Interatrial Conduction Block in Pediatric Patients with Ostium Secundum Atrial Septal Defect

<b>Background:</b> Atrial arrhythmias represent a frequent long-term complication in patients with atrial septal defects (ASDs). Interatrial block (IAB), reflecting delayed or impaired conduction across Bachmann's bundle, has been proposed as an electrophysiological substrate predisposing to atrial arrhythmogenesis. However, evidence regarding its prevalence and clinical correlates in pediatric patients with ASD remains limited. The present study aimed to characterize interatrial conduction patterns and assess the occurrence of IAB in children with large secundum ASD undergoing percutaneous closure. <b>Methods:</b> Between January 2020 and March 2024, 37 consecutive pediatric patients (median age 6 years, range 5-11) with large ostium secundum ASD were included in a retrospective analysis of a prospectively maintained institutional database. Standard 12-lead electrocardiograms were recorded before and within 24 h after defect closure. P-wave morphology and duration were systematically analyzed, and IAB was classified according to the Bayés de Luna criteria. <b>Results:</b> The median Qp/Qs ratio was 1.69 (1.32-2.24), with a mean pulmonary artery pressure of 19 mmHg (17-22). IAB was identified in 24.3% of patients before the procedure, predominantly as first-degree IAB. Following device implantation, IAB prevalence (29.7%) and P-wave parameters remained unchanged, with no significant differences compared with baseline. No associations were observed between IAB and defect size, hemodynamic burden, or device characteristics, whereas anthropometric variables, including weight, height, and body surface area, showed a significant correlation with IAB occurrence. During a median follow-up of 199 days, no atrial arrhythmias were documented. <b>Conclusions:</b> In this pediatric cohort with large ASD, IAB was present in approximately one quarter of patients and appeared unrelated to anatomical or procedural factors, supporting the hypothesis of an underlying congenital conduction abnormality. Early recognition of IAB may therefore have implications for long-term arrhythmic risk stratification in this population.