A Method to Minimise the Impact of ECG Marker Inaccuracies on the Spatial QRS-T angle: Evaluation on 1,512 Manually Annotated ECGs

Figures

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  Fig. 2. Effect of systematically moving manually annotated reference VCG markers within ± 20 ms, on the estimation error of peak (A) and mean (B) QRS-Ta using the standard approach. Markers and bars represent the mean and standard deviation of the absolute error. From left to right, changes were made to QRSon, QRSend or Tend only.

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  Fig. 1. QRS-T angle measurement using our proposed approach. A: X, Y and Z leads showing the QRS and T-wave in orange and blue, respectively. The solid grey block prior QRS complex represents the interval for the calculation of the vectors’ origin. B: VCG loops in the XYZ space. The red dot represents the vectors’ origin and the dashed lines the peak QRS and T-wave vectors.

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  Fig. 3. Effect of moving all three reference VCG markers, on the estimation error of peak (A) and mean (B) QRS-T angles using standard (blue) and our proposed robust (red) approaches. Top two sub-plots: markers and bars represent the mean and standard deviation of the absolute error. Bottom two sub-plots: change in correlation coefficient between reference QRS-Ta (time point 0) and QRS-Ta calculated having systematically shifted the VCG marker. In this simulation, QRSon, QRSend and Tend were moved simultaneously in the same direction.

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  Fig. 4. QRS-T angles for all 1,512 ECGs were measured using standard (blue) and robust(red) algorithms after systematically moving the manually annotated reference VCG markers in 2 ms steps until ± 20 ms. Sensitivity and precision of abnormal angle detection (αP or αM >105 deg) were assessed using standard (blue) and robust (red) algorithms after moving reference VCG markers in 2 ms steps. In this simulation, QRSon, QRSend and Tend were moved simultaneously in the same direction.

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  Fig. 5. Effect of noise on the detection of abnormal QRS-T angle using the robust approach. QRS-T angles for all 1,512 ECGs were measured after white noise was added to the 10 sec ECG recordings and sensitivity and precision of abnormal angle detection (αP or αM >105 deg) were assessed for both peak (left) and mean (right) QRS-T angles.

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  Fig. 6. Histogram showing peak and mean QRS-T angle distributions for 34,150 individuals with a 12-lead ECG recorded in the UK Biobank study. Vertical dotted line shows cut off for abnormality (> 105°).