COMPARATIVE-STUDY OF THE VARIOUS CLASSES OF ANTIARRHYTHMIC DRUGS ON ISCHEMIC VENTRICULAR-FIBRILLATION

A comparative study of the various classes of antiarrhythmic drugs as agents protecting against ischaemia-induced ventricular fibrillation w as undertaken in the pig in situ heart, in anaesthetized animals which were subjected to complete temporary occlusion of the left anterior d escending coronary artery. This occlusion resulted in fibrillation aft er a time which varied in inverse ratio to vulnerability to fibrillati on. However, as this time did not exceed a few minutes, time to onset of fibrillation could be repeatedly measured in the course of an exper iment, in the absence or in the presence of an antiarrhythmic drug. Un der ventricular pacing at a constant rate, 180 beats/min, all the clas s I; antiarrhythmic drugs, flecainide, disopyramide and lidocaine, in clinical dose range, reduced time to fibrillation to a large extent (2 5 to 50 %) at the maximum of their action, with gradual return to cont rol values within less than one hour. The enhancement of vulnerability to fibrillation was accompanied by reduction in intraventricular cond uction velocity and fibrillation rate. With the same ventricular pacin g, no change was observed in time to fibrillation under the influence of propranolol or amiodarone. As for verapamil, it lengthened this tim e considerably, up to 600 %. However, bradycardia produced in usual ci rcumstances ensures a real protection against ischaemic fibrillation w ith propranolol and amiodarone and enhances protection directly exerte d by verapamil.