Dose of cardiac rehabilitation to reduce mortality and morbidity: A population-based study

BACKGROUND: There is wide variability in cardiac rehabilitation (CR) dose (ie, number of sessions) delivered, and no evidence-based recommendations regarding what dose to prescribe. We aimed to test what CR dose impacts major adverse cardiovascular events (MACEs). METHODS AND RESULTS: This is an historical cohort study of all patients who had coronary artery disease and who initiated su-pervised CR between 2002 and 2012 from a single major CR center. CR dose was defined as number of visits including exercise and patient education. Follow-up was performed using record linkage from the Rochester Epidemiology Project. MACEs included acute myocardial infarction, unstable angina, ventricular arrhythmias, stroke, revascularization, or all-cause mortality. Dose was analyzed in several ways, including tertiles, categories, and as a continuous variable. Cox models were adjusted for factors associated with dose and MACE. The cohort consisted of 2345 patients, who attended a mean of 12.5±11.1 of 36 prescribed sessions. After a mean follow-up of 6 years, 695 (29.65%) patients had a MACE, including 231 who died. CR dose was inversely associated with MACE (hazard ratio, 0.66 [95% CI]; 0.55– 0.91) in those completing ≥20 sessions, when compared with those not exposed to formal exercise sessions (≤1 session; log-rank P=0.007). We did not find evidence of nonlinearity (P≥0.050), suggesting no minimal threshold nor ceiling. Each additional session was associated with a lower rate of MACE (fully adjusted hazard ratio, 0.98 [95% CI, 0.97– 0.99]). Greater session frequency was also associated with lower MACE risk (fully adjusted hazard ratio, 0.74 [95% CI, 0.58– 0.94]). CONCLUSIONS: CR reduces MACEs, but the benefit appears to be linear, with greater risk reduction with higher doses, and no upper threshold.