The lowest effective intensity of prophylactic anticoagulation for patients with atrial fibrillation

Background: Stroke prevention trials in patients with atrial fibrillation (AF) mainly studied the use of warfarin in Caucasians, and the international normalized ratio (INR) was targeted in the range of 2-4. The result may not necessarily be applicable to other ethnic groups. This study aimed to determine the optimal intensity of anticoagulation for stroke prevention in Chinese patients.

Methods: We performed a retrospective study on all Chinese patients with AF taking warfarin for stroke prevention in our hospital from January 1, 2000, to June 30, 2002. Patients with a mechanical heart valve were excluded. We systematically studied their indication of using warfarin, duration of therapy and all INR results. Only those patients whose indications of using warfarin were consistent with the ACC/AHA/ESC Executive Summary were included. Thrombo-embolic episodes, sudden death, major bleeding, intracranial haemorrhage and the INR at the time of the event were recorded. The INR range was divided into six categories: <1.5, 1.5-1.9, 2.0-2.5, 2.6-3.0, 3.1-3.5, >3.5. The number of events was recorded for each category, and this formed the numerator. The denominator was the summation of time each patient stayed in each category of INR. The event rate was then calculated for each INR category.

Results: 555 patients were included in the analysis, they constituted 893 patient-years. The INR was kept below 2.6 in 84.9% of the time and between 1.5 and 1.9 in 35% of the time. The overall event rate in our patients was 6.0%, of which 3.9% were due to thrombo-embolic events and 2.1% were due to serious bleeding. The overall event rate was lowest in the INR range from 1.5 to 1.9. which is not significantly different from that of INR 2.0-2.5 and 2.6-3.0. The overall event rate was 3.6% in INR 1.5-3.0 which was significantly lower than 15.1% in INR <1.5 and 20.5% in INR >3.0 (p < 0.01).

Conclusions: Our retrospective cohort showed that a lower INR range of 1.5-3.0 was safe and effective for stroke prevention in Chinese patients treated in a single hospital.