This chapter is also covered by accompanying online material
Catherine Fredouille
CHAPTER CONTENTS
First step. Verification of the position: 2 key points
Second step. Verification of the inlet: 4 key points
Third step. Verification of the outlet: 4 key points
Just as we would do before any clinical examination, we begin by taking a medical history and through our questioning look to uncover several important points, including:
• Family history of CHD. Known congenital cardiopathies in the parents or siblings,1 as well as unexplained neonatal deaths in relatives.
• Teratogen factors. Administration of lithium or an anti-epileptic (even in the case of treatment by folic acid), diabetes,2 or phenylketonuria. Remember that the consumption of alcohol is rarely obvious.3
• The presence of a known normal karyotype practiced for increased risk raised from markers positive for aneuploidies at first trimester. We know that these markers are also effective in identifying congenital cardiac anomalies4,5 (see Chapter 5).
After taking this history, we then verify cardiac architecture in three steps and ten key points. These have been designed to exclude all the important pathologies that can be seen in the fetus.
Using this method, the practice of an ultrasound (US) examination can be compared to reading a large book (Figs 3.1–3.3).
FIGURE 3.1 Left view with the “book” cover open.
FIGURE 3.2 Open “book”, vertical view.
FIGURE 3.3 Diagram of the different views with the heart seen vertically.
1. The transabdominal diameter (TAD) is the cover of the book.
2. After several pages of introduction we reach the inlet chapter. Of course we can read each of the pages of this chapter, but all the important information can be found summarized on one page. This page is the “optimal” four-chamber view, which we will introduce later and define how you can obtain it.
3. This book has also certain “dangerous” pages for the fetal US practitioner. Situated at the junction between the chapters on inlet and outlet, where the membranous septum is explored, here we see the location of the small ventricular septal defects (VSDs) which we can clearly differentiate from VSDs of the inlet septum or outlet septum. The VSDs of the membranous septum—translated clinically after birth by heart murmurs—are the most frequent pathologies in pediatric cardiology. Prenatally, aside from their chance association with a pathologic context, finding these small VSDs, which are strictly confined within the membranous septum, will have no great consequence during the entire pregnancy, except prematurely worrying the parents about a problem, which in most cases, will disappear spontaneously in early infancy. Their discovery in the postnatal pediatric examination will not affect their prognosis either.
4. Past this “zone to avoid”, the outlet chapter needs to be consulted thoroughly—start to finish, up and down, right to left, even diagonally—to be fully understood.
At the end of this examination the US specialist will be able to attach images of these normal findings to the medical dossier of the patient.
In the case of an anomaly, the specialist will do his or her best to produce images in several views. This provides the opportunity to eliminate those false images which are always possible. In the case of the discovery of a cardiac pathology by the first physician, or during the course of the first examination, the most complete morphological examination should be made before referring the patient to a more specialized US practitioner of reference. In the case of an isolated cardiopathy, a pediatric cardiologist should be consulted to confirm the diagnosis, and above all, the prognosis.
First step. verification of the position: 2 key points
• Point 1: This concerns the elements of lateralization. Here we look to the right of the fetus for the gall bladder and the inferior vena cava (IVC). To the left of the fetus we find the stomach (Fig. 3.4) at the abdominal level, and then we look at the apex of the heart at the thoracic level (Fig. 3.5) with always only one vessel in front and to the left of the spine, and then behind the LA, the descending aorta.
FIGURE 3.4 Ultrasound TAD view. Note the stomach and aorta on the left.
FIGURE 3.5 The same view as in Figure 3.4 with a superimposed diagram of the heart at the level of the four-chamber view. Note the aorta and apex on the left.
• Point 2: This relates to the axis of the heart. The apex of the heart is normally directed towards the left and the interventricular septum (IVS), which represents this axis, making an angle of about 45° (Fig. 3.6) with the anteroposterior axis.6
FIGURE 3.6 Normal axis of the fetal heart at 45° in relation to the anteroposterior axis.
In Practice
These two points can be confirmed by passing between the TAD and the four-chamber view by taking the “elevator” (Fig. 3.7).
FIGURE 3.7 The fetus seen from the front showing the levels of the different views. The black arrows show the TAD/four-chamber view translation. 3VT, three vessels and trachea view; 4CV, four-chamber view.
