Prognostic value of combined exercise and recovery electrocardiographic analysis

Background: Heart rate-adjusted ST-segment depression (ST/HR) analysis improves the diagnostic accuracy of exercise testing, but its prognostic value has not been evaluated in unselected populations. We prospectively used comparative exercise-recovery ST/HR analysis to predict outcome in a consecutive cohort of outpatients referred for exercise testing. Methods: The stress-recovery index, defined as the difference between ST/HR areas during exercise and recovery, was derived in 1163 patients (median age, 60 years; interquartile range, 54-65 years). All-cause mortality and the combination of death or nonfatal myocardial infarction were target end points. The individual effect of clinical and exercise-testing data on outcome was evaluated by Cox regression analysis using separate models for each group of variables. Model validation was performed using bootstrap methods adjusted by the degree of optimism in estimates. Survival analysis was performed with the product-limit Kaplan-Meier method. Results: During a 33-month follow-up, 48 deaths and 72 nonfatal myocardial infarctions occurred. After adjusting for confounding variables, hypertension (hazard ratio, 1.80; 95% confidence interval, 1.26-2.59), ST/HR index (hazard ratio, 1.32; 95% confidence interval, 1.04-1.66; for interquartile difference), and stress-recovery index (hazard ratio, 0.75; 95% confidence interval, 0.65-0.86; for interquartile difference) were predictive of death or nonfatal myocardial infarction, whereas hypertension (hazard ratio, 3.67; 95% confidence interval, 2.00-6.73) and stress-recovery index (hazard ratio, 0.55; 95% confidence interval, 0.48-0.63; for interquartile difference) were predictive of all-cause mortality. In addition, stress-recovery index increased the prognostic power of the model on top of clinical and exercise-testing variables and provided significant discrimination for survival. Conclusion: Combined evaluation of ST/HR analysis during exercise and recovery improves the prognostic capacity of standard exercise electrocardiography.