We want to compare and contrast the cardiac and hemodynamic profiles of immediate-acting dihydropyridines-type calcium channel blockers (CCBs) and the nondihydropyridines verapamil and diltiazem (benzothiazepines). The most striking difference is that compared with nifedipine, verapamil and diltiazem?
|A||Are suitable for use in conjunction with a βblocker or digoxin|
|B||Cause a much higher incidence of reflex tachycardia|
|C||Cause significant dose-dependent slowing of A-V nodal conduction velocity|
|D||Have significant positive inotropic effects|
a. The dihydropyridines are relatively “selective” for their vascular effects. They cause significant arteriolar dilation, which usually activates the baroreceptor reflex that increases sympathetic influences on the heart: positive inotropy, positive chronotropy (reflex tachycardia can be severe), and increased automaticity and conduction velocity (dromotropic effects).
b. In contrast, diltiazem and verapamil not only exert arteriolar dilation (via calcium channel blockade there), but also direct cardiac depressant effects (due to calcium channel blockade).
c. These cardiac effects oppose, or blunt, reflex sympathetic cardiac activation: such problems are much less— often nonexistent—with the nondihydropyridines.
d. In fact, when reflex cardiac stimulation caused by other drugs (e.g., nitroglycerin) is problematic and must be controlled, either verapamil or diltiazem may be a reasonable alternative to the traditional agents for blocking the unwanted cardiac responses: the blockers. Moreover, a nondihydropyridine CCB is the drug of choice for controlling cardiac responses when a 3 blocker is contraindicated (e.g., in asthma).
e. Clavidpine is a new calcium channel blocker that has been approved for intravenous use. The drug is used in hypertensive emergencies.