After determining the fetal position (cephalic or breech presentation, the position of the back), we perform the TAD view. We see to the left of the spine the descending aorta with, in front of it, the stomach, and in the center a part of the umbilical vein. To the right, behind the gall bladder, the IVC is situated in front of the right adrenal. In the transverse views, a good visualization of the larger part of the distal rib(s) (as proximally the US beam passes between two ribs) confirms the axial character of the fetal view. In apical incidences we try to view two lateral complete ribs.
Once the localization has been verified, the view is stable, and the TAD image is taken, we take the “elevator” and do a cephalic translation (Fig. 3.8) along the two vascular axes which constitute the aorta and the IVC. Several intercostal spaces higher, we arrive at the level of the optimal four-chamber view with its reference points: the apex and the two inferior pulmonary veins (PVs). In paying particular attention to the IVC during this translation, we note that it receives the subhepatic veins, and then crosses the diaphragm and emerges into the right atrium (RA) in contact with the foramen ovale (FO).
FIGURE 3.8 The fetus seen in profile showing the levels of the different views. Note the acute angle between the four-chamber view/LV–Ao.
Verification Of Lateralization
Position of the organs
The gall bladder is to the right, the stomach and the heart to the left. It is not enough to see these two organs on the same side: you must ensure that you are in fact looking at the left side of the fetus. To do this, we use our Situs wheel, created for the US operator who works directly in front, facing the patient (Fig. 3.9).
FIGURE 3.9 The Situs wheel showing cephalic and breech presentations.
The outer circle of the Situs Wheel's outer ring is used to date the pregnancy. The Wheel is composed of two sides, which correspond to fetal presentation (cephalic or breech). In front of each fetal position, we see a diagram of the four-chamber view corresponding to the orientation for this specific position. In comparing the diagram situated directly in front of the position of the fetus being examined with that of the screen image, we can verify the lateralization. In this way we ensure that the stomach and heart, seen to be situated on the same side, are definitely on the left side of the fetus. In fact, for the same position of the fetal back, depending on whether the fetus is in a cephalic or breech presentation, the image of the four-chamber view is mirrored on the screen and the Wheel. Comparing the US image and the diagram on the Wheel with the presentation of the position of the fetal back allows us to eliminate complete situs inversus.
Vessel position
The abdominal aorta is situated in front and to the left of the spine. The IVC (Fig. 3.10) has been located at the abdominal level, more to the front of the right kidney. The gall bladder is included in the right lobe of the liver, which is normally very large in the fetus. In left isomerisms of visceroatrial heterotaxia (VAH), the suprarenal part of the IVC can be missing. There is then seen a voluminous azygos venous return, which forms a large parallel vessel (Fig. 3.11) alongside the aorta, before crossing the posterior part of the thorax to reach the superior vena cava (SVC).7
FIGURE 3.10 Transabdominal diameter US view. Location of the aorta and the IVC.
FIGURE 3.11 Two parallel vessels in a sagittal thoracic-abdominal view in the case of a pathology (visceroatrial heterotaxia).
Axis of the heart
The apex of the heart is normally directed towards the left, its axis represented by the IVS (see Fig. 3.5). This axis normally makes an angle close to 45° with the anteroposterior axis.6 As in anatomy, where it is represented by the position of the anterior interventricular coronary artery, which passes over the IVS, it is an excellent measure of the size, and thus the balance, between the ventricular chambers of the inlet.
Second step. verification of the inlet: 4 key points
We will verify the following:
• Point 3: That the heart is placed flat on the diaphragm, anchored to the lungs by the inferior PVs.
• Point 4: There are four chambers (simply said, exactly four: neither three nor five).
• Point 5: The chambers are contractile, balanced, and concordant.
• Point 6: The crux of the heart is composed of two anuli that are permeable and offset.
In Practice
Point 3: the heart is attached by the inferior PV
This finding is one of the keys in obtaining the optimal four-chamber view (Fig. 3.12). As for the TAD, seeing one—or even two—complete ribs guarantees the axial character of this view: the heart flat on the diaphragm (Fig. 3.13).
FIGURE 3.12 Diagram of the four-chamber view on the “verticalized” heart.
FIGURE 3.13 The heart–lung block—with a view of the four chambers which is parallel to the plane of the diaphragm.
The localization of the two inferior PVs and the apex (Fig. 3.14) is ideal in confirming the view used in studying the crux of the heart. Its axial character is confirmed by seeing at least one complete rib (Fig. 3.15).
FIGURE 3.14 Anatomic “optimal” four-chamber view of cardiac—pulmonary block. The probe passes to the Eustachian valve to the right and the flap valve to the left.
FIGURE 3.15 The “optimal” four-chamber thoracic US view on which we can see the 4 key points, with the ribs as reference points.
