Normal Heart and Great Arteries

A cross-section of the upper abdomen demonstrates the stomach lying to the left of the fetus. The abdominal aorta lies anterior and to the left of the spine, with the inferior vena cava anterior and to the right of the aorta. Further, the correct horizonal plane demonstrates a circular shape of the thorax and one nearly complete rib.

The fetal heart is seen in a ‘back up’ four-chamber view, the least favourable fetal position. However, the four features (position, size, structure and function) of normality can be evaluated.

• The heart lies in the left thorax within its normal axis (about 45 degrees) occupying about one-third of the thorax.
• The atria, ventricles and atrioventricular valve orifices are of approximately equal size. The walls and septum are of approximately equal thickness.
• The moderator band, a marker of the morphological right ventricle, is a muscle bundle in the apex of the right ventricle.
• There is an intact interventricular septum and normal ‘off-setting’ of the atrioventricular valves.
• The foramen ovale occupies about one third of the atrial septum.
• The right and left pulmonary veins are seen connecting to the back of the left atrium on either side of the descending aorta on the 2D image.

Further sweep towards the fetal head reveals normal great artery connections. The aorta is arising first, just above the four- chamber view. The ventricular septum is in continuity with the aorta. The pulmonary artery, which arises anteriorly and crosses over the aorta, is close to the chest wall and is directed straight back towards the spine

Next, the three-vessel view and the transverse arch, the most superior arterial vessel, crossing the midline in front of the trachea from right to left is demonstrated.

Colour flow mapping demonstrates equal flow from the atria to the ventricles during ventricular diastole and forward flow in the great arteries, arterial duct and transverse arch in systole.