Abstract Background AV node ablation combined with permanent pacing is an established therapy for rate control in patients with symptomatic atrial fibrillation (AF) refractory or intolerant to pharmacological rate or rhythm control and not eligible for rhythm control by left atrial catheter ablation. The threshold for performing this so-called "pace-and-ablate" strategy has decreased since the introduction of conduction system pacing, and especially left bundle branch area pacing (LBBAP). Purpose To investigate the change of the left-ventricular (LV) ejection fraction (EF) and left-atrial volume index (LAVI) in patients with symptomatic AF, twelve months after LBBAP and AV-node ablation. Methods Consecutive patients with symptomatic AF intolerant or refractory to pharmacological rate and symptom control and deemed not eligible for left atrial catheter ablation were included. At baseline, the EHRA score was noted and the LVEF and LAVI were measured echocardiographically. Patients were subdivided in a normal baseline LV ejection fraction (LVEF >50%) or diminished baseline LVEF (LVEF <50%) group. After LBBAP, patients underwent AV node ablation in the same procedure or four weeks later. After twelve months, the LVEF and LAVI were reassessed in the entire cohort and the two subgroups. Results Twenty-two patients (68% female, mean age 79±4 years) scheduled for pace-and-ablate therapy were prospectively included. Three (14%) had paroxysmal, sixteen patients (72%) had persistent AF and three patients (14%) long-standing persistent AF. An EHRA class IIb or higher was found in eighteen patients (82%). At baseline, the mean LVEF was 51 ± 7%, the mean LVEDD 47 ± 6 mm and LAVI 54 ± 18 ml/m2. Twelve patients (55%) had a preserved LVEF, whereas ten patients (45%) had an LVEF <50%, fig. 1. After twelve months, the overall ejection fraction increased to 54 ± 5% (p=0.016), fig. 2A. This was mostly attributed to the increase in LVEF to 51 ± 5% in the subgroup with a reduced baseline LVEF (p=0.009 compared to baseline 44 ± 5%), fig. 2A. The LVEF was unaffected in the other group (57 ± 3% vs. 57 ± 4%, p=0.63), fig. 2A. The LAVI was not significantly reduced in the overall cohort or the subgroups (54 ± 18 ml/m2 to 51 ± 19 ml/m2, p=0.16), fig 2B. Conclusion AV node ablation combined with LBBAP results in a significant improvement in LVEF at twelve months follow-up. This is mainly driven by an improvement in LVEF in those patients with a diminished LVEF at baseline. The data suggests that the therapy can reverse a tachycardiomyopathy without inducing a pacing-induced cardiomyopathy. No significant reduction in LAVI was found.Baseline characteristicsChanges in LVEF (A) and LAVI (B)