Left septal fascicular block following left bundle branch area pacing: single center experience

Abstract Introduction Left bundle branch area pacing (LBBAP) is a novel approach in cardiac pacing and resynchronization therapy, offering an alternative to traditional pacing methods by directly stimulating the left bundle branch. However, the occurrence and implications of left septal fascicular block (LSFB) as an ECG manifestation post-LBBAP are not well-documented. Our study aimed to investigate LSFB development following LBBAP, comparing demographic, procedural, and clinical parameters in patients with and without LSFB. Methods We performed the analysis of 50 patients (mean age: 66.04 ± 13.98 years) to whom we performed LBBAP. Patients were classified into LSFB-positive (LSFB +) and LSFB-negative (LSFB-) groups based on the presence of LSFB post-procedure. The transient prominent anterior QRS forces in V2–V3 and the disappearance of the initial q wave in I and aVL on the ECG (indicating absence of the first vector of ventricular activation due to LSFB) reinforce the diagnosis of LSFB. Results Among the 50 patients, 15 (30%) developed LSFB following the LBBAP. Patients with LSFB demonstrated a higher incidence of ischemic cardiomyopathy (46.7% vs. 20%, p=0.085) compared to patients without the LSFB. Baseline QRS duration did not significantly differ between groups (165.53 ± 36.02 ms in LSFB+ vs. 179.85 ± 36.62 ms in LSFB-, p=0.152). Both groups showed reductions in QRS duration post-pacing, with final QRS durations averaging 137.00 ± 26.35 ms and 138.31 ± 22.10 ms for LSFB+ and LSFB-, respectively (p=0.856). Post-procedure troponin levels increased significantly in both groups. Although post procedure troponin levels were higer in LSFB group compared to patients without LSFB, this difference did not reach statistical significance. No significant difference was observed in LBBAP success rates, procedural characteristics, or pacing types. Discussion The development of LSFB following LBBAP was associated with certain clinical and biochemical characteristics, including increased troponin levels and a distinct pattern of underlying cardiomyopathy. These findings suggest that LSFB following the LBBAP may correlate with a higher ischemic burden and specific cardiac structural changes. The increase in post-procedural troponin levels in LSFB+ patients warrants further investigation, as it may reflect an underlying myocardial response to LBBAP-induced electrical remodeling, stress, or possible damage of septal coronary vessels. Overall, this study highlights the need for close monitoring of LSFB in patients undergoing LBBAP, as it may serve as a marker for adverse cardiac events. Figure-1: ECG obtained after the procedure P duration: 200 ms, terminal mode negative of P in V1 > 40 ms, Morris index >0.04 mm/s, QRS axis -46°, R peak time in aVL ≥ 45 ms, QIII>QII: inferior infarction + LAFB, QRS duration 108 ms, increased ventricular activation time in V1 and V2: ≥ 35 ms.: LSFB. Figure-2: TablesFigure 1 Figure 2