The correct answer is E. The calcium chan- nel blockers verapamil and diltiazem are both effective in slowing the rate and contractility of the heart. Both drugs decrease the magnitude of inward calcium current through L type calcium channels and also decrease the rate of recovery of the channel. It is this latter effect that depresses the sinus node pacemaker and slows atrioventricular conduction. Verapamil is a stronger negative inotrope than diltiazem, and therefore is more effective in decreasing heart rate and contractility.
Answer A is incorrect. Dihydropyridines are the family of drugs to which nifedipine belongs. The dihydropyridines are more potent vasodilators than verapamil or diltiazem and in general have less potent effects on the heart.
Answer B is incorrect. Diltiazem is a calcium channel blocker but is not as effective as verapamil in reducing the rate and contractility of the heart.
Answer C is incorrect. Nifedipine is least effective in reducing the rate and contractility of the heart; conversely, it is most effective in evoking vasodilation. Although nifedipine has some negative inotropic effect on the heart, the decrease in arterial blood pressure secondary to vasodilation elicits sympathetic reflexes that result in increases in heart rate and inotropy.
Answer D is incorrect. Nimodipine is another member of the dihydropyridine family with similar properties, but it is approved only for the management of stroke with subarachnoid hemorrhage.