An infant born at term to a 27-year-old mother develops profound bradycardia on day 2 of life. Electrocardiogram shows complete atrioventricular block with ventricular rate of 55/min. The mother has a history of photosensitive rash and arthralgia and is found to have high titre anti-Ro (SSA) antibodies. What is the mechanism of this condition?
- A Transplacental transfer of maternal anti-Ro and anti-La antibodies causing fibrosis of the fetal atrioventricular node ✓
- B Maternal hypergammaglobulinemia compressing the fetal conduction system
- C In utero parvovirus B19 infection of fetal myocardium
- D Autosomal recessive mutation in the SCN5A gene
Explanation
Congenital complete heart block is the hallmark of neonatal lupus erythematosus, caused by transplacental passage of maternal anti-Ro (SSA) and anti-La (SSB) antibodies, which bind fetal cardiac antigens and trigger inflammatory fibrosis of the atrioventricular node, typically between 16 and 24 weeks of gestation. Many mothers are minimally symptomatic or have undifferentiated connective tissue disease. Parvovirus B19 causes hydrops fetalis through myocarditis and anaemia, and SCN5A mutations cause familial progressive conduction disease, neither involving maternal autoantibodies.
Reference: Nelson Textbook of Pediatrics, 22nd ed.
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Written and medically reviewed by the StethoPrep medical team.