New-onset atrial fibrillation, thrombocytopenia, and short-term outcomes in patients with cancer requiring intensive care: a retrospective ICU cohort study

Abstract Background Cancer and atrial fibrillation frequently coexist. Intensive care adds hemodynamic stress, organ failure, and competing bleeding risk. The interaction between new-onset atrial fibrillation and thrombocytopenia in patients with cancer requiring intensive care remains insufficiently defined. Methods We performed a retrospective ICU cohort study using de-identified critical care data. Adult ICU stays with solid or hematologic malignancy were included. The main exposure was new-onset atrial fibrillation surrogate. Early thrombocytopenia was defined from the minimum platelet count within 48 hours and categorized as > = 150, 100–149, 50–99, and < 50 x10^9/L. The primary outcome was in-hospital death. Secondary outcomes were 28-day death, major bleeding identified by ICD coding, and ischemic stroke identified by ICD coding. Multivariable logistic regression tested interaction between new-onset atrial fibrillation and platelet category. Results Among 9,640 cancer ICU stays, 1,788 (18.5%) met criteria for new-onset atrial fibrillation surrogate. In-hospital death occurred in 1,724 (17.9%) stays, 28-day death in 2,394 (24.8%), major bleeding ICD in 1,001 (10.4%), and ischemic stroke ICD in 410 (4.3%). In complete-case interaction models (n = 9,505), the association between new-onset atrial fibrillation and in-hospital death differed by platelet category (P for interaction = 0.069). Severe thrombocytopenia (< 50 x10^9/L) showed the strongest mortality signal (adjusted OR 1.607, 95% CI 1.090–2.370). For major bleeding, platelet category significantly modified the association (P for interaction = 0.040). In the platelet 50–99 x10^9/L stratum, new-onset atrial fibrillation was associated with lower odds of major bleeding (adjusted OR 0.534, 95% CI 0.306–0.933). In the platelet > = 150 x10^9/L stratum, new-onset atrial fibrillation was associated with higher odds of ischemic stroke (adjusted OR 1.663, 95% CI 1.231–2.248). Conclusions New-onset atrial fibrillation identified a clinically distinct short-term risk phenotype in patients with cancer requiring intensive care. Platelet strata differentiated mortality and bleeding patterns. Severe thrombocytopenia marked the subgroup with the strongest mortality signal.