Association between platelet-white cell ratio and all-cause mortality in critically ill patients with atrial fibrillation: a retrospective cohort study

Atrial fibrillation is common in intensive care units and portends poor prognosis. The platelet-to-white blood cell ratio is an emerging inflammatory-coagulatory biomarker with prognostic value in cardiovascular diseases. This study examines the association between platelet-white cell ratio (PWR) and all-cause mortality in this high-risk population. In this retrospective cohort study, clinical data were obtained from the MIMIC-IV database. We included adult intensive care unit (ICU) patients with a diagnosis of atrial fibrillation. The PWR was evaluated as the primary exposure, analysed both as a continuous measure and by quartiles. The primary endpoint was 28-day all-cause mortality, with secondary endpoints comprising mortality at 90 days, 180 days, and 1 year. Multivariable Cox models were used to evaluate the association between PWR and mortality, with adjustment for established confounders including demographics, comorbidity, and illness severity. Non-linearity was examined using restricted cubic splines, and subgroup analyses were conducted to evaluate the consistency of the association. The analysis included 2,401 patients. After full adjustment, a unit increase in PWR was independently associated with a 2% decrease in the hazard of 28-day mortality (HR 0.98, 95% CI 0.97–0.99, p < 0.001). When analysed by quartiles, a significant inverse dose-response relationship was observed (P for trend < 0.001). Compared to the lowest quartile (Q1), patients in the highest PWR quartile (Q4) exhibited a substantially reduced hazard of death at 28 days (adjusted HR 0.55, 95% CI 0.43–0.72, p < 0.001). This inverse association remained statistically significant for 90-day and 180-day mortality but was absent at 1 year. The relationship was linear across the range of PWR values for 28-day (P for non-linearity = 0.213), 90-day (P for non-linearity = 0.476), and 180-day mortality (P for non-linearity = 0.377). The results were robust across all predefined subgroups, with no evidence of significant effect modification. Among critically ill patients with atrial fibrillation, a higher platelet-to-white blood cell ratio at ICU admission is inversely and linearly associated with short- and intermediate-term mortality, demonstrating a clear dose-response relationship. As an easily derived biomarker, PWR has potential utility for enhancing risk assessment in this clinical setting.