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 We 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 χ2: ~141) and discriminate (c-index: 0.69) mortality. Peak VO2 (mL·kg−1·min−1) was the strongest predictor of mortality among men (Wald χ2: 129) and exercise duration among women (Wald χ2: 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 mlkg−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 V2 differed by sex.