Fetal Cardiac Malformations and Arrhythmias: Detection, Diagnosis, Management, and Prognosis

Extracardiac Evaluation

Prenatal screening for CHD should include an evaluation for extracardiac abnormalities associated with CHD. The umbilical cord should have three vessels, the heart and stomach should both be on the fetal left (above and below the diaphragm, respectively), and there should be no ascites ( Fig. 23.1 ) or pericardial or pleural effusions. A trivial amount (up to 2 mm) of pericardial fluid may normally be seen adjacent to the right and left ventricular free walls. Abnormalities of any of these findings should raise the level of suspicion for CHD and prompt more than just a routine evaluation. Before moving to the thorax, evaluation of the fetal abdomen should demonstrate, at a minimum, the stomach on the left and an absence of ascites. More thorough evaluation of the abdomen is recommended even in low-risk pregnancies but is required in high-risk pregnancies (see Visceroatrial Situs, later).

Beating Four-Chamber View

The 4CV ( Figs. 23.2 and 23.3 ; see Video 23.1 ) deserves a close, detailed evaluation, even as part of a general screening fetal ultrasound study. Evaluation of the beating 4CV should assess situs, size, symmetry, structure, and squeeze.

Outflow Tracts

Prenatal screening for CHD should include visualization of both outflow tracts ( Video 23.3, Video 23.4 ; see Video 23.2 ). In practice, appropriate evaluation of the outflow tracts may be more challenging than visualization of the 4CV, in part because, unlike the 4CV, the outflow tracts do not lie in a single plane. Nevertheless, because the outflow tract views are part of many critical forms of CHD not visualized with the 4CV, evaluation of both outflow tracts in all pregnancies has appropriately become standard of care throughout much of the developed world. Like imaging of the 4CV, imaging of the outflow tracts requires multiple views and angles for a thorough evaluation.

After obtaining the 4CV relatively perpendicular to the ventricular septum, slight angulation of the transducer cephalad from the 4CV should demonstrate the aortic valve and ascending aorta arising from the left ventricle ( Figs. 23.4 and 23.5 ; see Video 23.2, Video 25.3 ). The aortic valve should appear thin, symmetric, and delicate, disappearing during systole. The ventricular septum should extend, uninterrupted, from the cardiac apex all the way to the anterior aspect of the ascending aorta. The inlet ventricular septum is not seen with this view. The ascending aorta should point toward the right of the spine. The ascending aorta should be followed up toward the beginning of the aortic arch to rule out posteriorly directed bifurcation (a possible sign of TGA).

With just slightly further cephalic angulation of the transducer, the right ventricular outflow tract (RVOT) (pulmonary valve and pulmonary artery) can be visualized arising from the right ventricle and crossing the aortic root ( Figs. 23.6 and 23.7 ; Video 23.5 ). The pulmonary valve should be thin, symmetric, and delicate, also disappearing during systole, and the pulmonary valve and main pulmonary artery should be slightly larger than the aortic valve and aortic root. The main pulmonary artery should point to the left of the spine. Evaluation of the aortic and pulmonary valves should be included as part of the outflow tract evaluation.

Although current US guidelines for fetal cardiac screening do not require the use of color flow Doppler or inclusion of the three-vessel tracheal view in low risk-pregnancies, ^, the use of both can dramatically increase detection rates for CHD. The three-vessel view is discussed in detail in the following section, and its use even in low-risk pregnancies is strongly encouraged. Likewise, cine-loop clips can be helpful, even for low-risk pregnancies (included in 2013 in the International Society of Ultrasound in Obstetrics and Gynecology [ISUOG] practice guidelines but not in 2018 by the American Institute of Ultrasound in Medicine [AIUM] practice guidelines). Sweeps to show the relationship of one portion of the fetal heart to the next, as recommended for high-risk pregnancies in the 2014 scientific statement issued by the American Heart Association, should be strongly considered for low-risk pregnancies as well.

