New-Onset Atrial Fibrillation as an Early Marker of Anthracycline-Associated Cardiotoxicity and Mortality: A Retrospective Study.

New-onset atrial fibrillation and early readmission after anthracycline initiation may signal a higher risk of mortality and adverse clinical outcomes, but their prognostic value has not been well established. We therefore sought to evaluate this association. Using the TriNetX federated electronic health record network, we identified adults initiating anthracycline chemotherapy. Among patients with 30-day readmission, we compared those who developed new-onset atrial fibrillation with those who did not. Propensity score matching (1:1) was performed. The outcomes of interest were heart failure hospitalization and all-cause mortality. The final matched cohort included 2,540 patients. Among patients with 30-day readmission, new-onset atrial fibrillation was associated with significantly worse outcomes than no atrial fibrillation, including higher rates of heart failure hospitalization and all-cause mortality. The subgroup with both new-onset atrial fibrillation and early readmission had the highest cumulative event rates. New-onset atrial fibrillation during anthracycline therapy, particularly when accompanied by early readmission, identifies a high-risk subgroup for subsequent heart failure hospitalization and death. Incorporating arrhythmia surveillance and post-discharge risk stratification into anthracycline care pathways may improve long-term cardiovascular and survival outcomes in this vulnerable population.