Prevalence and Incidence Rates of Atrial Fibrillation in Denmark 2004-2018.

Purpose: To estimate the prevalence and incidence of atrial fibrillation (AF) in Denmark during 2004-2018 and to investigate whether methodological choices influence these estimates.

Patients And Methods: A register-based cohort study was conducted of all individuals aged ≥18 years in Denmark 2004-2018. The cumulative prevalence of AF at the end of the study period was calculated as the number of AF cases alive with at least one inpatient or two outpatient diagnoses during 1994-2018 divided by the number of Danish residents in 2018. Incidence rates were calculated as the number of annual AF cases with no previous diagnosis in the past 10 years (ie, a 10-year washout period) divided by the person-time contributed by the population free of AF on 1 January in the same calendar year. Furthermore, the influence of varying case definitions was investigated.

Results: The cumulative prevalence of AF was 3.0% in 2018. The incidence rate increased from 391 to 481 per 100,000 person-years (PYs) from 2004 to 2015 (1.7% average annual increase) after which it declined to 367 per 100,000 PYs in 2018 (8.5% average annual decrease). This pattern was observed in both sexes irrespective of age. Methodological choices, particularly the case definition's strictness and the length of the washout period, had a substantial influence on the reported estimates.

Conclusion: The cumulative prevalence of AF is currently around 3.0% in the Danish population, but the incidence has declined since 2015. As these estimates are influenced by methodological choices, future studies should strive for precise reporting of study methodology.