Venous Drainage

Although evaluation of systemic and pulmonary venous drainage may be accomplished with 2D imaging alone, color flow imaging helps to confirm the anatomy and to demonstrate areas of obstruction, and spectral Doppler may help to assess cardiovascular status still further. ^{, ,} With slight inferior angulation or tilting of the transducer from the 4CV, the coronary sinus should be seen coursing from left to right just above the mitral groove ( Fig. 23.14 ). At the level of the 4CV the coronary sinus sometimes may be seen in cross section laterally, adjacent to the left atrial free wall just above the mitral annulus. However, enlargement of the coronary sinus ( Fig. 23.15 ) should prompt evaluation for either a left-sided superior vena cava (LSVC) ( Fig. 23.16 ) or anomalous pulmonary venous drainage into the coronary sinus. All four pulmonary veins may be seen, but such visualization can be time consuming and challenging; therefore visualization by color flow Doppler of even one or two pulmonary veins ( Figs. 23.17 and 23.18 ; see Fig. 23.3 ) draining normally to the left atrium is generally sufficient in the absence of suspected disease ( note: the presence of mesocardia/dextrocardia may be associated with partial anomalous pulmonary venous return [PAPVR] in the context of scimitar syndrome). The presence of a ridge of tissue (normal pericardial reflection or infolding of tissue between the left atrial appendage and left pulmonary vein) extending a short distance medially from the posterior and lateral aspect of the left atrium helps to rule out TAPVR, and an increased distance or the presence of a vascular structure between the descending aorta and the left atrium (twig sign) raises suspicion for TAPVR. ^, Color flow imaging should be performed to confirm normal, unobstructed pulmonary venous return to the left atrium. Spectral Doppler analysis may be useful if color Doppler suggests pathology. Structural abnormalities of pulmonary or systemic venous return raise the possibility of heterotaxy. ^{, ,}

Atrial Septum

Because the foramen ovale normally shunts oxygenated blood from the right atrium to the left atrium, the flap of the foramen ovale should be deviated toward the left atrium. Although this flap typically moves back and forth during the cardiac cycle, the dominant position should be leftward (see Fig. 23.2 ). The flap itself should occupy a central position in the atrial septum, and it should extend increasingly farther into the left atrium with advancing gestational age. Both the superior and inferior aspects of the atrial septum should appear intact, although the superior rim may not always be seen with routine screening. Occasionally when dilated the coronary sinus (seen longitudinally) may generate the appearance of an absent inferior portion of the atrial septum ( Fig. 23.19 ). For this reason, if this portion of the atrial septum appears deficient, care must be taken to confirm that the image plane has not simply been directed too far posteriorly and inferiorly from the 4CV.

Atrioventricular Valves

The atrioventricular valve morphology and function should be evaluated, along with the rest of the heart, during real-time motion. Both valves may be evaluated in their entirety from the 4CV (see Figs. 23.2 and 23.3 ), although visualization from other views may be useful, particularly if abnormalities are present or suspected. The tricuspid valve annulus should be the same size as or slightly larger than the mitral annulus. The leaflets should appear thin and delicate, with unrestricted diastolic excursion into their respective ventricles. A subtle abnormality of either valve early in the second trimester may progress to a severe abnormality, or even to hypoplastic right or left heart syndrome, at term. The septal leaflet of the tricuspid valve should insert slightly more apically onto the ventricular septum than the septal leaflet of the mitral valve. The papillary muscles of the tricuspid valve should have attachments to the ventricular septum and the right ventricular free wall. In contrast, the papillary muscles of the mitral valve should have no attachments to the ventricular septum. Whereas evaluation of the crux of the heart should include imaging perpendicular to the ventricular septum, evaluation of the atrioventricular valves should always include color flow imaging parallel to the septum to assess for diastolic turbulence or valvar regurgitation. A trace amount of early systolic tricuspid regurgitation may be normal, although previously many investigators considered any prenatal tricuspid regurgitation to be abnormal. Prenatal regurgitation of any other valve is generally considered abnormal. Fetuses with trisomy may have an increased incidence of tricuspid regurgitation, even in the presence of a structurally normal heart. Measurement of tricuspid and mitral valve annulus size and spectral Doppler evaluation of inflow patterns ^, should be performed if an abnormality is suspected and are called for routinely in the AIUM practice parameter.

