This study aims to evaluate whether posterosuperior bundle (PSB) pacing reduces the incidence of atrial fibrillation (AF) in patients with sinus node dysfunction (SND) undergoing pacemaker implantation. Approximately 300 patients will be enrolled and randomized to receive atrial pacing at either the PSB region or the right atrial appendage (RAA). The primary endpoint is the occurrence of AF episodes lasting ≥6 minutes, as detected by device or surface electrocardiogram. Patients will be followed for up to 24 months.