title: Relation between beat-to-beat QT interval variability and T-wave amplitude in healthy subjects.
abstract: OBJECTIVE
  Elevated beat-to-beat QT interval variability (QTV) has been associated with increased cardiovascular morbidity and mortality.The aim of this study was to investigate interlead differences in beat-to-beat QTV of 12-lead ECG and its relationship with the T wave amplitude.
  
  
  METHODS
  Short-term 12-lead ECGs of 72 healthy subjects (17 f, 38 ± 14 years; 55 m, 39 ± 13 years) were studied. Beat-to-beat QT intervals were extracted separately for each lead using a template matching algorithm. We calculated the standard deviation of beat-to-beat QT intervals as a marker of QTV as well as interlead correlation coefficients. In addition, we measured the median T-wave amplitude in each lead.
  
  
  RESULTS
  There was a significant difference in the standard deviation of beat-to-beat QT intervals between leads (minimum: lead V(3) (2.58 ± 1.36 ms), maximum: lead III (7.2 ± 6.4 ms), ANOVA: P < 0.0001). Single measure intraclass correlation coefficients of beat-to-beat QT intervals were 0.27 ± 0.18. Interlead correlation coefficients varied between 0.08 ± 0.33 for lead III and lead V(1) and 0.88 ± 0.09 for lead II and lead aVR. QTV was negatively correlated with the T-wave amplitude (r =-0.62, P < 0.0001). There was no significant affect of mean heart rate, age or gender on QT variability (ANOVA: P > 0.05).
  
  
  CONCLUSIONS
  QTV varies considerably between leads in magnitude as well as temporal patterns. QTV is increased when the T wave is small.
authors: School of Electrical and Electronic Engineering             Centre for Heart Rhythm Disorders, The University of Adelaide, Adelaide, SA, Australia.
authors: Muhammad A
authors: MA
authors: Hasan
authors: Derek
authors: D
authors: Abbott
authors: Mathias
authors: M
authors: Baumert
mesh_terms: D000328:Adult; D000367:Age Factors; D000704:Analysis of Variance; D015331:Cohort Studies; D004562:Electrocardiography / Q000379:methods*; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008133:Long QT Syndrome / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D012737:Sex Factors; D012815:Signal Processing, Computer-Assisted; D055815:Young Adult