Prenatal Imaging and Therapy of Congenital Heart Disease

Visceral/Atrial Situs and Cardiac Position

Proper identification of situs at the beginning of a fetal echocardiogram is of paramount importance for framing the rest of the examination. The positions of the viscera within the abdomen and the heart within the thorax should be identified. In normal abdominal situs, the liver is right-sided and the stomach is left-sided. The normal position of the heart within the thorax is on the left (levocardia); additional possibilities are dextrocardia and mesocardia, wherein the majority of the cardiac mass is rightward or midline, respectively. The direction of the cardiac apex should also be identified. The apex normally points leftward, but rightward or posterior-anterior orientations are possible.

Once abdominal situs and cardiac position have been determined, delineation of atrial morphology should follow ( Fig. 70.1 ). The right atrium receives the coronary sinus and inferior vena cava, and its appendage is broad-based and triangular. The left atrium is characterized by the presence of septum primum, the “valve” of the foramen ovale and its appendage, which is slender and finger-like. The pulmonary veins usually connect to the left atrium, but there is significant variability of the pulmonary venous connections in CHD. Although “right” and “left” atria are typically in their usual right- and left-sided locations respectively, it is important to note that they may be inverted or ambiguous in nature.

Right and Left Ventricles

The right and left ventricles should be identified by their distinguishing morphologic features. The right ventricle has a moderator band, attachments of its atrioventricular (tricuspid) valve to the ventricular septum (septophilic), an atrioventricular valve annulus apical to its left ventricular counterpart, and coarse trabeculations. The left ventricle, in contrast, has an atrioventricular (mitral) valve without attachments to the septum (septophobic), and appears smooth due to its fine trabeculations (see Fig. 70.1 ). As with the atria, although “right” and “left” ventricles are typically in their usual right- and left-sided locations, it is critical to note that other anatomic arrangements are possible, and ventricles may be left-right inverted (ventricular inversion) and, rarely, may assume a superior-inferior relationship. Ventricular function may be qualitatively assessed in both a four-chamber transverse view and a short-axis view. Calculation of left ventricular shortening fraction (left ventricular end diastolic—systolic/end diastolic diameter) and ejection fraction (left ventricular end diastolic—systolic/end diastolic volume) is possible with meticulous attention to imaging technique and precise measurements.

Atrioventricular and Semilunar Valves

The tricuspid and pulmonary valve annuli measure slightly larger than the mitral and aortic valves. Valves should be measured when they are maximally open: in diastole for the atrioventricular valves and systole for the semilunar valves. Significant size discrepancy between the two semilunar and/or atrioventricular valves should prompt careful evaluation for CHD. The mitral valve should be supported by two well-spaced ventricular papillary muscles easily identifiable on short-axis imaging. Color Doppler should readily identify any atrioventricular or semilunar valve regurgitation. Pulsed-wave Doppler assessment of all valves should be performed. Both atrioventricular valves should have biphasic flow patterns, and both semilunar valves should have a brisk upstroke with a narrow spectrum of normal velocities and no aliasing or increased velocity to suggest stenosis.

Aorta, Pulmonary Artery, and the Aortic and Ductal Arches

The relationship of the aorta and pulmonary outflow to the ventricles should be determined. The aorta and pulmonary artery arise from the left and right ventricles, respectively, and should cross over one another. Any relationship where the great vessels do not cross should prompt consideration of transposed great arteries and significant CHD.

The aortic arch, main and branch pulmonary arteries, and ductal arch should be assessed in multiple planes. In addition to the sagittal view, where the entirety of the aortic and ductal arches can be assessed, the three-vessel trachea view is particularly useful in assessing location, size, and flow pattern of the aortic and ductal arches. Arch sidedness can be determined from the three-vessel view; the usual arrangement being the aorta and ductus arteriosus coursing to the left as they pass in front of the trachea ( Fig. 70.2 ). Additionally, the three-vessel-trachea view is of particular utility in diagnosing aortic arch hypoplasia and/or ductus arteriosus abnormalities.