Water distribution and phase angle based on bioelectrical impedance analysis: a convenient approach for identifying acute decompensated heart failure with preserved ejection fraction in older adults

Acute decompensated heart failure with preserved ejection fraction (ADHFpEF) is highly prevalent in older adults, but early recognition is difficult. Bioelectrical impedance analysis (BIA) provides a non-invasive and convenient assessment of fluid status, but its discriminative value for ADHFpEF in older patients requires further systematic evaluation. This cross-sectional study included 377 older hospitalized patients (age 74.9 ± 8.3 years, 57.0% female), of whom 33 (8.8%) had ADHFpEF. Extracellular water/total body water (ECW/TBW) ratios and phase angle (PA) were measured by multifrequency BIA at the whole body, trunk, and leg levels. Associations between BIA parameters and ADHFpEF were evaluated using logistic regression and a restricted cubic spline (RCS) model. Discriminative performance was assessed by a receiver operating characteristic (ROC) model. Whole body, trunk, and leg ECW/TBW were positively associated with ADHFpEF (odds ratio [OR] = 3.02 ~ 3.61, all P < 0.001). Whole body and leg PAs were negatively associated with ADHFpEF (OR = 0.18 ~ 0.19, all P < 0.001). Trunk PA was not significantly associated with ADHFpEF. The RCS model showed a J-shaped nonlinear association of whole body and trunk ECW/TBW with ADHFpEF (inflection points: 39.5% and 39.7%, respectively). The base clinical model combined with trunk ECW/TBW had the highest AUC of 0.904. In older adults, BIA-derived ECW/TBW and PA are significantly associated with ADHFpEF. Elevated ECW/TBW and reduced PA may help identify older patients with a higher likelihood of ADHFpEF. Adding BIA parameters to a basic clinical model improved discrimination for ADHFpEF, supporting their potential as adjunctive bedside markers in older adults.