Inspiratory muscle strength and six-minute walking distance in heart failure: Prognostic utility in a 10 years follow up cohort study

BACKGROUND: Maximal inspiratory pressure (PI(max)) and 6-minutes walk distance test (6MWD) may be more available and feasible alternatives for prognostic assessment than cardiopulmonary testing. We hypothesized that the PI(max) and 6MWD combination could improve their individual accuracy as risk predictors. We aimed to evaluate PI(max) ability as a mortality predictor in HF and whether the combination to 6MWD could improve risk stratification. METHODS: Prospective cohort from HF Clinics of three University Hospitals. PI(max), 6MWD and pVO(2) were obtained at baseline. The end point was all cause mortality. RESULTS: Consecutive 256 individuals (50% woman, 57.4±10.4years) with low ejection fraction (LVEF) (31.8±8.6%) were followed up to 10years. During a median follow-up of 34.7 (IQR 37) months, 110 participants died. Mean±SD values were: pVO(2) 14.9±5.1mL/kg/min, PI(max) 5.5±1.3kPa and 6MWD 372±118m. In multivariate Cox regression, pVO(2), PI(max), 6MWD and LVEF were independent mortality predictors. The pVO(2) showed gold standard accuracy, followed by PI(max) (AUC = 0.84) and 6MWD (AUC = 0.74). Kaplan-Meier mean survival time (MST±SE) for lower (≤5.0kPa) and higher (>6.0kPa) PI(max) tertiles, were 37.9±2.8months and 105.0±5.2months respectively, and addition of 6MWD did not restratified risk. For intermediate PI(max) tertile, MST was 81.5±5.5months, but adding 6MWD, MST was lower (53.3±7.6months) if distance was ≤350m and higher (103.1±5.7months) for longer distances. CONCLUSION: PI(max) is an independent mortality predictor in HF, more accurate than 6MWD and LVEF. Addition of 6MWD empowers risk stratification only for intermediate PI(max) tertile. Although less accurate than pVO(2), this simpler approach could be a feasible alternative as a prognostic assessment.