Comparison of maximum versus submaximum exercise testing in providing prognostic information after acute myocardial infarction and/or coronary artery bypass grafting.

Abstract

Exercise testing after acute myocardial infarction (AMI) provides prognostic information. In many studies submaximum exercise tests performed until a given work load, metabolic equivalents (METs) level, or heart rate were used or patients discontinued the exercise test prematurely because of symptoms. We showed recently that peak oxygen uptake during maximum exercise provides independent prognostic information in patients with coronary artery disease. It is, however, not known whether maximum exercise testing is superior in predicting mortality than testing until a target level. Second, it is unclear which target end point best classifies patients at increased risk. Therefore, the independent relation between mortality and indexes of, respectively, maximum and submaximum exercise capacity, were analyzed in 527 patients, who were tested until exhaustion. To express submaximum exercise capacity dichotomous variables (the ability to reach a target METs level or not), and a continuous variable relative to maximum exercise capacity (the ventilatory anaerobic threshold) were used. After adjustment for significant covariates, peak oxygen uptake was significantly related to all-cause and cardiovascular mortality. The target level of 5 METs and the ventilatory anaerobic threshold, when expressed in absolute workload, were related to mortality when unadjusted, but after adjustment for age and other confounders significancy was lost. In multiple Cox regression analysis, the prognostic power of peak oxygen uptake remained significant when 5 METs or the anaerobic threshold were forced into the equations. When analyzing the relation of various METs levels with mortality, the 7 METs level was independently related to all-cause and cardiovascular mortality and yielded the highest diagnostic accuracy. We conclude that maximum exercise testing is more potent in predicting mortality than the ability to reach a predetermined level of exercise, such as the commonly used 5 METs level or the anaerobic threshold. Otherwise, the use of a higher target level of 7 METs is recommended.