Importance of Electrode Selection and Number in Reconstructing Standard Twelve Lead Electrocardiograms

Figures

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  Figure 1. ECG electrode placement: The name and placement of the standard ten electrodes used to collect and calculate a standard twelve-lead ECG. These ten electrodes include the limb leads (RA—right arm, LA—left arm, RL—right leg, and LL—left leg) as well as the chest leads (V1–V6). Typically, the RL lead is used as a ground electrode.

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  Figure 2. Simplified AI reconstruction: Simplified example of model training in which artificial intelligence attempts to fill in missing leads. The loss function quantifies the difference or “error” between the model’s reconstruction and the actual patient signal. This quantified error informs the model about how faithfully it reconstructed the signal.

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  Figure 3. Combinatoric ECG Reconstruction: (A) Leads were removed from the same signal in a systematic, combinatoric process, and the model was tasked with reconstructing the ECG based on the remaining leads. The reconstructions were compared against the actual signal to calculate performance metrics. (B) The equation that governs the combinatoric inclusion and exclusion of ECG lead information, explicitly defining the number of missing lead ECGs created from just one patient ECG.

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  Figure 4. Lead Frequency in top 10% of Reconstructions: The top 10% of reconstructions for each of the number of lead combinations. For each of the best reconstructions, the specific leads used to reconstruct the signal were tallied and reported based on how frequently they were used. This was normalized based on how frequently each lead would be chosen if reconstruction performance was randomized (represented by 0 on the y-axis). Leads that appear more frequently than chance are shown as positive frequencies while leads chosen less frequently appear as negative.

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  Figure 5. Lead Cross-Correlation Matrix: The cross-correlation matrix quantifying the extent to which two leads were linearly correlated. A value of 1 denotes perfect linear correlation, −1 perfect inverse correlation, and 0 no correlation. Values close to 0 are depicted as darker blue. Values on the diagonal (when each lead was compared against itself) all equal 1. This matrix is a Hankel matrix—symmetric when reflected across the descending left-to-right diagonal.

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  Figure 6. Electrode Frequency in the Top and Bottom 20% of Reconstructions: The electrode frequencies shown in the top and bottom 20% of reconstructions. For each of the best reconstructions, the specific electrodes used to reconstruct the signal were tallied and reported based on how frequently they were used. This frequency was normalized based on how frequently the electrode would be chosen if reconstruction performance was randomized (represented by 0 on the y-axis). Electrodes that appeared more frequently than chance are shown as positive frequencies while those chosen less frequently appear as negative.

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  Figure 7. Absolute Signal-to-Noise Ratio (SNR for each Signal: (A) A scatterplot of the absolute value of SNR for each of the 1,023,500 signals used in this analysis. (B) A box-and-whisker plot for each signal binned based on its |SNR|. Outliers are visualized as black diamonds.