Pregnant patients with low anti-Ro titers have ‘little to no’ risk for fetal heart block
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SAN DIEGO — Pregnant patients with very low anti-Ro antibody titers of less than 1,000 units per mL have minimal-to-no risk for fetal atrioventricular block, according to data presented at ACR Convergence 2023.
“[Fetal atrioventricular block] is a really serious problem,” Jill Buyon, MD, of the New York University Grossman School of Medicine, said at a press conference during the meeting. “It occurs in about 1% [of mothers with anti-Ro antibodies], but the recurrence rate can be as high as 18%. The fatality rate is about 17%, and if you have cardiac abnormalities on top of that with regard to function, this can actually go up to as high as 35%.
“So, this is a pretty serious disease, and to date third-degree block, which is the most serious form, is completely immutable,” she added. “So, for clinicians, OB, MFM, rheumatologists — how do we surveil these patients? We’re trying to weigh the severity of a lifelong disease, because they all need pacemakers sooner or later, and some die of course, and it’s irreversible. How do we weigh that against the rarity and the surveillance that might be needed on a weekly basis to try to find a reversable problem?”
To assess the impact of anti-Ro antibody titers in pregnant patients on fetal heart block outcomes, as well as the utility of frequent fetal heart rate monitoring, Buyon and colleagues analyzed prospective data from the ongoing Surveillance to Prevent AV Block Likely to Occur Quickly — or STOP BLOQ — trial. Initiated in 2020, STOP BLOQ is a large, multi-racial national study of pregnant women from 21 sites across the United States. To date, a total of 405 participants have been enrolled.
Researchers risk stratified participants with positive anti-Ro autoantibodies into high and low anti-Ro60 and anti-Ro52 titer groups, based on previous data demonstrating that patients with titers of less than 1,000 units per mL demonstrated no risk for fetal atrioventricular block. Those with low titers were assessed with echocardiograms and EKGs at birth. Meanwhile, patients who exceeded the 1,000-unit per mL threshold underwent fetal heart rate monitoring three times daily, as well as weekly or biweekly fetal echocardiography from 18 to 26 weeks. Abnormal results triggered echocardiography to identify fetal heart block.
Among the enrolled participants, 150 demonstrated low titers of anti-Ro60 and anti-Ro52 antibodies. According to the researchers, none of these cases resulted in fetal atrioventricular block after 26 weeks. Among the 241 patients with titers above the 1,000-unit threshold who completed surveillance, fetal heart rate monitoring was performed a total of 44,187 times. In all, results were considered abnormal in 37 audios, nine of which were confirmed via urgent echocardiography to be fetal heart block. Meanwhile, surveillance echocardiogram — performed 1,871 times — found no fetal atrioventricular block when the fetal heart rate monitoring results were normal.
According to the researchers, fetal atrioventricular block risk increased with higher titers. Among patients in the top quartile, the rate of fetal heart block was 7.1% overall, and 8.3% for those never having prior fetal atrioventricular block. Meanwhile, demonstrating anti-Ro60 antibodies in the top quartile, and having a previous birth with fetal atrioventricular block resulted in the highest risk for fetal heart block, at 22%.
The researchers additionally wrote that although high titer anti-Ro antibodies are “necessary,” they are by no means “sufficient” for fetal atrioventricular block. For example, four participants with prior fetal atrioventricular block during pregnancy, but without it in the current pregnancy, demonstrated titers equal to those detected during their impacted pregnancies.
“The bottom line is that when we evaluated women who had gotten to 26 weeks, we could see that high titer very strongly related to the greatest risk for block, so that if you had low titer there seemed to be no risk,” Buyon said. “That risk went from almost nothing with low titer, all the way to 7% in the highest titer. It also turned out that with fetal heart monitoring, of which we did 40,000, only 45 were abnormal, and of those, 10 were atrioventricular block. And of those, seven were second-degree, which, we hope, represents a reversible problem.
“Low titer women are probably at little to no risk, which can be very helpful,” she added. “Also, high titer makes a difference, and fetal heart rate monitoring, done at home by the mother, can pick up a potentially reversible abnormality. This may actually change the way we care for women with anti-Ro antibodies, regardless of whether they have lupus, or Sjogren’s, or if they are asymptomatic.”
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Rovin B. Abstract 1682. Presented at: ACR Convergence 2023; Nov. 10-15, 2023; San Diego.
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