Value of an exercise workload higher or equal to 10 metabolic equivalents for predicting low risk of inducible myocardial ischemia

Abstract

Objectives: To identify the prevalence of extensive ischemia on exercise echocardiography (ExE) relative to workload in patients without known coronary artery disease (CAD), and to investigate whether ExE is useful to assess outcome in those with high exercise capacity (≥10 metabolic equivalents (METs) plus a maximal test (≥85% of their Maximal Age-Predicted Heart Rate (MAPHR). Background: Recent work has suggested low reach of imaging in patients who achieve ≥10 METs and ≥85% of their MAPHR during exercise. Methods: Retrospective analysis on 4,269 patients who underwent ExE, of whom 3,995 achieved ≥85% of their MAPHR. These patients were divided according to the reached workload (<7, 7 to 9, or ≥10 METs) and were compared for ExE results, particularly the prevalence of extensive ischemia (≥3 ischemic segments). Outcome in the group achieving ≥10 METs plus ≥85% of their MAPHR (n=2,221) was specifically assessed. Ischemia was defined as the development of new/worsening wall motion abnormalities with exercise. Results: ExE results were significantly different between groups as the achieved METs were lower. Still, among patients achieving ≥10 METs plus ≥85% of their MAPHR, 6% had extensive ischemia and 9.3% multiterritory disease. During follow-up of 4.3±3.4 years in this group, 108 patients died and 42 had a MACE. The 5-year mortality and MACE rates were 4.2% and 1.6% in patients without ischemia vs. 11.3% and 4.2% in those with ischemia (p <0.001, and p=0.002, respectively). Ischemia was an independent predictor of mortality (hazard ratio [HR] 1.88, 95% confidence interval [CI] 1.23-2.89, p=0.004) and MACE (HR 2.39, 95% CI 1.22-4.71, p=0.01). Conclusions: Patients with theoretically good prognosis by exercise testing, such those without known CAD achieving ≥10 METs plus ≥85% of their MAPHR may still have significant risk. Switching these patients to exercise ECG testing alone could deny important medical treatment or revascularization procedures.