title: J-shaped association between QTc interval duration and the risk of atrial fibrillation: results from the Copenhagen ECG study.
abstract: OBJECTIVE
  The aim of this study was to investigate whether the heart rate-corrected QT (QTc) interval on the electrocardiogram (ECG) is associated with the onset of atrial fibrillation (AF).
  
  
  BACKGROUND
  Patients with hereditary short-QT or long-QT syndromes, representing the very extremes of the QT interval, both seem to have a high prevalence of AF.
  
  
  METHODS
  A total of 281,277 subjects were included, corresponding to one-third of the population of the greater region of Copenhagen. These subjects underwent digital ECG recordings in a general practitioner's core facility from 2001 to 2010. Data on drug use, comorbidities, and outcomes were collected from Danish registries.
  
  
  RESULTS
  After a median follow-up period of 5.7 years, 10,766 subjects had developed AF, of whom 1,467 (14%) developed lone AF. Having a QTc interval lower than the first percentile (≤372 ms) was associated with a multivariate-adjusted hazard ratio of 1.45 (95% confidence interval: 1.14 to 1.84; p = 0.002) of AF, compared with the reference group (411 to 419 ms). From the reference group and upward, the risk of AF increased with QTc interval duration in a dose-response manner, reaching a hazard ratio of 1.44 (95% confidence interval: 1.24 to 1.66, p < 0.001) for those with QTc intervals ≥99th percentile (≥464 ms). The association with respect to longer QTc intervals was stronger for the outcome of lone AF, as evidenced by a hazard ratio of 2.32 (95% confidence interval: 1.52 to 3.54, p < 0.001) for having a QTc interval ≥99th percentile (≥458 ms).
  
  
  CONCLUSIONS
  In this large ECG study, a J-shaped association was found between QTc interval duration and risk of AF. This association was strongest with respect to the development of lone AF.
authors.affiliation: Danish National Research Foundation Centre for Cardiac Arrhythmia, Copenhagen, Denmark. jonas.bille.nielsen@gmail.com
authors.forename: Jonas Bille
authors.initials: JB
authors.lastname: Nielsen
authors.forename: Claus
authors.initials: C
authors.lastname: Graff
authors.forename: Adrian
authors.initials: A
authors.lastname: Pietersen
authors.forename: Bent
authors.initials: B
authors.lastname: Lind
authors.forename: Johannes Jan
authors.initials: JJ
authors.lastname: Struijk
authors.forename: Morten Salling
authors.initials: MS
authors.lastname: Olesen
authors.forename: Stig
authors.initials: S
authors.lastname: Haunsø
authors.forename: Thomas Alexander
authors.initials: TA
authors.lastname: Gerds
authors.forename: Jesper Hastrup
authors.initials: JH
authors.lastname: Svendsen
authors.forename: Lars
authors.initials: L
authors.lastname: Køber
authors.forename: Anders Gaarsdal
authors.initials: AG
authors.lastname: Holst
mesh_terms: D000328:Adult; D000368:Aged; D001281:Atrial Fibrillation / Q000175:diagnosis* / Q000453:epidemiology / Q000503:physiopathology*; D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D004562:Electrocardiography / Q000379:methods; D005260:Female; D005500:Follow-Up Studies; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D013997:Time Factors