Six-minute walking test but not ejection fraction predicts mortality in elderly patients undergoing cardiac rehabilitation following coronary artery bypass grafting

Background: Age-related effects on the ability of 6-min walking test (6MWT) and ejection fraction (EF) to predict mortality in coronary artery bypass grafting (CABG) patients undergoing cardiac rehabilitation (CR) is still debated. Design and methods: In order to verify the role of 6MWT and EF on all-cause mortality in patients undergoing CR following CABG, 882 CABG patients undergoing CR stratified in adults (<65 years) and elderly (>= 65 years) were studied. Results: At the admission, EF was 52.6 +/- 9.1% in adults and 51.3 +/- 8.9% in elderly (p = 0.234, NS) while 6MWT was 343.8 +/- 93.5 m in adults and 258.9 +/- 95.7 m in elderly (p < 0.001). After 42.9 +/- 14.1 months follow up, mortality was 8.2% in adults and 10.9% in elderly (p = 0.176, NS). Cox regression analysis shows that EF >= 50% and 6MWT >= 300 m are protective on mortality in all CABG patients before CR. However, EF >= 50% in adults (HR 0.18, 95% CI 0.06-0.49, p < 0.005) but not in elderly (HR 1.16, 95% CI 0.45-3.42, p = 0.354, NS) and 6MWT >= 300 m in elderly (HR 0.34, 95% CI 0.10-0.79, p = 0.033) but not in adults (HR 0.76, 95% CI 0.31-2.12, p = 0.654, NS) exert a protective role on mortality. Conclusions: Our results indicate that both EF >= 50% and 6MWT >= 300 m independently protect against mortality in CABG patients before CR. However, their protective role is age dependent. In fact, EF >= 50% is protective in adults but not in elderly while 6MWT >= 300 m is protective in elderly but not in adult patients.