ECG artefact or life-threatening arrhythmia? A neonatal presentation of Long QT syndrome type 3 with a de novo SCN5A mutation

Electrocardiogram interpretation is critical in neonatal care, as artefacts may mimic life-threatening arrhythmias. We report the case of a preterm newborn girl, delivered at 31 weeks of gestation due to acute fetal distress, who developed tachycardia shortly after birth. The initial ECG showed chaotic electrical activity, initially raising suspicion of artifact; however, a subsequent tracing confirmed a life-threatening arrhythmia with wide QRS complexes, prolonged QTc, and torsades de pointes. As the patient remained haemodynamically stable, intravenous lidocaine and magnesium sulphate were administered, achieving pharmacological cardioversion. Propranolol was subsequently initiated, and the lidocaine infusion was tapered and replaced with oral mexiletine. Serial electrocardiograms showed QTc interval improvement, left ventricular function normalised, and the patient was discharged on the 39th postnatal day following stabilisation and supportive care for prematurity. Genetic testing identified a de novo SCN5A c.796C > G (p.L266V) mutation associated with Long QT syndrome type 3. At 1 year of age, the patient remains stable and asymptomatic while receiving combined therapy with propranolol and mexiletine.