Introduction: Cross-sectional area of arterial vessels is proportional to the flow through them. To assess the relative distributions of cardiac output (CO) between the left and right ventricles in fetuses with CDH, neonates with diaphragmatic defects were evaluated for quantitative morphometric analysis of the size of the great arteries.

Methods: 2-D echocardiograms were performed within 24 hours of birth on 19 neonates with uncomplicated CDH (2 right, 17 left-sided), having severe pulmonary artery hypertension prior to cannulation for ECMO. Standard suprasternal notch and parasternal short-axis views were used to determine pulmonary valve (PV) and aortic valve (AV) diameters. The ratio of pulmonary valve (PV) to aortic valve (AV) cross-sectional area was determined as the ratio of squares, PV2/AV2. Left ventricular mass (LVM) and end systolic stroke volume were measured using area-length methods. Ten normal neonates were compared to the CDH study subjects. The Mann-Whitney-Wilcoxin Rank-sum test was used to compare medians between CDH v normals.

Results: In CDH infants compared to normal subjects respectively, AV diameter was smaller (median, range 5.1, 3.2-7.6 v 6.8, 5.5-8.8 mm, P<0.002) and PV diameter larger (7.9, 5.7-13.0 v 7.0, 5.1-8.0 mm, P=0.17). The ratio PV2/AV2 in CDH neonates was 1.73, 1.25-16.50 and 0.96, 0.79-1.69 in normals (P<0.0002). Median LVM was 2.1, 1.2-3.3 in CDH v 4.0, 3.4-5.5 gm/kg in normals (P<0.0001).

Conclusions: Severely low LVM in CDH infants corresponded with markedly increased PV2/AV2 ratio. This marked redistribution of fetal cardiac output toward the RV and away from the LV in utero may not be entirely explained by decreased pulmonary blood flow on the side of the hernia. We speculate that decreased pulmonary blood flow combined with altered left atrial hemodynamics causes major redistribution of cardiac output in the fetus with CDH.