High Familial Risk of Atrial Fibrillation/Atrial Flutter in Multiplex Families: A Nationwide Family Study in S weden

Background Although the heritability of atrial fibrillation/atrial flutter ( AF / AF l) has been determined, the familial risk in multiplex families is unclear. The main aim of this nationwide study was to determine the familial risk of AF / AF l in multiplex families. Methods and Results We examined the familial risk of AF / AF l in the entire Swedish population. We linked Multigeneration Register data on individuals aged 0 to 76 years with Hospital Discharge Register data for 1987–2008 and Outpatient Register data for 2001–2008 to compare AF / AF l risk among relatives of all 300 586 individuals with AF / AF l with that among relatives of unaffected individuals. We used conditional logistic regression to investigate differences in exposure between cases and controls. Parents (odds ratio [ OR ] 1.95 [95% CI 1.89 to 2.00]) and siblings ( OR =3.08 [3.00 to 3.16]) of cases had higher odds of AF / AF l than did parents and siblings of controls. AF / AF l OR s were increased in both sexes. For 2% of cases, both parents had AF / AF l, compared with only 0.7% of controls ( OR =3.60 [3.30 to 3.92]). Moreover, 3% of cases had ≥2 siblings with AF / AF l, compared with 1% of controls ( OR =5.72 [5.28 to 6.19]). In premature cases (diagnosed at age <50 years), the OR s were 5.04 (4.36 to 5.82) and 8.51 (6.49 to 11.15) for AF / AF l in both parents and AF / AF l in ≥2 siblings, respectively. The overall spouse OR was 1.16 (1.13 to 1.19). Conclusions Family history of AF / AF l increases the odds of AF / AF l in first‐degree relatives. High familial risks were observed in multiplex families.