Silent ischemia and beta-blockade

Ambulatory electrocardiographic monitoring now makes it possible to document silent ischemic type ST segment changes that are seen in patients who suffer from stable angina and that often occur during periods of modest physical activity and mental arousal. These observations suggest that ischemic episodes occur as a consequence of a relatively complicated interplay of changes in oxygen supply and demand. Furthermore, silent ischemia displays a circadian variation with the greatest frequency in the morning, a pattern similar to that noted for the onset of acute myocardial infarction and the occurrence of sudden death. Ischemic episodes, whether symptomatic or silent, carry a serious prognosis in subsets of patients with coronary artery disease; therefore, prophylactic treatment may be desirable. Ideally this should be based on an understanding of the pathophysiological processes involved and should also be directed at the other coronary artery risk factors of the patients. The effects of beta-blockers, which reduce the duration and frequency of silent ischemic episodes, is well described. The effect is most pronounced in the morning, when the frequency of ischemia is highest, and the mechanism of action seems mainly mediated through a reduction in myocardial oxygen demand. beta-Blockers have shown effectiveness in both effort-induced angina and mixed angina, and increased anti-ischemic potency may be achieved by combination therapy with a calcium antagonist. Abrupt withdrawal of beta-blockers is associated with a rebound increase in ischemic activity, which is mainly silent. Further studies are needed to determine whether improved control of silent ischemia reduces the risk of adverse cardiac outcomes.