Impact of early detection and steroid treatment on fetal ventricular heart rate and pacemaker implantation in anti-Ro/SSA positive congenital heart block.

Introduction: We investigated the effects of timing of detection and transplacental fluorinated steroid treatment on ventricular heart rate (HR) and age at pacemaker implantation in fetal third-degree atrioventricular block (AVB).

Material and methods: Twenty-five of 31 fetuses diagnosed with Ro/SSA autoantibody-positive AVB II-III at our tertiary fetal cardiology center (2000-2020) and AVB III as final feto-neonatal outcome were reviewed.

Results: AVB was detected approximately 5 weeks earlier in pregnancy if followed in a surveillance program compared to cases referred from primary care for bradycardia (20.6 [2.3] [mean (SD)] vs. 25.4 [3.2] weeks, p = 0.001). AVB detected before 24 weeks had higher HR than those detected later in gestation (63.3 [6.9] vs. 57.2 [6.9] bpm, p = 0.042), with a larger proportion having HR >60 bpm (80% vs. 33%, p = 0.041). The 17/25 cases that received treatment with fluorinated steroid were diagnosed earlier in gestation, with higher HR at diagnosis (61.7 [7.1] vs. 54.7 [6.3] bpm, p = 0.026), 1-2 weeks after diagnosis/treatment start, and before birth (65.4 [12.4] vs. 54.9 [5.7] bpm, p = 0.030) than untreated cases. Overall, 11 cases were commenced on betamimetics: three at diagnosis and eight at or after the examination made 1-2 weeks after diagnosis/treatment start, without any HR improvement. Two of 24 surviving babies were born preterm, and 4/24 received a neonatal pacemaker. Age at pacemaker implantation correlated significantly with HR before birth (Spearman R 0.57, p = 0.004), and fetuses with HR >60 bpm had a higher rate of pacemaker-free survival at three (90% vs. 40%, p = 0.018) and 12 months of age (80% vs. 13%, p = 0.002). The same trend was observed in pacemaker-free survival at 3 months of age in fluorinated steroid-treated compared to untreated cases (71% vs. 38%, ns).

Conclusions: Our data confirm that AVB III detected earlier in gestation have a higher HR, and suggest that this higher HR can be successfully maintained to the end of gestation in cases treated with fluorinated steroids. Fetuses with HR >60 bpm before birth had a lower rate of pacemaker implantation at 3 and 12 months of age.