Successful Outcome in a Fetus with an Extremely Low Heart Rate Due to Isolated Complete Congenital Heart Block

Isolated complete congenital heart block (CCHB) in a fetus is usually associated with the presence of autoantibodies to SSA (Ro) and SSB (La) antigens in the maternal circulation. Although the prognosis for the majority of fetuses is good, it is less favorable 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 the occasional fetus with isolated non-autoimmune CCHB. We report a case of a single fetus with an isolated non-autoimmune CCHB with an extremely low ventricular rate (37 bpm) in which the outcome was favorable. Dilated cardiomyopathy is a rare complication in patients with isolated CCHB, despite early institution of cardiac pacing, and is usually recognized after several months of relative well-being. It is assumed that in the majority of patients it represents a sequel to in utero autoimmune or postnatal reactivation myocarditis. However, the possibility of a tachycardia-induced cardiomyopathy caused by an excessively high pacing rate should also be taken into consideration, as was clearly demonstrated in our patient.