Changes in 6-min walk test is an independent predictor of death in chronic heart failure with reduced ejection fraction

Abstract

Aims Functional capacity provides important clinical information in patients with heart failure (HF) and reduced ejection fraction (HFrEF). The 6-min walk test (6MWT) is a simple and inexpensive tool for assessing functional capacity and risk. Although change in 6MWT is frequently used as a surrogate outcome in HF trials, the association with mortality is unclear. We aimed to assess the prognostic importance of changes in 6MWT.

Methods and results Patients with chronic HFrEF referred to HF outpatient clinics in Norway completed a 6MWT at the first visit (baseline) and at a stable follow-up visit after treatment optimization (follow-up). Absolute and relative changes in 6MWT were analysed in association with mortality risk using Cox regression models and flexible cubic splines. The study included 3636 HFrEF patients aged 67.3 ± 11.6 years, 23% women, with left ventricular ejection fraction 30 ± 7%. At baseline, mean 6MWT was 438 ± 125 m, median N-terminal pro-B-type natriuretic peptide (NT-proBNP) 1574 (732–3093) ng/L, and 27% had New York Heart Association (NYHA) class III/IV. After optimization of guideline-directed medical therapy (median 147 [86–240] days), 6MWT increased by mean 40 ± 74 m, NT-proBNP decreased by median 425 (14–1322) ng/L, and NYHA class improved in 38% of patients. Patients with greater improvements in 6MWT were younger, with greater improvements in NYHA class (r = 0.27, p < 0.001) and larger reductions in NT-proBNP concentrations (r = 0.19, p < 0.001). After mean 845 ± 595 days, 419 (11.5%) patients were dead. Both absolute and relative changes in 6MWT were non-linearly associated with survival, attenuating as 6MWT increased. A 50 m increase in 6MWT was associated with a 17% lower mortality risk (hazard ratio 0.84, 95% confidence interval 0.77–0.90, p < 0.001) in the fully adjusted model, including changes in NYHA class, NT-proBNP concentrations, and other established risk factors. The associations were more pronounced in patients with lower baseline 6MWT and higher age.

Conclusion Improvement in 6MWT in patients with HFrEF is associated with increased survival, independent of changes in NT-proBNP and NYHA class. These findings support 6MWT change as a surrogate outcome in HF trials.