An Index for Evaluating Exercise Capacity Improvement after Cardiac Rehabilitation in Patients after Myocardial Infarction

Abstract

Objective We investigated relationships among predictors of improvement in exercise capacity after cardiac rehabilitation programs in patients after acute myocardial infarction. Methods We carried out a secondary analysis of data from 41 patients with a left ventricular ejection fraction ≥ 40% who underwent cardiac rehabilitation after the first myocardial infarction. Participants were assessed using a cardiopulmonary exercise test and stress echocardiography. A cluster analysis was performed, and the principal components were analyzed. Results Two distinct clusters with significantly different (P =.005) proportions of response to treatment (peak VO2 ≥ 1 mL/kg/min) were identified among patients. The first principal component explained 28.6% of the variance. We proposed an index composed of the top 5 variables from the first component to represent the improvement in exercise capacity. The index was the average of scaled O2 uptake and CO2 output at peak exercise, minute ventilation at peak, load achieved at peak exercise, and exercise time. The optimal cutoff for the improvement index was 0.12, which outperformed the peak VO2 ≥ 1 mL/kg/min criterion in recognizing the clusters, with a C-statistic of 91.7% and 72.3%, respectively. Conclusion The assessment of change in exercise capacity after cardiac rehabilitation could be improved using the composite index.