title: Diagnostic performance of QT interval variables from 24-h electrocardiography in the long QT syndrome.
abstract: OBJECTIVE
  The long QT syndrome is mainly defined by QT interval prolongation (QTc > 0.44s). However, data obtained in genotyped patients showed that resting QTc measurement alone may be inaccurate for ascertaining the phenotype. The aim of this study was to evaluate the diagnostic performance of QT interval rate-dependence in untreated chromosome 11-linked patients.
  
  
  METHODS
  The study population consisted of 25 untreated long QT patients linked to chromosome 11 and 25 age- and gender-matched controls. QTc intervals were measured on 12-lead resting ECG recordings. From 24-h Holter recordings, the slope of the relationship between ventricular repolarization and heart rate was studied separately day and night to assess neural modulation. Mean heart rates and rate-dependences of QT and Q-maximum of T (QTm) intervals were compared between long QT patients and controls for both time periods.
  
  
  RESULTS
  In both groups, the rate-dependences were modulated by day-night influences. When compared to controls, long QT patients showed a significant increase at night in QT/RR slopes (0.158 +/- 0.05 vs 0.117 +/- 0.03, P = 0.002) and QTm/RR slopes (0.163 +/- 0.05 vs 0.116 +/- 0.04, P = 0.0006). Multivariate analysis, adjusting QTc interval on age and gender, discriminated between long QT patients and controls with a 76% sensitivity and a 84% specificity. A 96% sensitivity and a 96% specificity were reached by taking into account the QTm/RR slope at night, the QTc interval and the mean heart rate during the day.
  
  
  CONCLUSIONS
  QT interval variables obtained from 24-h ECG recordings improve long QT syndrome diagnosis by showing an increased nocturnal ventricular repolarization rate-dependence in genotyped chromosome 11-linked patients.
authors.affiliation: Lariboisière Hospital, Paris, France.
authors.forename: N
authors.initials: N
authors.lastname: Neyroud
authors.forename: P
authors.initials: P
authors.lastname: Maison-Blanche
authors.forename: I
authors.initials: I
authors.lastname: Denjoy
authors.forename: S
authors.initials: S
authors.lastname: Chevret
authors.forename: C
authors.initials: C
authors.lastname: Donger
authors.forename: E
authors.initials: E
authors.lastname: Dausse
authors.forename: J
authors.initials: J
authors.lastname: Fayn
authors.forename: F
authors.initials: F
authors.lastname: Badilini
authors.forename: N
authors.initials: N
authors.lastname: Menhabi
authors.forename: K
authors.initials: K
authors.lastname: Schwartz
authors.forename: P
authors.initials: P
authors.lastname: Guicheney
authors.forename: P
authors.initials: P
authors.lastname: Coumel
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D016009:Chi-Square Distribution; D002648:Child; D002880:Chromosomes, Human, Pair 11; D002940:Circadian Rhythm; D015716:Electrocardiography, Ambulatory / Q000295:instrumentation*; D005260:Female; D005838:Genotype; D006329:Heart Conduction System / Q000503:physiopathology*; D006339:Heart Rate / Q000502:physiology; D006352:Heart Ventricles / Q000294:innervation; D006801:Humans; D016015:Logistic Models; D008133:Long QT Syndrome / Q000175:diagnosis* / Q000235:genetics / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D012680:Sensitivity and Specificity; D018709:Statistics, Nonparametric