Fetal atrioventricular heart block.

As part of routine prenatal care, the obstetrician of a 25-year-old gravida 1, para 0 woman performed fetal heart-rate monitoring at 22 weeks gestational age. The fetal heart rate was 90 bpm, below the expected range of 120 –160 bpm. This finding prompted a subsequent fetal ultrasound and echocardiogram. The ultrasound exam showed no evidence of hydrops. Cardiac anatomy was normal, with 4 appropriately sized chambers, no valvular defects, and no abnormal communications between the right and left circulations. However, the electrocardiogram demonstrated a 2:1 atrioventricular heart block (1 ventricular beat for every 2 atrial beats). Previously, a firsttrimester screen to detect fetal aneuploidy had been performed and the results were normal. Results of serologic testing for hepatitis B, varicella, and rubella viruses were consistent with maternal immunity. Results of syphilis and HIV antibody tests were also negative. The expectant mother had no significant medical history, was taking no medications, and had no history or symptoms of autoimmune disease.