Extravascular Implantable Cardioverter-Defibrillator Therapy for Malignant Ventricular Arrhythmias in a Child with Congenital Long QT Syndrome: A Case Report

Background/Objectives: Children with congenital long QT syndrome (cLQTS) are at extremely high risk of torsades de pointes (TdP) and sudden cardiac death (SCD). Although the implantable cardioverter-defibrillator (ICD) is a cornerstone in SCD prevention, traditional transvenous ICDs are associated with venous access occupation, lead wear or fracture due to somatic growth, and difficulties with long-term lead revision or extraction. The extravascular ICD, which places the lead in the substernal extravascular space, has the potential to circumvent these lead-related complications. We report the experience of successful extravascular ICD implantation in a young child with drug-refractory cLQTS type 2 (cLQTS2). Methods: The clinical data of a 9-year-old boy with cLQTS2 were retrospectively analyzed. The patient carried a heterozygous KCNH2 variant (c.1810G>A, p.Gly604Ser) and had been on long-term oral propranolol and mexiletine. He presented with a cardiac arrest out of hospital during nocturnal sleep, was transferred to our hospital after successful cardiopulmonary resuscitation, and had TdP captured on ambulatory monitoring. Following multidisciplinary discussion, preoperative chest computed tomography (CT) assessment of the substernal anatomy, and informed consent, extravascular ICD implantation was performed on hospital day 11. The procedure involved the creation of a substernal tunnel via a subxiphoid incision, placement of the defibrillation lead in the anterior mediastinum with lead slack reserved for growth, and positioning of the pulse generator in a left axillary subcutaneous pocket. Intraoperative defibrillation testing succeeded with a single 30 J shock. Results: The postoperative recovery was uneventful without procedure-related complications. At the 2-month follow-up, device parameters were satisfactory and no inappropriate shocks had occurred. The corrected QT interval (QTc) decreased from 563 ms on admission to 522 ms. Ambulatory monitoring detected asymptomatic episodes of non-sustained ventricular tachycardia, but no ventricular fibrillation or syncope was observed. Venous access was fully preserved. Conclusions: In children with drug-refractory cLQTS2, the extravascular ICD provides defibrillation and antitachycardia pacing (ATP) while avoiding transvenous lead complications and preserving venous access. This case shows that with precise preoperative planning and lead redundancy, the device appears feasible and can be implanted without short-term complications in young children. Larger studies with longer follow-up are needed to evaluate long-term device performance.