Cardiac electrophysiological effects of falipamil in the conscious dog: comparison with alinidine.

We studied the cardiac electrophysiological effects of falipamil, a specific bradycardic agent, in conscious dogs, in comparison with those of alinidine. Sinus rate, corrected sinus recovery time, and Wenckebach point were measured in six intact dogs. Atrial rate, ventricular rate, and atrial effective refractory period were measured in six atrioventricular-blocked dogs. In both groups, blood pressure was also monitored. Each dog received, with at least a three-day interval, falipamil (hydrochloride) and alinidine (hydrobromide) in four successive intravenous injections, 30 min apart, at 0.5, 0.5, 1, and 2 mg kg-1. Falipamil increased sinus rate and atrial rate, but decreased ventricular rate, whereas alinidine decreased sinus rate and ventricular rate, but increased atrial rate. Falipamil shortened corrected sinus recovery time and increased Wenckebach point, whereas alinidine lengthened corrected sinus recovery time and decreased Wenckebach point. Falipamil and alinidine increased atrial effective refractory period. Neither falipamil nor alinidine modified mean blood pressure in either group. Overall, these results show that (a) falipamil exhibits effects on the electrical activity of the heart, reflecting the predominant direct vagolytic effect of this drug, (b) alinidine exhibits effects reflecting the marked antiarrhythmic potential of this agent, and (c) thus indicate that two drugs with almost identical specific bradycardic properties can produce quite different electrophysiological effects in the conscious dog.