocking agents, diltiazem, verapamil and nifedipine, on the sinus node function were examined in 43 anesthetized closed-chest dogs in comparison with the effects of propranolol. The parameters of sinus node function, i.e. sinus cycle length (SCL), sinus node recovery time determined by overdrive suppression (SRT), both of which are thought to reflect sinus node automaticity, and sinoatrial conduction time estimated by Strauss method (SACT), were evaluated. Intravenously administered diltiazem (0.2 mg/kg), verapamil (0.1 mg/kg) and propranolol (0.1 approximately 0.2 mg/kg) increased SCL and SRT significantly although the increase of these parameters induced by nifedipine (0.03 mg/kg) was not statistically significant. The calcium channel blocking agents did not significantly affect SACT in contrast with propranolol which showed a prolonging effect. Thus calcium channel blocking agents suppressed sinus node automaticity yet had little effect on sinoatrial conduction.