title: Reproducibility of computerized measurements of QT interval from multiple leads at rest and during exercise.
abstract: BACKGROUND
  Accurate measurement of the QT interval is important for diagnosing long QT syndrome (LQTS), and in research on determinants of ventricular repolarization time. We tested automatic analysis of QT intervals from multiple ECG leads on chest.
  
  
  METHODS
  Eleven healthy volunteers and 10 genotyped LQTS patients were tested at rest and during exercise with a bicycle ergometer twice 1-31 months apart. Electrocardiograms were recorded with the body surface potential mapping system, and 12 precordial channels were selected for analysis. Averaged QT peak and QT end intervals were determined with an automated algorithm, and the difference QT end minus QT peak (Tp-e) was calculated. Repeatability was assessed by coefficient of variation (CV) between measurements.
  
  
  RESULTS
  Within one test at rest the QT end intervals were highly repeatable with CV 0.6%. In repeated tests CV was 4.4% for QT end interval and 3.5% when the QT interval was corrected for heart rate. In exercise test at specified heart rates, mean CV was 3.0% for QT end and 2.9% for QT peak interval. The CV of Tp-e interval was 10.2% at rest, and 9.3% in exercise test. Reproducibility was comparable between healthy subjects and LQTS patients.
  
  
  CONCLUSIONS
  The BSPM system with automated analysis produced accurate and highly repeatable QT interval measurements. Reproducibility was adequate also over prolonged time periods both at rest and in exercise stress test. The method can be applied in studying duration of ventricular repolarization time in different physiologic and pharmacologic interventions.
authors.affiliation: Helsinki University Hospital, Department of Cardiology, Helsinki, Finland. anna-mari.hekkala@hus.fi
authors.forename: Anna-Mari
authors.initials: AM
authors.lastname: Hekkala
authors.forename: Heikki
authors.initials: H
authors.lastname: Väänänen
authors.forename: Heikki
authors.initials: H
authors.lastname: Swan
authors.forename: Lasse
authors.initials: L
authors.lastname: Oikarinen
authors.forename: Matti
authors.initials: M
authors.lastname: Viitasalo
authors.forename: Lauri
authors.initials: L
authors.lastname: Toivonen
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D018780:Body Surface Potential Mapping; D004562:Electrocardiography; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008133:Long QT Syndrome / Q000175:diagnosis* / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012146:Rest / Q000502:physiology*; D018709:Statistics, Nonparametric