MONDAY, Aug. 31 (HealthDay News) -- Older patients, or those with a prior history of stroke, are most likely to get a benefit when using warfarin to treat atrial fibrillation, a common heart rhythm disorder, a new study finds.
Kaiser Permanente and Massachusetts General Hospital researchers also say the drug is especially beneficial for patients with multiple risk factors for stroke.
Atrial fibrillation, which occurs when the heart's upper chambers quiver instead of contract, affects more than 2 million Americans. Because the disturbance promotes the formation of blood clots that can travel to the brain and block an artery, atrial fibrillation greatly increases the risk of stroke.
Researchers know that warfarin can prevent such strokes, but the treatment is difficult to control and often leads to hemorrhage. In fact, warfarin is associated with the most emergency admissions for drug-related adverse reactions, according to a Massachusetts General Hospital news release.
Balancing the benefits of warfarin against its severe risks is key to making the best therapeutic decisions for atrial fibrillation patients, study senior author Dr. Alan S. Go, director of the Comprehensive Clinical Research Unit at the Kaiser Permanente Division of Research, said in the news release.
The study appears in the Sept. 1 Annals of Internal Medicine.
Researchers followed almost 13,600 adults with atrial fibrillation treated within Kaiser Permanente of Northern California from 1996 to 2003.
The researchers analyzed rates of the most significant adverse events associated with warfarin therapy -- ischemic stroke, the type produced by arterial blockage; and intracranial hemorrhage, bleeding within and around the brain.
For patients who did and didn't take warfarin, the investigators balanced the reduction in ischemic stroke attributable to treatment against the increase in intracranial bleeding associated with the drug. Since intracranial hemorrhages usually have worse outcomes than ischemic strokes, bleeding events were given greater weight in the comparison.
While warfarin therapy benefited most atrial fibrillation patients, the balance of benefits over risks was greatest in those at highest risk of stroke -- those with multiple risk factors, those with a history of stroke and the oldest patients. Benefits of treatment increased with age, with no clear value seen in patients younger than 65. However, a reduction of more than two strokes per 100 patients was seen in people 85 and older.
The American Heart Association has more on atrial fibrillation here.
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