Background: The optimal antithrombotic regimen for patients with atrial fibrillation (AF) who had an acute coronary syndrome (ACS) or have undergone percutaneous coronary intervention (PCI) is not known., Objectives: The authors sought to determine which antithrombotic regimen best balances safety and efficacy., Methods: AUGUSTUS, a multicenter 2 × 2 factorial design randomized trial compared apixaban with vitamin K antagonist (VKA) and aspirin with placebo in patients with AF with recent ACS and/or PCI treated with a P2Y 12 inhibitor. We conducted a 4-way analysis comparing safety and efficacy outcomes in the 4 randomized groups. The primary outcome was a composite of all-cause death, major or clinically relevant nonmajor bleeding, or hospitalization for cardiovascular causes over 6-month follow-up. Secondary outcomes included individual components of the primary endpoint., Results: A total of 4,614 patients were enrolled. All patients were treated with a P2Y 12 inhibitor. The primary endpoint occurred in 21.9% of patients randomized to apixaban plus placebo, 27.3% randomized to apixaban plus aspirin, 28.0% randomized to VKA plus placebo, and 33.3% randomized to VKA plus aspirin. Rates of major or clinically relevant nonmajor bleeding and hospitalization for cardiovascular causes were lower with apixaban and placebo compared with the other 3 antithrombotic strategies. There was no difference between the 4 randomized groups with respect to all-cause death., Conclusions: In patients with AF and a recent ACS and/or PCI, an antithrombotic regimen that included a P2Y 12 inhibitor and apixaban without aspirin resulted in a lower incidence of the composite of death, bleeding, or cardiovascular hospitalization than regimens including VKA, aspirin, or both. (An Open-label, 2 x 2 Factorial, Randomized Controlled, Clinical Trial to Evaluate the Safety of Apixaban vs. Vitamin K Antagonist and Aspirin vs. Aspirin Placebo in Patients with Atrial Fibrillation and Acute Coronary Syndrome or Percutaneous Coronary Intervention; NCT02415400)., Competing Interests: Funding Support and Author Disclosures The AUGUSTUS study and this analysis were funded by Bristol Myers Squibb and Pfizer. Dr Berwanger has received research grants from AstraZeneca, Pfizer, Bayer, Amgen, Novartis, Servier, and Boehringer Ingelheim. Dr Fanaroff has received research grants from the American Heart Association and National Institutes of Health; and has received consulting fees from Abbott Laboratories. Dr Granger has received research grants from Bayer, Boehringer Ingelheim, Bristol Myers Squibb, Daiichi-Sankyo, Janssen, Pfizer, Armetheon, AstraZeneca, U.S. Food and Drug Administration, GlaxoSmithKline, The Medicines Company, Medtronic Foundation, Medtronic Inc, and Novartis; and has received consulting fees from Bayer, Boehringer Ingelheim, Boston Scientific, Bristol Myers Squibb, Daiichi-Sankyo, Janssen, Pfizer, Abbvie, Armetheon, AstraZeneca, Eli Lilly, Gilead, GlaxoSmithKline, Hoffmann-La Roche, The Medicines Company, National Institutes of Health, Novartis, Sirtex, Verseon, Apple, Medscape, LLC, Merck, Novo Nordisk, Roche Diagnostics, and Rho Pharmaceuticals. Dr Mehran has received institutional research grants from AstraZeneca, Bayer, Beth Israel Deaconess, Bristol Myers Squibb/Sanofi, CSL Behring, Eli Lilly/Daiichi-Sankyo, Medtronic, Novartis, and OrbusNeich; has received consulting fees from Boston Scientific, Abbott Vascular, Medscape, Siemens Medical Solutions, Roivant Sciences Inc, and Sanofi; has consulted (no fees) for Regeneron Pharmaceuticals Inc; has received institutional consulting fees from Abbott Vascular, Spectranetics/Phillips/Volcano Corporation, Bristol Myers Squibb, Novartis, and Watermark Research; is an executive committee member for Janssen Pharmaceuticals and Bristol Myers Squibb; and has <1% equity in Claret Medical and Elixir Medical. Dr Aronson is an employee of Bristol Myers Squibb. Dr Windecker has received institutional research and educational grants from Abbott, Amgen, Bayer, Bristol Myers Squibb, CSL Behring, Boston Scientific, Biotronik, Edwards Lifesciences, Medtronic, Polares, and Sinomed. Dr Goodman has received research grant support and/or speaker/consulting honoraria from Amgen, AstraZeneca, Bayer, Boehringer Ingelheim, Bristol Myers Squibb, CSL Behring, Daiichi-Sankyo, Eli Lilly, Esperion, Fenix Group International, Ferring Pharmaceuticals, GlaxoSmithKline, HLS Therapeutics, Janssen/Johnson and Johnson, Luitpold Pharmaceuticals, Matrizyme, Merck, Novartis, Novo Nordisk A/C, Pfizer, Regeneron, Sanofi, Servier, Tenax Therapeutics, Heart and Stroke Foundation of Ontario/University of Toronto, Canadian Heart Research Centre and MD Primer, Canadian VIGOUR Centre, Duke Clinical Research Institute, and PERFUSE. Dr Alexander has received research grants from Bristol Myers Squibb, Boehringer Ingelheim, AstraZeneca, CryoLife, CSL Behring, U.S. Food and Drug Administration, National Institutes of Health, Sanofi, and VoluMetrix; and has received consulting fees from Pfizer, Bristol Myers Squibb, AbbVie Pharmaceuticals, CSL Behring, Novo Nordisk, Portola Pharmaceuticals, Quantum Genomics, Teikoku Pharmaceuticals, VA Cooperative Studies, and Zafgen. Dr Lopes has received research grants or contracts from Amgen, Bristol Myers Squibb, GlaxoSmithKline, Medtronic, Pfizer, and Sanofi; has received funding for educational activities or lectures from Pfizer, Daiichi-Sankyo, and Novo Nordisk; and has received funding for consulting or other services from Bayer, Boehringer Ingelheim, Bristol Myers Squibb, and Novo Nordisk. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2024 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)