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Intensity of Anticoagulation To Prevent Stroke in Patients with Atrial Fibrillation
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TO THE EDITOR:
In their “Update in General Internal Medicine,” Sheffield and Larson [1] cite the conclusions of a case–control study [2] reporting that the lowest effective intensity of warfarin for atrial fibrillation is an international normalized ratio (INR) of 2.0. This is an oversimplification of available information.
In the case–control study by Hylek and colleagues [2], INRs of 2.0 or more seemed to provide optimal protection against stroke. However, INRs between 1.6 and 1.9 were associated with an 80% or greater reduction in risk for stroke compared with INRs of 1.0 to 1.1 (equivalent to untreated patients). This partial efficacy of INRs of 1.6 to 1.9 has been confirmed by time-dependent analysis of a recent randomized trial [3]. Two clinical trials with estimated target INRs between 1.4 and 2.8 reported the highest efficacy for stroke prevention in patients with nonvalvular atrial fibrillation (the trials were done by using prothrombin time ratios, with INRs estimated post hoc by the trial investigators on the basis of Institute for Scientific Information values).
Substantial, if incomplete, protection is afforded by INRs between 1.6 and 2.0. This may be important for selected elderly patients who have special risks for bleeding, in whom a target INR of 2.0 (range, 1.6 to 2.5) may be a sensible option. Achieved INRs between 1.6 and 2.5 seemed to provide more than 90% of the protection afforded by higher ranges (Figure 1).
Robert G. Hart, MD
University of Texas Health Science Center; San Antonio, TX 78284
The Editors welcome submissions for possible publication in the Letters section. Authors of letters should:
•Include no more than 300 words of text, three authors, and five references
•Type with double-spacing
•Send three copies of the letter, an authors' form signed by all authors, and a cover letter describing any conflicts of interest related to the contents of the letter.
Letters commenting on an Annals article will be considered if they are received within 6 weeks of the time the article was published. Only some of the letters received can be published. Published letters are edited and may be shortened; tables and figures are included only selectively. Authors will be notified that the letter has been received. If the letter is selected for publication, the author will be notified about 3 weeks before the publication date. Unpublished letters cannot be returned.
Annals welcomes electronically submitted letters.
- Copyright ©2004 by the American College of Physicians
