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Importance  In patients with atrial fibrillation (AF), oral anticoagulants (OACs) reduce the risk of stroke.

Objective  To investigate if patients with less prior OAC exposure respond differently to a new OAC than patients with more OAC exposure.

Design, Setting, and Participants  In this prespecified exploratory subgroup analysis of the Oral Factor 11a Inhibitor Asundexian as Novel Antithrombotic–Atrial Fibrillation (OCEANIC-AF) randomized clinical trial, patients enrolled in the OCEANIC-AF trial were categorized as OAC naive or OAC experienced based on whether they had 6 or fewer weeks or more than 6 weeks of prior OAC use. The effect of asundexian vs apixaban was then compared on outcomes among patients who were OAC naive and OAC experienced. The study setting included 1035 sites in 38 countries, and participants were those enrolled in the OCEANIC-AF trial. Data were analyzed from June to July 2024.

Interventions  Asundexian, a novel factor XIa inhibitor, was compared with apixaban in patients with AF.

Main Outcomes and Measures  The primary efficacy outcome was stroke or systemic embolism. The main safety outcome was major bleeding.

Results  Of patients in the OCEANIC-AF trial, 2493 (17%) were OAC naive (mean [SD] age, 72.6 [8.6] years; 1464 male [59%]) and 12 317 (83%) were OAC experienced (mean [SD] age, 74.2 [7.5] years; 8132 male [66%]). In the asundexian arm, patients who were OAC naive had a stroke or systemic embolism rate of 0.8% (10 of 1238) compared with 1.4% (88 of 6177) in those who were OAC experienced. In the apixaban arm, patients who were OAC naive had a stroke or systemic embolism rate of 0.6% (7 of 1255) compared with 0.3% (19 of 6140) in those who were OAC experienced. Thus, patients who were OAC naive had a smaller increase in stroke or systemic embolism with asundexian compared with apixaban (hazard ratio [HR], 1.42; 95% CI, 0.54-3.73) than patients who were OAC experienced (HR, 4.66; 95% CI, 2.84-7.65; P for interaction =.03). Bleeding rates were lower among both OAC-naive patients (0.2% [2 of 1228]) and OAC-experienced patients (0.2% [15 of 6145]) assigned asundexian than among OAC-naive patients (1.0% [13 of 1249]) and OAC-experienced patients (0.7% [40 of 6115]) assigned apixaban.

Conclusions and Relevance  In the OCEANIC-AF randomized clinical trial, patients with AF who were OAC naive had a smaller increase in stroke or systemic embolism and a similar lower rate of bleeding with asundexian compared with apixaban than patients who were OAC experienced. The mechanism of these findings is unknown and deserves further research.

Trial Registration  ClinicalTrials.gov Identifier: NCT05643573