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Heart 1998;80:453-458 ( November )
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
Objective
To 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.
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