High-degree atrioventricular block in a child with an ANK2 variant and long QT phenotype requiring leadless pacemaker implantation.

Ankyrin-B syndrome, which has been linked to variants in ANK2 and classified as long QT syndrome type 4, is characterised by heterogeneous arrhythmic manifestations, including sinus node dysfunction and conduction abnormalities. Clinically significant atrioventricular block requiring permanent pacing in paediatric patients has rarely been described. We report a 10-year-old boy who presented with recurrent syncope and seizure-like episodes. Electrocardiography demonstrated QT prolongation, and continuous monitoring revealed persistent high-degree atrioventricular block. Genetic testing identified a heterozygous ANK2 variant of uncertain significance (NM_001148.4:c.5626G>A, p. Glu1876Lys), which was also detected in his mother and brother, while his father tested negative. Family evaluation revealed variable phenotypic expression, and a sister who died suddenly at 12 years of age had no available genotype but had autopsy findings of structural cardiac abnormalities. This case highlights clinically significant conduction disease in a child found to harbor an ANK2 VUS and long-QT phenotype and underscores the importance of detailed family phenotyping, rhythm surveillance, and individualised management.