Prognostic implications of myocardial ischemia during daily life in low risk patients with coronary artery disease

Cardiology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892.

OBJECTIVES. The purpose of this study was to determine the incidence and prognostic importance of myocardial ischemia detected by ambulatory monitoring in low risk, medically managed patients with coronary artery disease. BACKGROUND. Previous studies have demonstrated that certain high risk subsets of patients with coronary artery disease have improved survival with revascularization. The remaining low risk medically managed patients may still have episodes of silent ischemia during daily living, but the frequency and prognostic implications of such episodes in this group are unknown. METHODS. We prospectively studied the incidence and prognostic significance of ST segment changes recorded during daily activities in 116 asymptomatic or mildly symptomatic low risk patients with native coronary artery disease who were followed up for 29 +/- 13 months. Low risk patients were selected after excluding patients with 1) left main disease; 2) three-vessel coronary artery disease and left ventricular dysfunction at rest; 3) three-vessel disease and inducible ischemia during exercise; and 4) two-vessel disease, left ventricular dysfunction and inducible ischemia. RESULTS. Forty-five patients (39%) had transient episodes of ST segment depression during 48-h electrocardiographic (ECG) monitoring (total 217 episodes, lasting 7,223 min, 82% of episodes silent). There were eight acute cardiac events (seven myocardial infarctions, one episode of unstable angina) and nine patients underwent elective revascularization. Seven of the eight acute events occurred in patients without silent ischemia during monitoring. Kaplan-Meier survival analysis revealed no significant differences in event-free survival from either acute or total events in subgroups with or without silent ischemia during ambulatory ECG monitoring. None of the clinical, treadmill exercise, radionuclide ventriculographic or cardiac catheterization variables were predictive of outcome by Cox multivariate proportional hazard function analysis. Analysis of coronary arteriograms before and after acute cardiac events revealed that in five of the six patients studied, acute occlusion occurred in a coronary artery different from the artery with the severest stenosis on initial angiography. CONCLUSIONS. In patients categorized as at low risk on the basis of the results of cardiac catheterization and stress testing, silent myocardial ischemia during daily life was not uncommon, and its presence failed to predict future coronary events.

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