Study of the ventricular antifibrillatory effects of calcium channel blocking agents in comparison with lidocaine on canine normal heart in situ.

The ventricular antifibrillatory effects of two calcium channel blocking agents have been studied by determining fibrillation threshold several times in the course of an experiment on dogs placed under total cardiopulmonary by-pass to avoid the impairment of the myocardium properties subsequent to the interruption of blood circulation. These drugs were used in therapeutic or even higher doses (verapamil 0.40 mg.kg-1, diltiazem 0.60 mg.kg-1). They failed to modify fibrillation threshold significantly, and did not influence fibrillation rate or the effective refractory period of contractile fibres. Lidocaine, on the contrary, under the same experimental conditions, induced a dose-dependent rise in fibrillation threshold of up to nearly 200%, correlated to a fall in fibrillation rate and a prolongation in effective refractory period.