Occurring when the upper chambers of the heart quiver instead of contract smoothly, atrial fibrillation affects more than 2.3 million Americans. Because the heart rhythm disturbance promotes the formation of blood clots, which can travel to the brain and block an artery, atrial fibrillation increases the risk of stroke fivefold. The condition is highly age-dependent and affects 10 percent of those over age 80. Researchers have long known that warfarin is effective in preventing such strokes, but the treatment can be difficult to control and often leads to hemorrhages. In fact, warfarin is associated with the most emergency admissions for drug-related adverse reactions, according to the researchers. Balancing the benefits of warfarin against its most severe risks is critical to making the best therapeutic decisions for individual atrial fibrillation patients, explains the study's senior author Alan S. Go, MD, Director of the Comprehensive Clinical Research Unit at the Kaiser Permanente Division of Research in Oakland, Calif.

Daniel Singer, MD, of the Massachusetts General Hospital Clinical Epidemiology Unit, the report's lead author, adds, "This comparative effectiveness study gives us more information about which atrial fibrillation patients are most likely to benefit from carefully administered warfarin therapy." He explains 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.

Go explains that Kaiser Permanente physicians in Northern California partner with pharmacist-run anticoagulation clinics to provide thorough and nimble administration and careful monitoring of warfarin therapy for atrial fibrillation patients. This allows for delivery of high-quality anticoagulation therapy through frequent testing and appropriate dose adjustment to account for changes in diet, medications and clinical status that may impact the therapy's narrow therapeutic window.

Singer adds, "One of our distinctive findings is that stroke risk continues to increase in patients age 85 and older and that warfarin provides substantial net protection for these elderly patients. 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."

Source: kaiserpermanente