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 (MIP) and 6-minute walk distance test (6MWT) are considered more available and feasible alternatives for prognostic assessment in heart failure (HF) than gold standard cardiopulmonary testing. However, their combined value in HF mortality risk was not yet established. Objectives To evaluate MIP ability as a mortality predictor in HF and whether its combination with 6MWT could improve risk stratification. Methods: Prospective cohort from HF Clinics of three University Hospitals in Brazil. Consecutively, 256 individuals (50% woman, 57.4 ± 10.4years) with low ejection fraction (LVEF) (31.8 ± 8.6%) were enrolled, and followed up to 10years. Peak VO2 (pVO 2 ), MIP and 6MWT were obtained at baseline. The endpoint was all-cause mortality. Results Mean ± SD pVO 2 was 14.9 ± 5.1mL/kg/min, MIP 5.5 ± 1.3kPa and 6MWT 372 ± 118m. During follow up (mean 41.5 ± 28.7months), 110 participants died. In multivariate Cox regression, pVO 2 , MIP 6MWT, LVEF were independent mortality predictors ( TABLE ). The pVO 2 showed gold standard accuracy, followed by MIP (AUC = 0.84) and 6MWT (AUC = 0.74). Kaplan-Meier mean survival time (MST) for lower (≤5.0kPa) and higher (>6.0kPa) MIP tertiles, were 37.9 ± 2.8months and 105.0 ± 5.2months respectively, and 6MWT did not restratified risk. For the intermediate MIP tertile, MST was 81.5 ± 5.5months, however, MST was lower (53.3 ± 7.6months) if 6MWT performance was ≤350m, and higher (103.1 ± 5.7months) if >350m (FIGURE). Conclusion MIP is an independent mortality predictor in HF, more accurate than 6MWT and LVEF. Addition of 6MWT empowers risk stratification only for intermediate MIP tertile. Although less accurate than pVO 2 , employing MIP, and further 6MWT if needed, could be a reasonable alternative as a prognostic assessment in HF.