Warfarin treatment and risk of stroke among primary care patients with atrial fibrillation

Objective. Our aim was to study the risk of a first ischaemic stroke (IS) in patients with atrial fibrillation (AF) treated in primary healthcare. Design. The study population included all adults (n=11,517), 45 years and older diagnosed with AF, from 75 primary care centres in Sweden between 2001 and 2007. IS was defined as a hospital care event of stroke between 2001 and 2010. Association between incident stroke and warfarin treatment was explored using Cox regression analysis, with hazard ratios (HRs), and 95% confidence intervals (95%CIs). Adjustment was made for age, socioeconomic factors and co-morbidity. Results. Persistent treatment with warfarin was present among 33.7% of women and 40.0% among men. Persistent warfarin treatment, compared to no persistent treatment, was associated with a stroke preventing effect with fully adjusted HRs of 0.25 (95%CI 0.18-0.36) in women, and 0.25 (95%CI 0.19-0.32) in men. A CHA(2)DS(2)-VASc score of at least two among women, and three among men, was associated with a stroke risk exceeding 18% during a mean follow-up of 5.4 years. Risk of haemorrhagic stroke was not increased. Conclusions. Warfarin is effective in preventing stroke in AF patients in primary healthcare.