Copyright © 1996 by the European Society of Cardiology.
© 1996 The European Society of Cardiology
Reproducibility and automatic measurement of QT dispersion
Department of Medicine and Therapeutics, University of Leicester Leicester, U.K.
*Department of Engineering, University of Leicester Leicester, U.K.
revised 15 November 1995; accepted 21 November 1995.
Correspondence: J. M. Glancy, Department of Cardiology, The County Hospital, Union Walk, Hereford HR1 2ER
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.
Key Words: QT dispersion • reproducibility • automatic measurement
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