Background Neonatal lupus syndrome (NLS) includes congenital heart block (CHB) and cardiomyopathies. Its optimal management is debated.

Objectives We analyzed the mortality and morbidity of CHB, with special focus on risk factors.

Methods This was a retrospective study of the French national registry of NLS. Inclusion criteria were high-degree CHB associated with maternal anti-SSA/SSB antibodies.

Results 214 CHB were included (202 in utero cases and 12 neonatal cases). These 214 fetuses or children were born to 195 mothers anti-SSA (99.5%) and/or anti-SSB antibodies (60%) positive. 51 mothers (26.2%) fulfilled the classification criteria for an autoimmune disease: systemic lupus erythematosus (n=23), Sjögren syndrome (n=14), undifferentiated connective tissue disease (n=7), or other autoimmune disease (n=7).

The factors associated with feto-neonatal deaths (15.7%) were hydrops (p<0.001; HR: 12.4 [95%CI: 4.7-32.7]) and prematurity (p=0.002; HR: 17.1 [95%CI: 2.8-103.1]).

During a median follow-up of 7 years [birth to 36.1 years], 148 of 187 surviving children (79.1%) had a pacemaker, 35 (18.8%, one missing data) had dilated cardiomyopathy (DCM), and 22 (11.8%) died. DCM was neonatal (n=13) or late-onset (n=22, diagnosed at a median age of 15.2 months [3.6 months-22.8 years]).

Factors associated with neonatal DCM were maternal treatment with hydroxychloroquine, in utero cardiomegaly, in utero DCM, and hydrops. By contrast, only non-white race origin and significant in utero valvulopathy were associated with late-onset DCM. On multivariate analysis, only in utero DCM was associated with neonatal DCM (p=0.0001; HR 15.99 [95%CI: 3.93-65.01]), whereas non-white race origin was associated with late-onset DCM (p=0.0147; HR 3.65 [95%CI: 1.28-10.0]).

For children who survived the neonatal period (n=179), the risk of death during follow-up was 7.8%. On multivariate analysis, the only factor associated with late mortality was postnatal DCM (neonatal and late-onset DCM) (p<0.0001; HR 36.48 [95% CI 8.11-164.13]). The probability of survival at 10 years of age for a child with CHB born alive was 87.1%: 23.1% in the presence of neonatal DCM, 53.9% for those who developed a late-onset DCM requiring treatment versus 98.6% in those without DCM.

Fluorinated steroid in utero treatment was not associated with CHB regression, survival or absence of late-onset DCM.

Conclusions The factors associated with late-onset DCM differ completely from those associated with neonatal DCM. Our findings do not support the use of fluorinated steroids for CHB.

Disclosure of Interest None declared