Reproducibility and automatic measurement of QT dispersion

• Published in: European heart journal Vol. 17; no. 7; pp. 1035 - 1039
• Main Authors: Glancy, J. M., Weston, P. J., Bhullar, H. K., Garratt, C. J., Woods, K. L., de Bono, D. P.
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 01-07-1996
• Subjects: automatic measurement; Biological and medical sciences; Cardiology. Vascular system; Coronary heart disease; Diagnosis, Computer-Assisted - methods; Electrocardiography - methods; Heart; Humans; Long QT Syndrome - diagnosis; Medical sciences; Myocardial Infarction - diagnosis; Observer Variation; QT dispersion; reproducibility; Reproducibility of Results; Sensitivity and Specificity; Human; QT interval; Infarct; Cardiovascular disease; Exploration; Coronary heart disease; Dispersion; Electrodiagnosis; Reproducibility; Electrocardiography; Myocardium; Automatic analysis; Computer aid
• ISSN: 0195-668X; 1522-9645
• DOI: 10.1093/oxfordjournals.eurheartj.a014999

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.