title: Consistency of heart rate-QTc prolongation consistency and sudden cardiac death: The Rotterdam Study.
abstract: BACKGROUND
  A prolonged heart rate-corrected QT (QTc) interval is a well-known risk indicator for sudden cardiac death (SCD) and a contraindication for drugs with potentially arrhythmogenic adverse effects.
  
  
  OBJECTIVE
  We aimed to study the consistency of QTc interval prolongation and whether a consistent QTc interval prolongation correlates differently with SCD than does an inconsistently prolonged QTc interval.
  
  
  METHODS
  We used a population-based cohort study of persons 55 years and older. We excluded participants using QTc-prolonging drugs or with bundle branch block. The QT interval was corrected for heart rate using Bazett and Fridericia formulas. Using a Cox regression model, we assessed the association between QTc interval prolongation consistency and the occurrence of SCD.
  
  
  RESULTS
  A total of 3484 participants had electrocardiograms (ECGs) recorded on 2 consecutive visits. In 96%-98% of participants with a normal QTc interval on the first ECG, the QTc interval remained normal, but only in 27%-35% of those with a prolonged QTc interval, the QTc interval was prolonged on the second ECG after a median of 1.8 years. A consistently prolonged QTc interval was associated with an increased risk of SCD as compared with a consistently normal QTc interval (Bazett: hazard ratio 2.23; 95% confidence interval 1.17-4.24, Fridericia: hazard ratio 6.67; 95% confidence interval 2.96-15.06). A prolonged QTc interval preceded or followed by a normal QTc interval was not significantly associated with an increased risk of SCD.
  
  
  CONCLUSIONS
  Persons with an inconsistently prolonged QTc interval did not have a higher risk of SCD than those with a consistently normal QTc interval. Persons with a consistently prolonged QTc interval did have a higher risk of SCD. Our results suggest that repeated measurements of the QTc interval could enhance risk stratification.
authors.affiliation: Department of Epidemiology.
authors.forename: Maartje N
authors.initials: MN
authors.lastname: Niemeijer
authors.affiliation: Department of Medical Informatics.
authors.forename: Marten E
authors.initials: ME
authors.lastname: van den Berg
authors.affiliation: Department of Cardiology.
authors.forename: Jaap W
authors.initials: JW
authors.lastname: Deckers
authors.affiliation: Department of Epidemiology.
authors.forename: Oscar H
authors.initials: OH
authors.lastname: Franco
authors.affiliation: Department of Epidemiology.
authors.forename: Albert
authors.initials: A
authors.lastname: Hofman
authors.affiliation: Department of Medical Informatics.
authors.forename: Jan A
authors.initials: JA
authors.lastname: Kors
authors.affiliation: Department of Epidemiology; Department of Internal Medicine, Erasmus MC - University Medical Center Rotterdam, Rotterdam, The Netherlands; Inspectorate of Health Care, Utrecht, The Netherlands. Electronic address: b.stricker@erasmusmc.nl.
authors.forename: Bruno H
authors.initials: BH
authors.lastname: Stricker
authors.affiliation: Department of Medical Informatics.
authors.forename: Peter R
authors.initials: PR
authors.lastname: Rijnbeek
authors.affiliation: Department of Epidemiology; Department of Internal Medicine, Erasmus MC - University Medical Center Rotterdam, Rotterdam, The Netherlands.
authors.forename: Mark
authors.initials: M
authors.lastname: Eijgelsheim
mesh_terms: D000368:Aged; D016757:Death, Sudden, Cardiac / Q000453:epidemiology* / Q000209:etiology; D004562:Electrocardiography; D005260:Female; D005500:Follow-Up Studies; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008133:Long QT Syndrome / Q000150:complications / Q000401:mortality / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D011159:Population Surveillance / Q000379:methods*; D011379:Prognosis; D016016:Proportional Hazards Models; D012189:Retrospective Studies; D012307:Risk Factors; D015996:Survival Rate
keywords: Electrocardiogram; Epidemiology; Population-based; QT interval; Sudden cardiac death