A Complex Arrhythmic Phenotype in a Pediatric Patient with Variants in SCN5A and KCNH2

Long QT Syndrome type 2 (LQT2) and Brugada syndrome are inherited cardiac channelopathies that predispose affected individuals to ventricular arrhythmias and sudden cardiac death. We report the case of a 15-year-old male carrying two pathogenic variants: one in SCN5A and one in KCNH2, genes classically associated with Brugada syndrome and LQT2, respectively. The patient presented with an atypical phenotype characterized predominantly by atrial arrhythmias, atrioventricular (AV) conduction abnormalities, and wide complex tachycardia and sinus node disease without the characteristic electrocardiographic features of either syndrome. The phenotype was most likely driven predominantly by the SCN5A variant. Given his unpredictable episodes of high-grade conduction block and potential risk of ventricular arrhythmias, a transvenous implantable cardioverter-defibrillator (ICD) was implanted. Family screening revealed segregation of SCN5A and KCNH2 variants in different relatives, each with mild or absent phenotype. This case highlights the complexity of genotype-phenotype correlations in inherited arrhythmia syndromes and the importance of individualized genetics-informed management.