Thursday, August 30, 2007

Warfarin Versus Aspirin for Stroke Prevention in an Elderly Community Population With Atrial Fibrillation

Title: Warfarin Versus Aspirin for Stroke Prevention in an Elderly Community Population With Atrial Fibrillation (the Birmingham Atrial Fibrillation Treatment of the Aged Study, BAFTA): A Randomised Controlled Trial

Topic: Arrhythmias

Date Posted: 8/28/2007

Author(s): Mant J, Hobbs FD, Fletcher K, et al.

Citation: Lancet. 2007;370:493-503.

Clinical Trial: Yes

Study Question: Does warfarin reduce the risk of major stroke, arterial embolism, or other intracranial hemorrhage, compared with aspirin in elderly patients with atrial fibrillation?

Methods: The authors report the results of the Birmingham Atrial Fibrillation Treatment of the Aged (BAFTA) study, a randomized, open-label trial of aspirin versus warfarin in subjects over age 75 with atrial fibrillation. Patients were excluded if they had increased risk for gastrointestinal bleeding, rheumatic heart disease, intracranial hemorrhage, blood pressure >180/110 mm Hg, or at prohibitive risk for bleeding with warfarin, in their physician’s judgment. Subjects were randomized to warfarin (target INR 2-3), or aspirin 75 mg daily, for a mean of 2.7 years’ follow-up. The primary outcome was fatal or nonfatal stroke, intracranial hemorrhage, or clinically significant arterial embolism. Secondary outcomes were major hemorrhage, other vascular events, and all-cause mortality.

Results: The authors report 973 subjects were randomized from April 2001 to November 2004, among whom there were 24 primary events in the warfarin group (21 strokes, two other intracranial hemorrhages, and one systemic embolus), and 48 events in the aspirin group (44 strokes, one other intracranial hemorrhage, and three systemic emboli), (relative risk, 0.48; 95% confidence interval, 0.28-0.80; p = 0.003). This resulted in a yearly risk for primary event of 1.8% and 3.8% in the two groups, respectively. The yearly risk of extracranial hemorrhage was 1.4% (warfarin) versus 1.6% (aspirin) (relative risk, 0.87; 0.43-1.73).

Conclusions: The authors concluded that the data support the use of warfarin in patients with atrial fibrillation over age 75, unless there are contraindications, or the patient refuses warfarin therapy.

Perspective: There is a common misconception that benefits of medical therapy are fixed, while risks associated with medical therapy vary. This fallacy has led to the belief that greater risk of bleeding with advancing age makes warfarin therapy in the elderly more risky. Forgotten is the fact that risk of thromboembolic stroke from atrial fibrillation also increases with age. This same phenomenon is seen in a number of other medical conditions. Our training to compare ‘risk versus benefits’ leads, I believe, to this error in thinking. Benefits are reported and thought of as fixed (e.g., ‘warfarin lowers risk of stroke in atrial fibrillation x%’), whereas risks of therapy are seen as relative to the patient’s condition, age, and other risk factors. This error of medical decision making is compounded by the exclusion of the elderly from clinical trials—leaving us without adequate data. Ideally, we should assess both the risk of therapy, as well as the risk of not taking therapy, on an individual basis for each patient, based on available data (a ‘risk vs. risk’ comparison, rather than ‘risk vs. benefit’). Clearly, more clinical trial data that include the elderly are crucial. And we should remember that if a treatment is effective, it is logically more effective in groups at higher risk from complications of disease, and that usually means the elderly

No comments: