Congenital heart block is rare; it is acquired in utero, definitive and, more often than not, complete. It can be diagnosed by the appearance of fetal
bradycardia around the 23rd week of gestation, during ultrasonographic monitoring of pregnancy.
Heart block is usually associated with the presence of anti-Ro and/or anti-La
antibodies in the mother's serum. These maternal immunological abnormalities can be isolated or associated with an
autoimmune disease, usually
systemic lupus erythematosus, but also Sjögren's syndrome, or more rarely still, an as yet unclassified
connective tissue disease. Anti-Ro and anti-La
antibodies cross the placental barrier and react with a fetal heart, leading to acute fetal
myocarditis by the 17th week of gestation. When severe, it is lethal, otherwise it can result in degeneration and
endocardial fibroelastosis, disrupting conduction and leading to
congenital heart block. The ideal treatment would be prevention with
corticosteroids. When the mother is Ro or La antibody-positive before pregnancy, elimination of these circulating
antibodies can be attempted by treatment with 0.5 mg/kg body wt/d of
prednisolone for 3 months. If the treatment is successful, corticotherapy can be prescribed early in the pregnancy to try to protect the fetus. However, there is not always a relationship between maternal anti-
Ro antibodies and fetal heart block. If the Ro/La antibody-positive woman is already pregnant, but before her 17th week, it is possible to prescribe
dexamethasone, which crosses the placenta and remains active, sometimes in association with
plasmapheresis.