High familial risk of atrial fibrillation/atrial flutter in multiplex families: a nationwide family study in Sweden.

Although the heritability of atrial fibrillation/atrial flutter (af/afl) 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/afl in multiplex families. we examined the familial risk of af/afl 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/afl risk among relatives of all 300 586 individuals with af/afl 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/afl than did parents and siblings of controls. af/afl ors were increased in both sexes. for 2% of cases,both parents had af/afl,compared with only 0.7% of controls (or=3.60 [3.30 to 3.92]). moreover,3% of cases had ≥2 siblings with af/afl,compared with 1% of controls (or=5.72 [5.28 to 6.19]). in premature cases (diagnosed at age <50 years),the ors were 5.04 (4.36 to 5.82) and 8.51 (6.49 to 11.15) for af/afl in both parents and af/afl in ≥2 siblings,respectively. the overall spouse or was 1.16 (1.13 to 1.19). family history of af/afl increases the odds of af/afl in first-degree relatives. high familial risks were observed in multiplex families.