The effect of low-dose warfarin on the risk of stroke in patients with nonrheumatic atrial fibrillation

Article Abstract:

Atrial fibrillation, rapid and disorganized heartbeats originating in the upper chambers of the heart, may produce blood clots that cause stroke. There is general agreement that patients with atrial fibrillation and rheumatic valvular disease (obstruction of the mitral valve, which controls blood flow from the left atrium to the left ventricle) should be treated with long-term warfarin (coumadin) anticoagulant therapy to prevent stroke. However, treatment of nonrheumatic atrial fibrillation (without accompanying mitral valve stenosis, or obstruction) is still controversial. These patients have a risk of stroke fives times greater than normal. This report summarizes the results of the Boston Area Anticoagulation Trial for Atrial Fibrillation (BAATAF) on the efficacy of low-dose warfarin in preventing strokes. A total of 420 patients with nonrheumatic atrial fibrillation were divided almost equally into warfarin and control groups. The average age of the participants was 68 years, and 72 percent were men. The controls were allowed to take aspirin, also an anticoagulant. The results suggest that low-dose warfarin was effective in preventing stroke among these patients during a follow-up period of over two years, and that side effects, including hemorrhage, were few. There was one death from stroke and one from hemorrhage in each group. Two nonfatal strokes occurred in the warfarin group, compared with 13 in the control group. Eight of the 13 controls who suffered nonfatal strokes were taking aspirin, most at a dosage of at least 325 milligrams (mg) per day, supporting the view that aspirin is not useful for preventing stroke in this patient population. Advanced age also increased the risk of stroke. Some of the 19 deaths from cardiac causes may have been due to undiagnosed stroke or hemorrhage, but there were also fewer of these events in the warfarin group. The findings confirm those of earlier large-scale warfarin trials. Future research should identify which patients with nonrheumatic atrial fibrillation need long-term anticoagulant therapy, and develop less risky and more convenient treatments. (Consumer Summary produced by Reliance Medical Information, Inc.)

Evaluation, Complications and side effects, Aspirin

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Warfarin in the prevention of stroke associated with nonrheumatic atrial fibrillation

Article Abstract:

Treatment with the anticoagulant warfarin may prevent a stroke in individuals suffering from nonrheumatic atrial fibrillation, or rapid heart beat, especially in those with no prior history of stroke. Individuals suffering from atrial fibrillation have a higher risk of a stroke than other individuals, and this risk increases with age. Among 525 men with chronic nonrheumatic atrial fibrillation without a prior history of stroke, 260 were treated with warfarin and 265 received a placebo, an inactive substance. During the following two years, four patients (0.9% per year) treated with warfarin suffered a stroke, compared with 19 patients (4.3% per year) who received a placebo. Of 46 patients with atrial fibrillation who had a history of stroke, 21 were treated with warfarin for approximately two years and 25 received a placebo. Two patients (6.1% per year) in the warfarin group suffered a stroke, compared with four (9.3% per year) in the placebo group.

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Optimal oral anticoagulant therapy in patients with nonrheumatic atrial fibrillation and recent cerebral ischemia

Article Abstract:

The best dosage of anticlotting drugs for atrial fibrillation patients who have recently experienced a cerebral ischemic event may be one that produces an international normalized ratio (INR) of coagulation between 2.0 and 3.9. A cerebral ischemic event, such as a stroke, is a lack of blood supply to brain tissue, caused by blockage of a blood vessel. For an average of 2.1 years, researchers monitored 214 nonrheumatic atrial fibrillation patients receiving anticlotting drugs, such as acenocoumarol. Too low of a dosage is ineffective in preventing further events, while too high of a dosage causes bleeding. Patients with INRs above 5.0 had the highest rates of hemorrhages, at 60 per 100 patient-years. Patients with INRs below 2.0 had the highest rates of blood vessel blockage, at 18 per 100 patient-years. An INR between 2.0 and 2.9 reduced the rate of events by 80%. An INR of 3.0 may be the best target in administering anticlotting drugs.

Anticoagulants (Medicine), Anticoagulants, Cerebral ischemia

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