Introduction: Patients with nonvalvular atrial fibrillation are at increased risk for systemic embolism, predominantly disabling stroke. To study how stroke and mortality rates vary with different degrees of anticoagulation reflected by the international normalised ratio (INR) we critically assess information from different sources.
Materials and methods: 1. Computerized search of the medical literature published between 1980 and July 2004 was performed using MEDLINE applied to various combinations of the search terms of atrial fibrillation, warfarin, anticoagulation, anticoagulation intensity, and INR, not restricted by language. 2. We performed a record linkage analysis with death hazard estimated as a continuous function of INR based on 21,967 patients. Similarly the risk of admission to hospital or death due to diseases of the vessels of the brain was estimated. 3. Re-analysis of data earlier published by Hylek et al. from year 2003.
Results and conclusions: 1. One randomised study showed a significantly lower risk of stroke for mean INR 2.4 compared to mean INR 1.3 combined with aspirin. Remaining studies found INRs of 2-2.5 to be as efficacious as higher anticoagulation intensities.2. Mortality as well as risk of admission to hospital or death due to diseases of the vessels of the brain followed U-shaped curves with minimum at INR 2.2 and 2.4, respectively. At high INR the risk increased 2.3 times per 1 unit increase of INR for death and 1.7 times for events in the vessels of the brain.3. The re-analysing of data of Hylek et al. indicated that there might be a substantial increase of the risk of intracranial hemorrhage when INR is increased from 2.5 to 4. We conclude that INRs in the interval 2.0--2.5 give the lowest risk of stroke and death in patients with nonvalvular atrial fibrillation.