Study Says Warfarin Underused in Treatment of Atrial Fibrillation


October 6, 2008

October 5, 2008 - New research shows warfarin therapy is significantly underused in patients being treated for atrial fibrillation (AF) in the U.S.

The new study is published in the October edition of the HeartRhythm Journal, the official journal of the Heart Rhythm Society. It concludes that not only is warfarin not prescribed as often as it could be, in many cases when warfarin is administered, it is not used at optimal therapeutic levels.

Untreated, AF and atrial flutter can lead to stroke and arterial thromboembolism. Warfarin is the most common treatment, but can also cause bleeding. The new study, led by Dimitri Bennett, M.D., and Alexander Walker, M.D., documents how frequently and how effectively anticoagulants are used in patients with AF or atrial flutter in the U.S. Bennett and Walker examined health insurance claims and laboratory results from a population of more than 10 million U.S. patients to quantify the association of AF outcomes with treatment, patient characteristics and the International Normalized Ratio (INR) – a laboratory measurement of warfarin efficacy.

Among 116,969 patients over the age of 40 with an insurance claim for AF or atrial flutter between 1999 and 2005, warfarin was prescribed to 45 percent of the patient population, and 48 percent had no insurance claim for an anticoagulant or antiplatelet agent. Of the 45 percent of patients who received warfarin therapy, records showed that, as expected, INR levels outside of the accepted therapeutic range increased the risk of stroke, arterial thromboembolism and intracranial hemorrhage:

− μ Subtherapeutic, or low INR levels, more than doubled the incidence of stroke and arterial thromboembolism;

− Supratherapeutic, or high INR levels, doubled the incidence of intracranial hemorrhage.

As a result, only 19 percent of patients spent all or most of their time within the therapeutic INR range. Most of the out-of-range time was spent with a low INR, indicating insufficient doses of warfarin.

“It appears that many doctors prescribe warfarin at a lower dose than required, or simply not at all,” stated author Alexander Walker, M.D., World Health Information Science Consultants in Wellesley, MA. “It is important that we address this problem because, unfortunately, it is the misuse of warfarin that can put patients at a higher risk of stroke, bleeding and other medical complications.”

More than 2 million people in the U.S. have AF, making it a very common heart rhythm disorder. In addition to the associated risks of stroke and arterial thromboembolism, AF can lead to other heart rhythm problems, chronic fatigue and congestive heart failure. When used properly, there are a number of effective treatments, including warfarin therapy, to control AF and/or reduce the risk that it will cause serious health problems.

“When used at an optimal level, warfarin is very effective, but warfarin can be a difficult drug to manage. We will begin to see more and more alternatives to warfarin developed for the treatment of AF,” states Walker.

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