A term newborn has persistent bradycardia with a heart rate of 58 per minute shortly after birth. ECG shows atrial activity completely dissociated from narrow QRS complexes at a fixed rate. The mother has long-standing Sjogren syndrome. The most likely mechanism of this arrhythmia is:

• A Structural interruption at the level of the sinus node
• B Autosomal dominant mutation in the SCN5A gene
• C Maternal anti-Ro/SSA antibody mediated destruction of the fetal conduction system ✓
• D Fetal exposure to maternal beta blockers causing reversible sinus bradycardia

Explanation

Congenital complete atrioventricular block presents in utero or in the neonatal period with ventricular rates of 50 to 70 per minute and atrioventricular dissociation. Transplacental passage of maternal anti-Ro/SSA and anti-La/SSB antibodies causes fibrosis of the fetal AV node, classically in mothers with Sjogren syndrome or lupus. SCN5C mutations cause familial progressive conduction disease later in life, and the fixed narrow QRS escape rhythm localizes the block below the AV node rather than to the sinus node.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.