Calcium antagonists and angina at rest

Prinzmetal's variant angina is associated with transmural myocardial ischemia due to coronary arterial spasm with or without obstructive coronary artery disease. Unstable angina may be caused by a reduction in coronary blood flow due to spasm or enhanced platelet aggregability or to an increase in myocardial oxygen requirements precipitated by physical activity, emotional excitement, or other factors. Since calcium channel blocking agents both prevent coronary spasm and reduce one or more determinants of myocardial oxygen consumption, they should be useful in the treatment of both Prinzmetal's and unstable angina. Many clinical trials, including some randomized and controlled studies, have convincingly demonstrated the efficacy of verapamil, nifedipine, and diltiazem in Prinzmetal's angina. Although there are few comparative trials, studies from this laboratory have found verapamil and nifedipine similar in efficacy. In unstable angina, three randomized and controlled clinical trials demonsrated that angina was reduced by verapamil in most but not in all patients. One large trial using nifedipine showed it to be superior to placebo, especially in patients whose angina was accompanied by ST-segment elevation. Only uncontrolled reports are available for diltiazem, but calcium antagonists, either alone or in combination with conventional medical therapy, appear effective in unstable angina.