Ventricles

The structure and function of both ventricles should be evaluated in detail. The 4CV provides the single best perspective to evaluate ventricular structure (see Figs. 23.2 and 23.3 ). Both ventricles should extend to the cardiac apex, and both should squeeze symmetrically during systole. The left ventricle should be smooth walled, aligned with the mitral valve, and located leftward and posterior to the right ventricle. The right ventricle should be more heavily trabeculated and should have a moderator band that crosses it near the apex; it should be aligned with the tricuspid valve and located rightward and anterior to the left ventricle. The right ventricle should be equal in size to or, more commonly, slightly larger than the left ventricle, and the right heart predominance increases normally with advancing gestational age. Right heart disproportion ( Fig. 23.20 ) has been associated with trisomy 21. Quantitative assessment of ventricular systolic and diastolic function ^{, , , ,} is called for routinely in the AIUM practice parameter. Additionally, close attention to ventricular systolic function should always be made qualitatively and from multiple views, including the 4CV and the basal short-axis view (obtained from a sagittal fetal orientation) ( Video 23.6 ). Ventricular dysfunction may be isolated and primary, or it may be associated with structural heart disease.

In the absence of related structural/functional pathology, the presence of small, circumscribed, echogenic densities, foci, or reflectors in the chordal apparatus of the mitral valve (or, less commonly, the tricuspid valve) should be considered benign normal variants ( Fig. 23.21 ). If doubt exists regarding the diagnosis, further evaluation should be performed to rule out CHD. Such echogenic foci appear to be more prevalent among fetuses with aneuploidy than among those with normal chromosomes. An important but sometimes subtle distinction should be made between these echogenic reflectors and a more diffuse echogenicity along the mitral and tricuspid valve annuli, throughout the supportive apparatus of the mitral and tricuspid valves, and occasionally more generally in other aspects of the endocardium ( Fig. 23.22 ); this unusual manifestation of fibroelastosis can represent damage related to maternal anti–SS-A/SS-B antibodies.

Ventricular Septum

The ventricular septum should be evaluated for thickness, motion, and the presence of a VSD. The ventricular septum should be roughly the same thickness as the left ventricular posterior free wall, and it should contract symmetrically with the left ventricular free wall. Ventricular septal thickness may be evaluated from the 4CV and the basal short-axis view. In cases of suspected septal hypertrophy the septal thickness should be measured, typically during both diastole and systole. The entirety of the ventricular septum then needs to be evaluated for VSDs. Using multiple views and multiple sweeps, 2D imaging should be performed to identify any defect in any portion of the ventricular septum. To avoid false-positive dropout in the inlet and membranous or outlet portions of the ventricular septum, the 2D imaging should be performed relatively perpendicular to the ventricular septum and with the transducer angled slowly from the 4CV into the left ventricular long-axis view (see Figs. 23.4 and 23.5 and Video 23.3 ). Color flow imaging should also always be performed in search of VSDs ( Fig. 23.23 ), using the same perpendicular orientations and sweeps; some defects may not be visualized with 2D imaging alone. On the other hand, some defects, particularly before 18 to 20 weeks’ gestation, may be evident with 2D imaging but have no visible shunting with color flow evaluation.

Semilunar Valves

The semilunar (aortic and pulmonary) valves should be evaluated with at least as much attention to anatomy and function as is given to the evaluation of the atrioventricular valves. Consistent with the right-sided predominance seen at the levels of the atrium, atrioventricular valve, and ventricle, the pulmonary valve annulus should be equal in size to or, more commonly, slightly larger than the aortic valve annulus. The aortic valve can be best visualized with a left ventricular long-axis view (see Fig. 23.5 ), which is obtained with slight anterior/superior angulation from the 4CV. In addition, ideally the probe can be rotated slightly from a transverse cut toward a partially sagittal plane. The aortic valve may be evaluated further with a basal short-axis view, which is obtained from a sagittal orientation of the fetus. The pulmonary valve (RVOT crossing view; see Fig. 23.7 ) may be evaluated with slight anterior/superior angulation from the left ventricular long-axis view. In addition, the pulmonary valve may be evaluated further with a basal short-axis view (see Video 23.4 ). The aortic valve should arise from the anterior aspect of the left ventricle and the pulmonary valve from the anterior aspect of the right ventricle. Both aortic and pulmonary valves should be thin and delicate, with unrestricted excursion during systole, resulting in the valve practically disappearing when fully open (see Fig. 23.5 ). During diastole the aortic and pulmonary valves should appear as central points or symmetric, thin plates. The aortic valve during diastole should appear on the left ventricular long-axis view as a thin, central plate, commonly parallel to the axis of the aortic root. The pulmonary valve during diastole, in contrast, should appear on the basal short-axis view as a thin plate but perpendicular to the axis of the main pulmonary artery. A subtle abnormality of either valve ( Figs. 23.24 and 23.25 and Video 23.7 ; see Video 23.5 ) during the early second trimester may progress to a significant valve abnormality, or rarely even to HLHS or HRHS, at term. Measurement of aortic or pulmonary valve annulus size and evaluation of the systolic Doppler flow profile are called for routinely in the AIUM practice parameter. Evaluation of aortic and pulmonary valves should also include color flow imaging to assess for aortic or pulmonary ( Fig. 23.26 ) regurgitation (always abnormal) or systolic turbulence ( Fig. 23.27 ) suggestive of increased flow volume or anatomic obstruction.

