Abstract 3589: Warfarin Therapy, Anticoagulation Intensity and Outcomes in Older vs. Younger Patients with Atrial Fibrillation: The ATRIA Study
Background. Warfarin is highly efficacious for stroke prevention in atrial fibrillation (AF) in selected randomized trial populations. However, controversy exists about its effectiveness and safety and the target INR range in the old and oldest old AF patients in usual clinical care.
Methods. We examined anticoagulation-related outcomes associated with older vs. younger age among 13,559 patients with AF within Kaiser Permanente of Northern California between July 1996 and September 2003. Longitudinal warfarin use was characterized using a validated algorithm from filled prescriptions and INR tests found in pharmacy and lab databases. Anticoagulation intensity was characterized using linear interpolation from outpatient INR tests. Risk factors for stroke and bleeding were obtained from clinical and administrative databases. Thromboembolic (TE) and intracranial hemorrhage (ICH) events were identified from hospitalization databases and confirmed by chart review.
Results. During 66,754 person-years of follow-up, a large fraction was contributed by older patients: <60 (12.3%), 60 – 69 (18.5%), 70 –79 (37.8%), 80+ (31.4%) years. Older patients were more likely to be women and have a higher prevalence of stroke and bleeding risk factors. Among warfarin users, the proportion of time in therapeutic INR range was similar across age groups (64 – 66%, P=NS). We validated 1041 TE and 279 ICH events. Absolute event rates were higher with older age, but the relative effectiveness of warfarin for preventing TE increased and relative harm due to ICH decreased between ages 60 – 69 and 80+ years (Table⇓). In separate multivariable analyses, INR 2.0 –3.0 provided the optimal risk-benefit ratio for TE and ICH events across each age category.
Conclusion. Among persons with nonvalvular AF, the net clinical benefit of warfarin was greater at older ages. INR 2.0 –3.0 is the optimal target anticoagulation range across the spectrum of age to maximize TE prevention at an acceptable risk of ICH.