40 percent of those with major cardiac anomalies before 22 weeks' gestation, and specialized sonography may identiy 80 percent (Romosan, 2009; Trivedi, 2012). For selected anoma lies, prenatal detection may improve neonatal survival. his requiring prostaglandin infusion after birth to keep the duc tus arteriosus open (Franklin, 2002; Mahle, 2001; Tworetzky, 2001).
Standard cardiac assessment includes a four-chamber view, evaluation of rate and rhythm, and evaluation of the left and right ventricular outlow tracts (Figs. 10-27 and 10-28A-C).
Examination of the cardiac outflow tracts aids detection of abnormalities that might not be appreciated in the four-cham ber view. hese include tetralogy of Fallot, transposition of the great vessels, and truncus arteriosus.
heour-chamber view is a transverse image of the fetal tho rax at a level immediately above the diaphragm. It allows evalu ation of cardiac size, position in the thorax, cardiac axis, atria and ventricles, foramen ovale, atrial septum primum, interven tricular septum, and atrioventricular valves (see Fig. 10-27).
he atria and ventricles should be similar in size, and the apex of the heart should form a 45-degree angle with the left anterior chest wall. Abnormalities of cardiac axis are frequently encoun tered with structural cardiac anomalies and occur in more than a third (Shipp, 1995).
The lt ventricular oulow tract view is a transverse image just above the diaphragm and demonstrates that the ascending aorta arises entirely from the left ventricle. The inteventricular septum is shown to be in continuity with the anterior wall of the aorta, and the mitral valve in continuity with the posterior wall of the aorta (see Fig. 10-28B). Ventricular septal defects and outflow tract abnormalities are often visible in this view (Fig. 10-29).
The right ventricular oulow tract view shows the right ventricle giving rise to the pulmonary artery (see Fig. 10-28C). Together, the left and right outflow tract views demonstrate the normal perpendicular orientation of the aorta and pulmonary artery, and the comparable size of these great arteries. Structures visible in the right ventricular outlow tract view include the right ventricle and the main pulmonary artery, which subsequently branches into the right and left pulmonary arteries. hese structures are also visible in the short axis view, shown in Figure 10-28E.
This is a specialized examination of fetal cardiac structure and function designed to identiy and characterize abnormalities. Guidelines for its performance have been developed collaboratively by the American Institute of Ultrasound in Medicine,
FIGURE 10-27 The four-chamber view. A. Diagram demonstrat ing measurement of the cardiac axis from the four-chamber view of the fetal heart. B. Sonogram of the four-chamber view at 22 weeks' gestation shows the normal symmetry of the atria and ventricles, normal position of the mitral and triscuspid valves, pulmonary veins entering the left atrium, and descending aorta (Ao). L = left; LA = left atrium; LV = left ventricle; R = right; RA = right atrium; RV = right ventricle.