CARMEL, CALIF. — Many clinicians underprescribe warfarin in elderly patients with atrial fibrillation because of the perceived risks of anticoagulation therapy, results from a study of Department of Veterans Affairs patients showed.
“Knowing how our practices measure up to current guidelines will increase awareness,” said Dr. Rose Do, who presented the findings with Dr. Reza Habibzadeh at the Western regional meeting of the American Federation for Medical Research.
Current guidelines from the American College of Cardiology, the American Heart Association, and the European Society of Cardiology recommend anticoagulation with a vitamin K antagonist for patients with more than one moderate risk factor for stroke or for patients with a history of cerebrovascular accident (J. Am. Coll. Cardiol. 2001;38:1266i-lxx). Risk factors for stroke include being aged 75 years or older and having hypertension, impaired left ventricular systolic function (an ejection fraction of 35% or less or a fractional shortening of less than 25%), diabetes, prior thromboembolism, or rheumatic mitral stenosis.
Dr. Habibzadeh pointed out that despite evidence in favor of anticoagulation, warfarin is consistently underprescribed for patients with atrial fibrillation (AF). One study of long-term care patients found that only 53% of ideal candidates were receiving warfarin (Arch. Intern. Med. 2001;161:2458–63).
Another study found that among AF patients discharged from the hospital, only 50% received a prescription for warfarin (Chest 2006;130: 1296–9).
One poll found that the risk of falls is the most commonly cited reason for not using anticoagulation in AF patients (J. Am. Med. Dir. Assoc. 2006;7:23–8). However, Dr. Habibzadeh noted that few studies in the medical literature have assessed the use of anticoagulation in elderly AF patients who are at risk for falls (Arch. Intern. Med. 1999;159:677–85). One of the main studies concluded that the risk-to-benefit ratio favored anticoagulation.
Dr. Do and Dr. Habibzadeh sought to determine warfarin prescribing patterns in 66 patients with AF who were part of the Southern Arizona VA Medical Center Home-Based Primary Care Program. AF diagnoses were confirmed by reviews of electrocardiograms, echocardiography reports, and Holter monitor reports. If patients were not anticoagulated, the reasons for deferring this therapy were explored through extensive chart review.
The researchers found that 59.1% of patients had a prior cerebrovascular accident or more than one risk factor for stroke and therefore met criteria for warfarin therapy. However, among patients with a history of cerebrovascular accident, only 19.7% received warfarin.
Among patients with one risk factor for stroke, 3% received clopidogrel, 13.6% received aspirin, and 9.1% received warfarin.
Among patients with two risk factors for stroke, 24.2% received warfarin. The percentages of patients with three and four risk factors for stroke who received warfarin were 7.6% and 1.5%, respectively.
Dr. Do and Dr. Habibzadeh, who are both third-year residents in the department of internal medicine at the University of Arizona, Tucson, pointed out that 9.1% of patients with more than one risk factor received no anticoagulation at all.
Reasons cited for not using warfarin included risk of falls (31.8%, even though only 21.2% of these patients had a documented history of falls), “other” (18.2%), patient refusal (7.6%), adherence issues (6.1%), alcohol dependence (3%), and life expectancy (1.5%).
Dr. Do noted certain limitations of the study, including that it was retrospective, was not randomized, that it relied heavily on documentation, and that it involved a mostly male population.
Even so, the study serves as “more background for future cardiovascular research,” she said.
Despite its limitations, the study serves as 'more background for future cardiovascular research.' DR. DO