SAN DIEGO – Pregnant women with anti-SSA/Ro autoantibodies at titer levels of less than 1,000 ELISA units per mL are at minimal to no risk for fetal atrioventricular (AV) block and may be able to forgo traditional echocardiographic heart rhythm monitoring, results from an ongoing, prospective, multicenter trial demonstrated.
However, pregnant patients with higher titer antibodies seem to be at greatest risk for fetal AV block and may benefit from ambulatory fetal heart rhythm monitoring (FHRM), which can detect emergent AV block, according to the study findings. The findings were published online in Arthritis & Rheumatology and will be presented Nov. 13 at the American College of Rheumatology (ACR) 2023 Annual Meeting by Jill P. Buyon, MD, a rheumatologist who directs the division of rheumatology and the Lupus Center at NYU Langone Health in New York.
Dr. Jill P. Buyon
“While anti-Ro antibodies have been known to be associated with AV block for decades, it has become increasingly clear that antibody titers matter,” Dr. Buyon said in an interview.
For the investigation, which is the largest of its kind, researchers at 22 sites drew from the large multiracial national study of pregnant women, Surveillance To Prevent AV Block Likely to Occur Quickly (STOP BLOQ), to address the impact of anti-Ro titers and use of frequent ambulatory FHRM on outcomes in women with no previously affected children and those at risk for recurrence. Monitoring occurred during the second trimester of pregnancy (from 17 weeks through 26 weeks) and consisted of daily fetal home testing by mothers using handheld, commercially available Doppler devices.
These were followed up by weekly or biweekly echocardiograms, and ultrasound tests to evaluate fetal heart rhythm and function, as well as to show any structural problems. Three times per day, the pregnant women texted the Doppler sound recordings in real time to a pediatric cardiologist, who immediately ordered an additional echocardiogram in cases of irregular or slowing fetal heart rates. If second-degree heart block was detected, drug therapy was initiated.
No AV block seen with low anti-Ro titers
Dr. Buyon, who led the study with Bettina Cuneo, MD, clinical scholar and professor of surgery and pediatrics at the University of Arizona in Tucson, presented findings from 413 pregnant subjects with a mean age of 33 years who finished monitoring surveillance: 152 women had low titers of both anti-Ro60 and –Ro52 (defined as < 1,000 ELISA units per mL), and 261 women with titers above the threshold for either antibody (defined as ≥ 1,000 ELISA units per mL). Of the 152 women with low titers of both anti-Ro60 and –Ro52, none of the pregnancies past 26 weeks resulted in AV block. Of the 261 women with titers above the threshold for either antibody, 10 of the pregnancies resulted in AV block (3.8%). The incidence of AV block increased with higher antibody titer levels, reaching 7.7% for those in the top quartile for anti–60-kD SSA/Ro; this increased to 27.3% in study participants with a previous child who had AV block, although numbers in this category were small.
Analysis of cumulative FHRM recordings between surveillance echocardiograms revealed that no case of second-degree or third-degree AV block was missed. In addition, 70% of AV blocks detected by FHRM were second-degree and all occurred less than 12 hours from normal FHRM and within another 45 minutes to 4.5 hours to echocardiogram. The one case of second/third-degree and two cases of third-degree AV block were diagnosed by urgent echocardiogram more than 17 to 72 hours from a previously normal FHRM episode.
Other factors besides high anti-Ro titer likely play a role
“STOP BLOQ nicely demonstrates that low titer is associated with a very low risk AV block, and intense monitoring may not be needed,” Dr. Buyon told this news organization. “However, high titer is not the whole answer since even women with the very highest titers can have healthy babies. This report also shows that titers stay constant through pregnancies in the same mother, whether there is the complication of AV block or not. This suggests other factors contribute to AV block.”
She added that FHRM can be easily performed by the mother, but at this time is still best interpreted by a cardiologist. “FHRM detected all cases of AV block, which can happen in hours,” she said. “FHRM should decrease the need for frequent echocardiograms. Some mothers do have more difficulty in deciding whether the baby’s heart is beating irregularly. We need [to improve our teaching] and for how best to have a cardiologist or trained listener interpret. FHRM can be done by the mother but needs interpretation by a cardiologist until we develop a device which can identify abnormalities.”
She acknowledged certain limitations of the study, including the fact that a commercial test for anti-SSA/Ro antibody levels is not available to all clinicians. “Try to find a lab that measures high titer anti-Ro antibodies, but if not, then use one of the common commercial tests such as the BioPlex 2000 autoimmune panels and consider decreased surveillance if titer is < 8,” Dr. Buyon advised.
Vaneet K. Sandhu, MD, a rheumatologist with Loma Linda (Calif.) Medical Center, who was asked to comment on the work, said that the study not only justifies the limited use of FHRM in those with high titer antibodies (followed by urgent fetal echocardiography where indicated), but also risk stratification for fetal AV block.
Loma Linda University Health
Dr. Vaneet K. Sandhu
“For years, we have recommended frequent fetal echocardiography testing in pregnant women with positive anti-SSA/Ro,” Dr. Sandhu said. “This study tells us we need to look deeper. On one hand, recognizing that low titer anti-Ro antibodies do not confer a risk of AV block is cost effective. On the other hand, while the titer of the antibody appears to contribute to fetal AV block, we need to delve deeper into additional factors contributing to fetal AV block risk in order to better navigate our surveillance methods.”
The study was supported by NIH grants from the National Institute of Child Health and Human Development and the National Institute of Arthritis and Musculoskeletal and Skin Diseases. Dr. Sandhu has disclosed no relevant financial relationships.
A version of this article first appeared on Medscape.com.