Association between warfarin use and thromboembolic events in patients post-Fontan operation: propensity-score overlap weighting analyses.

Objectives: The appropriate antithrombotic regimen after a Fontan operation is yet to be elucidated. Hence, this study aimed to compare the incidence of thromboembolic events in patients with and without receiving warfarin for thromboprophylaxis in a large post-Fontan population.

Methods: This retrospective cohort study used data from the Diagnosis Procedure Combination database in Japan between April 2011 and March 2022. We identified all patients who underwent a Fontan operation and excluded those who were born before 2010, died during the hospitalization or received mechanical heart replacement. Propensity score overlap weighting was performed between patients discharged with warfarin (with or without aspirin) and the control group (only aspirin or neither aspirin nor warfarin). Cox and Fine-Gray hazards models compared thromboembolic and bleeding events.

Results: We identified 2007 eligible patients, including 1670 warfarin users and 337 non-users. The mean follow-up duration was 2.1 years. The crude proportions of thromboembolic events were 3.0% and 3.0% and those of bleeding events were 0.4% and 0.3% in the warfarin and control groups, respectively. There was no significant difference in thromboembolic events between the groups (sub-distribution hazard ratio: 0.77; 95% confidence interval 0.39-1.51; P = 0.45) or bleeding events (sub-distribution hazard ratio: 0.78; 95% confidence interval 0.09-7.03; P = 0.83).

Conclusions: Warfarin use at discharge after a Fontan operation may not be necessary for thromboembolism prophylaxis in paediatric patients, based on large-scale real-world data, with a mean postoperative follow-up duration of 2.1 years. There is room for further studies to reconsider routine warfarin use in patients post-Fontan operation.