Influence of diphenylhydantoin on electrophysiological properties of the canine heart.

These studies were designed to examine the electrophysiological effects of diphenylhydantoin (Dilantin) on the heart of awake dogs. Recording electrodes were implanted over the sinoatrial node, bundle of His, and right bundle branch, and studies were performed 2 to 6 weeks following recovery. Diphenylhydantoin (10 mg/kg) increased heart rate, shortened A-V conduction time and had little or no effect on conduction velocity in Purkinje tissue or total ventricular activation time. Similar effects were noted when heart rate was controlled by pacing. Following cardiac denervation, diphenylhydantoin decreased heart rate and prolonged A-V conduction time. It raised the threshold of atrial and ventricular muscle with no change of refractory periods. In dogs with heart block, it decreased the maximal rate at which the atria would respond to stimulation. When ventricular tachycardia was induced in dogs with heart block, by toxic doses of deslanoside, diphenylhydantoin abolished the ectopic tachycardia and restored the control rhythm. ADDITIONAL