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Heart Disease/Stroke

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Improvements are needed in the management of warfarin therapy for patients with atrial fibrillation

A trial fibrillation (AF), rapid irregular heartbeat, can increase the risk for stroke five-fold. Use of the anticoagulant warfarin can reduce the incidence of stroke among AF patients by 64 to 87 percent. However, therapy with this potent medication is not always optimally managed in primary care settings, according to a study by the Stroke Prevention Patient Outcomes Research Team, which is supported by the Agency for Healthcare Research and Quality (Contract 290-91-0028). David Matchar, M.D., of Duke University, and colleagues examined anticoagulation management of AF patients (up to 9 months from their initial visit) in 8 primary care practices in North Carolina and 13 Rochester, NY, practices.

The researchers found that only 35 percent of AF patients who were candidates for warfarin received it. Of those who were treated with warfarin, 50 percent of the time their international normalized ratios (INRs), an indicator of blood clotting time, were not in the therapeutic range (2 to 3). Levels below this range indicate that the blood is not sufficiently thinned to prevent clot formation and stroke; levels above the target range thin the blood too much and increase risk of hemorrhage. The researchers also found that patients' likelihood of being prescribed warfarin was only weakly related to stroke risk and not at all related to documented contraindications to their taking the medicine.

Anticoagulation management is not easy. Laboratory test results (INRs) may not be available until after the patient has left the clinic, thus complicating dosage adjustment; inadequate recordkeeping systems can result in the physician being unaware of laboratory results; and poor communication practices can lead to dosage changes being communicated to the patient late or not at all. However, the two Rochester practices with access to an anticoagulation service (ACS, which has one person responsible for dosing changes, scheduling, patient education, etc.) had better warfarin management than the other practices (44 percent vs. 33 percent of eligible patients on warfarin, and 55 percent of INRs in the target range vs. 34 to 44 percent). The researchers conclude that use of an ACS may improve warfarin management of patients with AF receiving outpatient treatment in primary care settings.

See "Quality of anticoagulation management among patients with atrial fibrillation," by Gregory P. Samsa, Ph.D., Dr. Matchar, Larry B. Goldstein, M.D., and others, in the April 10, 2000, Archives of Internal Medicine 160, pp. 967-973.

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