Heart 1998;80:453-458 ( November )

Measurement error as a source of QT dispersion: a computerised analysis

J A Kors, G van Herpen

Department of Medical Informatics, Faculty of Medicine and Health Sciences, Erasmus University, PO Box 1738, 3000 DR Rotterdam, Netherlands

Correspondence to: Dr Kors.

Accepted for publication 30 April 1998

ObjectiveTo establish a general method to estimate the measuring error in QT dispersion (QTD) determination, and to assess this error using a computer program for automated measurement of QTD.
SubjectsMeasurements were done on 1220 standard simultaneous 12 lead electrocardiograms.
DesignThe computer program was validated against two observers on a random subset of 100 electrocardiograms. Simple laws of physics require that at least five of the six extremity leads have the same QT duration. This allows the direct assessment of the error in measuring QTD derived from five extremity leads (QTD₅). It also enables ST-T amplitude dependent distributions of measurement error in determining QT duration to be established. These QT error distributions were then used to estimate the error in measuring QTD from all 12 leads (QTD₁₂).
Main outcome measuresMean and standard deviation of error in measuring QT duration, QTD₅, and QTD₁₂.
ResultsPerformance of the program was comparable to that of observers. Errors in measuring QT duration (measured QT minus reference QT) fell from a mean (SD) of 6.9 (17.1) ms for ST-T amplitudes < 50 µV to 1.4 (6.3) ms for amplitudes > 350 µV. Measurement errors of QTD₅ and QTD₁₂ were 20.4 (11.5) ms and 29.4 (14.9) ms.
ConclusionsThe fact that no QTD can exist between five of the six extremity leads provides a means of estimating QTD measurement error. Measuring error of QT duration is dependent on ST-T amplitude. QTD measurement error is large compared with typical QTD values reported.

Keywords: automated ECG analysis;  QT measurement;  QT dispersion;  measurement error

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© 1998 by Heart
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