Current concepts of silent myocardial ischemia

The definition, pathogenesis, incidence and characteristics, detection, treatment, and prognosis of silent myocardial ischemia (SMI) are reviewed. SMI is the occurrence of myocardial ischemia for which there is objective evidence (electrophysiological, hemodynamic, and metabolic changes) but no angina. Patients with SMI are classified as type 1 (completely asymptomatic), type 2 (SMI after myocardial infarction), and type 3 (both symptomatic and silent ischemia). Episodes of SMI are true ischemic events. The absence of pain may be due to defects in pain perception, an altered physiological response to ischemia, or a lesser degree of ischemia. The incidence of SMI is 2-5% in totally asymptomatic patients, 20-30% in patients who have suffered myocardial infarction, and 44-84% in patients who have symptomatic ischemia. SMI can be detected by exercise testing, portable electrocardiographic monitoring, or imaging techniques. Patients with SMI have more frequent adverse cardiac events (except death) than patients without SMI. The frequency of adverse cardiac events is similar in patients with angina and patients with SMI. SMI has been treated with nitrates, calcium-channel blockers, and beta blockers. Beta blockers appear to be the most consistent in reducing the number and duration of episodes. Combination therapy with beta blockers and nifedipine may be more effective than therapy with either agent alone. Because of the limited number of studies and the possible contribution to the results of spontaneous variability in the occurrence of SMI, no definite conclusions can be drawn about drug efficacy. There is no evidence that the prognosis of patients with SMI is altered by drug therapy; routine treatment with anti-ischemic drugs cannot be recommended. Patients must be evaluated individually, with aggressive management being reserved for those at high risk for myocardial infarction or other serious cardiac events.