The impact of warfarin use on clinical outcomes in atrial fibrillation: a population-based study.
BACKGROUND
Atrial fibrillation (AF) is the most common adult arrhythmia, and significantly increases the risk of ischemic stroke. Oral anticoagulation may be underused and may be less effective in community settings than clinical trial settings.


OBJECTIVE
To determine the rates of thromboembolism and bleeding in an ambulatory cohort of patients with AF.


METHODS
Observational study of Nova Scotian residents with AF identified by electrocardiogram in ambulatory settings between November 1999 and January 2001. Main outcome measures were rates of thromboembolism and bleeding over two years.


RESULTS
Four hundred twenty-five patients were included in the study. The mean (+/-SD) age was 70.6+/-11.1 years, and 40% were women. Warfarin therapy was used by 68% of patients. Sixty-two per cent of patients had hypertension, 21% had a previous stroke or transient ischemic attack, 44% had congestive heart failure and 20% were diabetic. The overall rate of thromboembolic events was 2.7% in warfarin users and 8.5% in nonwarfarin users over two years, with an RR reduction of 68% (OR 0.31, 95% CI 0.09 to 0.91; P=0.047). The annual rate of ischemic stroke was 1.2% and 3.1% in warfarin and nonwarfarin users, respectively, with an RR reduction of 62% (OR 0.29, 95% CI 0.08 to 1.04; P=0.057). The overall rate of major bleeding was 2.6% in warfarin users and 1.4% in nonwarfarin users (P=0.667). The annual mortality rate was 7.79% in warfarin users and 9.93% in nonwarfarin users (P=0.192).


CONCLUSIONS
Warfarin use was found to significantly reduce the rate of thromboembolic events without a concomitant increase in hemorrhagic events. The present study confirms the effectiveness of warfarin therapy in a population-based cohort.
Parkash
Ratika
R
Department of Medicine, Dalhousie University and Capital Health, Halifax, Canada. ratika.parkash@cdha.nshealth.ca
Wee
Vinnie
V
Gardner
Martin J
MJ
Cox
Jafna L
JL
Thompson
Kara
K
Brownell
Brenda
B
Anderson
David R
DR
D000284:Administration, Oral; D000368:Aged; D000553:Ambulatory Care; D000925:Anticoagulants / Q000008:administration & dosage / Q000627:therapeutic use*; D001281:Atrial Fibrillation / Q000150:complications / Q000175:diagnosis / Q000188:drug therapy*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D009674:Nova Scotia / Q000453:epidemiology; D017063:Outcome Assessment, Health Care; D011159:Population Surveillance; D011446:Prospective Studies; D020521:Stroke / Q000453:epidemiology / Q000209:etiology / Q000517:prevention & control; D013923:Thromboembolism / Q000453:epidemiology* / Q000209:etiology / Q000517:prevention & control*; D016896:Treatment Outcome; D014859:Warfarin / Q000008:administration & dosage / Q000627:therapeutic use*
D000925:Anticoagulants; D014859:Warfarin