Fetal Aortic and Pulmonary Outflow Screening
Most major malformations of the feral heart may be identified on a four chamber view; however, abnormalities of the outflow tract can easily be missed. The incorporation of outflow tract screening will enhance the sensitivity of diagnosis of anomalies that may be difficult to identify on a four chamber view.
Small Pulmonary Outflow tract
(a) Tetraolgy of fallot- A large aorta may be the first clue to diagnosis of Fallot’s tetralogy. M-mode echocardiography is useful in quantitating the aortic diameter. Doppler may identify a stenotic pulmonary valve as well as showing increased flow through the aorta. The VSD may be difficult to identify on a four chamber view.
(b) Pulmonary atresia- The pulmonary trunk is small or
absent and may be difficult to visualize on sonography. It is small in
comparison to the aortic root, and may be abnormally sited. If the
ventricular septum is intact the RV is hypertrophied. In early pregnancy the RV may appear enlarged but in late pregnancy the RV
appears hypoplastic.
(c) Truncus arteriosus- TA is identical in many respects to TF, the only distinguishing feature being that the pulmonary outflow tract is not identified arising from the RV.
Small Aortic Root
(a) Aortic atresia- The aorta is small or absent. The LV is also small. Blood enters the aorta via the ductus arteriosus and thus flow in the ascending aorta may be reversed on color flow Doppler imaging.
(b) Coaractation of the aorta- The aorta appears to be almost half the size of the dilated pulmonary artery. There is right ventricular and right atrial dilatation. Mmode echocardiography may reveal the aortic root diameter at or below the 5th percentile.
