Abstract 262

Background: The American College of Cardiology Foundation and American Heart Association guidelinerecommends aspirin 81-325 mg or warfarin use for Non-Valvular Atrial Fibrillation (NVAF) patients with one risk factor for stroke. This study evaluated outcomes associated with antithrombotic treatment among NVAF patients with CHADS₂=1 in an integrated healthcare system.

Methods: Patients age ≥18 years newly diagnosed with NVAF with a CHADS₂ score=1 at diagnosis were identified between 01/01/2006-12/31/2011 within Kaiser Permanente Southern California’s membership and followed until 12/31/2012. The rate of stroke or systemic embolism (SE) and major bleeding events per 100 person-years were evaluated for: 1) aspirin (ASA) only, 2) warfarin time in therapeutic range (TTR) ≥55%, 3) warfarin TTR <55%, and 4) no antithrombotic therapy. The 55% threshold was selected as the lower bound of reported means from previous studies.

Results: Among 7,899patients with CHADS₂=1, 336 stroke and 34 SE events were observed during the 22,542 person-years of follow-up. ASA only therapy was associated with 2.3 times higher risk of stroke/SE (Rate Ratio [RR] = 2.34 [95% CI: 1.61-3.39]) compared to warfarin TTR ≥55%. ASA only events were similar to warfarin TTR <55% but were 23% lower than no antithrombotic therapy. Major bleeding events were lower in ASA therapy compared to warfarin TTR ≥55% (RR = 1.50 [1.23-1.83]) or warfarin TTR <55% (RR= 4.09 [1.23-1.83]). The higher bleeding rates in no therapy compared to warfarin TTR ≥55% or ASA only needs to be further investigated.

Conclusion: ASA therapy was associated with a higher rate of stroke/SE but with a lower rate of bleed compared to TTR ≥55% warfarin in NVAF patients with CHADS₂=1. These results suggest that treatment decisions should be carefully made based on the risk and benefit assessment in patients whose CHADS₂=1.