Warfarin therapy for patients with atrial fibrillation appears to be most beneficial for the oldest patients, those who have had a prior stroke and for patients with multiple risk factors for stroke, according to a comparative effectiveness research study in the Sept. 1 issue in the Annals of Internal Medicine.
Researchers have long known that warfarin is effective in preventing such strokes, but the treatment can be difficult to control and often leads to hemorrhage. Balancing the benefits of warfarin against its most severe risks is critical to making the best therapeutic decisions for individual atrial fibrillation patients, explained the study's senior author Alan S. Go, MD, director of the Comprehensive Clinical Research Unit at the Kaiser Permanente Division of Research.
As part of the ongoing ATRIA (AnTicoagulation and Risk Factors In Atrial Fibrillation) study, the researchers followed 13,559 adults with atrial fibrillation treated within Kaiser Permanente of Northern California from 1996 to 2003.
To evaluate the risks and benefits of warfarin treatment and give patients and physicians quantitative guidance in making therapeutic decisions, lead author Daniel Singer, MD, of the Massachusetts General Hospital’s clinical epidemiology unit in Boston, and colleagues analyzed rates of the two most significant adverse events associated with warfarin therapy—ischemic stroke and intracranial hemorrhage. For patients who did and did not take warfarin, the investigators balanced the reduction in ischemic stroke attributable to treatment against the increase in intracranial bleeding associated with warfarin. Since intracranial hemorrhages usually have worse outcomes than ischemic strokes, the authors said that 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, the authors reported. The benefits of treatment increased strikingly with age, with no clear benefit in the average patient younger than 65, but a reduction of more than two strokes per 100 patients in those 85 and older.
Singer said that this “comparative effectiveness study gives us more information about which atrial fibrillation patients are most likely to benefit from carefully administered warfarin therapy." He explained that, by assessing warfarin within a "real-world" practice setting, the study provides a more contemporary assessment of the therapy's overall effects than do older clinical studies.
"One of our distinctive findings is that stroke risk continues to increase in patients aged 85 and older and that warfarin provides substantial net protection for these elderly patients,” Singer noted. “A caution is that all these patients were presumably judged by their physicians to be reasonable candidates for warfarin therapy, so these results do not automatically apply to all elderly atrial fibrillation patients."