Congenital heart block

Congenital heart block (CHB), also called autoimmune congenital heart block when caused by maternal autoantibodies, is a rare disorder in which the electrical signals that coordinate the heartbeat become slowed or blocked before birth or during the newborn period. In the autoimmune form, antibodies produced by the pregnant mother, most commonly anti-Ro/SSA and anti-La/SSB antibodies, cross the placenta and trigger inflammation that can damage the developing cardiac conduction system. This damage may lead to scarring of the atrioventricular (AV) node, resulting in first-, second-, or third-degree (complete) heart block. Congenital heart block is considered one of the cardiac manifestations of neonatal lupus.

Not all congenital heart block is autoimmune. Some cases occur because of structural congenital heart defects, genetic conditions, infections, or other rare causes. However, autoimmune-associated congenital heart block accounts for most cases occurring in fetuses with structurally normal hearts. Although complete heart block is usually permanent, early recognition of pregnancies at risk allows close fetal monitoring and, in selected situations, treatments that may reduce complications or recurrence in future pregnancies.

A slow fetal or newborn heart rate (bradycardia), decreased fetal movement, fetal distress, hydrops fetalis, fatigue during feeding, poor feeding, poor weight gain, lethargy, bluish skin (cyanosis), shortness of breath, heart failure, or, in severe cases, fetal or neonatal death. Mild first-degree heart block may cause no obvious symptoms and may only be detected during fetal echocardiography or electrocardiography.

Most commonly associated with maternal Sjögren disease, systemic lupus erythematosus (SLE), undifferentiated connective tissue disease, mixed connective tissue disease, rheumatoid arthritis, or the presence of anti-Ro/SSA and/or anti-La/SSB antibodies in mothers without a previously diagnosed autoimmune disease. Some affected infants also develop other manifestations of neonatal lupus, including endocardial fibroelastosis, cardiomyopathy, valvular disease, liver abnormalities, skin rash, or blood cell abnormalities such as thrombocytopenia or other cytopenias.

Congenital heart block is rare, occurring in approximately 1 in 20,000 live births overall, although not all cases are autoimmune. Among pregnancies in women with anti-Ro/SSA antibodies, autoimmune congenital heart block develops in approximately 2% of pregnancies. The risk increases substantially, to approximately 15–20%, in women who have previously had a child affected by autoimmune congenital heart block. The condition most commonly develops between 18 and 24 weeks of pregnancy, which is why serial fetal echocardiography is typically recommended during this period for pregnancies considered to be at high risk.