title: The impact of posture on cardiac repolarization: more than heart rate?
abstract: BACKGROUND
  The effect of standing on heart rate and QT is well known but its impact on QTc is less clear.
  
  
  METHODS
  Serial supine and standing 12-lead ECGs (seven pairs each day) were recorded from 54 healthy volunteers each day of a three-day period. ECGs were captured digitally and over-read by a cardiologist.
  
  
  RESULTS
  A statistically significant shortening of RR (216 ms), QT (40 ms), and decreases in QTc-F (Fridericia) and QTc-LR (Framingham) were demonstrated on standing (8.3 and 6.9 ms, respectively). In contrast, QTc-B (Bazett's) significantly increased by 9.6 ms. Two subject-individualized correction methods were derived using each subject's supine measurements. Both showed significant decreases in QTc of approximately 13-14 ms upon standing. Using the bin analysis method, comparisons between positions using 25 ms interval RR bins revealed significant QT shortening of up to 15 ms upon standing.
  
  
  CONCLUSIONS
  We have demonstrated a postural effect on cardiac repolarization independent of heart rate using two individualized correction methods, as well as QTc-F and QTc-LR, and the bin method. Characterization of postural differences in QT/QTc (other than QTc-B) may provide a safe and inexpensive physiological control to validate the ECG methodology used in clinical trials to assess potential drug-induced QT interval changes.
authors.affiliation: Yamanouchi Pharma America, Paramus, New Jersey, USA.
authors.forename: Gregory C
authors.initials: GC
authors.lastname: Williams
authors.forename: Katherine M
authors.initials: KM
authors.lastname: Dunnington
authors.forename: Ming-Yi
authors.initials: MY
authors.lastname: Hu
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Zimmerman
authors.forename: Zhiming
authors.initials: Z
authors.lastname: Wang
authors.forename: Kerry B
authors.initials: KB
authors.lastname: Hafner
authors.forename: Maxine
authors.initials: M
authors.lastname: Stoltz
authors.forename: Edward K
authors.initials: EK
authors.lastname: Hill
authors.forename: Jean T
authors.initials: JT
authors.lastname: Barbey
mesh_terms: D004562:Electrocardiography; D005260:Female; D005500:Follow-Up Studies; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D011187:Posture / Q000502:physiology*; D012016:Reference Values