Prevalence and prognostic significance of exercise-induced silent myocardial ischemia detected by thallium scintigraphy and electrocardiography in asymptomatic volunteers.

Abstract

Although a silent ischemic electrocardiographic response to treadmill exercise in clinically healthy populations is associated with an increased likelihood of future coronary events (i.e., angina pectoris, myocardial infarction, or cardiac death), such a response has a low predictive value for future events because of the low prevalence of disease in asymptomatic populations. To examine whether detection of reduced regional perfusion by thallium scintigraphy improved the predictive value of exercise-induced ST segment depression, we performed maximal treadmill exercise electrocardiography (ECG) and thallium scintigraphy (20`T1) in 407 asymptomatic volunteers 40-96 years of age (mean=60) from the Baltimore Longitudinal Study on Aging. The prevalence of exercise-induced silent ischemia, defined by concordant ST segment depression and a thallium perfusion defect, increased more than sevenfold from 2% in the fifth and sixth decades to 15% in the ninth decade. Over a mean follow-up period of 4.6 years, cardiac events developed in 9.8% of subjects and consisted of 20 cases of new angina pectoris, 13 myocardial infarctions, and seven deaths. Events occurred in 7% of individuals with both negative 20MT1 and ECG, 8% of those with either test positive, and 48% of those in whom both tests were positive (p<0.001). By proportional hazards analysis, age, hypertension, exercise duration, and a concordant positive ECG and 201TT result were independent predictors of coronary events. Furthermore, those with positive ECG and 201T1 had a 3.6-fold relative risk for subsequent coronary events, independent of conventional risk factors. Thus, in an asymptomatic population, the presence of exercise-induced silent myocardial ischemia increases progressively with age and identifies a small group of subjects with a strikingly high incidence of subsequent coronary events. (Circulation 1990;81:428-436) A lthough much recent attention has focused on the detection of silent myocardial ischemia in patients with known coronary artery disease, there remains considerable controversy concerning the prevalence and prognosis of silent ischemia in asymptomatic populations. Numerous studies'1-" have shown that an ischemic ST segment response to exercise is a risk factor for future coro-

Severity of Coronary Artery Calcification by Electron Beam Computed Tomography Predicts Silent Myocardial Ischemia

“…7 In the Baltimore Longitudinal Study on Aging, few asymptomatic subjects had an abnormal stress ECG (16%) or thallium perfusion scan (14%). 8 Although subjects who had abnormal results for both tests had a reduced event-free survival (52%), this was observed in only 5% of individuals screened; likewise, only 4.4% of our subjects had both abnormal ETT and perfusion imaging. The low incidence of abnormal ETT or SPECT precludes their use as primary screening tests for early detection and treatment of CAD.…”

“…The presence and extent of stress-induced myocardial ischemia detected by SPECT are known to predict subsequent outcome. [3][4][5][6][7][8] Our results indicate that most subjects with coronary calcium do not have inducible ischemia but that the likelihood of ischemia increases with total CACS, particularly with scores Ն400. In fact, total CACS Ն400 identified a group in whom a large percentage of subjects (46%) had demonstrable ischemia.…”

“…Our results support previous studies demonstrating that asymptomatic subjects with cardiac risk factors generally have normal ETT and perfusion scans. [7][8][9] In the Lipid Research Clinics trial, 9 only 8.3% of 3775 asymptomatic men with hyperlipidemia had exercise-induced ECG ischemia. In a study of middle-aged siblings of patients with premature CAD, the stress ECG was abnormal in only 10% and thallium imaging in 22%.…”

“…However, currently available noninvasive techniques, such as exercise treadmill testing (ETT) and myocardial single photon emission computed tomography (SPECT), can identify only patients with advanced CAD who manifest myocardial ischemia. 1,2 Although the presence and extent of left ventricular ischemia can accurately identify individuals at high risk for cardiac events, [3][4][5][6][7][8] the low prevalence of a positive test result among asymptomatic subjects with cardiac risk factors mitigates against this approach. [7][8][9] Electron beam computed tomography (EBCT) is a new noninvasive technique that can detect coronary atherosclerosis even at its earliest stages on the basis of the presence and severity of coronary artery calcification.…”

“…1,2 Although the presence and extent of left ventricular ischemia can accurately identify individuals at high risk for cardiac events, [3][4][5][6][7][8] the low prevalence of a positive test result among asymptomatic subjects with cardiac risk factors mitigates against this approach. [7][8][9] Electron beam computed tomography (EBCT) is a new noninvasive technique that can detect coronary atherosclerosis even at its earliest stages on the basis of the presence and severity of coronary artery calcification. 10 Although calcification severity predicts the presence of significant anatomic CAD, 11,12 there is little information as to whether the coronary artery calcium score (CACS) can identify asymptomatic individuals at high risk for having myocardial ischemia among a larger, asymptomatic, heterogeneous population with cardiac risk factors.…”