Association between blood eosinophil count and 28-day mortality among critically ill patients with atrial fibrillation: A retrospective cohort study

Blood eosinophil count has been associated with prognosis in patients with cardiovascular disease. However, its prognostic value among critically ill patients with atrial fibrillation (AF) remains unclear. This study aimed to investigate the association between admission blood eosinophil count and 28-day all-cause mortality in this population. This retrospective cohort study used data from the Medical Information Mart for Intensive Care IV database, version 3.1. Multivariable Cox regression, restricted cubic spline analysis, threshold-effect analysis, and Kaplan-Meier survival analysis were used to evaluate the association between blood eosinophil count and 28-day mortality. A total of 2787 critically ill patients with AF were included, of whom 1948 (69.9%) were male. The mean age was 70.4 ± 10.9 years, and the overall 28-day mortality rate was 9.8% (n = 273). Compared with patients in the lowest eosinophil count quartile (Q1), the adjusted hazard ratios for 28-day mortality were 0.51 (95% confidence interval [CI]: 0.37-0.70; P < .001) for Q2, 0.37 (95% CI: 0.25-0.55; P < .001) for Q3, and 0.45 (95% CI: 0.32-0.63; P < .001) for Q4. Restricted cubic spline analysis showed an L-shaped association between blood eosinophil count and 28-day mortality (P for nonlinearity <.001). Threshold-effect analysis identified an inflection point at 0.08 × 109/L. Below this threshold, a higher eosinophil count was associated with lower 28-day mortality (hazard ratio per 0.01 × 109/L increase, 0.864; 95% CI: 0.794-0.940; P < .001), whereas no significant association was observed above the threshold. In critically ill patients with AF, blood eosinophil count showed an L-shaped association with 28-day mortality. Lower eosinophil count was associated with a higher risk of short-term mortality.