Late‐Onset Atrioventricular Block and Significant Conduction Disturbances After Cardiac Interventions in Children

Introduction Late‐onset postoperative atrioventricular (AV) block is a rare condition with a reported incidence ranging between 0.3% and 0.7%, and it may be associated with high mortality rates (28%–100%). The aim of this study was to evaluate the clinical characteristics of pediatric patients who developed late AV block at our center. Methods In this retrospective case series, pediatric patients evaluated for permanent pacemaker implantation during the study period were retrospectively reviewed. Patients who developed late‐onset (>1 month) atrioventricular block or another clinically significant conduction disturbance requiring consideration of permanent pacing following surgical, transcatheter, or electrophysiological cardiac interventions between 2007 and 2025 were included. Patients with early postoperative block (<1 month), congenital AV block, congenitally corrected transposition of the great arteries (CCTGA), or atrial isomerism were excluded. Demographic data, underlying congenital heart disease, type and timing of the prior intervention, symptoms at presentation, pre‐block rhythm data when available, electrocardiographic and Holter findings, heart rate, type of block, temporary pacing requirement, pacemaker implantation status, and follow‐up outcomes were collected from electronic medical records. Results A total of 14 patients were included. The median age was 4.75 years (interquartile range [IQR]: 2.33–8.75)the mean body weight was 20.7 ± 16.8 kg. Seven patients were male. The mean age at the initial cardiac intervention was 2.17 ± 3.40 years (range: 0–12). The median interval between the index cardiac intervention and development of late conduction disease was 3.0 years (IQR: 1.75–4.62). At presentation, six patients were asymptomatic, three presented with syncope, four with signs of heart failure, and one was referred after resuscitated cardiac arrest. The index intervention was cardiac surgery in 10 patients, transcatheter structural intervention in three, and repeated AVNRT ablation in one. Nine patients had persistent complete AV block, four had intermittent complete AV block, and one had left bundle branch block with clinicallysignificantventricular pauses. Three patients had Down syndrome. Permanent pacemakers were implanted in 12 patients; one patient died after cardiac arrest, and one patient did not undergo implantation because of parental refusal. At the most recent available device interrogation, most implanted patients had a high ventricular pacing burden, generally ranging from approximately 72% to 100%, whereas two patients had low ventricular pacing burdens of approximately 1%–2% and 0.7%–2.5%, respectively Conclusion Late‐onset postoperative AV block is a rare but potentially fatal condition that may occur even years after cardiac interventions. Although it is most commonly observed after surgeries involving regions close to the AV node, such as atrioventricular septal defect or ventricular septal defect repair, it may also occur following atrial septal defect repair or transcatheter procedures. It may present as persistent or intermittent block. Down syndrome was observed in three patients; however, because of the small sample size, no conclusions regarding an independent association can be drawn. Routine electrocardiographic evaluation of the conduction system should be performed during follow‐up after surgical, transcatheter, or ablation procedures, and additional assessments such as Holter monitoring should be considered, particularly in symptomatic patients.