Comparison of manual and automatic QT dispersion measurements in clinical groups

We investigated whether automatic QT dispersion measurements are more discriminating than manual measurement in three clinical groups: myocardial infarction, arrhythmia and normals. Four automatic techniques of QT interval measurement, based on models of T-wave shape, were used: (i) intersection of the maximum slope of the T-wave with the baseline (QTsi), (ii) intersection of linear best-fit over the region 30% to 70% of the peak T-wave amplitude with the baseline (QT30/70), (iii) intersection of linear best-fit over the region 10% to 30% of the peak T-wave amplitude (QT10/30) with the baseline, and (iv) minimum/maximum of 2nd-order polynomial best-fit over a 0.1-s interval commencing at 50% of the peak amplitude (QT2nd). There were no significant differences between dispersion in the groups when measured manually. There were significant differences between the normal and infarct groups for all automatic techniques (p<0.05), and between the normal and arrhythmia groups for QT30/70 and QT2nd (p<0.05). The automatic techniques were better able to discriminate between the normal and cardiac patient groups