Association between systemic immune-inflammation index(SII) and all-cause and cardiovascular mortality in heart failure patients: a single-center retrospective analysis.

Objective: This study aimed to investigate the association between the systemic immune-inflammatory index (SII) and mortality in patients with heart failure (HF). Method: We conducted a retrospective cohort study of 1,084 HF patients. In this retrospective cohort study, we enrolled patients hospitalized for heart failure between January 2022 and June 2023. Follow-up was conducted via telephone and outpatient visits until death or July 22, 2025, with all-cause and cardiovascular mortality as primary endpoints. Patients were categorized by log-transformed SII (LnSII). Cox models assessed associations between LnSII and mortality, while restricted cubic splines evaluated nonlinearity. Subgroup, mediation (NT-proBNP, LVEF), and sensitivity analyses were performed. Results: A higher LnSII was significantly associated with an increased risk of all-cause mortality (fully adjusted HR = 1.59, 95% CI: 1.03-2.46), No statistically significant association was detected with cardiovascular mortality, which may be attributable to the limited number of cardiovascular deaths ( Conclusion: Elevated SII is independently associated with an increased risk of all-cause mortality in HF patients, particularly among smokers, and may serve as a useful prognostic biomarker.