Neurologic presentation unmasks arrhythmogenic channelopathy: KCNH2 variant Long-QT syndrome managed with subcutaneous implantable cardioverter-defibrillator. A case report

A previously healthy 10-year-old boy developed febrile seizure-like episodes after an appendectomy, which were diagnosed as epilepsy despite a normal electroencephalogram. He later presented with dyspnea and palpitations and was prescribed propafenone for frequent premature ventricular complexes. The electrocardiogram showed a markedly prolonged QTc interval of 550 ms with a notched T wave in lead V2. Phenytoin and propafenone were discontinued, and propranolol was initiated, but QTc prolongation persisted. The combination of severely prolonged QTc, characteristic T-wave morphology, and absence of structural heart disease redirected the diagnosis toward a repolarization channelopathy; genetic testing confirmed long-QT syndrome type 2 due to a pathogenic KCNH2 c.1814C>T variant. β-blocker therapy was optimized, QT-prolonging triggers were avoided, and a subcutaneous implantable cardioverter-defibrillator was implanted. Cascade genetic screening identified no additional KCNH2 carriers. One variant-negative sister had frequent idiopathic right ventricular outflow tract premature ventricular complexes and was referred for catheter ablation.