Great Arteries and Ductal and Aortic Arches

The ascending aorta (aortic root) and main pulmonary artery should arise from the left and right ventricles, respectively, and then cross at an angle of roughly 45 to 90 degrees. Demonstration of great artery crossing represents an important finding on the normal fetal echocardiogram. This crossing can be seen either with transverse imaging (slight anterior/superior angulation from the 4CV to left ventricular long-axis view to RVOT crossing view; see Video 23.2 ) or with sagittal imaging (slight leftward angulation from sagittal aortic arch view to ductal arch view; Video 23.8 ). In general the aortic root should point to the right of the spine (see Fig. 23.5 ), and the main pulmonary artery should point to the left of the spine (see Fig. 23.7 ). The use of a sweep, from the 4CV to the three-vessel tracheal view, can be a powerful way to rule out TGA. As with other right-left ratios in the fetal heart, the main pulmonary artery should be equal in size to or, more commonly, slightly larger than the aortic root. The ductal arch and basal short-axis views ( Figs. 23.28–23.30 ) should demonstrate the trifurcation of the main pulmonary artery into the right pulmonary artery (which wraps around the aorta in the basal short-axis view), the left pulmonary artery (which extends more posteriorly than the right pulmonary artery), and the ductus arteriosus (the largest of the three branches). The left pulmonary artery may be difficult to demonstrate, given its unusual course and easy overlapping/confusion with the ductal arch. Demonstration of the main pulmonary artery bifurcating is not adequate; both pulmonary artery branches along with the ductus must be clearly delineated. In some cases, bifurcation of the pulmonary artery into right and left branches may be best seen at the level of the three-vessel view; in other cases, the branch pulmonary arteries may be best visualized with sagittal imaging. Measurements of the pulmonary valve diameter and peak velocities in the vessels are called for routinely in the AIUM practice parameter.

In cases of suspected pathology, the branch pulmonary arteries should be measured and their Doppler flow profiles obtained. For example, fetal pulmonary artery diameter may correlate with outcome in cases of congenital diaphragmatic hernia. In cases of suspected ductal constriction (i.e., tricuspid and pulmonary regurgitation across normal-appearing valves or fetal exposure to indomethacin ), the flow profile of the ductus arteriosus should be obtained parallel to flow on the sagittal ductal arch view. A pulsatility index of less than 1.9 suggests ductal constriction, whereas a pulsatility index greater than 3 suggests increased right ventricular output and left heart obstruction. The sagittal aortic arch view ( Figs. 23.31 and 23.32 ), obtained with rightward angulation from the ductal arch view, demonstrates the aortic arch in its entirety, including aortic root, transverse aortic arch, aortic isthmus, and descending aorta. Color flow imaging should always be performed of the entire aortic ( Fig. 23.33 ) and ductal arches. Measurements of aortic dimensions ^, are called for routinely in the AIUM practice parameter.

The Three-Vessel Trachea View

The three-vessel tracheal view has been demonstrated to be exceptionally powerful, both as a screening tool and as a component of the detailed fetal echocardiogram. ^, (See Figs. 23.33.1 and 23.33.2 ). As with other elements of the fetal echocardiogram, imaging should be performed with and without color Doppler and always with the real-time imaging, rather than only still-frame images. The three-vessel tracheal view should address vessel number, size, location, and direction of flow, along with the relationship of the transverse aorta to the trachea. Although in theory this view can be demonstrated simply with cephalad migration of the transverse views through the 4CV and outflow tracts, typically subtle changes in transducer pressure and angulation will be necessary to obtain optimal image quality.

