Beta-adrenergic blockers in silent myocardial ischemia

Factors contributing to the development of exercise-induced painful ischemia, such as actions of the central nervous system and catecholamines, have been well identified, but the mechanisms by which nonexercise-related silent episodes of ischemia are provoked are unknown. Possible mechanisms receiving much study in recent years are those having the potential to influence the myocardial oxygen supply-demand relation. Beta-adrenergic receptor stimulations, by increasing myocardial oxygen demand through augmentation of heart rate and contractility (beta 1), may mediate responses that cause ischemia or perpetuate ischemic episodes induced by other means. Other receptors (beta 2) may mediate coronary and peripheral vascular constriction, limiting myocardial oxygen supply and further increasing myocardial oxygen demand. Studies have investigated the effect of beta blockade on ischemic episodes in patients with a variety of clinical forms of coronary heart disease. Beta blockade has been shown to reduce the frequency and duration of silent and painful ischemic episodes in patients with effort angina and rest angina. The data suggest that heart rate and perhaps other changes observed with use of beta blockade play an important role in silent ischemia; heart rate at specific times throughout the day, particularly in the late A.M., and the increase in heart rate seen in conjunction with silent ischemic episodes are all decreased with administration of beta blockade. Results of a recent study focusing only on silent ischemia showed that beta-blocker treatment with metoprolol, compared with placebo, significantly reduced total silent ischemic time (frequency and duration of episodes) in all periods examined.