Asymmetry in Fetal Ventricular Size: Right Ventricle Larger than Left Ventricle
· Normal- Although the ventricles are usually the same size, in the later stages of pregnancy the right ventricle may be slightly larger than the left.
· Coarctation of the aorta-This may range from a minor stenosis to a severe long atresia. It accounts for 10% of CHD, but only the most severe forms are detected in utero. US features: dilatation of the right ventricle and the pulmonary artery. The aortic lesion is occasionally visible. Coarctation of the aorta is associated with Turner’s syndrome, cystic hygroma and fetal hydrops.
· Hypoplastic left heart- This is often associated with atresias of mitral and aortic valves. The left ventricle is rudimentary and may be difficult to see. The appearances are those of almost a single ventricle and outflow tract.
· Fallot's tetralogy- The aorta is transposed to the right and overlies the ventricular septum. As the aorta overlies the interventricular septum, a VSD is effectively present. Associated features include dextroposition of the aorta, VSD, pulmonary stenosis and right ventricular hypertrophy.
· Dysrhythmias- SVT or atrial flutter may result in dilatation of all four chambers or ventricular disproportion. RV enlargement has also been noted with frequent atrial ectopy in the absence of observed tachycardia.
· Constriciton of occlusion of the ductus arteriosus- May cause RV, right atrium and systemic vein dilatation.
· Ventricular dysfunction- RV dysfunction, whatever the cause, may lead to dilatation. Such dysfunction may cause overall cardiac enlargement and secondary tricuspid incompetence.
· Tricuspid regurgitation- RV dilatation in tricuspid regurgitation is related to volume overload. Tricuspid regurgitation may be related to twin—twin transfusion syndrome, RV dysfunction, Ebstein’s anomaly, cardiomyopathies, anemia, etc.
· IUGR- A sizeable proportion of IUGR fetuses has a right ventricle larger than the left.
· Left sided obstructive lesions- Besides coarctation of the aorta and hypoplastic left heart syndrome, mitral stenosis, aortic stenosis/atresia and aortic arch hypoplasia may have a similar effect on ventricular size.
Miscellaneous conditions- These include parachute mitral valves, some forms of double outlet right ventricle and atrioventricular canal.
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