Results
A total of 300 different ventricular activations (51 spontaneous rhythms, 46 c-Sp, 61 m-Sp, 48 RV anterior wall, 48 RV lateral wall, and 46 RV apical captures) were recorded in 51 patients – their characteristics are shown in Table 1. The average procedural time was 98 ± 23 min., and one procedural complication was observed (a pericardial effusion that resolved spontaneously). Other procedural characteristics are shown in Table 1. Of 48 RV anterior wall positions, 9 were found to be septal since they exceeded the 25° angle to the horizontal plane in the LAO (all of them were classified as RVOT). Of the 60 mSp positions, 30 were classified as RVIT and 30 as RVOT. Two records (one marked as mSp and one as the lateral wall) were not analyzed since the X-ray images were not stored. As a result, definitive analyses were performed on 32 spontaneous rhythms without a bundle branch block (narrow QRS group), 46 cSp, 69 mSp (30 RVIT, 39 RVOT), 39 RV anterior wall, 47 RV lateral wall, and 46 RV apical wall captures.
The average height of the position with cSp capture was 40 ± 5% of the heart silhouette in the RAO. The mean A/V ratio was 4 ± 4%, and in 29 of 46 patients with cSp, the atrial signal amplitude was lower than 0.05 mV on the EGM in the cSp location. A wide range of HV/RBBpoV intervals was observed (30–83 ms), with an average value of 50 ± 13 ms. There were seven patients with HV intervals shorter than 35 ms. Their LVLWd and RVLWd were similar compared to those with HV > 35 ms; 19 ms (10;27) vs 10 ms (7;14), p = 0.14 for LVLWd and 3 ms (−6;12) vs 1 ms (−3;5), p = 0.70 for RVLWd), but QRSd was significantly shorter (126 ms (112;139) vs 141 ms (135;146); p = 0.02). Their UHF-ECG maps with measured parameters are shown in Supplementary Figure 2.
Conductive system septal pacing showed superior depolarization patterns compared to all other pacing locations - Figure 4 and Supplementary Figure 3. QRSd and LVLWd were significantly shorter during cSp than during RVIT (p < 0.01 for both) and RVOT pacing (p < 0.001 for both). Although both RVIT and RVOT had virtually the same QRSd (p = 0.99), the LVLWd and V5-8d were significantly longer for RVOT capture (p < 0.001 for LVLWd and p < 0.05 for V5-8d). cSp capture resulted in wider QRS complexes compared to the ‘narrow QRS’ group, but RVLWd and LVLWd were similar (p = 0.2 and p = 0.6 respectively). cSp and RVIT capture caused the same V5-8d as the spontaneous narrow group (p > 0.99) – Figure 5 and table 2.
Regarding RV pacing locations without direct conductive tissue engagement, the shortest LVLWd was observed during mSp, followed by RV apical (p = 0.02 between them), lateral and anterior wall capture being the longest. Compared to each of the others, the longest RVLWd was observed during RV apical capture (p < 0.001). The V5-8d was significantly shorter in mSp compared to other RV myocardial captures (p < 0.001 to each of them) – Figure 6 and table 3.