EFFECTS OF DISOPYRAMIDE ON SA NODAL PACEMAKER ACTIVITY AND CONTRACTILITY IN THE ISOLATED BLOOD-PERFUSED ATRIUM OF THE DOG

The isolated blood-perfused preparations of canine atrium were suspended in a bath and perfused with arterial blood led from the carotid artery of the heparinized donor dog. Disopyramide caused dose-related negative chronotropic and inotropic effects in a dose range of 30-1000 μg when injected directly into the cannulated sinus node artery of the isolated atrium. The order of potencies for inducing the negative chronotropic effect in isolated atrium preparations was verapamil > propranolol > lidocaine = quinidine > phenytoin ≥ disopyramide > procainamide. On the other hand, the order of potencies for inducing the negative inotropic effect was verapamil = propranolol > lidocaine ≥ phenytoin > disopyramide > procainamide ≥ quinidine. When disopyramide (1 mg/ kg or 3mg/kg) was administered i.v. into the jugular vein of the donor dog,the systemic blood pressure atrium were donor dog was markedly decreased. However, the tension developed and sinus rate of the isolated atrium were only slightly decreased. Disopyramide produced greater suppression at higher frequencies and slightly depressed the calcium chloride-induced positive inotropic effects. © 1979.