The Haemodynamic Effects of Nifedipine, Verapamil and Diltiazem in Patients with Coronary Artery Disease

Summary

Of the 3 most widely used calcium antagonists — nifedipine, verapamil and diltiazem — nifedipine is the most potent arterial vasodilator. Increases in cardiac output and coronary blood flow following nifedipine administration result in part from the afterload reduction. Reflex adrenergic stimulation produces an increase in heart rate and masks a direct inhibitory effect on myocardial contractility. The negative inotropic action of nifedipine is observed during intracoronary administration or may be made apparent by concurrent β-blocker therapy.

While verapamil is also a potent vasodilator, negative inotropic and dromotropic properties are more apparent in therapeutically used dosages. Reflex sympathetic activation is also triggered by verapamil, with an offsetting of the negative inotropic effects such that little change in cardiac output results. A decrease in myocardial oxygen consumption, with or without a decrease in coronary sinus blood flow, has regularly been observed following verapamil administration. Reduced oxygen demand appears to he a major mechanism of its antianginal effect. The heart rate × systolic pressure product is decreased both by the fall in arterial pressure and, particularly after oral administration, by a decrease in heart rate.

Diltiazem produces similar haemodynamic and electrophysiological effects to those of verapamil but has less potency in inducing arterial dilatation and more of a tendency to slow the heart rate. Diltiazem does not appear to cause significant increases in coronary blood flow or bring about improvement in ejectional and isovolumic indices of myocardial contraction — evidence of its intrinsic negative inotropic effect.