LBBB is incomplete in the majority of patients with HF and LV systolic dysfunction submitted to conduction system pacing

Abstract

Background: There is increased interest in fusion CRT pacing and physiological cardiac pacing in patients with heart failure with reduced ejection fraction (HFrEF) and left bundle branch block (LBBB). The left bundle branch (LBB) is conventionally described as dividing into 2 principal fascicles, anterior and posterior, although anatomical studies have identified a septal branch in the majority of specimens. Persistent conduction through this septal fascicle may still be present in many LBBB patients.

Purpose: Assessment of residual conduction heterogeneity within LBB using intraprocedural measurements during CIED implantation in patients with LBBB and HFrEF.

Methods: We conducted an observational study including patients with sinus rhythm, typical LBBB, normal A-V conduction and HFrEF who underwent Left Bundle Branch Area Pacing (LBBAP). Demographic, clinical, electrocardiographic (ECG), and echocardiographic parameters, along with device indication, procedural characteristics, and outcomes, were prospectively collected. Surface ECGs and intracardiac electrograms (iEGMs) were digitally recorded at a paper speed of 100 mm/s. In 40 consecutive patients, QRS duration, PR interval, and the presence of q waves in leads I and aVL, as well as r waves in leads V1–V2, were analyzed pre-procedurally. During the procedure, the interval from QRS onset to local ventricular (V) activation at the right ventricular apex (RVA), RV mid-septum (RVS), or left ventricular septum (LVS) was measured using unipolar (UP) iEGMs recorded from the distal electrode, defined as the first negative or intrinsic deflection, whichever occurred earlier.

Results: 40 consecutive patients were included (65.3 ± 9.7 years, 57% male). The most frequent comorbidities were paroxysmal atrial fibrillation (75%), hypertension (80%), diabetes mellitus (32%) and chronic kidney disease (40%). Baseline left ventricular ejection fraction (LVEF) was 30.3 ± 9.4%, a tricuspid annular plane systolic excursion (TAPSE) of 18.8 ± 3.5 mm and an s′ velocity of 11.2 ± 2.2 cm/s. Mean delays were 86.48 ± 30.96 msec at the RVA vs. 58.98 ± 11.69 at RVS vs. 12 ± 14.70 msec at LVS. RVA delay was longer than RVS delay in 90% of cases. RVS delays were longer than LVS delays in 60% with additional 10% of the cases having similar LVS and RVS delays. The comparison between intraprocedural measurements and surface ECG analysis showed that true incomplete LBBB is highly predictable on surface ECG (≈ 90%) while true complete LBBB was severely overestimated (> 2x).

Conclusion(s): The present study showed that approximately 90% of patients with LBBB and HFrEF maintains some degree of residual left-sided native conduction. This observations may improve understanding of conduction patterns and guide individualized physiological pacing strategies.