Accuracy of automatic QT measurement techniques

The aim of this study was to compare, against manual measurement, 3 algorithms for automatic QT interval measurement using eight 4 lead ECGs recorded from normal subjects. The algorithms investigated determined T wave end from (a) the intercept of the isoelectric line and maximum T wave slope, thresholds applied to (b) the T wave and (c) the differential of the T wave. Mean manual-automatic QT measurement differences of 27 to 29 ms for algorithm a, -2 to 20 ms for b and -5 to 4 ms for c were found. The standard deviations (SD) of the manual-automatic differences varied from 9 to 30 ms. Failure to measure the QT interval (1 to 12 cases) occurred with only algorithm b. Each algorithm performed differently with the mean and SD of the differences, and failure rate for b, dependent on threshold and isoelectric levels used