Effect of antiarrhythmic drugs on the ventricular fibrillation induced by low intensity train pulses.

We evaluated the effects of antiarrhythmic drugs on ventricular fibrillation threshold (VFT) by analysing the electrophysiologic parameters obtained from strength-interval curves. The VFT determined by low intensity train pulses was significantly increased from the control value under the administration of clinical dosage of procainamide, lidocaine, propranolol, bepridil and prenylamine, although not verapamil. The elevation of VFT could be explained by changes in the strength-interval curve induced by the drugs, including disappearance of dip phenomenon, supernormal period, prolongation of effective refractory period (ERP) and elevation of end diastolic threshold (EDT).