Abstract Body (Do not enter title and authors here): Background: Patients with recurrent ventricular tachycardia (VT) undergoing catheter ablation have risk of collateral injury to the conduction system (CICS), particularly if the targeted VT substrate involves the basal septum. The incidence and impact of CICS following catheter ablation of VT is unknown.

Aims: To characterize the incidence and prognostic significance of peri-procedural CICS in patients undergoing VT ablation.

Methods: We utilized the TriNetX research platform to identify adults (≥18 years) who underwent VT ablation between 2010 and 2024, using procedural ICD-10 codes. Patients were stratified into five cohorts based on the type of periprocedural CICS: (1) no CICS (reference group), and CICS which included (2) second- or third-degree AV block, (3) right bundle branch block (RBBB), (4) left bundle branch block (LBBB), and (5) left fascicular block. Propensity-score matching was performed 1:1 for demographics, comorbidities, and antiarrhythmic drug use. Primary endpoints included all-cause mortality, ventricular arrythmia (VA) recurrence, need for post-procedural device revision/upgrade, and heart failure exacerbation. Secondary outcomes included mortality, peri-procedural bleeding (within two weeks) and cardiac tamponade.

Results: A total of 7,792 patients underwent VT ablation. Peri-procedural CICS occurred in 726 patients (9.3%). The most frequently encountered CICS was LBBB (n=260, 36%), followed by RBBB (n=204, 28%), complete heart block (n=184, 25%), and left fascicular block (n=78, 11%). At 1-year follow-up, patients with CICS had a significantly increased risk of VA recurrence (HR 1.34, 95% CI 1.15-1.56; p < 0.0001) and post-procedural need for device revision/upgrade (HR 1.34, 95% CI 1.03-1.75; p = 0.049) compared to the reference group. A trend toward increased heart failure exacerbation (HR 1.01, 95% CI 0.82-1.23; p = 0.07) was also observed but did not reach statistical significance. No statistically significant differences were observed for mortality, cardiac tamponade and bleeding events.

Conclusion: In this large real-world cohort of patients undergoing VT ablation, peri-procedural CICS occurred in 9.3% of patients, with LBBB (36%) and RBBB (28%) being the most common subtypes. Periprocedural CICS was associated with an increased risk of VA recurrence at one year, presumably related to more challenging basal septal substrate locations, and higher rate of post-procedural device revision/upgrades.