Examination of the fetal heart: making a diagnosis and avoiding pitfalls

Great Arteries The third and forth scanning planes demonstrate the ventriculo-arterial connection. A careful assessment of this is important to differentiate conditions such as simple transposition of the great arteries (TGA) or double outlet right ventricle (DORV). DORV describes the ventriculo-arterial connection in a spectrum of malformations ranging from association with Tetralogy of Fallot to those with absent AV connection (mitral or tricuspid atresia) and outflow tract stenosis of one great artery (Fig. 3 and Fig. 5). Cases with overriding aorta may be differentiated from each other by determining, first, whether there are two semilunar valves or one. Common arterial trunk is characterized by a solitary outlet from the ventricle from which the pulmonary arteries arise, usually in a posterior position (Fig. 5.3, shown on right). However, it can be difficult to differentiate this from pulmonary atresia with ventricular septal defect (VSD), where there may be long segment muscular pulmonary atresia, and no communication between the pulmonary vasculature and the ventricular mass. Sagittal views will help to assess the relationship of the great arteries and colour flow mapping will differentiate these conditions as it will be pro-grade in common arterial trunk (Fig. 5.3, see above) and reversed in pulmonary atresia with ventricular septal defect (Fig. 6.6, shown below right). Velocities are often increased or show high volume flow in the branch pulmonary arteries in common arterial trunk, unlike pulmonary atresia with VSD where pulmonary flow is reduced. Pitfalls Sub-optimal imaging may make assessment of the ventriculo-arterial connections difficult in transverse views. Longitudinal or sagittal views of the fetus may help assess connections and arterial relationships. The great arteries can be examined using colour Doppler and the relative position and direction of flow in the arches compared (Fig. 6.5 and 6.6, see right). Colour Doppler of the single visible outlet valve may also help determine whether the diagnosis is common arterial trunk or pulmonary atresia with VSD. In the former, there may be stenosis and regurgitation, but this is unusual in the normal aorta in pulmonary atresia VSD. Flow is pro-grade directly from the Trunk into the pulmonary arteries in common arterial trunk.

Arch Abnormalities

The fifth scanning plane shows the three vessel and trachea view. In the normal heart this comprises a left sided transverse aortic arch and duct with the right superior caval vein (SVC) seen near the trachea (Fig. 1). In some CHD, the three-vessel view may show only one transverse arch, for example, in simple transposition of the great arteries or Tetralogy of Fallot, even though both arches are present. This is because of the superior-inferior relationship of the vessels and both arches can be visualized by adjusting the scanning angle in this plane (Fig. 6.1, see right). Additional vessels may be identified: if there is a persistent left SVC it can be seen lying anterior and leftward of the duct and a bridging vein to the right SVC may be noted (Fig. 6.2).

If a persistent left SVC is seen in association with ventricular disproportion, coarctation of the aorta should be suspected. ⁸ An aberrant right subclavian artery arising from the isthmus in a normal left-sided arch may be associated with fetal Trisomy 21. ⁹ A right aortic arch may be a normal variant, but a right arch with mirror-imaged branching is associated with CHD in more than 80% cases. ¹⁰ The combination of a right aortic arch and left duct or the origin of a left duct from left pulmonary artery may form the substrate for a postnatal vascular ring (Fig. 6.3, shown left). The affected neonate may present with stridor and require surgical relief of tracheal compression.

Pitfalls

The three-vessel view may show only one transverse arch when two are present (e.g. in TGA or Tetralogy of Fallot). This is usually due to their ‘superior-inferior’ relationship or sometimes to a marked difference in size, such as in Hypoplastic Left Heart Syndrome (Fig. 6.5). A right arch and left duct may be confused sonographically with a double aortic arch in the fetus, but in this instance an additional vessel, the arterial duct, should be visible either to the right or the left of the trachea (Fig. 6.4).

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Introduction & Cardiac Position | Four Chambers & Septal Defects | Great Arteries & Arch Abnormalities | Figures | References & Glossary || heart conditions | heart sketch

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