Assessment of inter-observer and intra-observer variability in the measurement of QT dispersion

This study investigates inter-observer (2 observers) and intra-observer variability in the measurement of QT dispersion, from 12 lead records of 10 cardiologically normal patients and 9 with previously documented myocardial infarction (M.I.). The mean absolute error in QT dispersion between observers was 17.4 ms (Normals) and 38.3 ms (M.I.s). For QTc dispersion, these values were 21.9 ms and 49.7 ms respectively. Using analysis adapted from Bland and Altman, inter-observer bias was negligible for RR intervals in both groups. For QT intervals these values were 1.74% (Normals) and 5.23% (M.I.s). Inter-observer variability of QT intervals was calculated at 6.77% (Normals) and 10.42% (M.I.s). Intra-observer variability, assessed using a mixture of 42 waveforms, indicated a range of variability from 0-38.6 ms for QT intervals (obs. I) and 0-36.6 ms (obs. 2).