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Blood Thinner Use in Patients with Atrial Fibrillation FREE

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The summary below is from the full report titled “Warfarin Use among Ambulatory Patients with Nonvalvular Atrial Fibrillation: The AnTicoagulation and Risk Factors in Atrial Fibrillation (ATRIA) Study.” It is in the 12 December 1999 issue of Annals of Internal Medicine (volume 131, pages 927-934). The authors are A.S. Go, E.M. Hylek, L.H. Borowsky, K.A. Phillips, J.V. Selby, and D.E. Singer.

Ann Intern Med. 1999;131(12):927. doi:10.7326/0003-4819-131-12-199912210-00025
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What is the problem and what is known about it so far?

Atrial fibrillation is a kind of irregular heart rhythm. People with atrial fibrillation sometimes develop blood clots in their hearts. This may lead to stroke if pieces of the clot break off and travel from the heart to the brain. Warfarin (Coumadin) is a medicine that makes the blood take longer to clot; it can prevent stroke in many people with atrial fibrillation. Nevertheless, doctors are sometimes reluctant to prescribe warfarin and patients may be reluctant to take the drug, partly because taking warfarin can lead to bleeding in the gastrointestinal tract or bleeding into the brain.

Why did the researchers do this particular study?

They wanted to find out how often patients with atrial fibrillation use warfarin and what factors were associated with a person using this medicine or not using it.

Who was studied?

The researchers studied 13,428 patients from a large health maintenance organization (HMO) who had atrial fibrillation and no known problem with their heart valves. Nonvalvular atrial fibrillation is the most common type of this heart rhythm problem.

How was the study done?

The researchers used computerized pharmacy and clinical records to find evidence of warfarin use by each patient during the 3 months before and after the diagnosis of atrial fibrillation. They also looked for reasons why the patient should not have gotten prescriptions for warfarin despite having atrial fibrillation (contraindications).

What did the researchers find?

Of the 13,428 patients, 11,082 had no known reason not to get warfarin, but only 55% of them actually got a prescription for it. Warfarin use was lower in patients younger than 55 years old and older than 85 years old and in patients with a previous bleeding problem. Even among patients who had other known risk factors for stroke, such as high blood pressure, and no contraindications to warfarin, less than 60% received warfarin prescriptions. Patients with previous strokes or heart failure were more likely to be given warfarin.

What were the limitations of the study?

This study involved patients from only one HMO, and the findings may not apply to other settings. Pharmacy data tell us only that the patients filled prescriptions for warfarin, but we do not know whether all patients who got the medicine at the pharmacy actually took it. In addition, some patients may have had reasons for not using warfarin that were not listed in the computerized records.

What are the implications of the study?

Many patients who have atrial fibrillation and no known contraindications to the use of warfarin do not receive it. These patients are therefore at unnecessary risk of having a stroke. It will be important to develop strategies to increase the use of warfarin to prevent strokes in people with atrial fibrillation who are good candidates for taking this drug.





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