Abstract 4136984: Low Occurence of Fetal Extranodal Findings and AV Interval Prolongation in Prospectively Followed High Titer Anti-Ro Pregnancies

. Background: Third-degree atrioventricular block (AVB) is the most common manifestation of Anti-Ro antibody associated fetal cardiac disease. Extranodal findings of isolated cardiac echogenicity, valvulitis with insufficiency and AV interval prolongation have been reported but not described in large prospective series. Aims: To report the occurrence and outcomes of extranodal findings in subjects followed prospectively since 2020 in STOP BLOQ (Surveillance and Treatment to Prevent Fetal AV block Likely to Occur Quickly) and the Registry for Neonatal Lupus (RNL). Methods: We reviewed fetal echo reports from pregnant STOP BLOQ and RNL Anti-Ro antibody subjects. Pregnancies with high (>1000 EU for anti-Ro52 or 60) antibody titers measured in a core research lab underwent surveillance with home fetal heart rate monitoring (FHRM) 3x/day and weekly or bi-weekly fetal echos from 17- 26 gestational weeks. Low titer subjects underwent echo or no surveillance based on local site protocol. We evaluated cardiac function, effusions, cardiac echogenicity and its location, any tricuspid (TV) or mitral (MV) insufficiency trivial or >trivial) and AV conduction times (<150, 150-170 or >170 ms) Results: Echo reports were available in 622 prospectively followed pregnancies (376 high (40/376 with a previously affected child) and 246 low-titer pregnancies. All had subjectively normal ventricular function and none had effusions. Seven fetuses, 2 low and 5 high titer at 19 (range 16.7-21.7) weeks demonstrated cardiac echogenicity (n=6), AV or semilunar valve insufficiency (n=2) or AV interval 150-170 ms (n=2) (Table). Subjects 1 and 2, both high titer and treated with prophylactic Plaquenil (400 mg/d before 10 gestational weeks), had prior fetal AVB. Subject #1 had normal AV conduction but MV and TV echogenicity and moderate insufficiency of both valves which resolved in days after IVIG and dexamethasone (dex) treatment, but 3° AVB developed at 19 weeks after dex wean. Subjects 2-7 received no treatment and extranodal findings did not progress to cardiac dysfunction or AVB. During the same time period, 10 high titer subjects developed 2° or 3° AVB. Conclusion: Anti-Ro associated extranodal findings are rare, occurring in 1% of pregnancies overall and in 5% of pregnancies with a previously affected child. Unlike AVB, extranodal findings can occur in low titer pregnancies. The role of treatment for isolated extranodal findings in the absence of cardiac dysfunction is unclear.