Effect of calcium-channel blocking drugs on focal ventricular arrhythmias induced by sub-epicardial epinephrine infusion in cats.

Sub-epicardial infusion of epinephrine (EP) in the dose of 3 x 10(-3) M in 2.5 x 10(-3) M CaCl2-0.9% NaCl (calcium-saline vehicle) at the rate of 10 microliters in the right ventricular myocardium of mongrel cats weighing between 2.8 and 3.3 kg, produced uniform, reversible and reproducible focal ventricular arrhythmia (VA) of varrying intensity and duration. Infusion of two calcium-channel blocking agents, verapamil (VP) and nifedipine (ND) at the site of arrhythmogenesis, in equimolar concentration of 3 x 10(-3) M alongwith EP in the same vehicle reduced the incidence, duration, peak and mean frequencies of arrhythmias while, the latent period of onset of arrhythmias increased significantly. Verapamil in equimolar concentration of 3 x 10(-3) M was found to be more effective than nifedipine in antagonizing EP-induced ventricular arrhythmias.