Long QT syndrome with a functional 2:1 block and multilevel conduction disease

A 2-year-old female presented acutely following a three-week history of intermittent fever and lethargy. She was paradoxically bradycardic in the context of fever. An electrocardiogram illustrated multilevel conduction disease and a markedly prolonged QT interval with functional 2:1 atrioventricular block and multilevel conduction disease. Routine baseline aetiological investigations confirmed normal renal and thyroid biochemistry and no evidence of an infective cause or systemic inflammatory response. There was no past history of autoimmune conditions in the patient or her mother. Long QT syndrome type 3 (LQTS3) was suspected and a pacemaker implanted. Routine phenotypic screening of her asymptomatic first-degree relatives was unremarkable. Genetic testing of the proband identified an SCN5A mutation of uncertain pathogenicity, precluding predictive testing of her parents for diagnostic purposes. The proband remains well and event-free.