A case of long QT syndrome and progressive cardiac conduction disorder with fetal arrhythmia and alternating bundle branch block during the neonatal period

Abstract

 The patient was a female infant with a history of fetal arrhythmia and she presented with a 2:1 atrioventricular block（AVB）and QT prolongation at birth. Two-to-one AVB due to congenital long QT syndrome was suspected, but the patient started to develop an alternating bundle branch block, and there were concerns that the condition might be due to a conduction disorder. The patient was placed under observation without medication, but at the age of 41 days, she developed a complete atrioventricular block. Thus, a pacemaker was implanted at the age of 70 days. The patient was later identified as carrying a SCN5A variant and was diagnosed with QT-prolongation syndrome due to SCN5A abnormality, accompanied by progressive cardiac conduction defects（PCCD）. This is the world’s first report of an alternating bundle branch block that was observed from the neonatal period, in which cardiac conduction defect progression was continuously confirmed.