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Atrial Fibrillation Study
Contact:     Ann-Marie White
                 Heart Rhythm Society
                 (202) 464-3476
Results of the first contemporary, US-based study on the usage of warfarin published in the

HeartRhythm Journal
WASHINGTON, October 1, 2008 – New research reveals that warfarin therapy is significantly
underused in patients being treated for atrial fibrillation (AF) in the United States. The new study
published in the October edition of the HeartRhythm Journal, the official journal of the Heart
Rhythm Society, 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,
MD, and Alexander Walker, MD, documents how frequently and how effectively anticoagulants
are used in patients with AF or atrial flutter in the US. Bennett and Walker examined health
insurance claims and laboratory results from a population of more than 10 million US 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:   
• 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
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
“It appears that many doctors prescribe warfarin at a lower dose than required, or simply not at
all,” stated author Alexander Walker, MD, World Health Information Science Consultants in
Wellesley, Massachusetts. “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 two million people in the United States 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.
For more information about this study, please visit www.heartrhythmjournal.com.
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About the Heart Rhythm Society
The Heart Rhythm Society is the international leader in science, education and advocacy for cardiac arrhythmia
professionals and patients, and the primary information resource on heart rhythm disorders. Its mission is to improve
the care of patients by promoting research, education and optimal health care policies and standards. Incorporated in
1979 and based in Washington, DC, it has a membership of more than 4,900 heart rhythm professionals in more
than 65 countries around the world.  
About HeartRhythm Journal  
HeartRhythm provides rapid publication of the most important science developments in the field of arrhythmias and
cardiovascular electrophysiology (EP). As the official journal of the Heart Rhythm Society, HeartRhythm publishes
both basic and clinical subject matter of scientific excellence devoted to the EP of the heart and blood vessels, as
well as therapy. The journal is the only EP publication serving the entire electrophysiology community from basic to
clinical academic researchers, private practitioners, technicians, industry and trainees. HeartRhythm has an Impact
Factor of 4.203 and is ranked tenth out of 72 cardiovascular medicine journals by the Institute for Scientific
Information. Additionally, the journal ranks sixth in the Immediacy Index among cardiology publications.  It is also
the official publication of the Cardiac Electrophysiology Society.   
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