Abstract
BackgroundAs the management of patients treated with anticoagulants and antiplatelet drugs entails balancing coagulation levels, we evaluated the net clinical benefit of warfarin and aspirin on stroke in a large cohort of patients with atrial fibrillation (AF).MethodsA population-based cohort study of all patients at least 18 years of age with a first-ever diagnosis of chronic AF during the period 1993–2008 was conducted within the United Kingdom General Practice Research Database. A nested case–control analysis was conducted to estimate the risk of ischemic stroke and intracranial hemorrhage associated with the use of warfarin and aspirin. Cases were matched up to 10 controls on age, sex, and date of cohort entry. The adjusted net clinical benefit of warfarin and aspirin (expressed as the number of strokes prevented per 100 persons per year) was calculated by subtracting the ischemic stroke rate (prevented by therapy) from the intracranial hemorrhage (ICH) rate (increased by therapy).ResultsThe cohort included 70,766 patients newly-diagnosed with chronic AF, of whom 5519 experienced an ischemic stroke and 689 an ICH during follow-up. The adjusted net clinical benefit of warfarin was 0.59 (95% CI: 0.45, 0.73). However, the benefit was not seen for patients below (0.08, 95%: -0.38, 0.54) and above (−0.49, 95% CI: -1.13, 0.15) therapeutic range. The net clinical benefit of warfarin, apparent after 3 months of continuous use, increased as a function of CHADS2 score. The net clinical benefit was not significant with aspirin (−0.07, 95% CI: -0.22, 0.08), though it was seen in certain subgroups.ConclusionsWarfarin provides a net clinical benefit in patients with atrial fibrillation, which is maintained with longer duration of use, particularly when used within therapeutic range. A similar net effect is not as clear with aspirin.
Highlights
As the management of patients treated with anticoagulants and antiplatelet drugs entails balancing coagulation levels, we evaluated the net clinical benefit of warfarin and aspirin on stroke in a large cohort of patients with atrial fibrillation (AF)
* Correspondence: samy.suissa@mcgill.ca 1Centre for Clinical Epidemiology, Lady Davis Research Institute, Jewish General Hospital, Montreal, 3755 Côte-Sainte-Catherine, H-461, Montreal, Quebec, CanadaH3T 1E2 5Department of Epidemiology, Biostatistics and Occupational Health, McGill University, Montreal, Quebec, Canada Full list of author information is available at the end of the article therapeutic range, and its association with a number of important complications. The use of this therapy must be balanced between its benefits and risks, with intracranial hemorrhage (ICH) representing the most feared complication of this therapy, an event associated with a high mortality rate [7]
The geographic distribution of the practices participating in the General Practice Research Database (GPRD) has been shown to be representative of the United Kingdom (UK) population, and age and sex distributions of patients in the GPRD are similar to those reported by the National Population Census [11]
Summary
As the management of patients treated with anticoagulants and antiplatelet drugs entails balancing coagulation levels, we evaluated the net clinical benefit of warfarin and aspirin on stroke in a large cohort of patients with atrial fibrillation (AF). Its efficacy has been well established in randomized controlled trials (RCTs), decreasing the risk of ischemic stroke by over 60% [2,3] This therapy remains largely underused in clinical practice [4,5,6], in part because of its narrow. Singer et al [8] showed the net clinical benefit of warfarin was greatest among high risk patients. The authors did not have access to INR information, and it was not possible to assess the net clinical benefit of warfarin according to different levels of anticoagulation
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