Isolated anti-Ro/La antibody-negative fetal complete atrioventricular block: a case report
Fetal complete atrioventricular block (CAVB) is a rare but serious condition affecting fewer than 1 in 20,000 pregnancies. Most cases are tied to maternal anti-Ro/La autoantibodies or congenital heart defects—but what happens when neither is present? A new case from China sheds light on this understudied scenario, following a child with “seronegative” CAVB for nearly a decade.
The story starts with a 28-year-old woman (pregnant with her first child) who visited the Second Affiliated Hospital of Xi’an Jiaotong University at 30 weeks gestation. She had no risk factors for fetal heart issues, and tests for maternal autoantibodies (anti-Ro/La, anti-dsDNA, and anti-nuclear antibodies) were negative. A full fetal ultrasound showed no structural problems, fluid buildup (hydrops), or other abnormalities.
During a detailed fetal echocardiogram—tracking heart activity across the right atrium, ventricular septum, and left ventricle—doctors found CAVB: the baby’s atria (upper chambers) beat regularly at 130–140 beats per minute (bpm), but the ventricles (lower chambers) were much slower, at 68 bpm. This meant electrical signals from the atria weren’t reaching the ventricles—a dangerous disconnect.
The pregnancy continued until 38 weeks, when the woman had a cesarean section. Amniotic fluid was “grade III” contaminated (a sign of fetal stress), but there was no premature membrane rupture, nuchal cord, or suffocation. The baby girl scored 9/10 on her 1-minute Apgar test and 10/10 at 5 minutes. A bedside ECG confirmed CAVB: atria at 136 bpm, ventricles at 68 bpm. A follow-up ultrasound showed her heart structure was normal; only the ductus arteriosus (a fetal blood vessel) and foramen ovale (a heart hole) remained open—typical for newborns.
Today, the girl is 9 years old. She plays normally, does well in school, and has no symptoms like fainting, fatigue, or heart failure. She still doesn’t need medications or a pacemaker. A recent echocardiogram showed her heart is structurally normal with a ventricular rate of 58 bpm. A 24-hour Holter monitor revealed an average heart rate of 54 bpm (lowest 43 bpm, highest 80 bpm)—safe for her age.
Why this case matters
CAVB has three main causes:
- 50%: Congenital heart disease (CHD) like corrected transposition of the great arteries.
- 40%: Maternal anti-Ro/La antibodies, which cross the placenta and damage the baby’s heart conduction system.
- 10%: No clear cause (like this case).
For antibody-linked CAVB, poor outcomes are linked to diagnosis before 20 weeks, ventricular rate below 50 bpm, fetal hydrops, or weak left ventricular function (per a 2011 Circulation study of 175 cases). For seronegative CAVB, data are scarce—but a 2012 European Heart Journal study found non-immune isolated CAVB often has better long-term results (no deaths or dilated cardiomyopathy). Another 2009 Journal of Rheumatology study of 9 anti-Ro/La-negative cases found all 3 children with ventricular rates below 50 bpm died—even with pacemakers.
In this case, the key difference was the ventricular rate: it stayed above 55 bpm from diagnosis. Researchers think this may be due to a “high pacing site”—meaning the ventricles used a more efficient backup rhythm.
What we learn
This case is rare because it’s anti-Ro/La negative and includes a 9-year follow-up—much longer than most studies. It adds evidence that ventricular rate is a critical predictor of outcomes for seronegative fetal CAVB. While more research is needed, the takeaway is hopeful: if a fetus with seronegative CAVB has a ventricular rate above 55 bpm, the prognosis may be better than previously thought.
This case was reported by researchers from the Department of Ultrasound at the Second Affiliated Hospital of Xi’an Jiaotong University (China), including Huan-Huan Huo, Ya-Juan Wei, Yan-Hua Qi, and corresponding author Bao-Min Liu. The original study was published in the Chinese Medical Journal in 2020.
https://doi.org/10.1097/CM9.0000000000000581
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