After zooming we will keep the sequence in cineloop of this optimal view. It is through this that we can then study (and save) the images of the 4 key points concerning the inlet.
Points 4 and 5: the four chambers should be balanced and concordant
Once the optimal view has been obtained, we can see (in the LA where the inferior PV arrives) the normal motion of the FO flap valve directed by the oxygenated blood flow from the IVC (Figs 3.16 and 3.17). The other atrium is the RA. Each atrium should be concordant with its respective ventricle: the RA with the RV, just as the LA is with the LV. Anteriorly, the RV is situated behind the sternum and is recognizable by its coarse trabeculations which leave it relatively echogenic. The LA communicates with the LV and must form the apex of the heart. The left side of the IVS should be very smooth. This chamber is clearly less echogenic than that of the RV.
FIGURE 3.16 Anatomic view of the “optimal” four-chamber view. Both * mark the offsetting.
FIGURE 3.17 Ultrasound view of the “optimal” four-chamber view.
Point 6: the two permeable and offset atrioventricular valves
The permeability (Fig. 3.18) of the mitral and tricuspid valves is dynamically explored. It is done in this manner because we can better observe the offsetting of the atrioventricular valves in systole by approaching tricuspid insertion in a direction perpendicular to that insertion (Fig. 3.19).8
FIGURE 3.18 “Optimal” four-chamber view in an apical incidence with the valves open.
FIGURE 3.19 The crux of the heart seen with a zoom using an approach perpendicular to the insertion of the tricuspid.
The fetal heart examination must begin at the abdominal level.
The first and second steps are studied by using short sequences of cineloops taken during the TAD view (through to the optimal four-chamber view), all of the highest quality.
The image from the optimal four-chamber view should be clear and evident, allowing any specialist to confirm the key points at any time afterwards (Fig. 3.20).
FIGURE 3.20 Verifying the four-chamber US view. The position (apex and aorta to the left with an axis of 45°) and the inlet (four balanced and concordant chambers with two anuli that are permeable and offset *). Note the complete ribs.
Third step. verification of the outlet: 4 key points
These key points are often difficult to verify in this order; but they all must be seen to confirm normal architecture.
• Point 7: The two outlet chambers are balanced and separated by a septum in alignment. We should also check the septal–aortic continuity and the mitral–aortic continuity.
• Point 8: The two vessels are crossed and superimposed.
• Point 9: Their size is balanced and they are concordant.
• Point 10: The aortic arch is regular.
In Practice
By multiplying the axial, sagittal, and coronal views of the fetus we can verify these 4 key points.
Point 7: the verification of septal– and mitral–aortic continuity
In “opening” the “book” and taking care not to venture into the membranous septum (MS) zone (Fig. 3.21), which we achieve by jumping from the optimal four-chamber view to the LV–Ao view, we can follow the trajectory of the LV–Ao which is normally tortuous (Fig. 3.22). The MS is very thin (Fig. 3.23) and can perhaps be mistaken for a defect in an apical view. To avoid any error, we must take a perpendicular image of the ring (Fig. 3.24). Outlet VSDs are usually large and particularly well seen here because they are due to the absence of a closing in the upper part of the muscular outlet IVS. There is a loss of the fibrous–muscular continuity with the aorta, which is found to be overriding and misaligned. The other wall of the aorta is in fibro–fibrous continuity to the aortic mitral leaflet (see Figs 1.40 and 1.41).
FIGURE 3.21 Anatomic four/five-chamber view passing through the atrioventricular zone of the membranous septum.
FIGURE 3.22 Thoracic US view of LV–Ao.
FIGURE 3.23 Histologic four/five-chamber view passing through the interventricular zone of the membranous septum (between the two asterisks). Note the two leaflets of the tricuspid. a, anterior leaflet; s, septal leaflet.
FIGURE 3.24 Ultrasound view of LV–Ao. The incidence is perpendicular to the wall making it appear echogenic.
Point 8: crossing of the two vessels
Statically we use the view called the ductus arteriosus (DA), which is a sagittal view that is slightly oblique (Fig. 3.25). It allows us to observe, on the same view, the two vessels cut at the level of their leaflets to see if the orifices are contiguous and orthogonal. However, strict criteria need to be used: the image must be taken at the level of the valvular leaflets and should be confirmed by seeing the echogenic valvular points in the lumen of each vessel. The anulus of the anterior PT is seen cut on a longitudinal plane. The aortic anulus is seen cut transversally at its origin in the center of the heart. At the level of the histologic view (Figs 3.25 and 3.26), passing by the IVC, one should see clearly, in the form of an echogenic arc, the anterior tricuspid valve equally in continuity with the aortic anulus (while the tricuspid and the valve of the PT are at a distance, separated by the infundibulum) (Fig. 3.27).
