Robert G. Hart, MD
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Hart RG. Intensity of Anticoagulation To Prevent Stroke in Patients with Atrial Fibrillation. Ann Intern Med. 1998;128:408. doi: 10.7326/0003-4819-128-5-199803010-00012
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Published: Ann Intern Med. 1998;128(5):408.
TO THE EDITOR:
In their “Update in General Internal Medicine,” Sheffield and Larson  cite the conclusions of a case–control study  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 , 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 . 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).
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Print ISSN: 0003-4819 | Online ISSN: 1539-3704
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