Conduction system pacing (CSP) modalities, including His-bundle pacing (HBP) and left bundle branch pacing (LBBP), are increasingly used as alternatives to biventricular (BiV) pacing in heart failure (HF) patients scheduled for pace and ablate strategy. The aim of the study was to compare clinical outcomes of HF patients with refractory AF who received either BiV pacing or CSP in conjunction with atrio-ventricular node ablation (AVNA). Fifty consecutive patients (male 48%, age 70 years (IQR 9), left ventricular ejection fraction (LVEF) 39% (IQR 12)) were retrospectively analysed. Thirteen patients (26%) received BiV pacing, 27 patients (54%) HBP and 10 patients (20%) LBBP. All groups had similar baseline characteristics and acute success rate. While New York Heart. Association (NYHA) class improved in both HBP (p < 0.001) and LBBP (p = 0.008), it did not improve in BiV group (p = 0.096). At follow-up, LVEF increased in HBP (form 39% (IQR 15) to 49% (IQR 16), p < 0.001) and LBBP (from 28% (IQR 13) to 40% (IQR 13), p = 0.041), but did not change in BiV group (p = 0.916). Conduction system pacing modalities showed superior symptomatic and echocardiographic improvement compared to BiV pacing after AVNA. With more stable pacing parameters, LBBP could present a more feasible pacing option compared to HBP.

Funding Acknowledgements Type of funding sources: None. Background "Ablate and pace" strategy is a reasonable therapeutic option in refractory atrial fibrillation (AF) when rhythm or rate control cannot be achieved with catheter ablation or pharmacological therapy. Atrioventricular node ablation (AVNA) combined with conduction system pacing (CSP), including His-bundle pacing (HBP) and left bundle branch pacing (LBBP), are increasingly adopted, as they offer more physiological activation of the left ventricle compared to other pacing modalities. However, the incidence of conversion to sinus rhythm after "ablate and pace" strategy with CSP is not known. Purpose To determine the incidence of spontaneous conversion to sinus rhythm and its predicting factors in patients undergoing AVNA and CSP. Methods Refractory AF patients undergoing AVNA with CSP at our institution between June 2018 and May 2022 were prospectively included. Echocardiographic and clinical parameters including ECG were assessed at baseline and 6 months after the procedure. Results Sixty-three patients (male 41.3%, age 71±9 years, left ventricle ejection fraction (LVEF) 40% (IQR 20)) were included. Thirty-seven patients (58.7%) received HBP and 26 patients (41.3%) LBBP. During follow-up, spontaneous conversion to sinus rhythm (SR) was registered in 5 patients (8%); 3 in HBP group and 2 in LBBP group. Baseline characteristics of patients who converted to SR did not differ from non-sinus rhythm (NSR) patients except for left atrial volume index (LAVI), which was smaller in SR group (43 mL/m2 (IQR 6) vs. 60 mL/m2 (IQR 19); p&lt;0.01). Multiple regression model confirmed an inverse association between LAVI and conversion to sinus rhythm even after considering other clinically relevant covariates (odds ratio=0.685, p=0.03). At follow-up, LAVI did not change in any group (SR: p=0.345; NSR: p=0.508). LVEF increased in both groups, from 40% (IQR 20) to 51% (IQR 18) in NSR group (p&lt;0.01) and from 41% (IQR 11) to 54% (IQR 11) in SR group (p=0.138), although the increase in SR group did not reach statistical significance due to small sample size. Similarly, ESVi decreased in both groups; in NSR group (from 47 mL/m2 (IQR 33) to 29 mL/m2 (IQR 24), p&lt;0.01) and in SR group (from 33 mL/m2 (IQR 19) to 25 mL/m2 (IQR 0), p=0.176), where statistical significance was not reached due to small sample size and small initial volumes. Symptomatic improvement according to NYHA class was more pronounced in SR group (p=0.026). Conclusion The results of our study show that spontaneous conversion to sinus rhythm after AVNA combined with CSP is not uncommon, especially in patients with smaller left atria. Patients who converted to SR showed superior symptomatic improvement compared to NSR patients. Larger studies are warranted to clarify the predicting variables of SR restoration in these patients, which should be considered for initial atrial pacing lead implantation (dual-chamber device) when "ablate and pace" strategy is adopted.

