Electrophysiologic effects of diltiazem, a calcium antagonist, in patients with impaired sinus or atrioventricular node function.

The electrophysiologic effects of diltiazem, a calcium antagonistic agent, were studied in 30 subjects with various degrees of sinus or AV node dysfunction. After diltiazem was administered, sinus activity was not depressed in control subjects, whereas marked inhibition was observed in some of the patients with sick sinus syndrome. Ventricular automaticity was little affected by this drug. The AV conduction system was significantly depressed, and there was no difference in degree between controls and AV block patients. The depression of the AV conduction system became more marked as the basic atrial cycle length was shortened. The drug had no apparent effects on atrial refractoriness, atrial echo zone, or the accessory pathway system. Conclusively, diltiazem affects mainly sinus and AV conduction systems. Its effect on the sinus mode may provide a hazardous problem in patients with the sick sinus sysdrome patients, while its effect on the AV node will have therapeutic value in patients with AV nodal re-entrant arrhythmias.