Effects of Transplacental Dexamethasone Therapy on Fetal Immune-Mediated Complete Heart Block

INTRODUCTION: Antibody-mediated complete atrioventricular block (CAVB) is considered irreversible. We sought to examine the effects of transplacental steroids on fetal AV conduction. METHODS: Fifty-nine fetuses diagnosed with CAVB at our center from 1996 to 2018 were reviewed. Routine dexamethasone administration to birth was used to limit cardiac inflammatory damage. Restoration of fetal AV conduction was classified as "unexpected" treatment response. RESULTS: CAVB resolved in 5/29 (17%) fetuses first treated ≤24-week gestation with 8 mg/day of dexamethasone, when compared with 0/30 (0%) when treatment was initiated later and/or at a starting dose of 4 mg/day (odds ratio 13.69; 95% confidence interval 0.72-260.13; p = 0.024). Treatment response was also associated with a faster ventricular rate at diagnosis (median [range]: 80 [60-97] beats per minute [bpm] vs. 58 [38-92] bpm; p = 0.0036). CAVB reappeared in all 5 responders either prenatally (n = 1) or postnatally before (n = 3) or after (n = 1) the first year of life. When compared with infants with treatment-resistant CAVB (median follow-up 10.3 years), responders (median follow-up 12.3 years) required postnatal pacing less frequent (2/5 [40%] vs. 45/49 [92%]; p = 0.013). CONCLUSIONS: In a subgroup of CAVB fetuses, dexamethasone transiently restored AV conduction. This was associated with a lower rate of postnatal pacing when compared with nonresponders.