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Warfarin underused in patients with AF
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Patients with atrial fibrillation often do not receive adequate levels of warfarin in the outpatient setting.
Nonrheumatic AF is a common cause of embolic stroke. Although warfarin therapy is known to reduce risk for stroke in patients with AF by as much as two-thirds, the researchers said that “it may not always be used or be used optimally.” The results were published in Heart Rhythm.
Researchers from the World Health Information Science Consultants and GlaxoSmithKline conducted a retrospective analysis of the insurance claims and laboratory results of 116,969 patients with a claim for AF or atrial flutter between 1999 and 2005 and attempted to quantify the association between AF outcomes with the international normalized ratio.
Forty-five percent had been prescribed warfarin, and 48% had no claim for warfarin or any other anticoagulant or antiplatelet agent, according to the study abstract.
There were 16,811 hospitalizations among 13,762 patients due to AF during follow-up, and stroke was identified as the most common event. A logistical regression model of predictors of anticoagulant dispensing in patients newly diagnosed with AF (n=41,244) revealed that patients with a history of stroke (OR=1.77; 95% CI, 1.37-2.28) and patients aged between 60 and 64 years (OR=1.73; 95% CI, 1.62-1.85) were the most likely to be prescribed anticoagulants.
Risk for stroke
The researchers also examined the time patients spent within the therapeutic range of the international normalized ratio for warfarin therapy. They reported that approximately one-third of patients with an international normalized ratio assessment (n=13,115) spent <20% of their time within the therapeutic range of the international normalized ratio and that 19% spent most of or all of their time within the therapeutic range. Subtherapeutic international normalized ratio levels were also associated with a higher risk for stroke (RR=2.39; 95% CI, 1.68-3.41) and were associated with double the risk for intracranial hemorrhage (RR=2.11; 95% CI, 1.16-3.84) compared with therapeutic levels.
“Taking into account physician and patient concerns regarding the practical use of warfarin, it seems that there is a clear unmet need for a simpler and safer anticoagulation program,” the researchers wrote. – by Eric Raible
For more information:
- Heart Rhythm. 2008;5:1365-1372.
This type of paper is very complex to analyze because of the multiple types of data that are included in an insurance database. It would have been a lot simpler if they had tried to calculate CHADS2 scores and then assessed use according to published guidelines. One other thing to remember is that between 25% to 35% of patients have fairly strong contraindications to warfarin, so you should never get 100% use. The right percentage is probably 70% of those who meet criteria.
– John Philip DiMarco, MD, PhD
Cardiology Today Editorial Board member