134 Cardiovascular fitness and mortality following contemporary cardiac rehabilitation

Abstract

Exercise capacity has been demonstrated to be predictive of mortality in adults with and without coronary artery disease (CAD). However, the association between exercise capacity and outcomes in contemporary cardiac rehabilitation (CR) programs has not been as thoroughly assessed. Furthermore, the association between improvements in exercise capacity achieved through CR and long-term outcomes remains unexplored. We conducted a retrospective study of 2867 subjects with CAD who participated in CR in Calgary, Canada between 1996 and 2009. All subjects underwent initial treadmill testing, attended a 12 week multi-modality CR program including prescribed medication and exercise, and then underwent repeat treadmill testing. Additionally, 1696 subjects underwent treadmill testing at one year. Based on Metabolic equivalents (METs) calculated from the speed and grade of the last stage of the maximal exercise testing, subjects were classified as ‘low fitness' (<5 METs), ‘moderate fitness' (5-8 METs), or high fitness (>8 METs). Clinical and demographic characteristics were compared across fitness classes. Using Cox proportional hazards models, mortality was compared across fitness classes. Change in fitness at 12 weeks and one year relative to baseline were also assessed as predictors of mortality. Subjects in the lowest fitness category were older and had a higher burden of comorbid illnesses including diabetes and hypertension (all P < 0.0001). A greater portion of low fitness subjects were obese or had an elevated waist circumference (both P < 0.0001). Baseline fitness was predictive of long-Term mortality: relative to the low fitness group, subjects with moderate fitness had a hazard ratio (HR) of 0.43 (95% CI 0.30, 0.62), and those with high fitness a HR of 0.17 (95% CI 0.11, 0.26) (Figure). In adjusted analyses this effect persisted (P < 0.0001). Improvement in exercise capacity in 12 weeks was associated with decreased mortality only in the low fitness group, with a 30% reduction in mortality with each MET increase (P < 0.0001). At one year, each MET increase in exercise capacity was associated with a 22% reduction in mortality in the whole group (P < 0.0001). In this study of contemporary CR patients, higher baseline fitness was predictive of decreased mortality. The novel finding was that improvement in fitness over a CR program was associated with decreased mortality in those with low fitness alone, and improvements at one year were associated with decreased mortality across the entire group. Patients with low fitness at baseline should be targeted to increase their functional capacity in an effort to reduce their mortality.