Calcium channel blockers have an important role in the
pharmacotherapy of cardiovascular disorders. These agents act by inhibiting the slow inward current into excitable cells, exert direct negative inotropic, chronotropic, and dromotropic activity, and are potent
vasodilators. These direct effects are modified by reflex autonomic stimulation and by pathologic states. Serious adverse effects of the
calcium channel blockers are most frequently observed in patients with
ventricular dysfunction, conduction system disease, or concomitant beta blockade.
Calcium channel blockers are indicated in the treatment of
angina pectoris, supraventricular arrhythmias, and
hypertension. The use of these agents in patients with
hypertrophic cardiomyopathy,
congestive heart failure, and
pulmonary hypertension is investigational. The
calcium channel blockers are gaining increased importance in the management of patients undergoing cardiac surgery.
Verapamil is indicated for the treatment of post-cardiac-surgical
atrial flutter and fibrillation; however, the
calcium antagonists are not effective as prophylaxis against postoperative supraventricular arrhythmias. Laboratory studies have shown that drug interactions exist between
calcium channel blockers and inhalational
anesthetics and nondepolarizing
neuromuscular blocking agents; clinical studies have demonstrated that these interactions are rarely significant. Perioperative coronary
spasm can be effectively treated with the
calcium channel blockers. The timing of
calcium antagonist withdrawal prior to surgery is controversial, but continuation of
therapy until surgery is usually safe. The clinical significance of platelet function inhibition by the
calcium antagonists is unknown. Protection of ischemic myocardium by
calcium channel blockers has been demonstrated. Important interactions between the
calcium antagonists,
hypothermia, and the ionic constituents of
cardioplegia require further study before the role of these agents as adjuncts to clinical
cardioplegia is defined. Expanded indications and the introduction of new
calcium channel blockers will result in increased use of these agents in the future.