Patients at high risk of stroke may need to continue Warfarin therapy after heart rhythm is controlled

Treatment with warfarin, a medication that prevents blood clotting, may reduce the risk of stroke by more than two-thirds in patients with atrial fibrillation (AF), a condition which places them at high risk of stroke, according to a study in the May 23 issue of Archives of Internal Medicine, one of the JAMA/Archives journals.

An estimated 2,260,000 individuals in the U.S. have atrial fibrillation, an irregular heartbeat in which the upper chambers of the heart (the atria) beat inconsistently and rapidly, according to background information in the article. The Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM ) study, a large multi-center comparison study of the two strategies for treatment of atrial fibrillation, rate control or sinus rhythm control therapy, found no difference in the risk of death for patients treated with either of the two therapies. Treatment with the anticoagulant, warfarin, was included in both therapies, although patients in the sinus rhythm control group could stop warfarin after at least four weeks of maintained sinus rhythm while receiving an anti-arrhythmic drug.

David G. Sherman, M.D., of the University of Texas Health Science Center, San Antonio, and colleagues assessed the occurrence and characteristics of strokes in patients in both treatment groups in the follow-up to the AFFIRM study, ranging from two to six years. The researchers analyzed the relationship of a number of variables for risk of ischemic stroke, a stroke caused by decreased blood flow to an area of the brain, most commonly due to narrowing of blood vessels or an embolism (small blood clot) leading to blockage of the blood supply. Variables in the analysis included age, sex, and history of stroke, diabetes, coronary artery disease, high blood pressure and smoking. Eighty-four percent of the rate control patients and 52 percent of the sinus rhythm control patients received warfarin throughout the study.

The type of treatment was not associated with risk of stroke in the 4,060 patients participating in the study. Two hundred eleven patients (8.2 percent) had a stroke event. Ischemic stroke (6.3 percent) was the most common type. The researchers found seven variables were significantly associated with risk of stroke, including increasing age, female gender, the episode of AF which qualified the patient for the study lasting two or more days, a history of stroke or TIA (mini-stroke), and a history of diabetes. The presence of AF was associated with a 60 percent increase in risk of having an ischemic stroke and the use of warfarin was associated with a 69 percent decrease in stroke risk.

"These data suggest that the beneficial effect of warfarin therapy exists not only for patients experiencing AF but also for patients who have a history of AF but who are presumably in sinus rhythm," the authors conclude. "Anticoagulation therapy should be maintained in patients who have a history of AF and risk factors for stroke, even when the recurrent AF has not been documented."