Comparative effects of three calcium antagonists, diltiazem, verapamil and nifedipine, on the sinoatrial and atrioventricular nodes. Experimental and clinical studies.

Diltiazem, verapamil and nifedipine suppress sinoatrial (SA) nodal function in the excised rabbit heart. Clinically, however, their suppressive effect on the SA node is modified considerably by the reflex increase in sympathetic tone as a result of the fall in blood pressure caused by the vasodilating action of the calcium antagonists. Diltiazem, verapamil and nifedipine suppress atrioventricular (AV) nodal conduction and prolong refractory periods in the excised rabbit AV node. Clinically, diltiazem and verapamil exert a similar suppressive effect on the AV node and are useful for treating and preventing AV nodal reentrant tachycardia. Nifedipine, in clinically practical doses, has no antiarrhythmic properties, probably because of reflex activation of the sympathetic system secondary to its hypotensive effect, which is greater than that of the other two calcium antagonists. Diltiazem and verapamil may sometimes worsen AV conduction, especially in patients with conduction disturbances. Nifedipine, on the other hand, can be used as a coronary vasodilator with the least untoward effect on AV conduction.