Effect of averaging for the automatic measurement of QT dispersion using multichannel magnetocardiography and electrocardiography

Multichannel magnetocardiograms (MCGs) and 12- Lead ECGs were recorded simultuneousiy using the PTB mulrickannel SQUID system from 8 normal volunteers. An automatic method for QT interval measurement was used to determine T wave end with measurements made over 10 consecutive beats in both the MCG and ECG. Channeldeads with small nbsoiute T wave amplitudes and smallest and longest QT measuremenrs were excluded from the analysis. QT dispersion, expressed as the QT interval range, was calculated for a single beat and the average QT interval for each channemead over IO beats. Mean QT dispersion measurement (standard deviation) for the single beat was 44 (26) ms for MCG and 37 {35) ms for ECG over all subjects. Averaging over IO beats reduced mean QT dispersion to 36.1 (14.6) ms for MCG and 20.9 (13.2) ms for ECG. QT dispersion in the MCG was greater than in the ECG, by 7 ms for the single beat and by 15 m (p < 0.03) for averaged datu over all subjects. Averaging influenced ventricular dispersion measurements in both MCG and ECG waveforms. There were differences in dispersion of ventricular repolarisation time between ECG and MCG, with MCG significantly greater than ECG for averaged data.