The effects of diltiazem hydrochloride on the cardiac conduction: a clinical study of His bundle electrogram.

The effects of diltiazem hydrochloride, a new Ca++ antagonistic antianginal drug, on the cardiac conductivity were evaluted in 10 patients with atherosclerotic heart disease. His bundle electrograms were obtained by catheter technique. R-R, A-H and H-V intervals were measured before and after intravenous administration of diltiazem. Diltiazem acted towards significant prolongation in A-H interval. R-R and H-V intervals were insensitive to diltiazem. Diltiazem did not interrupt the cardiac effects of atropine when A-H prolongation was still observed in the subject pretreated with atropine. In short, diltiazem depresses the conductivity of the atrioventricular node selectively and this is not mediated through vagus tone change. This Ca++ antagonist induced A-H prolongation strongly suggests the contribution of Ca++ current on the generation of atrioventricular nodal action potential in humans.