EP09.86: Left atrial isomerism with normal heart and interrupted inferior vena cava: the good among the bad?

Isomerism is a complex disease usually accompanied by severe congenital heart defects and extracardiac pathology. Two forms are described based on anatomical features: left or right atrial isomerism (LAI or RAI). Long-term outcome is generally described as guarded for both groups. However with the LAI group there are fetuses with structurally normal hearts and only interruption of the inferior vena cava (I-IVC) present. The aim of this study was to describe the outcome of fetuses with left atrial isomerism and structurally normal hearts with only I- IVC. A retrospective analysis was performed of all fetuses with LAI and normal intracardiac anatomy from two tertiary cardiac units from January 2014 to January 2024. 41 fetuses were included. LAI was diagnosed in the fetus based on the abdominal situs. I-IVC was present in all cases. Gestational week (GW) at diagnosis was mean 24 GW (range 14-37). All fetuses were live born (mean 39 GW, range 36-42). 41 had fetal rhythm disorders, 12/41 (29.2%) postnatally. Polysplenia was present in 14/41 (34.1%), asplenia in 8/41 (19.5%) and a normal spleen was found in 13/41(31.7%). In 6 fetuses the spleen could not be defined. Malrotation was present in 14/41 (34.1%), of which 5 needed surgery after birth. Other extracardiac anomalies were present in 4 children (polydactyly in 2, duodenal atresia in 1, and a complex cerebral malformation in 1). Genetic testing was performed in 20/41 (48.7%), and showed a chromosomal anomaly in 2 and 17 normal results, one result is pending. 38 (92.6%) children were noted to be alive, with 2 lost to follow up and one still in utero. LAI with normal intracardiac anatomy and I-IVC is associated with a good postnatal outcome. Malrotation of the gut is prevalent and may require surgery. Rhythm disorders need to be monitored postnatally. Fetal counselling should focus on abdominal disorders and possible rhythm anomalies in the fetus and the child.