Value of an Exercise Workload ≥10 Metabolic Equivalents for Predicting Inducible Myocardial Ischemia

Abstract

We sought to identify extensive ischemia on exercise echocardiography (ExE) relative to workload in patients without known coronary artery disease and to investigate whether ExE is useful in predicting outcomes in those with high exercise capacity (≥10 metabolic equivalents [METs]) plus a maximal test (≥85% of their maximal age-predicted heart rate [MAPHR]). The analysis was performed on 4269 patients who underwent ExE, of whom 3995 achieved ≥85% of their MAPHR. These patients were divided according to the reached workload (<7, 7-9, or ≥10 METs) and compared for ExE results. Outcomes in the group achieving ≥10 METs plus ≥85% of their MAPHR (n=2221) were specifically assessed. Ischemia was defined as new/worsening wall motion abnormalities with exercise. ExE results were different between groups because the METs were lower. Still, among patients achieving ≥10 METs plus ≥85% of their MAPHR, 9.3% had extensive ischemia and 6% multiterritory disease. During follow-up in this subgroup, 108 patients died and 42 had a major cardiac event. Annualized mortality and major cardiac event rates were 0.84% and 0.32% in patients without ischemia versus 2.26% and 0.84% in those with ischemia, respectively (P<0.001 and P=0.002, respectively). Ischemia was an independent predictor of mortality (hazard ratio, 1.88; 95% confidence interval, 1.23-2.89; P=0.004) and major cardiac event (hazard ratio, 2.39; 95% confidence interval, 1.22-4.71; P=0.01). Patients without known coronary artery disease achieving ≥10 METs plus ≥85% of their MAPHR may still have ischemia. However, the low event rates even in those with ischemia limit the usefulness of imaging for assessing outcomes in this group.