Variability of different methods for measurement of ECG intervals and ECG interval temporal variation

Effects of endurance training on standard and signal-averaged electrocardiograms of sled dogs

“…Values for QRS duration, PQ interval, and QT interval used for final data analysis were determined from the ECG, using a weighted mean for the 10 recorded leads. This method of analysis produces values for P-wave and QRS duration and amplitude and QT-interval duration identical to those obtained by cardiologists, 32 with a smaller coefficient of variation for repeated measures, particularly the QRS duration. 32,33 Therefore, the analysis procedure was the most appropriate method for detecting small changes in QRS duration.…”

Effect of body position on electrocardiographic recordings in dogs

“…Automated analysis produces values for P wave and QRS durations and amplitudes and QT interval duration in humans that are identical to those obtained by cardiologists, 31 with a smaller coefficient of variation for repeated measures. 31,34 We observed that lead II QRS duration was 4 ms longer when dogs were standing, compared with right lateral recumbency, and that lead II QRS duration was increased in recordings with ECG quality scores of 2 and 3. These results were most likely related to the higher incidence of muscle artefacts in the ECG recordings from standing dogs, with the ECG analysis software program incorrectly identifying an earlier or later time for the start and end of ventricular depolarisation, respectively.…”

“…A notch filter to minimise AC interference was not used. 31 QRS duration was measured from its onset to the ST-segment onset (J point). 10 When directed, the ECG unit recorded and stored, in digitised form at 500 Hz with 16-bit precision (Pagewriter Xli M1700 cardiograph software, Hewlett-Packard Medical Products Group), the signals from leads I, II, III, aVR, aVL, aVF, V4 and V10 obtained throughout a 10-s period.…”

“…This analogue-to-digital conversion procedure is adequate for accurate computer processing of the ECG. 31 The resultant ECG was printed at 25 mm/s and 10 mm/mV. The ECG analysis software program determines the predominant rhythm group based on the P, QRS and T wave morphologies and instantaneous heart rate.…”

“…The program then averages the amplitude and duration of all of the individual complexes in the predominant rhythm group to determine the onset and end of the P, QRS and T waves in each lead. 31 QRS duration was measured from its onset to the ST-segment onset (J point). Durations of the QRS wave and PQ or QT interval were determined to the nearest millisecond for each lead by the software program, using proprietary algorithms, and the mean value for all leads used for statistical analysis.…”