Calcium channel blockers prevent calcium from entering into the heart muscle, and also from entering into the smooth muscle cells that cause blood vessels to constrict. By reducing calcium influx into muscle cells, calcium channel blockers cause the muscle cells to "relax." This relaxing effect results in the dilation of blood vessels, and a reduced force of contraction of the heart muscle. Some calcium channel blockers also slow the heart rate. (It is their blood vessel dilating effect that makes calcium blockers useful in hypertension.)
All these effects (blood vessel dilation, reduction in heart muscle contraction, and slower heart rate) reduce the amount of oxygen required by the heart muscle. Reducing the amount of oxygen used by the heart allows the heart to function longer without developing ischemia, even when blood flow through the coronary arteries is partially blocked by atherosclerosis. In patients with stable angina, calcium blockers measurably increase the amount of exercise that can be performed before angina occurs. Calcium blockers can be especially useful in patients with angina due to Prinzmetal's angina (coronary artery spasm), since they can directly prevent spasm of the coronary arteries.
Several calcium blockers are on the market, and they are not all alike.
The drugs nifedipine (Procardia, Adalat), Cardene (nicardipine), Plendil (felodipine), and Norvasc (amlodipine), cause significant dilation of blood vessels, and much less effect on the heart muscle and heart rate. The drug verapamil (Calan, Covera, Isoptin, Veralan) effects the heart muscle and slows the heart rate, and little effect on blood vessels. Diltiazem (Cardizem, Dilacor, Tiazak) has modest effects on both the heart muscle and the blood vessels.
In treating angina, the most commonly used calcium blockers are the longer-acting forms of diltiazem and verapamil, Norvasc, or Plendil. Nifedipine, especially its short-acting forms, should generally be avoided in patients with angina, since the pronounced blood vessel dilation produced by this drug can increase in adrenaline, leading to a more rapid heart rate, and consequently an increase in cardiac oxygen requirements (which can increase the chances of developing cardiac ischemia).
Common side effects with calcium channel blockers include headache, dizziness, flushing, and foot and ankle swelling. Verapamil also tends to cause constipation. The calcium blockers that affect the heart muscle and slow the heart rate should be used with caution (if at all) in patients who have had heart failure or bradycardia (slow heart rate).
In general, calcium blockers are used as a second-line therapy in treating angina; they are usually added only after a beta blocker has already been prescribed.
Read here for more on the noninvasive treatment of angina.
Source:
Abernethy, DR, Schwartz, JB. Calcium-antagonist drugs. N Engl J Med 1999; 341:1447.
