The Comparative Electrophysiologic and Hemodynamic Effects of Verapamil in Puppies and Adult Dogs

Abstract

Verapamil has been studied extensively in adult animals. However, there is limited data about the effects of this antiarrhythmic agent in young animals. We studied the electrophysiologic and hemodynamic effects of verapamil in 5 awake, chronically instrumented puppies and in 6 anesthetized, acutely instrumented puppies. We compared the responses in puppies to those in 7 awake, chronically instrumented adult dogs and in 6 anesthetized, acutely instrumented adult dogs. In the awake, chronically instrumented animals, we measured heart rate and the effective refractory period of the atrio-ventricular specialized conduction system (ERP-AVSCS). In the anesthetized, acutely instrumented preparation, we measured heart rate, ERP-AVSCS, mean right atrial and systemic arterial blood pressure, and velocity of blood flow in the aorta, carotid and femoral arteries. We infused verapamil intravenously at doses of 50, 100, 200 and 400 microgram/kg. Verapamil (400 micrograms/kg) increased the ERP-AVSCS by 64% in awake, chronically instrumented puppies; 62% in awake, chronically instrumented adult dogs; 125% in anesthetized, acutely instrumented puppies, and 120% in anesthetized, acutely instrumented adult dogs. The effect of verapamil upon heart rate and ERP-AVSCS was more pronounced in anesthetized animals than in awake animals. Mean systemic arterial blood pressure was reduced by verapamil in anesthetized, acutely instrumented puppies and adult dogs. Verapamil reduced the velocity of aortic, femoral and carotid artery blood flow in anesthetized, acutely instrumented puppies.