PREVALENCE AND PROGNOSTIC-SIGNIFICANCE OF EXERCISE-INDUCED SILENT-MYOCARDIAL-ISCHEMIA IN APPARENTLY HEALTHY-SUBJECTS

The addition of thallium-201 (Tl-201) 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 Tl-201 scintigraphy immediately following maximal treadmill exercise. Four subsets of subjects were derived: (1) negative ECG and negative Tl-201; (2) positive ECG and negative Tl-201; (3) negative ECG and positive Tl-201; (4) positive ECG and positive Tl-201. A total of 66 individuals (16%) had positive ECGs and 55 (14%) had positive Tl-201 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 > 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 Tl-201 test results versus an event rate of 3-12% for the other 3 groups (p < 0.001). By proportional hazards analysis, age, hypertension, exercise duration, and a concordant positive ECG and Tl-201 scan were independent predictors of future coronary events. A concordant abnormal ECG and Tl-201 response imparted a 3.6-fold relative event risk. Although not practical for screening the general population, combined exercise ECG and Tl-201 scintigraphy warrants further investigation as a diagnostic strategy in high-risk subsets with additional coronary risk factors.