Effects of filtering and algorithm parameters on automatic QT measurement techniques

Automatic QT interval measurement methods of T wave end determination include: the threshold crossing point of (a) the T wave and (b) the differential of the T wave and (c) the intercept of the isoelectric level and the maximum T wave slope. The aim of this study was to assess the effects of ECG filtering and threshold and isoelectric levels on these techniques using thirty 12 lead ECGs with a range of T wave morphologies. Low pass filtering (40 Hz vs. 100 Hz) resulted in the following changes in QT measurement relative to manual reference values: a -1 ms, b +34 ms, c -19 ms. Increasing high pass filtering (0.05 to 0.5 Hz) decreased the mean value for all techniques. Reducing threshold levels increased mean values by 14 ms (a) and 8 ms (b). The choice of isoelectric level had little effect on c while a increased by 15 ms. Filtering and parameter choice influence automatic QT measurement techniques and their effects need to be considered when comparing results.<>