Abstract 2600: Exercise Capacity on Exercise Treadmill Test Predicts Future Cardiac Events
Background: Exercise capacity on exercise treadmill testing (ETT) predicts mortality, but little is known about the association between exercise capacity and non-fatal cardiac events. Furthermore, the prognostic value of exercise capacity independent of a broad range of contemporary ETT variables has not been evaluated.
Methods: This cohort study enrolled 9,569 consecutive patients referred for ETT in a large HMO. The outcomes of interest were myocardial infarction, unstable angina, and coronary revascularization. Secondary outcomes included cardiac and all cause mortality. The primary predictor variable was exercise capacity as measured by metabolic equivalents (METs). Cox proportional hazards regression assessed the association between exercise capacity and the outcomes, adjusting for demographic, clinical, and ETT variables.
Results: The median length of follow-up was 2.7 years. Patients with lower exercise capacity were older, more likely to be female and had more co-morbid conditions compared to those with greater exercise capacity. In addition, patients with poor exercise capacity were more likely to have chest pain with exercise, ST segment changes, abnormal heart rate recovery, and an abnormal chronotropic index. In adjusted models, lower exercise capacity remained strongly and independently associated with increased risk of myocardial infarction, unstable angina and all-cause mortality, with a trend towards increased risk of cardiovascular mortality and revascularization (Table⇓).
Conclusion: Independent of patient characteristics and other ETT parameters, reduced exercise capacity is a powerful predictor of both nonfatal cardiovascular events and mortality. Given the magnitude of the association, further evaluation of the benefits of aggressive diagnostic and therapeutic strategies specifically directed at preventing cardiovascular events in patients with reduced exercise tolerance is warranted.