Trends in Risk of Stroke in Patients with a Hospital Diagnosis of Nonvalvular Atrial Fibrillation: National Cohort Study in Denmark, 1980-2002

Aim: We examined trends in incidence of stroke of any nature (ischemic and/or hemorrhagic) in subjects with a hospital diagnosis of nonvalvular atrial fibrillation or flutter in Denmark from 1980 to 2002 by sex, age and conditions of comorbidity.

Methods: We identified all individuals, aged 40-89 years, with an incident hospital diagnosis of atrial fibrillation or flutter and no history of stroke or heart valve disease in the Danish National Registry of Patients, and subjects were followed in the Danish National Registry of Patients for occurrence of an incident diagnosis of stroke of any nature (ischemic and/or hemorrhagic) and in the Danish Civil Registration System (emigration and vital status). We used multivariate Cox proportional hazard regression analysis to estimate trends in incidence of stroke.

Results: Nonvalvular atrial fibrillation or flutter was diagnosed in 141,493 subjects (75,126 men and 66,367 women), and during follow-up 15,964 subjects had an incident diagnosis of stroke. The hazard ratios for stroke in the last 3-year period compared to the first 5-year period, adjusted for 10-year age group, conditions of comorbidity, and general stroke trend in the Danish population were 0.78 (95% CI 0.70-0.86) in men, and 0.80 (95% CI 0.72-0.88) in women. The reduction in risk of stroke by calendar year was most prominent in patients aged 40-74 years.

Conclusion: We observed a modest decrease in risk of stroke in subject with atrial fibrillation in Denmark during calendar years 1980-2002. However, we could not control for any changes in diagnostic performance, admission practice, and medical management of patients with atrial fibrillation.