Prospective Cardiac Monitoring in Fetuses at Risk of Congenital Heart Block

September 12, 2007

SMFM 27th Annual Meeting 2007

view the interview video: Fetal Congenital Heart Block

OBJECTIVE: Anti-Ro/La-associated congenital heart block (CHB) carries a 20% mortality. Nearly all survivors require pacemakers. Once established 3rd degree block is not reversible. We initiated the PRIDE Study to evaluate an early marker of cardiac injury prior to permanent scarring, the "mechanical PR interval".

STUDY DESIGN: Women with anti-Ro/La antibodies had fetal echocardiograms weekly from 16-26 weeks, then biweekly from 26-34 weeks. Mechanical PR interval >150 msec (mean + 3 SD) was considered abnormal, consistent with 1st degree block. All patients had anti-Ro titer >30 EU (normal <19); mean titer was 11,000. Mothers were excluded if taking >10 mg/day prednisone.

RESULTS: We enrolled 127 fetuses, with 94 delivered, 7 still pregnant, & 26 dropouts. There were 88 fetuses (91%) with normal PR intervals throughout. CHB occurred in 3 of 16 mothers with a previous CHB child (19%) and 3 of 70 with no previous CHB (4%). Three fetuses had 3rd degree block, all onset <23 weeks. Two terminated for hydrops, both developed hydrops despite maternal dexamethasone within 2 weeks of an echocardiogram showing normal PR interval, but with tricuspid regurgitation. The other is alive at 12 months of age with a pacemaker. There were 3 fetuses with 1st degree block detected by echo. Two of these were detected at 18-22 weeks and resolved with 3-7 days of dexamethasone 4 mg po qd. Both had normal EKG at birth. The third had normal PR through 30 wk and was born at 32 wk with 1st degree block on EKG that has persisted to 3 years.

CONCLUSION: 1st degree fetal heart block may be reversible with dexamethasone, supporting the utility of close monitoring, especially given the high recurrence rate substantiated in this study. Advanced block and cardiomyopathy can occur within 1 week of a normal echocardiogram, so even weekly evaluation may not be sufficient to detect early onset of disease. Third degree block is not reversible despite early intervention. Either a reliable marker of early disease, or a safe and economical method of prophylaxis, is needed.