Association between prognostic nutritional index and mortality in critically ill patients with atrial fibrillation: a retrospective cohort study

Abstract Background The prognostic nutritional index (PNI), a composite marker derived from serum albumin and total lymphocyte count, has been associated with adverse outcomes in several cardiovascular and critical care settings. However, its prognostic value in critically ill patients with atrial fibrillation (AF) remains unclear. This study aimed to evaluate the association between PNI and mortality in this high-risk population. Methods This retrospective cohort study included critically ill patients with AF from the Medical Information Mart for Intensive Care IV (MIMIC-IV, version 3.1). The primary outcome was 30-day all-cause mortality. Secondary outcomes included in-hospital mortality, 90- and 365-day mortality. Multivariable Cox proportional hazards and logistic regression models were used to assess the associations between PNI and outcomes. Kaplan-Meier survival analyses and restricted cubic spline (RCS) analyses were performed to further characterize these associations. The association between PNI and in-hospital mortality was further examined in an independent cohort from the eICU Collaborative Research Database (eICU-CRD). Results A total of 3,007 critically ill patients with AF were included in the MIMIC-IV cohort, and 2,741 patients were included in the independent eICU-CRD cohort. In the primary model (Model 2), each 10-unit increase in PNI was associated with a lower risk of 30-day mortality (HR, 0.63; 95% CI, 0.57–0.70; P < 0.001), 90-day mortality (HR, 0.64; 95% CI, 0.58–0.70; P < 0.001), and 365-day mortality (HR, 0.68; 95% CI, 0.63–0.74; P < 0.001) in the MIMIC-IV cohort. Higher PNI was also associated with lower in-hospital mortality in the MIMIC-IV cohort (OR, 0.58; 95% CI, 0.50–0.66; P < 0.001). In the independent eICU-CRD cohort, higher PNI remained significantly associated with lower in-hospital mortality (OR, 0.66; 95% CI, 0.57–0.76; P < 0.001). Kaplan-Meier analyses showed progressively better survival across increasing PNI quartiles, whereas RCS analyses demonstrated a nonlinear inverse relationship between PNI and mortality. Conclusions Lower PNI was independently associated with increased short- and long-term mortality in critically ill patients with AF. As a readily available laboratory-based index, PNI may provide simple adjunctive prognostic information in this high-risk population.