Prevalence and prognostic significance of exercise-induced silent myocardial ischemia in apparently healthy subjects.

The addition of thallium-201 (201Tl) scintigraphy to traditional exercise electrocardiography (ECG) was assessed to determine whether the combination was a more accurate predictor of future coronary events than exercise ECG alone in an apparently healthy population. There were 407 participants enrolled in the Baltimore Longitudinal Study of Aging. The participants, who had no clinical or resting ECG evidence of coronary artery disease, underwent 201Tl scintigraphy immediately following maximal treadmill exercise. Four subsets of subjects were derived: (1) negative ECG and negative 201Tl; (2) positive ECG and negative 201Tl; (3) negative ECT and positive 201Tl; (4) positive ECG and positive 201Tl. A total of 66 individuals (16%) had positive ECGs and 55 (14%) had positive 201Tl scans. Concordant positive results in both tests were seen in 23 subjects (6%), with a 7-fold increase in prevalence from ages 40-59 years to greater than 80 years. Over a mean follow-up of 4.6 years, cardiac events (angina pectoris, myocardial infarction, or cardiac death) occurred in 40 of 407 volunteers (9.8%). Analysis revealed a 48% incidence of cardiac events in the subset with concordant abnormal ECG and 201Tl test results versus an event rate of 3-12% for the other 3 groups (p less than 0.001). By proportional hazards analysis, age, hypertension, exercise duration, and a concordant positive ECG and 201Tl scan were independent predictors of future coronary events. A concordant abnormal ECG and 201Tl response imparted a 3.6-fold relative event risk. Although not practical for screening the general population, combined exercise ECG and 201Tl scintigraphy warrants further investigation as a diagnostic strategy in high-risk subsets with additional coronary risk factors.