Analysis of stimulation parameters temporal evolution in left bundle branch area pacing in cardiac resynchronization therapy

Introduction

In recent years, conduction system pacing has become an alternative to conventional resynchronization when CRT. In our center, the vast majority of CRT implants are carried out using left bundle branch area pacing. Since CRT involves patients with pathological myocardium and a high burden of fibrosis, achieving adequate stimulation parameters with selective LBBA capture is not always possible. In this study, our aim was to perform a descriptive analysis of the temporal evolution of pacing parameters in patients who underwent CRT in our center.

Methods

We analyzed 68 patients at our center who underwent CRT, either with an implantable cardioverter defibrillator (ICD) or a pacemaker (PM) witch LBBAp stimulation between 2022 and 2025. We included demographic and basic clinical variables, as well as the presence of fibrosis. A polygraphic system was employed to measure the duration of the QRS complex pre- and post-implantation, alongside the LVAT and the interpeak interval (PV6-PV1), as well as the presence or absence of R' in V1, which defines capture of the left bundle branch. Other measures were taken into account to define left bundle branch area stimulation (LVAT < 80 ms, PV6-PV1 > 44 ms) or likely-LBBAp (LVAT 80-100ms, PV6-PV1 33-44m) the rest being considered deep septal pacing (DSP) stimulation. The absence of R’ morphology in V1 lead was considered DSP stimulation. Identical measurs were conducted on surface ECGs during the follow-up visits one month later, to evaluate the temporal evolution of these parameters.

Results

In our cohort, 67% were male, with a mean age of 71 +/- 13 years. A total of 64% received ICD as CRT and the most frequent indication was left ventricular systolic dysfunction. One third of the patients who presented fibrosis. Regarding stimulation, 74% had LBBAp or likely LBBAp. Related to the implant of CRT, there was an improvement of 7% in LVEF (basal 34,6% - 41% 1 month p<0,01) and a reduction in NT-proBP levels (426 pg/ml; p<0,01). At the time of primo-implantation, 62% of patients demostrated R' in V1 lead, indicating LBBAp. Among them, 39% lost this finding, which suggest loss of capture of LBBAp. A significant narrowing of the baseline QRS interval (34 +/- 27 ms, IC95%, p < 0.01) was observed at the time of implantation compared to baseline QRS. Additionally, we observed a significant widening of stimulated QRS segment (8 +/- 14 ms IC95%, p<0,01) one month after implantation. We also noted a significant narrowing of LVAT (6 +/- 21ms IC95%, p<0,01).

Conclussion: Our study shows that there was a significant widening of QRS duration one month after CRT implantation with LBBA pacing. Furthermore, there were significant changes in the presence of an R’ wave in lead V1 at one month: 32.5% of patients who exhibited an R’ wave at the time of implantation no longer showed this finding at the one-month follow-up visit, suggesting loss of LBBA capture.