In a Systemic Lupus Erythematosus (SLE) pregnant woman, which antibody will induce fetal heart block?

Anti-Ro/SSA Antibodies Induce Fetal Heart Block in SLE Pregnancy

In a pregnant woman with SLE, anti-Ro/SSA antibodies are responsible for inducing fetal heart block. 1, 2

Mechanism and Risk

Anti-Ro/SSA antibodies cross the placenta and damage the fetal cardiac conduction system, particularly the atrioventricular (AV) node, leading to congenital heart block. This represents the most severe manifestation of neonatal lupus syndrome 3.

Key points about anti-Ro/SSA antibodies:

• They cause approximately 2% risk of complete heart block in pregnancies without prior history of neonatal lupus 2
• Risk increases to 13-18% in pregnancies with previous history of neonatal lupus 2
• When combined with anti-La/SSB antibodies, the risk may be further increased 2, 4
• Maternal anti-La/SSB levels have been found to be significantly higher in pregnancies complicated by fetal heart block 4

Monitoring and Management

For pregnant SLE patients with anti-Ro/SSA antibodies:

1. Screening and risk assessment:

   • Test for anti-Ro/SSA and anti-La/SSB antibodies in all pregnant women with SLE 1
   • Higher antibody titers correlate with increased risk 5

2. Fetal monitoring:

   • For women without history of a child with congenital heart block: serial fetal echocardiography starting at 16-18 weeks and continuing until 26 weeks 2
   • For women with history of a child with congenital heart block: weekly fetal echocardiography starting at 16-18 weeks 2

3. Preventive treatment:

   • Hydroxychloroquine is recommended for all pregnant women with positive anti-Ro/SSA antibodies 2, 6
   • Studies show hydroxychloroquine may reduce the risk of congenital heart block (5.6% vs 27.3% in untreated women) 6, 4

4. Management if heart block detected:

   • First or second-degree heart block: oral dexamethasone 4 mg daily is recommended 2
   • Complete heart block: dexamethasone is not recommended as the damage is usually irreversible 2
   • Delivery planning should include preparation for immediate pacemaker insertion if needed 7

Answer to Question

Based on the evidence, the correct answer is C. Anti-Ro (anti-SSA) antibodies. These antibodies are specifically linked to congenital heart block in pregnant women with SLE, while anti-Jo-1 and anti-Smith antibodies are not associated with this complication.

Anti-Jo-1 antibodies are primarily associated with inflammatory myopathies, and anti-Smith antibodies, while specific for SLE diagnosis, are not implicated in fetal heart block development.

Clinical Implications

The identification of anti-Ro/SSA antibodies in pregnant women with SLE should prompt:

• Close fetal cardiac monitoring
• Consideration of hydroxychloroquine therapy
• Preparation for potential cardiac complications in the newborn
• Multidisciplinary management involving rheumatology, maternal-fetal medicine, and pediatric cardiology

Early detection and management can significantly improve outcomes for affected infants, as permanent pacemaker implantation is often required but can lead to favorable outcomes when planned appropriately 7.