Left ventricular obstruction with restrictive inter-atrial communication leads to retardation in fetal lung maturation.

Objective: Intact atrial septum or highly restrictive inter-atrial communication (I/HRAS) combined with either severe aortic stenosis (SAS) or hypoplastic left heart syndrome (HLHS), respectively, is associated with adverse outcome. This study focusses on changes in alveolo-septal lung parenchyma due to increased left atrial pressure.

Method: In a retrospective cross-sectional autoptic study, we investigated fetal/neonatal lung specimens of 18 patients with SAS/HLHS with I/HRAS, 11 patients with SAS/HLHS and unrestrictive inter-atrial communications and 18 controls. Pulmonary maturation was investigated by means of morphometric and immunohistochemical analyses.

Results: In a comparison of all three groups, alveolo-capillary membrane maturation was significantly disturbed in I/HRAS fetuses from week 23 of pregnancy on. I/HRAS lungs showed angiomatoid hyper-capillarisation and significantly wider inter-airspace mesenchyme. Differences in width ranged between 34.58 µm (95% CI: 11.41-57.75 µm) and 46.74 µm (95% CI: 13.97-79.50 µm) in the second and third trimesters. In I/HRAS infants with HLHS, inter-airspace mesenchymal diameters steadily normalised with age; however, significant fibroelastosis of alveolar septae developed.

Conclusion: Fetal lung maturation with respect to alveolo-capillary membrane formation is severely disordered in patients with SAS/HLHS with I/HRAS. Our findings indicate that, from a morphological point of view, timing of fetal invention in fetuses with I/HRAS should be fixed within the second trimester of pregnancy.