Fetal Cardiac Abnormalities Detectable on Four Chamber View
Absent or small LV
(a) Hypoplastic LV- Often associated with atresias of the mitral and aortic valves. In these cases the heart appears almost to have a single ventricle and outflow tract, although detailed examination may reveal a rudimentary left ventricle and thready aorta.
(b) Mirtal atresia- Obstruction/atresia of the mitral valve may occur with an atretic aorta (hypoplastic LV) and with a double outlet RV. In hypoplastic LV syndrome, the aorta is narrow and LV small. The LV cavity may be impossible to demonstrate. In mitral atresia with a double outlet RV there is usually a VSD. The aorta and PA both arise from the RV in a parallel configuration.
(c) Aortic atresia- This may be a part of the hypoplastic left heart syndrome. The aorta is small or absent with a small LV. This is a relatively common condition occurring in up to 20% of cases of CHD detected antenatally. Blood enters the aorta via the ductus arteriosus and thus flow in the ascending aorta may be reversed on color flow Doppler.
Absent or small RV
(a) Hypoplastic RV- This may occur in isolation, or as part of a more complex defect.
(b) Pulmonary atresia- The pulmonary trunk is small or absent. If the ventricular septum is intact the right ventricle is hypertrophied. In early pregnancy
the RV may appear enlarged, but in late pregnancy the RV apps
small and hypoplastic. Pulmonary atresia may also occur with VSDs and more complex CHD.
(C) Tricuspid atresia- Atresia of the tricuspid valve results in a small RV, usually with a VSD. The position of the great arteries is variable and is a major prognostic factor.
Enlarged RV
(a)Tricuspid regurgitation- Regurgitation may be associated with an atretic tricuspid valve or may occur as a part of Ebstein’s anomaly.
(b) Pulmonary stenosis- This is likely to cause RV enlargement when the septum is intact.
(c) Coarcation of aorta- Sonographic features include dilatation of the RV and PA which feed the descending aorta via the ductus arteriosus. Narrowing of the aorta may be visible but is difficult to demonstrate.
Enlarged RA
(a)Ebstein's anomaly- Comprises prolapsed of the tricuspid vlave into the RV. Tricuspid regurgitation results in right atrial dilation. When RA dilatation is severe this will cause pulmonary hypoplasia, resulting in poor prognosis. Ultrasonography may also show RV dilatation.
(b) Tricuspid regurgitation
(c) Pulmonary stenosis- this causes RA dilatation when the septum is intact.
(d) Anomalous pulmonary drainage- Drainage is above the diaphragm in 90% of cases. Sonographic features include dilated RA and failure to show normal insertion of pulmonary veins.
Heart failure- This causes dilatation of the right heart chambers and secondary tricuspid regurgitation.
Absent crus
(a) AV canal/endocardial cushion defect- Common AV valve with large combined ASD/VSD. There may be associated conduction defects.
· VSDVSDs are the most common form of CHD found in childhood (20%), although only a quarter of these require surgery. The are not usually evident on antenatal sonography unless part of a complex cardiac malformation.
· Single ventricle- This anomaly is usually evident as atria draining into a solitary ventricle, which may mimic a right or left ventricle or represent an indeterminate/intermediate cavity.
· Anomalous pulmonary venous drainage- This may be total or partial. Abnormal connection of the pulmonary veins account for 2% of CHD. Abnormal pulmonary venous drainage is classified by the anatomy of the pulmonary venous drainage, which may be:
(1) supracardiac — usually to the left brachiocephalic veins or less often the SVC;
(2) cardiac — usually to the coronary sinus, occasionally to the right atrium;
(3) infracardiac — to the portal circulation, or the IVC;
(4) mixed — sonographic features include dilated right atrium and failure to show normal insertion of pulmonary veins.
· Common pulmonary vein atresia- CPVA is a rare condition in which
the pulmonary veins join a blind confluence. The latter has no gross connection either with an atrium or with a systemic vein. A midline
enlarged blood vessel may be indentified posterior to the heart at
the atrial level. It has been suggested that fetal cardiac failure
without cardiomegaly should raise the possibility of obstructed pulmonary venous return. Enlarged pulmonary veins are also seen in
cases of anomalous pulmonary venous drainage.
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