Cardiac resynchronization therapy guided by UHF-ECG: comparison between his bundle pacing and left bundle branch area pacing

Background

His Bundle Pacing (HBP) and Left Bundle Branch Area Pacing (LBBAP) are emerging alternatives to conventional cardiac resynchronization therapy (CRT) in patients with left bundle branch block (LBBB). However, conduction systema pacing (CSP) does not achieve complete correction in all cases. Ultra-high-frequency ECG (UHF-ECG) is a novel tool currently under investigation for its ability to provide real-time assessment of electrical synchrony and potentially enhance CRT optimization.

Objective

To assess the feasibility and efficacy of CSP in correcting LBBB, and to compare baseline and post-implantation electrical synchrony using 14-lead UHF-ECG.

Methods

Patients with basal LBBB referred for device implantation between October 2023 and April 2025 were included. HBP was the first-line pacing strategy, LBBAP the second-line and conventional coronary sinus CRT the third-line. Electrical dyssynchrony was quantified with UHF-ECG as the maximal time difference between the centers of mass of the UHF-QRS complexes in leads V1-V6 and V1-V8 (DYS16 and DYS18). QRS duration (QRSd) was automatically determined by UHF-ECG, distinguishing between total QRSd from the spike (QRSdt) and only pure QRS (QRSdp).

Results

75 patients underwent device implantation. CSP successfully corrected LBBB in 68 (90.1%), who were included in the analysis (54.4% male, mean age 73.4 ± 10.4 years, 47.1% HBP and 45.6% LBBAP). Main indications for implantation included new-onset LBBB post-transaortic valve implantation (TAVI) (23.5%), LBBB-induced cardiomyopathy (20.6%) and ischemic cardiomyopathy (19.1%). Mean basal left ventricular ejection fraction (LVEF) was 46.3 ± 13.8%.

Among patients with LVEF < 40%, CSP significatively improved LVEF (30.4 ± 6.7 vs 38.5 ± 12.7, p<0.001). QRSd, area and dyssynchrony were significantly reduced after CSP (p<0.001). Comparisons between basal LBBB, CSP, HBP and LBBAP are shown in Figure 1, with no significative differences in electrical synchrony between both CSP techniques, although HBP achieved a greater QRS narrowing compared with LBBAP (121.2 ± 13ms vs 132.7 ± 21ms, p=0.012).

At 24-hour follow-up, HBP thresholds improved significantly (p = 0.041) and remained stable in both CSP modalities at 4 [2–6] and 13 [12–17] months.. HBP R-wave sensing showed non-clinical improvement over time (p=0.002). Picture 2 summarizes comparisons between both CSP techniques, showing no clinically relevant differences in R-wave sensing and capture thresholds.

Conclusions

CSP is a highly effective strategy for correcting LBBB, achieving significant reductions in QRSd, area, and electrical dyssynchrony as assessed by UHF-ECG. HBP provided greater QRS narrowing, while LBBAP offered lower thresholds during follow-up, which remained stable in both CSP techniques, representing promising alternatives to conventional CRT.Electrical parameters and synchronyMain lead parameters