Technique

Three-dimensional fetal cardiac imaging may be performed with either a reconstructive ^{, , , ,} or a real-time ^{, , , , ,} approach. Reconstructive approaches, first described in 1996, ^, begin by acquiring a rapid sequence of parallel 2D images, with subsequent reconstruction of a volume or volumes, referred to as spatiotemporal image correlation (STIC). ^, Reconstructive approaches have a disadvantage in that they require the fetus and mother to be relatively motionless throughout the acquisition to minimize distortion of the reconstructed volume data set. In contrast, real-time approaches use specialized transducers to image the fetal heart as a volume, acquiring the entire fetal heart (or a portion thereof) virtually instantaneously. The volume data do not require reconstruction, and they do not require gating algorithms (as do reconstructive techniques) to view cardiac motion. Real-time approaches theoretically make the most sense for imaging the fetal heart, given their quick acquisition time, relative resistance to artifact derived from fetal motion, and lack of a need for cardiac gating. ^{, , , ,} However, real-time approaches have poorer image quality than those obtained by STIC.

After volume data have been acquired, volume data sets may be reviewed interactively, displaying any plane, ^, rendered volume, ^{, ,} or sweep of interest and theoretically allowing precise quantitative measurements of ventricular size and function. Investigators continue to develop new ways to display volume data ^{, , ,} in an effort to maximally exploit the potential clinical usefulness of 3D sonographic data.

The Future

Within the next 10 years, additional approaches to 3D/4D imaging of the fetal heart will likely evolve. However, without improvements in resolution, speed, and display algorithms, 3D (or 4D) fetal cardiac imaging is unlikely to become the standard of care for screening or for detailed evaluation of complex CHD. Ultimately, 3D or 4D technology may enable automated display of important planes and sweeps, representing a novel approach to computer-aided prenatal detection and diagnosis of CHD.

Persistent Right Umbilical Vein

Key Diagnostic Feature

The fetus is typically found to have a large vein arising from the abdominal cord insertion site and draining anomalously either into the liver or, in an unobstructed fashion, directly into the right atrium ( Fig. 23.37 ).

Persistent Left-Sided Superior Vena Cava

Definition and Pathogenesis

Normally, during embryogenesis the right-sided superior vena cava forms from the right anterior cardinal vein and the right common cardinal vein. Abnormal persistence of the left anterior cardinal vein, which normally involutes during embryogenesis, leads to the presence of a persistent LSVC in the fetus and newborn. A persistent LSVC typically drains through the coronary sinus into the right atrium ( Fig. 23.38 ; see Figs. 23.14 and 23.19 ). A right-sided superior vena cava (normal) may or may not be present ( Fig. 23.39 ). A persistent LSVC may be found as an incidental finding in approximately 0.5% of the adult population.

Interrupted Inferior Vena Cava

Key Diagnostic Features

Interrupted IVC with azygos continuation may be diagnosed prenatally from a transverse view of the abdomen. The cross-sectional image will show, in place of the IVC (in the liver), a cross-sectional image of an azygos vein located posterior to the descending aorta (see Fig. 23.13 ). Sagittal imaging confirms the absence of a direct connection from the IVC to the right atrium; only the hepatic veins are seen to connect directly. Using both 2D and low-velocity color flow sagittal imaging, the azygos vein can be seen longitudinally, located posterior to the aorta and coursing superiorly and anteriorly ( Fig. 23.40 ) to its termination in the superior vena cava.

Pulmonary Venous Abnormalities

Key Diagnostic Features

As with abnormalities of systemic venous return, both 2D and color flow imaging play important roles in the diagnosis of anomalous pulmonary venous return. Color flow imaging can facilitate visualization of normal (see Figs. 23.17 and 23.18 ) or anomalous ( Figs. 23.41 and 23.42 ) pulmonary venous return when the scale has been adjusted for low-velocity flows.

Partial Anomalous Pulmonary Venous Return

Because even detailed fetal echocardiography may not routinely demonstrate all four pulmonary veins, many cases of PAPVR are overlooked prenatally unless they are associated with other cardiac abnormalities. This section discusses two types of PAPVR that may be detectable before birth because of associated findings. In general, however, PAPVR does not usually require neonatal intervention and carries an excellent long-term prognosis.

Total Anomalous Pulmonary Venous Return