title: Reproducibility and automatic measurement of QT dispersion.
abstract: This study investigated interobserver (two observers) and intrasubject (two measurements) reproducibility of QT dispersion from abnormal electrocardiograms in patients with previous myocardial infarction, and compared a user-interactive with an automatic measurement system. Standard 12-lead electrocardiograms, recorded at 25 mm.s-1, were randomly chosen from 70 patients following myocardial infarction. These were scanned into a personal computer, and specially designed software skeletonized and joined each image. The images were then available for user-interactive (mouse and computer screen), or automatic measurements using a specially designed algorithm. For all methods reproducibility of the RR interval was excellent (mean absolute errors 3-4 ms, relative errors 0.3-0.5%). Reproducibility of the mean QT interval was good; intrasubject error was 6 ms (relative error 1.4%), interobserver error was 7 ms (1.8%), and observers' vs automatic measurement errors were 10 and 11 ms (2.5, 2.8%). However QTc dispersion measurements had large errors for all methods; intrasubject error was 12 ms (17.3%), interobserver error was 15 ms (22.1%), and observers' vs automatic measurement were errors 30 and 28 ms (35.4, 31.9%). QT dispersion measurements rely on the most difficult to measure QT intervals, resulting in a problem of reproducibility. Any automatic system must not only recognize common T wave morphologies, but also these more difficult T waves, if it is to be useful for measuring QT dispersion. The poor reproducibility of QT dispersion limits its role as a useful clinical tool, particularly as a predictor of events.
authors.affiliation: Department of Medicine and Therapeutics, University of Leicester, U.K.
authors.forename: J M
authors.initials: JM
authors.lastname: Glancy
authors.forename: P J
authors.initials: PJ
authors.lastname: Weston
authors.forename: H K
authors.initials: HK
authors.lastname: Bhullar
authors.forename: C J
authors.initials: CJ
authors.lastname: Garratt
authors.forename: K L
authors.initials: KL
authors.lastname: Woods
authors.forename: D P
authors.initials: DP
authors.lastname: de Bono
mesh_terms: D003936:Diagnosis, Computer-Assisted / Q000379:methods; D004562:Electrocardiography / Q000379:methods; D006801:Humans; D008133:Long QT Syndrome / Q000175:diagnosis*; D009203:Myocardial Infarction / Q000175:diagnosis*; D015588:Observer Variation; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity