Variables measured during cardiopulmonary exercise testing as predictors of mortality in chronic systolic heart failure

Background Data from a cardiopulmonary exercise (CPX) test are used to determine prognosis in patients with chronic heart failure (HF). However, few published studies have simultaneously compared the relative prognostic strength of multiple CPX variables. Objectives The study sought to describe the strength of the association among variables measured during a CPX test and all-cause mortality in patients with HF with reduced ejection fraction (HFrEF), including the influence of sex and patient effort, as measured by respiratory exchange ratio (RER). Methods Among patients (n = 2,100, 29% women) enrolled in the HF-ACTION (HF-A Controlled Trial Investigating Outcomes of exercise traiNing) trial, 10 CPX test variables measured at baseline (e.g., peak oxygen uptake [Vo₂], exercise duration, percent predicted peak Vo₂ [%ppVo₂], ventilatory efficiency) were examined. Results Over a median follow-up of 32 months, there were 357 deaths. All CPX variables, except RER, were related to all-cause mortality (all p < 0.0001). Both %ppVo₂ and exercise duration were equally able to predict (Wald chi-square: ∼141) and discriminate (c-index: 0.69) mortality. Peak Vo₂ (ml·kg^-1·min^-1) was the strongest predictor of mortality among men (Wald chi-square: 129) and exercise duration among women (Wald chi-square: 41). Multivariable analyses showed that %ppVo₂, exercise duration, and peak Vo₂ (ml·kg^-1·min^-1) were similarly able to predict and discriminate mortality. In men, a 10% 1-year mortality rate corresponded to a peak Vo₂ of 10.9 ml·kg^-1·min^-1 versus 5.3 ml·kg^-1·min^-1 in women. Conclusions Peak Vo₂, exercise duration, and % ppVo₂ carried the strongest ability to predict and discriminate the likelihood of death in patients with HFrEF. The prognosis associated with a given peak Vo₂ differed by sex.