Abstract Body (Do not enter title and authors here): Background: Atrioventricular node (AVN) ablation combined with pacing is a well-established therapy for refractory atrial fibrillation. Traditional right ventricular pacing has been shown to cause ventricular dyssynchrony and may worsen atrial remodeling. Left bundle branch area pacing (LBBAP) provides a more physiological ventricular activation than non-conduction system pacing (non-CSP). However, the effects of LBBAP on left atrial (LA) remodeling and left ventricular (LV) function after AVN ablation in atrial fibrillation patients remain underexplored. We aimed to compare LA and LV functional outcomes between LBBAP and non-CSP in this population.

Hypothesis: LBBAP preserves or improves LA and LV function compared to non-CSP in patients with atrial fibrillation following AVN ablation.

Methods: We retrospectively identified patients with atrial fibrillation undergoing AVN ablation followed by either LBBAP or non-CSP (biventricular, leadless, or septal right ventricular pacing) between 2019 and 2023. Pre- and post-pacing echocardiograms were analyzed for LA volumes and emptying fraction, LA strain, LV global longitudinal strain (GLS), LV volumes and ejection fraction, and diastology parameters. Changes in these parameters were compared between groups using analysis of covariance, while accounting for baseline differences and clinical factors.

Results: In the study group (n=73), 35 patients underwent LBBAP while 38 underwent non-CSP. Mean age was 79.3 years, and 74% were female. After a mean interval between pre- and post-pacing echocardiograms of 17.1 months, LBBAP was associated with greater adjusted improvement in LA reservoir strain (+3.9%, p=0.001), LA contractile strain (-2.1%, p=0.02), and LV GLS (-2.2%, p=0.02). LA volumes and volume indexes were also significantly lower in the LBBAP group compared to the non-CSP group, indicating improved LA unloading following LBBAP (Figure 1).

Conclusion: LBBAP was associated with improved LA strain, LV GLS, and LA volumes compared to non-CSP in patients with atrial fibrillation undergoing AVN ablation and pacemaker implantation. These findings highlight the physiologic benefits of LBBP in improving both LA and LV function and further support LBBP as a preferred approach in patients undergoing AVN ablation.