The epidemiology of atrial fibrillation in adults depends on locale of diagnosis.

BACKGROUND: Previous studies on atrial fibrillation (AF) epidemiology have used various case definitions for AF, but the effect of location of diagnosis on the apparent epidemiology of AF is unknown.
METHODS: Population-based study of 46,440 consecutive patients with newly diagnosed AF in Alberta, Canada, from 2000 to 2005.
RESULTS: Of adults newly diagnosed with AF (52.8% men, median 73 years), 51.8% were first diagnosed in hospital, 19.2% in emergency department (ED), and 29.0% in outpatient clinics. Prevalence of AF increased from 613 per 100,000 to 1,148 per 100,000 population over 5 years; however, the age- and sex-standardized incidence of AF remained relatively stable (350 per 100,000 in 2000 and 352 per 100,000 in 2005). The proportion of AF cases diagnosed in hospital declined 21% between 2000 and 2005, whereas the proportion of cases diagnosed in the outpatient setting rose by 50% (P < .0001). Patients diagnosed with AF in the hospital or the ED had more comorbidities and higher CHADS(2) (congestive heart failure, hypertension, age ≥75 years, diabetes mellitus, and prior stroke or transient ischemic attack) scores than those diagnosed in the outpatient setting (all P < .0001). Multivariate adjusted risk of cerebrovascular events or mortality (adjusted odds ratios 4.3, 95% CI 3.9-4.7) was significant for hospital and ED AF diagnosis (adjusted odds ratios 2.4, 95% CI 2.2-2.7) compared with those diagnosed in primary care clinics. New heart failure in the year after diagnosis of AF was 4.5% for inpatients, 3.8% in ED patients, and 2.5% in outpatients.
CONCLUSIONS: Use of hospitalizations alone to define an AF cohort may underestimate incidence while overestimating comorbiditities, thromboembolic risk, and outcomes.