Funding Acknowledgements Type of funding sources: None. Background Atrioventricular node ablation (AVNA) with biventricular (BiV) pacing is an established treatment option for heart failure (HF) patients with drug refractory atrial fibrillation (AF) (1). However, compared to conduction system pacing (CSP) modalities, including His bundle pacing (HBP) and left bundle branch pacing (LBBP), BiV pacing delivers non-physiological ventricular activation (2). Purpose To compare clinical outcomes of BiV pacing and both CSP modalities in HF patients with symptomatic AF who underwent AVNA. Methods Consecutive AF patients with LV ejection fraction (LVEF &lt;50%) who received either BiV pacing or CSP in conjunction with AVNA between May 2015 and July 2021 were retrospectively analysed. Procedural characteristics, electrocardiographic, echocardiographic, and clinical parameters were assessed at baseline and 6 months after the procedure. Results Fifty-five patients (male 43.6%, age 71 years (IQR 10), LVEF 39% (IQR 14)) were included. Thirteen patients (23.6%) received BiV pacing, 30 patients (54.5%) HBP and 12 patients (21.8%) LBBP. All groups had similar baseline characteristics, acute success rate and adverse events. Post-procedural QRS duration was significantly shorter (p&lt;0.01) in CSP (118 ms (IQR 28)) than in BiV pacing (172 ms (IQR 18)). While NYHA class improved in both HBP (p&lt;0.01) and LBBP (p=0.01), it did not improve in BiV group (p=0.1) At follow-up, end systolic volume (ESVi) decreased in both HBP (48±20 to 32±12 mL/m2, p&lt;0.01) and LBBP (62±22 to 52±22 mL/m2, p=0.02), but did not differ in BiV pacing group (51±12 to 53±14 mL/m2, p=0.6). Similarly, LVEF increased in HBP (form 39% (IQR 16) to 53% (IQR 14), p&lt;0.01) and LBBP (from 41% (IQR 23) to 40% (IQR 25), p=0.04), but did not change in BiV group (from 38% (IQR 5) to 37% (IQR 6), p=0.9). Significantly lower (p&lt;0.01) pacing thresholds were achieved in LBBP (0.75 V at 0.5 ms (IQR 0.3)) than in HBP group (1.0 V at 0.5 ms (IQR 1)). Two patients in HBP group were switched to right ventricular pacing due to rise in HBP threshold. In the remaining patients threshold remained stable during follow-up. Conclusion Conduction system pacing modalities showed superior symptomatic and echocardiographic improvement compared to BiV pacing after AVNA. While LBBP offered lower and more stable pacing parameters, there were no differences in clinical outcomes and echocardiographic remodelling when compared to HBP.

Funding Acknowledgements Type of funding sources: None. Background In patients with persistent atrial fibrillation (PeAF) and heart failure with reduced ejection fraction (HFrEF) current guidelines recommend treatment of AF with catheter ablation (CA) (1). Recurrence of either AF or atrial flutter, often requiring additional procedures, are not uncommon, thus optimal long-term treatment of these patients is still unknown. Recently conduction system pacing (CSP), with more physiological ventricular activation, has made the ‘’pace and ablate’’ strategy an attractive alternative for the treatment of PeAF refractory to medical therapy (2). Purpose Long term data comparing CA with conduction system pacing and AV node ablation (CSP/AVNa) for treatment of patients with PeAF and HFrEF is lacking. Hence, we sought to compare clinical outcomes of both treatment modalities. Methods In a retrospective study consecutive patients under 75 years of age, with PeAF and left ventricular ejection fraction (LVEF) less than 50%, treated with CSP/AVNa from 2018 to 2021 in UMC Ljubljana were included. A control patient treated with CA for PeAF matched in age, sex and LVEF was assigned for each included CPS/AVNa patient. Both groups were compared for procedure-related characteristics, echocardiographic parameters, hospitalisations for heart failure and all-cause mortality. Results Among 771 patients referred for interventional treatment of AF, 23 patients treated with CSP/AVNa were included and compared with 23 CA matched controls. The general characteristics of both groups are summarised in Table 1. The mean follow-up was 20 ± 10 and 21 ± 8 months for CPS/AVNa and CA group, respectively (p=0.76). In CPS/AVNa group 83% received his bundle pacing and 17% left bundle branch area pacing. A selective CSP was achieved in 43% of CSP/AVNa patients. In addition to pulmonary vein isolation, additional ablation lines were performed in 35% of patients in the CA group. Significant improvement in LVEF was observed in both groups, 12% ± 11% (p&lt;0.001) in CSP/AVNa and 21% ± 12% (p&lt;0.001) in CA group. Hospitalisations for HF were rare during the follow-up, with 9% in CSP/AVNa and 4% in the CA ablation group (p=0.561). All-cause mortality was 9% in CSP/AVNa and 0% in CA group (p=0.153). However, major comorbidities were more common in the CSP/AVNa group than in the CA group, 3.4 ± 1.6 and 2.3 ± 1.5, respectively (p=0.017). Procedure-related characteristics are summarised in Table 1. In each group, 2 minor procedure-related adverse events were observed: 2 acute rises in pacing threshold post-AVNa in CSP/AVNa group and puncture site hematoma and transient pericardial effusion in CA group. Conclusion In patients with PeAF and HFrEF, CSP/AVNa treatment strategy seems to derive similar clinical outcomes compared to CA approach. Larger prospective randomised data are needed to further confirm these initial findings and determine optimal long-term treatment strategy for this group of patients.