FIGURE 3.25 Ultrasound view of the ductus arteriosus (DA).
FIGURE 3.26 Histologic view of the DA.
FIGURE 3.27 The sagittal RV–PT view allows us to compare the diameters of these vessels and confirm the concordance.
Dynamically, visualization is accomplished by passing from the RV–PT to the LV–Ao special views (Figs 3.28 and 3.29). This is often difficult to approach apically so we try to obtain the intersection of the oblique views as near as possible to the coronal views of the heart. We call the guédoufle views (in reference to the distinctive oil and vinegar bottle; see Fig. 1.48). These views of the ventricles are accomplished at the level of the papillary muscles. The LV is recognized by its rounded form and the presence of these two papillary muscles. The RV, with its trabeculated structure, forms a “crescent moon” surrounding the LV. Unlike the LV, only one papillary muscle is present in the lumen of the RV. Anterior to the RV, the PT moves in a short, straight trajectory towards the descending aorta, posteriorly and to the left. The aorta, coming out of the rounded ventricle with two papillary muscles, has a tortuous trajectory, whose beginning is quasi-perpendicular to that of the PT. These two vessels are at first contiguous but then move in an initial direction that is quasi-perpendicular, finally joining at the level of the descending aorta.
FIGURE 3.28 Guédoufle view of RV–PT.
FIGURE 3.29 Guédoufle view of LV–Ao.
The trajectory of the PT to the descending aorta is short, straight and anteroposterior. That of the aorta takes an arched pathway.
Point 9: balance and concordance of the vessels
In all of the previously described views it is important to appreciate the relative diameters of the great vessels. These vessels are known to be very similar in size, with a small superiority in diameter to that of the PT over the aorta, due to differences in the flow that passes through them. The concordance is confirmed by the exit of the PT from the RV, which is situated behind the sternum (Fig. 3.30). Its trajectory is anteroposterior, almost in a straight line. The aorta begins in the LV and the center of the heart (see Fig. 3.24). Taking a tortuous trajectory, it rejoins the same vessel, the descending aorta.
FIGURE 3.30 Ultrasound concordance on the small axis of RV–PT.
The size of these vessels can be appreciated in different ways, either at the level of the DA view for the anuli, or at the level of the three-vessel view for the ducts (Fig. 3.31).9 This last view allows us to pay special attention to the junction between the aortic arch and the descending aorta. It is at this level that we can appreciate the size of the aortic isthmus, the zone implicated in the development of most coarctations occurring after the postnatal closure of the DA.
FIGURE 3.31 The three-vessel US view showing the relative sizes of the arches.
While the verification of normal cardiac architecture does not require the systematic use of Doppler, the verification of the direction of flow of the arches in the three-vessel view in Doppler mode (Figs 3.31 and 3.32) gives us an extra degree of normality; inverted flow at this level is always pathologic.10
FIGURE 3.32 The three-vessel view in Doppler showing that flows are in the same direction.
Point 10: regular aortic arch
Paradoxically this is easier to see in a fetus from the back than from the front. The view of the aortic arch is obtained parasagittally, passing to the left of the fetal spine. From the point where the aorta emerges, from its shape and the size of its anulus, we can gather diverse information. A normal aortic arch begins in the center of the heart in the form of a candy cane, and from its arch three vessels emerge (Fig. 3.33).
FIGURE 3.33 Anatomic view of the aortic arch.
You must confirm the diameter of the entire arch globally on a parasagittal view (Figs 3.33 and 3.34), especially at the level of the aortic isthmus between the left common carotid artery (LCCA) and the junction of the DA with the descending aorta.11 We also try to check (with the three-vessel view) the horizontal aorta between the right common carotid artery (RCCA) and the LCCA. In the case of an anomaly of the aortic arch, a stenosis, or an interruption, the presence of a VSD—often difficult to discern but important to confirm—should be investigated. This is done in order to diagnose a syndrome of coarctation or an IAA. Cases such as these belong to the CT spectrum, and abnormality of the aorta is always associated with an outlet VSD. Complementary research of a 22q11 deletion should be requested.
FIGURE 3.34 Ultrasound view of the aortic arch.
The third step requires static and dynamic studies obtained using complementary views.
References
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