Abstract 11396: Early-Onset Recurrent Malignant Arrhythmias in a Child With Hypertrophic Cardiomyopathy

Case presentation: A male newborn was diagnosed with severe hypertrophic cardiomyopathy (HCM) because of a heart murmur. A genetic test identified the previously described pathogenic variant Arg719Trp in MHY7, which was not present in the parents. An additional variant in KCNE2, Ile57Thr, considered as a risk factor for acquired long QT, was found in the patient. Corrected QT interval was normal. At age 3, the child suffered cardiac arrest from which he was successfully defibrillated. Maximal wall thickness was 20 mm (z-score +18). With the patient weighing 18 kg, a subcutaneous implantable cardioverter defibrillator (s-ICD) was implanted with the two-incision technique and nadolol 2 mg/kg/day was started. After 3 appropriate ICD therapies in the following 3 months, amiodarone was associated to betablockers, with no QT prolongation. He suffered 8 more ventricular fibrillation-terminating ICD shocks in the following year, prompting the indication of thoracoscopic bilateral cardiac sympathectomy denervation (BCSD) and referring him for heart transplant evaluation. Following BCSD he was symptom free for 6 months, after which he presented with a prolonged cardiac arrest, needing sedation, 4 ICD shocks and external defibrillation to recover consciousness. After experiencing another electrical storm in the following month, he underwent successful cardiac transplantation at age 5. Discussion: This clinical case is noteworthy for different reasons. First of all, even if Arg719Trp mutation in MHY7 has been associated with full penetrance and early expressivity of HCM (mean age at diagnosis 24 years), the child presented with an extremely rare early-onset of recurrent fatal arrhythmias. The pathogenicity of the associated KNCE2 variant, Ile57Thr, has not yet been elucidated but it has been suggested to confer proarrhythmic susceptibility in the presence of other environmental or genetic risk factors. Another worth-mentioning clinical aspect is that s-ICD proved to be a safe and effective therapy in a child weighing much less than 30 kg. In this case in which heart transplant could not be avoided due to life-threatening arrhythmias, the benefit of the preservation of the central venous circulation with the absence of intravascular leads cannot be overstated.