Prognostic utility of the exercise thallium-201 test in ambulatory patients with chest pain: Comparison with cardiac catheterization

The goal of this study was to determine the prognostic utility of the exercise thallium-201 stress test in ambulatory patients with chest pain who also referred for cardiac catheterization. Accordingly, 4 to 8 year (mean ± 1SD, 4.6 ± 2.6 years) follow-up data were obtained for all but one of 383 patients who underwent both exercise thallium-201 stress testing and cardiac catheterization from 1978 to 1981. Eighty-three patients had a revascularization procedure performed within 3 months of testing and were excluded from analysis. Of the remaining 299 patients, 210 had no events and 89 had events (41 deaths, nine nonfatal myocardial infarctions, and 39 revascularization procedures ≥ 3 months after testing). When all clinical, exercise, thallium-201, and catheterization variables were analyzed by Cox regression analysis, the number of diseased vessels (when defined as ≥ 50% luminal diameter narrowing) was the single most important predictor of future cardiac events (χ² = 38.1) followed by the number of segments demonstrating redistribution on delayed thallium-201 images (χ² = 16.3), except in the case of nonfatal myocardial infarction, for which redistribution was the most important predictor of future events. When coronary artery was defined as 70% or greater luminal diameter narrowing, the number of diseased vessels significantly (p < .01) lost its power to predict events (χ² = 14.5). Other variables found to independently predict future events included change in heart rate from rest to exercise (χ² = 13.0), ST segment depression on exercise (χ² = 13.0), occurrence of ventricular arrhythmias on exercise (χ² = 5.9), and β-blocker therapy (χ² = 4.3). The exclusion of myocardial revascularization procedures as an event did not change the results significantly. Although the number of diseased vessels was the single most important determinant of future events, the exercise thallium-201 stress test when considered as a whole (which included the number of segments demonstrating redistribution on delayed thallium-201 images, change in heart rate from rest to exercise, ST segment depression on the electrocardiogram, and ventricular premature beats on exercise) was equally powerful (χ² = 41.6). Combination of both catheterization and exercise thallium-201 data was superior to either alone (χ² = 57.5) for determining future events. Exercise stress test alone (without thallium-201 data) was inferior to the exercise thallium-201 stress test or cardiac catheterization for predicting future events (χ² = 30.6). Thus the exercise thallium-201 stress test provides important prognostic information in ambulatory patients presenting with chest pain. When cardiac catheterization findings are known, exercise thallium-201 stress test data are additive in identifying patients at high risk for subsequent events.