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Anticoagulation in Atrial Fibrillation
Abstract & Commentary
By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco is a consultant for Novartis, and does research for Medtronic and Guidant.
Sources: Rowan SB, et al. Trends in Anticoagulation for Atrial Fibrillation in the U.S. An Analysis of the National Ambulatory Medical Care Survey Database. J Am Coll Cardiol. 2007;49:1561-1565.
Synposis: Appropriate and seemingly inappropriate use of anticoagulation is occurring among patients with atrial fibrillation.
Rowan et al describe results from the National Ambulatory Medical Care Survey (NAMCS) Database with regard to the use of warfarin anticoagulation in patients with atrial fibrillation (AF). The NAMCS Database for the 1994 to 2003 time period contains data from 40.5 million AF patient visits. Among all AF patients, age and the use of rate control agents only were associated with anticoagulant usage. The overall frequency of warfarin anticoagulation in patients with AF increased from 40.3% of all patients between 1994 and 1997 to 49.1% between 2001 and 2003. Of interest, the use of anticoagulation increased by 80% in the 18 to 59 year old population, decreased by 8% in the 60 to 75 year old population and increased by 45% in the 76 and older population. Patients with co-morbid conditions associated with thromboembolic phenomena showed a higher use of anticoagulation in all age groups. Patients taking rate control agents more frequently received anticoagulation than patients taking rhythm control agents only. Finally, among patients thought to be at low risk for a thromboembolic event, i.e., individuals under 65 years of age without congestive heart failure, previous cerebrovascular events, hypertension or diabetes, 30% of the patients were anticoagulated. The authors argue that both appropriate and seemingly inappropriate use of anticoagulation is occurring among patients with atrial fibrillation.
This paper provides an interesting view of the use of warfarin anticoagulation in patients with atrial fibrillation the United States. The National Ambulatory Medical Care Survey Database provides data from a very large number of patient visits allowing true national patterns to be detected. However, interpreting the data in a paper like this is somewhat difficult. In the late 1980's a series of trials demonstrated the benefit of warfarin in patients with atrial fibrillation and identified risk factors for embolic events. These and later studies also characterized risk factors for bleeding associated with warfarin therapy. The data from these trials have led to the increase in warfarin use documented here. It must be remembered however that about 1/3 of elderly patients have true contraindication to warfarin and so the attainable goal will never be 100% usage. Since many of the risk factors for embolic events (ago, co-morbidities, etc.) overlap with risk factors for bleeding, physicians continue to be often faced with a difficult clinical decision. One other limitation in the survey here is that the database doesn't provide a good reason why so many " low risk patients" were anticoagulated, particularly if they were seeing a cardiologist. It is likely that a substantial number of these latter patients were symptomatic younger individuals in whom a cardioversion was planned or was being considered. Use of warfarin in such patients would be completely appropriate. Unfortunately, the data available in a database like NAMCS does not allow us to answer questions such as this.