Subclinical congestion assessed by whole-body bioelectrical impedance analysis in HFrEF outpatients.

Background: Persistent congestion in heart failure (HF) carries a dismal prognosis. Bioimpedance analysis (BIA) non-invasively identifies extracellular water (ECW) redistribution associated with acute HF. However, its role in detecting subclinical congestion in HF outpatients still needs to be explored.

Methods: Eighty-three adult outpatients with HFrEF were recruited for a single-center prospective study. Segmental multi-frequency BIA was used to assess body composition and the extracellular-to-total body water ratio (ECW/TBW), a marker of fluid redistribution. Subclinical congestion was defined as ECW/TBW_z‑score > 2 without clinical signs of congestion. The primary outcome was a composite of all-cause death and worsening HF (WHF) events.

Results: In this cohort, 57% of patients had subclinical congestion. Higher congestion grades were associated with age, female sex, and comorbidities. ECW/TBW_z‑score correlated linearly with NT-proBNP levels and low muscular indexes were associated with congestion severity. During a median follow-up of 10 months, 27% of patients experienced the primary outcome, mostly WHF events. Both subclinical and clinical congestion were independently associated with an increased risk of the primary outcome, with hazard ratios (HR) of 9.4 (1.04-85.1; p = 0.046) and 17 (1.11-261; p = 0.042), respectively. NT-proBNP and ECW/TBW_z‑score showed similar power in predicting the outcome.

Conclusions: BIA detects subclinical congestion-a condition highly prevalent in outpatients with HFrEF. An increased ECW/TBW ratio correlates with established markers of congestion and is associated with adverse events in this population. These findings support the integration of BIA into routine HF care; however, further studies are needed to establish the clinical benefits of BIA-guided management and its impact on patient outcomes.