Extremely low ventricular rate in a fetus with an isolated non-autoimmune complete congenital heart block. Case report.

Congenital complete heart block (CCHB) is an uncommon disorder with an incidence of about 1/20,000 in liveborn infants. It can occur in the setting of structurally normal heart or with structural disease; it is associated with high mortality and morbidity and requires a high index of suspicion for early diagnosis and therapy. Isolated CCHB in a fetus is usually associated with the presence of autoantibodies to SSA (Ro) and SSB (La) antigens in the maternal circulation. Such antibodies cross into the fetal circulation and cause inflammation of the conduction tissues; the causal mechanism is not known. Although the prognosis for the majority of fetuses is good, it is less favourable in fetuses with a ventricular rate <55 bpm in early pregnancy or with a decrease in the ventricular rate by >5 bpm during pregnancy. It is not known if the same prognostic criteria apply for fetuses with isolated non-autoimmune CCHB. This article reports authors' experience in managing a pregnancy with an extremely low fetal heart rate (47 bpm) in a single fetus with an isolated non-autoimmune CCHB in which the outcome was favorable.