SCN5A mutation-associated sick sinus syndrome revealed by atrial flutter in a pediatric patient.

Atrial flutter (AFL) is uncommon in children without underlying heart disease. This report details the case of a 7-year-old boy with AFL detected during school electrocardiogram (ECG) screening. He had no prior arrhythmias, congenital heart disease, or cardiomyopathy. Initial evaluations showed AFL with right bundle branch block but no structural heart abnormalities. Radiofrequency catheter ablation (RFCA) was performed, initially resolving the AFL but resulting in a 13-s sinus arrest requiring atrial pacing. Post-RFCA, the patient experienced a sinus arrest lasting up to 7 s, leading to a diagnosis of sick sinus syndrome (SSS). A second RFCA was needed due to AFL recurrence, and post-ablation ECGs revealed saddleback-type ST-segment elevation and Brugada-type patterns, raising suspicion of Brugada syndrome (BrS). Genetic testing identified a loss-of-function (LOF) SCN5A variant (c.2678G > A p.R893H) in the patient, his mother, and his sister. This case underscores that AFL in children without structural heart disease, especially when associated with SSS, may be linked to LOF SCN5A variants, which are also associated with BrS. Learning objective: Atrial flutter in children without structural heart disease can be linked to genetic factors with Brugada syndrome (BrS). This case highlights the importance of thorough diagnostic evaluation, including family history and genetic testing, when rare arrhythmias are present. Early detection of BrS through detailed electrocardiographic findings and family screening can help identify at-risk individuals and guide appropriate management to prevent serious arrhythmias and sudden cardiac death.