Renal Dysfunction and Cardiorenal Syndrome in Acute Heart Failure: A Systematic Review of Residual Congestion and Decongestion Response.

Renal dysfunction is common during hospitalization for acute heart failure and is traditionally considered a defining feature of cardiorenal syndrome type 1. However, the prognostic significance of worsening renal function may depend on the clinical context, particularly whether congestion persists or effective decongestion is achieved. This systematic review evaluated contemporary evidence regarding the relationships among renal dysfunction, residual congestion, decongestion response, and clinical outcomes in adults hospitalized with acute heart failure or cardiorenal syndrome type 1. PubMed/MEDLINE, Scopus, and Web of Science were systematically searched for studies published between January 1, 2021, and December 31, 2025. Eligible studies included randomized controlled trials, prespecified analyses of clinical trials, and post hoc analyses of trial-derived data that reported both renal and congestion-related outcomes. Five studies met the inclusion criteria. Residual congestion was consistently associated with worse clinical outcomes, whereas worsening renal function during effective decongestion did not uniformly predict adverse renal or cardiovascular events. Studies evaluating venous excess ultrasound (VExUS)-guided and bioimpedance-guided strategies suggested that objective congestion assessment may improve decongestion phenotyping, although the available evidence remains limited. Overall, the findings support a renal-congestion framework in which kidney function is interpreted alongside congestion burden, diuretic response, perfusion status, and the trajectory of renal recovery. This approach may better distinguish high-risk persistent congestion from transient renal changes occurring during successful decongestion. Future prospective studies should determine whether combined renal-congestion phenotypes improve risk stratification beyond creatinine-based definitions of cardiorenal syndrome alone.