Atrio-ventricular node ablation (AVNA) with subsequent permanent pacemaker implantation provides definite rate control and represents an alternative therapeutic approach in patients with symptomatic atrial fibrillation (AF) and rapid ventricular rate, refractory to optimal medical treatment or catheter ablation. However, optimal pacing modality remains unclear. Previous studies have demonstrated that biventricular (BiV) pacing followed by AVNA resulted in significant reduction in mortality, heart failure (HF) hospitalizations, significant improvement in symptoms and left ventricular (LV) remodeling. Although, its benefit was much less transparent in patients with narrow QRS and LV impairment, as it still causes abnormal cardiac activation with potential worsening of electrical dyssynchrony. To avoid the detrimental effects of BiV pacing a new concept, conduction system pacing (CSP), including His bundle Pacing (HBP) and left bundle branch pacing (LBBP), was proposed as a potential alternative. Both CSP modalities offer advantages over BiV pacing by providing more physiological activation, avoiding cardiac dyssynchrony and left ventricular dysfunction. Moreover, LBBP showed some advantages over HBP. Since the lead is implanted in the region of the left bundle, which has an adequate distance from the AVNA site, this modality could minimize the risk of increase in capture threshold after AVNA. Additionally, the pacing parameters of LBBP were stable in long-term follow-up studies precluding the need for back-up pacing. Therefore compared to HBP and BiV pacing, LBBP may offer a more feasible physiologic pacing option to be adopted into clinical practice. Some observational studies have already shown positive outcomes of HBP and LBBP in symptomatic AF patients who underwent AVNA with the favorable clinical and echocardiographic improvement compared to BIV pacing, especially in HF patients with narrow baseline QRS and reduced ejection fraction (EF\<50%). However, prospective randomized study evaluating the value of CSP as an alternative approach to BiV pacing in combination with AVNA is lacking.

The purpose of this study is to compare the effects of CSP and conventional BiV pacing on echocardiographic and clinical outcomes in HF patients with symptomatic AF and narrow QRS scheduled for AVNA. In this multicentric study, 82 patients will be randomized into one of two arms: a BiV pacing arm with BiV pacemaker implantation + AVNA or CSP arm with the implantation of a CSP device + AVNA. In patients randomized in CSP group, LBBP will be the preferred pacing technique. If LBBP will be unobtainable, HBP implantation will be attempted. In both arms additional defibrillator backup will be implanted at the discretion of the physician according to the ESC guidelines. In short-term analysis after 6 months, echocardiographic, laboratory and symptomatic parameters will be evaluated. Long-term analysis to assess HF hospitalization, cardiovascular mortality and pacing parameters will be performed after at least 24 months of follow-up.

Investigators hypothesize that CSP could represent a feasible and safe alternative to BiV pacing in terms of clinical and echocardiographic outcomes.