Atrial fibrillation and risk of stroke: a nationwide cohort study

Although the relation between stroke risk factors and stroke in patients with atrial fibrillation (AF) has been extensively examined, only few studies have explored the association of AF and the risk of ischaemic stroke/systemic thromboembolism/transient ischaemic attack (stroke/TE/TIA) in the presence of concomitant stroke risk factors. From nationwide registries, all persons who turned 50, 60, 70, or 80 from 1997 to 2011 were identified. Persons receiving warfarin were excluded. The absolute risk of stroke/TE/TIA was reported for a 5-year period, as was the absolute risk ratios for AF vs. no AF according to prior stroke and the number of additional risk factors. The study cohort comprised of 3 076 355 persons without AF and 48 189 with AF. For men aged 50 years, with no risk factors, the 5-year risk of stroke was 1.1% (95% confidence interval 1.1-1.1); with AF alone 2.5% (1.8-3.2); with one risk factor and no prior stroke or AF 2.5% (2.3-2.7); and with one factor, no prior stroke and AF 2.9% (1.4-4.3). In men aged 50 years with prior stroke as the only risk factor, 5-year risk was 10.2% (9.1-11.3). In men aged 70 years, the corresponding risks were 4.8% (4.7-4.9), 6.8% (5.7-7.9), 6.6% (6.3-6.8), 8.7 (7.4-9.9), and 19.1% (18.1-20.1), respectively. In women aged 50 years, the risk was of 0.7% (0.7-0.7), 2.1% (0.9-3.2), 1.6% (1.4-1.8), 4.1% (0.6-7.6), and 7.2% (6.3-8.2), respectively, and in women aged 70 years 3.4% (3.3-3.5), 8.2% (7.0-9.5), 4.6% (4.4-4.8), 9.1% (7.5-10.6), and 15.4% (14.5-16.4), respectively. Stroke/TE/TIA risk was particularly increased when prior stroke/TE/TIA was present. Atrial fibrillation is associated with an increase in risk of stroke/TE/TIA in the absence of other risk factors but only a moderate increase in risk when other risk factors are present.