Loss of RBB delay pattern in lead V1 at follow-up and persistent left bundle branch area pacing: can it be possible?

Abstract Background The appearance of a right bundle branch (RBB) delay pattern in lead V1 (qR/QR/rSr`) is a necessary criterion to confirm successful LBBAP; however, whether this pattern persists during follow-up is unknown Purpose To determine persistence of RBB delay pattern in confirmed LBBA captures at follow-up and factors related to its disappearance. Methods Consecutive patients with successful LBBAP for bradycardia pacing indication and preserved LVEF were selected. At follow-up, a 12-lead ECG was recorded after programming in VVI mode with lower rate at least 10 bpm over patient´s intrinsic rhythm and unipolar pacing configuration. Results 149 patients were analyzed (mean age 77.3±9.9years, 52.3% male). Non-diseased LBB was present in 73.2% of patients. Average baseline QRS complex duration was of 116.6±28.2 and it was 115.7±12.9 ms after LBBAP. LBBP was demonstrated in 114 patients (76.5%) and LVSP in 35 patients (23.5%). A qR/QR/rSr` pattern in lead V1 of the paced QRS complex was present in 142 out of 149 patients with successful LBBAP at implant. After 18.2 ± 7.3 months of follow-up visit, in 113 patients (79.6%) the RBB delay pattern in lead V1 during unipolar pacing remained, it disappeared in 29 patients (20.4%) and was not demonstrated in none of the 7 patients who did not show it at implant. In patients who lost the RBB delay pattern at follow-up, paced QRS morphology remained narrow and without W or LBB morphology (figure 1). Duration of the paced QRS complex persisted unchanged: p-QRS-stim at implant was 111.3±10.7 vs 109.6±12.5 at follow-up (p=0.413) and p-QRS-onset at implant was 141.4±10.4 vs 138.9±14.3 at follow-up (p=0.266). Moreover, V6-RWPT at implant was similar to V6-RWPT at follow-up, among patients with confirmed LBB capture (73.4±5.9 vs 73.1±6.9 ms, respectively; p=0.860) and among LVSP captures (86.3±5.6 vs 85.3±8.1 ms, respectively; p=0.658). Baseline characteristic were similar among patient with and without RBB delay pattern in lead V1 at follow-up. However, loss of RBB delay pattern at follow-up tended to be less frequent in cases with proven left conduction potential, it did not appear in any case of left bundle trunk pacing and was significantly more frequent among left fascicular captures, especially when pacing the left anterior fascicle (p=0.002) (table 1). In patients with confirmed LBB capture, paced QRS complex at implant was shorter among those who lost the RBB delay pattern at follow-up compared to captures that kept this pattern (table 1). A multivariate logistic regression analysis revealed that shorter p-QRS-stim at implant (OR 0.925, 95% confidence interval (CI): 0.876-0.976; p=0.005) and left anterior fascicular pacing (OR 13.085, 95% CI: 1.750-97.808; p=0.012) were predictors of loss of RBB delay pattern at follow-up. Conclusions In 1 out of 5 patients receiving LBBAP the qR/QR/rSr` pattern in lead V1 disappeared at follow-up and therefore delay in RV activation might be buffered over time.Figure 1 Table 1