Incidence of atrial fibrillation and flutter in Denmark in relation to country of origin: a nationwide register-based study.

Background: Atrial fibrillation and flutter (AF) is the most common sustained arrhythmia with an increasing prevalence in Western countries. However, little is known about AF among immigrants compared to non-immigrants.

Aim: To examine the incidence of hospital-diagnosed AF according to country of origin.

Method: Immigrants were defined as individuals born outside Denmark by parents born outside Denmark. AF was defined as first-time diagnosis of AF. All individuals were followed from the age of 45 years from 1998 to 2017. The analyses were adjusted for sex, age, comorbidity, contact with the general practitioner and socioeconomic variables. Adjustment was conducted using standardised morbidity ratio weights, standardised to the Danish population in a marginal structural model.

Results: The study population consisted of 3,489,730 Danish individuals free of AF and 108,914 immigrants free of AF who had emigrated from the 10 most represented countries. A total of 323,005 individuals of Danish origin had an incident hospital diagnosis of AF, among the immigrants 7,300 developed AF. Adjusted hazard rate ratios (HRRs) of AF for immigrants from Iran (0.48 [95%CI:0.35;0.64]), Turkey (0.74 [95%CI:0.67;0.82]) and Bosnia-Herzegovina (0.42 [95%CI:0.22;0.79]) were low compared with Danish individuals. Immigrants from Sweden, Germany and Norway had an adjusted HRR of 1.13 [95%CI:1.03;1.23], 1.12 [95%CI:1.05;1.18] and 1.11 [95%CI:1.03;1.21], respectively (Danish individuals as reference).

Conclusions: Substantial variation in the incidence of hospital-diagnosed AF according to country of origin was observed. The results may reflect true biological differences but could also reflect barriers to AF diagnosis for immigrants. Further efforts are warranted to determine the underlying mechanisms.