Characterization of Septal Scar After Left Bundle Branch Area Pacemaker Implantation.

Background: Left bundle branch area pacing (LBBAP) is increasingly used in patients with a ventricular pacing indication but necessitates precise septal localization. The resulting effects of intraoperative lead repositioning on septal fibrosis remain unknown.

Objective: To assess the safety of cardiac magnetic resonance imaging (cMRI) in patients with LBBAP pacemakers and evaluate the septal myocardium via cMRI following LBBAP implantation compared with standard RV endocardial pacing (RVP).

Methods: Patients aged > 18 y.o. with bradycardia, LBBAP or RVP implant from 2021 to 2023, and at least one cMRI after implant were identified. LBBAP versus RVP was verified per established criteria. Delayed-enhancement cMRI and native T1 relaxation times were used to characterize myocardial scar.

Results: A total of 34 patients were identified-20 with LBBAP implants (9 with matched pre-implant cMRI) and 14 with RVP implants (3 with matched pre-implant cMRI)-with no evidence of ventricular septal defects post-implant. LBBAP lead parameters were stable pre-/post-cMRI and out to 9 months. Comparing pre- versus post-implant cMRIs (median 579 days apart), 1/9 patients following LBBAP showed a new scar on the RV inferoseptal side directly adjacent to the pacing lead on post-implant cMRI, suggestive of potential implant-related scarring with LBBAP.

Conclusions: CMRI appears safe for patients with LBBAP pacemakers, with stable short- and long-term device parameters. In patients with matched pre/post-implant cMRIs, the new septal scar can be identified with LBBAP implantation, raising the possibility of lead-related fibrosis. Larger studies are required to substantiate whether the single case of lead-related fibrosis is an exception or occurs more frequently.