Abstract
<title>Abstract</title> <p>Purpose This study aimed to evaluate the clinical characteristics, natural history, and follow-up outcomes of children with isolated secundum atrial septal defect (ASD). Methods This retrospective cohort study included children aged 3 months to 18 years with ASD who were followed in a tertiary pediatric cardiology center over a 10-year period. Among 10,316 children with ASD, 1,395 patients with isolated secundum ASD were included. Demographic characteristics, clinical findings, echocardiographic measurements, spontaneous closure rates, and intervention outcomes were retrospectively evaluated. Results Of the 1,395 patients, 776 (55.6%) were female and 619 (44.4%) were male. The mean age at diagnosis was 3.56 ± 3.82 years. ASD size was classified as small in 870 patients (62.3%), moderate in 201 (14.4%), and large in 324 (23.2%). Longitudinal follow-up data were available for 543 patients (38.9%). During follow-up, spontaneous closure occurred in 261 patients (48.1%), transcatheter closure was performed in 147 (27.1%), and surgical closure in 84 (15.4%). The cumulative spontaneous closure rate at 5 years was 76% for small ASDs and 68% for moderate ASDs. Right ventricular enlargement was significantly associated with larger ASD diameter, with an optimal cutoff value of 8.05 mm. Conclusion ASD diameter and age at diagnosis are important determinants of spontaneous closure and clinical outcomes. Most small and moderate ASDs closed spontaneously during follow-up, whereas larger defects were associated with right ventricular enlargement and a higher likelihood of intervention.</p>