UHF-ECG data acquisition and analysis
A VDI monitor (Ventricular Dyssynchrony Imaging monitor, ISI Brno, Cardion, FNUSA, CZ, 2018) was used to record and analyze the 5 kHz 14-lead ECG signals with a 3 nV resolution and a frequency range of 1.5 kHz. UHF-ECG data were collected during 2–3 minutes of the RV apical, cSp, mSp, anterior wall, and lateral wall pacing at 100–120 beats per minute. Signal processing and UHF-ECG map construction are described in detail elsewhere [6]. To describe the time course of depolarization propagation in the ventricles, the centers of mass (Mxc) under specific leads (i.e., Vx) were determined. Mxc was calculated as the center of mass of UHF-QRS amplitudes above the 50 percent threshold of the baseline to peak magnitude. To quantify LV and RV dyssynchrony, time delays from the earliest center of mass (first activation) to M8c and M1c were measured (LVLWd and RVLWd, respectively). To describe the duration of LV lateral wall depolarization, the time delay between M5-8c (V5-8d) was measured – Figure 3. The onset and the end of the QRS complex were marked manually using custom-made software, providing high-resolution QRS signals. Global QRS durations (QRSd) were measured from the earliest to the latest deflection in any of the 12 leads (V7 and V8 were excluded from QRSd calculations). During ventricular pacing, the beginning of the QRS was measured from the highest amplitude of the pacing artifact.