Coronary Artery DiseaseRelationship Between Exercise Workload During Cardiac Rehabilitation and Outcomes in Patients With Coronary Heart Disease

The purpose of this retrospective, observational study was to describe the relation between exercise workload during cardiac rehabilitation (CR), expressed as metabolic equivalents of task (METs), and prognosis among patients with coronary heart disease. We included patients with coronary heart disease who participated in CR between January 1998 and June 2007. METs were calculated from treadmill workload. Cox regression analysis was used to describe the relationship between METs and time to a composite outcome of all-cause mortality, nonfatal myocardial infarction, or heart failure hospitalization. Among 1,726 patients (36% women; median age 59 years [interquartile range, 52 to 66]), there were 467 events (27%) during a median follow-up of 5.8 years (interquartile range, 2.6 to 8.7). In analyses adjusted for age, sex, Charlson co-morbidity index, hypertension, diabetes, and CR referral diagnosis, METs were independently related to the composite outcome at CR start (Wald chi-square 43, hazard ratio 0.59 [95% confidence interval 0.51 to 0.70]) and CR end (Wald chi-square 47, hazard ratio 0.68 [95% confidence interval 0.61 to 0.76]). Patients exercising below 3.5 METs on exit from CR represent a high-risk group with 1- and 3-year event rates ≥7% and ≥18%, respectively. In conclusion, METs during CR is available at no additional cost and can be used to identify patients at increased risk for an event who may benefit from closer follow-up, extended length of stay in CR, and/or participation in other strategies aimed at maximizing adherence to secondary preventive behaviors and improving exercise capacity.