A Case of Infantile Mitochondrial Cardiomyopathy Treated with a Combination of Low-Dose Propranolol and Cibenzoline for Left Ventricular Outflow Tract Stenosis

Hypertrophic cardiomyopathy is a common cardiac complication in mitochondrial disorders, and the morbidity rate in neonatal cases is up to 40%. The mortality rate within 3 months for neonatal-onset mitochondrial cardiomyopathy is known to be high because there is currently no established treatment.We report the case of a male infant with neonatal-onset mitochondrial disorder presenting lactic acidosis and hypertrophic cardiomyopathy. Genetic analysis of the patient revealed recurrent m.13513GA, p.Asp393Asn in mitochondrially encoded NADH dehydrogenase 5 gene (MT-ND5). Low-dose propranolol was initially administered for cardiomyopathy; however, he developed hypertrophic obstructive cardiomyopathy (HOCM) at 3 months of age. To reduce the risk of hypoglycemia associated with high-dose propranolol, cibenzoline, a class Ia antiarrhythmic drug, was added at a dose of 2.5 mg/kg/day and increased weekly to 7.5 mg/kg/day with monitoring of the blood concentration of cibenzoline. Left ventricular outflow tract stenosis (LVOTS) dramatically improved from 5.4 to 1.3 m/second in LVOTS peak velocity after 6 weeks, without notable adverse effects. The plasma N-terminal pro-brain natriuretic peptide level decreased from 65,854 to 10,044 pg/mL. Furthermore, myocardial hypertrophy also improved, as the left ventricular mass index decreased from 173.1 to 108.9 g/m