Abstract 13792: Increased Risk of Ischemic Stroke among Patients With Atrial Fibrillation at the Start of Warfarin Therapy: Assessment via a Large Insurance Database
Introduction: Clinical trials and case-control studies have suggested an increased risk of stroke during the first 30 days of warfarin therapy. Because of the brief time period of interest, large sample sizes are needed. This study compared 30-day rates of ischemic stroke between atrial fibrillation (AF) patients initiating warfarin therapy to controls not on warfarin in a large database.
Method: We identified adult AF patients via one inpatient or two outpatient AF diagnosis claims from the MarketScan insurance database, 1/1/2008 to 3/31/2012. Warfarin naïve patients who started warfarin based on prescription claims from 1/1/2009-12/31/2010 were defined as warfarin initiators. Controls were AF patients who didn’t use warfarin from 7/1/2008-12/31/2010 and who were 1:1 matched to warfarin initiators on age, sex and date of AF diagnosis. Follow-up began on the date of warfarin initiation (index date or IDD). Patients were censored at discontinuation or switch of therapy. We report crude event rates and adjusted hazard ratios (HRs).
Result: We studied 45,052 AF patients with an average follow-up of 1.9 years. Warfarin initiators and controls were the same age (73.0) and sex (50% female) but had slightly lower CHADS2 scores (1.7 vs. 1.8). The initial ischemic stroke rate following the IDD was higher among warfarin initiators compared to controls but lower after 30 days (Table). Notably, the control rate was essentially the same in both periods. Multivariable Cox regression confirmed a significant interaction between time period from the IDD and warfarin use (p=0.002) with the HRs for warfarin/control estimated as 1.75 in the first 30 days and 0.69 after 30 days (Table).
Conclusion: Using these real-world administrative data, warfarin appears to paradoxically increase the risk of ischemic stroke for AF patients for a brief period after initiation but decrease the risk thereafter. Future studies of ischemic stroke risk among AF patients initiating warfarin use are warranted.
- © 2013 by American Heart Association, Inc.