Successful Treatment of a Newborn With Genetically Confirmed Long QT Syndrome 3 and Repetitive Torsades De Pointes Tachycardia

A 2-day-old female term newborn (body weight 2900 g, height 48 cm) was admitted to our clinic for further evaluation and therapy of bradycardia. The first signs of dysrhythmia were premature beats and bradycardia, noted at 30th gestational week. Fetal echocardiography showed structural normal anatomy. Delivery and early postnatal clinical assessment were unremarkable. There was no family history of syncope, palpitation, or sudden cardiac death. On day 2 of life, a brief episode of hemodynamic and respiratory impairment occurred. The patient was then referred to our clinic. On admission we saw a healthy-looking neonate. Twelve-lead electrocardiography (ECG) showed sinus bradycardia with T-wave alternans and QTc of 730 ms, frequent single premature ventricular beats and couplets (Fig. 1, left). ECG confirmed the normal anatomy, and blood work was without pathological findings. Within the first hour after admission, the patient developed two episodes of Torsades de Pointes (TdP) tachycardia requiring cardiopulmonary resuscitation with cardiac massage and intubation (Fig. 2). Both episodes were terminated using direct current defibrillation (2 J/kg). Intravenous beta blockade with esmolol (100 lg/kg/min) was started immediately. Intravenous lidocaine testing shortened the QTc interval (Fig. 1, right). Intravenous esmolol was ceased, and oral propranolol was started. No further episodes of TdP tachycardia occured, and the patient was extubated shortly thereafter. T-wave morphology on surface ECG and a positive response to lidocaine testing highlighted the suspicion of Long QT 3 syndrome (LQTS3). Oral mexiletine (8.4 mg/kg) was added to propranolol (5 mg/ kg). Holter recording showed effective limitation of maximum heart rate and decreasing incidence of ventricular premature beats under ongoing propranolol and mexiletine. Further shortening of the QT and QTc intervals during maximum heart rate was seen. The patient was discharged home on day 32 of life in good clinical condition. The parents received pediatric basic life support training, and home monitoring was recommended. Genetic testing confirmed heterozygote mutation in the transmembrane domain of SCN5A (c.5314C[G) gene. Follow-up studies showed normal development without evidence of recurrent circulatory compromise, and measured QTc intervals varied between 480 and 580 ms on drug therapy with propranolol 4 mg/kg/d and mexiletine 9 to 10 mg/kg/d.