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Antithrombotic Therapy for Atrial Fibrillation

To determine whether antithrombotic therapy is appropriate, physicians should evaluate patients’ stroke risk, not just their AF classification.

Patients with atrial fibrillation (AF) are at high risk for thromboembolism if they are older (age, >75); have cardiovascular risk factors such as prior ischemic stroke, transient ischemic attack, systemic embolism, left ventricular systolic dysfunction, or congestive heart failure; or have hypertension or diabetes (Chest 2004; 126:429S). Logically, all such patients should be protected with antithrombotic therapy, but, in a recent study, investigators found otherwise.

Researchers from the Group Health Cooperative in Seattle reviewed the records of 596 patients with newly diagnosed AF. Of 437 patients (76%) who were at high risk for thromboembolism, 24% did not receive antithrombotic therapy, and the rest were treated with warfarin (48%), aspirin (17%), or both agents (11%). The data indicated that only AF classification was significantly related to whether warfarin was prescribed: More than 70% of patients with intermittent or sustained AF were prescribed warfarin, compared with 25% of those with transitory AF, regardless of thromboembolism risk. However, even among patients who received warfarin, the target international normalized ratio (INR) was within the therapeutic range only 48% of the time. Although contraindications to warfarin use, such as renal insufficiency, prior hemorrhage, predisposition to falls, barriers to adherence, or alcohol or drug abuse, were noted in 32% of all cases, 28% of warfarin users had such contraindications. The exclusion of 181 subjects with possible contraindications to warfarin use did not substantially change the distribution of warfarin or aspirin use across risk groups. The authors concluded that many patients at high risk for stroke failed to receive antithrombotic therapy and that warfarin use was associated with AF classification, rather than stroke risk.

Comment: Physicians often are reluctant to prescribe warfarin anticoagulation to frail elders because of concerns about bleeding; however, such bleeding is most likely to occur in patients whose INRs exceed the therapeutic range. Another article in this issue of Archives of Internal Medicine confirms that risk for death, major bleeding, and stroke in patients with AF is related to INR control (Arch Intern Med 2007; 167:239). A major reason for physicians’ lack of adherence to anticoagulant guidelines is the dearth of dedicated anticoagulation clinics in the U.S. An important goal is to establish a network of such clinics to assist health professionals in the management of the growing number of patients with AF.

— David Green, MD, PhD

Published in Journal Watch Oncology and Hematology February 12, 2007

Citation(s):

Glazer NL et al. Newly detected atrial fibrillation and compliance with antithrombotic guidelines. Arch Intern Med 2007 Feb 12; 167:246-52.

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