Current Status

Most infants born with serious congenital heart disease undergo rapid evaluation and life-saving treatment. Most fetuses with significant cardiac malformations, however, are not diagnosed prenatally. Those not diagnosed prenatally cannot receive state-of-the-art fetal cardiology evaluation and treatment, a situation tantamount to sending a cyanotic newborn home without the benefit of currently available diagnostic and treatment methods.

Cardiac malformations are the most frequent anomalies of human development. Cardiac defects occur in about 8/1000 live births. Among congenital abnormalities tabulated in the United States, cardiac malformations are the number one cause of death. Even today, 1 out of 10 infants dying from congenital heart disease do so without diagnosis until autopsy, a sobering fact that universal fetal cardiac evaluation could alter. Nonetheless, fetal cardiac evaluations are currently limited to those women who are referred because of risk factors for fetal heart disease (Table 16-1). Studies, however, show that most newborns with congenital heart disease are born to women without risk factors¹; hence, most infants with congenital heart disease are not diagnosed prenatally.

The first reports on the use of ultrasound to evaluate the fetal heart appeared in the 1960s and 1970s. The work by Kleinman and colleagues, first published in 1988,² marked the beginning of modern fetal echocardiography and the birth of fetal cardiology as a new super specialty of pediatric cardiology. Thus, prenatal cardiac diagnosis has been possible for over 30 years. With today’s clinical knowledge and technical advancements, the prenatal diagnosis of serious congenital heart diseases by fetal echocardiogram approaches 100%. Because of limitations placed on the use of fetal cardiac evaluation, these advancements have not improved the general prenatal detection of serious cardiac abnormalities.³

Most pregnant women undergo only a general obstetric ultrasound which, following the joint recommendations by the American Institute of Ultrasound in Medicine, the American College of Radiology, and the American College of Obstetrics and Gynecologists, includes a limited evaluation of the 4 chambers of the heart, and if possible, a view of the outflows.⁴ By following these current strategies, we and other investigators have shown that ⅔ of fetuses with serious congenital heart diseases remain undiagnosed.^3,5 Primarily for financial reasons, most fetuses still do not undergo a useful cardiac evaluation.

Screening Fetal Echocardiogram

We have previously proposed universal screening fetal-cardiac evaluation as the best method for detecting serious cardiac malformations prenatally.³ In our opinion, a screening fetal echocardiogram, as proposed by Yagel and colleagues,⁶ should replace the current four-chamber view strategy. The screening evaluation includes five axial slices of the fetal abdomen and chest obtained by sliding the transducer cephalad beginning from the upper abdomen view (Figure 16-1). The five axial slices include (1) upper abdomen to evaluate abdominal situs (Figure 16-1A); (2) four-chamber view to evaluate cardiac chambers, atrial septum, ventricular septum, and atrioventricular valves (Figure 16-1B); (3) left outflow (Figure 16-1C); (4) right outflow (Figure 16-1D); and (5) the three-vessel trachea view (Figure 16-1E). A more detailed fetal echocardiogram than these five axial views is reserved for patients with risk factors, and those with clear or suspected abnormalities noted in screening fetal echocardiograms. Experienced specialists should perform the detailed fetal echocardiographic studies.

Normal Screening Fetal Echocardiogram

The description of normal findings in the screening fetal echocardiogram’s slices are as follows. Deviations from normalcy require further evaluation by detailed fetal echocardiographic study.

1. Upper Abdomen

The upper abdomen slice evaluates the abdominal situs (Figure 16-2). In the normal situs solitus, the stomach is on the left side of the abdomen, the descending aorta is to the left of the spine, the inferior vena cava is anterior and to the right of the aorta, and the umbilical vein turns toward the right into the portal sinus; when visible, the gallbladder is to the right of the umbilical vein.

2. Four-chamber View

The four-chamber view is obtained from a transverse slice of the fetal chest slightly above the upper abdomen. Before concentrating on the intracardiac anatomy, the examiner should pay attention to the position of the heart within the chest, the cardiac axis, the cardiac size, and the structures surrounding the heart.

Cardiac position.

The heart is normally positioned toward the left chest, and in the four-chamber view, the left lung usually appears slightly smaller than the right (Figure 16-3). The right ventricular free wall is in contact with the anterior chest wall (Figure 16-3 and Figure and Video 16-7). Mass effect on either side of the chest, from diaphragmatic hernias, tumors, or pleural effusions, may deviate the heart toward the contralateral chest side (Figure 16-4). Mass impingement on cardiovascular structures may significantly affect hemodynamics and cause hydrops.

Cardiac axis.

The normal angle between the ventricular septum and the midline of the chest is about 45° (Figure 16-5). Extreme levocardia with angles above 50° (Figure 16-5) and dextrocardia are associated with increased incidence of congenital heart disease.

Cardiac size.

The normal cardiac area is about 1/3 of the chest area (Figure 16-6). Modern ultrasound equipment software facilitates measurements of heart and chest areas to calculate the cardiac/thoracic ratio. Area cardiothoracic ratios above 35% indicate cardiomegaly.

Structures surrounding the heart.

The descending aorta is anterior and to the left of the spine, and the left atrium is anterior to the descending aorta (Figure and Video 16-7). The echogenicity of the lungs is homogeneous. Areas of significant increased or decreased echogenicity may represent masses and deserve careful evaluation (Figure 16-8).Areas of absent echogenicity indicate the presence of abdominal viscera within the chest, cysts, or effusions.

The cardiac four-chamber view.

The four-chamber shows the two atria, two ventricles, two atrioventricular valves, and atrial and ventricular septae (Figure 16-9).

Both atria are about the same size. The atrial septum contains the foramen ovale. The foramen ovale flap normally opens toward the left atrium; the foramen ovale flap excursion is normally 50% of the left atrial width or less. Exaggerated foramen ovale flap excursion, also known as atrial septal aneurysm or foramen ovale aneurysm, is associated with fetal arrhythmias, congenital heart diseases, and increased incidence of postnatal atrial septal defects.^7–9 The normal tricuspid valve is slightly closer to the apex than the mitral valve. Both ventricles are about the same size, but the right ventricle contains the moderator band (Figure 16-9). Large ventricular septaldefects are seen with twodimensional (2D) imaging (Figure 16-10). Smaller defects are visualized only with the help of color Doppler.

3. Left Outflow

Angling cephalad from the four-chamber view the aorta appears exiting the left ventricle. The anterior wall of the aorta is in continuity with the interventricular septum. The aortic valve is seen opening and closing between the left ventricle and the ascending aorta (Figure and Video 16-11).

4. Right Outflow

The right ventricular outflow lies immediately cephalad to the left outflow. The right outflow is usually seen together with the ascending aorta and the superior vena cava (Figure 16-12). The ascending aorta is immediately to the right of the right outflow, and the superior vena cava is just to the right of the ascending aorta. Increased distance between the ascending aorta and the superior vena cava in the three-vessel view may indicate the presence of a right diaphragmatic hernia¹⁰ (Figure 16-13).