Analysis of the High-Frequency Content in Human QRS Complexes by the Continuous Wavelet Transform: An Automatized Analysis for the Prediction of Sudden Cardiac Death

Figures

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  Figure 1. Electrocardiogram (ECG) recording and characteristics of the EPTracer sensor. (A) Schematic diagram representing the standard position of the exploring electrodes (green dots) on the body surface. (B) According to the position of the exploring electrodes on the body surface, and the configuration of pairs for computing differences in potential, the ECG signals receive standardized names. L, R, F, V1, V2, V3, V4, V5, and V6 constitute the differences in potential between the corresponding electrode and an indifferent electrode (central terminal of Wilson). In addition, three ECG signals are computed as the algebraic sum of potentials at different pairs of electrodes (lead I = L + R; lead II = R + F; Lead III = L + F). (C) EPTracer sensor front panel.

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  Figure 2. Example of the ECG processing and the QRS extraction. (A): Surface ECG (12 consecutive seconds). The blue arrow indicates a QRS complex. (B) Signal after derivation, square elevation and typification. The 0.6 threshold to detect the QRS complexes is denoted (red line). The blue arrow indicates a QRS complex after processing. (C) Example of an extracted QRS complex. The tMaxQRS is indicated by the red line. ECG: electrocardiogram.

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  Figure 3. Example of a Wavelet continuous transform on a QRS complex (frequency range: 85–130 Hz). (A) Power spectrum of the QRS complex. (B) Cumulative power of the high-frequency content at each time epoch. The red dotted line marks the Peak Power and the green dotted line marks the Time to Peak Power. (C) Intensity Function. Final Intensity is marked by blue dotted line; Time to Peak Intensity is marked by the green dotted line; and Peak Intensity is marked by the red dotted line.

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  Figure 4. High-frequency content along the QRS Complex. (A) Cumulative high-frequency content for each group at each time epoch. The final error bars represents the Total Power with its standard error for each group. (B) Boxplot comparing the Total Power. (C) Time distribution of the high-frequency content for each group at each time epoch. (D) Boxplot comparing the Peak Power.

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  Figure 5. Example of different QRS complexes at different times in a patient with BrS. The precordial leads (V1 through V6) are shown. (A) Basal ECG, before Flecainide administration. Flecainide is an antiarrhythmic drug with major effects on cardiac cell’s depolarization. Due to its effects on the cardiac sodium channel (main alteration in BrS), it is used in patients with suspected BrS to unmask the characteristic electrocardiographic pattern. No Brugada pattern is observed. (B,C) ECG showing a Brugada pattern immediately and a few minutes after Flecainide administration. A moving wave becomes apparent with increasing delay (black arrows and time intervals). (D) Resumption to basal conditions demonstrating the returning of the moving wave to more proximal parts of the QRS. BrS: Brugada syndrome. ECG: electrocardiogram.

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  Figure 6. Intensity analysis. (A) Intensity function. It shows the value of the intensity function for each group in each time epoch. The final error bars represent the Final Intensity with its standard error for each group. (B) Boxplot comparing different measures of the intensity function between both groups. From left to right: Final intensity, Peak intensity and Total Intensity.