How: conducting the examination and its pitfalls - Fetal Heart Ultrasound: How, Why and When; 3 Steps and 10 Key Points

Fetal Heart Ultrasound: How, Why and When; 3 Steps and 10 Key Points, 3th Ed.

4. How: conducting the examination and its pitfalls

This chapter is also covered by accompanying online material

Jean-Eric Develay-Morice

CHAPTER CONTENTS

Taking the history

A fast glance

Verification of lateralization and its pitfalls: the elevator

In this chapter we further develop our method that allows us to say that the fetal heart is normal, proving this by our choice of the critical reference images. This point also has important medicolegal implications.¹

Taking the history

We begin by taking a family history of congenital heart disease (CHD) in the current or previous pregnancies. This information should not be neglected and will direct us in the way we conduct the examination itself. Even though the study of the crux of the heart should be systematic, the knowledge of a nuchal translucency or of the triple test could place this particular type of pregnancy in a risk category, with the subsequent need to more clearly demonstrate the normal alignment of the atrioventricular valves. This is the case in diabetes, where the septal thickness needs to be measured by precise criteria.

For those who practice obstetric ultrasound (US), the heart is considered the most difficult organ to investigate.

Our examination of the heart begins with the transabdominal (TAD) view. If we are experienced and comfortable in doing this we have the foundation for what follows—a cranial translation of the probe from the TAD position will provide an excellent review of the state of the entire heart, and in most instances will also allow us to appreciate the normality of the heart.

The fetal heart examination is less a problem of acquisition than to recognize different structures, requiring a precise knowledge of the positioning of each element we study.

The main difficulty in the acquisition of reference views in studying the heart comes from the skeletal cage that surrounds it. We must use our knowledge to avoid bony obstacles such as the ribs, the spine, and even sometimes limbs, which will get in between the probe and the thorax. If the fetal position makes studying the heart too difficult, e.g., when the fetal back is anterior, we should not hesitate to study other, more accessible organs such as the kidneys. In most cases, the fetus will move so that later in the examination we will have a better position for studying the heart.

Let us first look at the position of these views compared with the TAD reference scan and then examine sagittal and transversal views of the fetus (Figs 4.1 and 4.2).

If we discipline ourselves to use a good quality abdominal view the essential elements of heart US will consist of moving in the direction of the fetal head by a movement of the wrist.

FIGURE 4.1 (A) Diagram of a global view of the heart. (B) Axis of the heart. Transverse views compared by superposition with the TAD: (C) Four chambers; (D) Left outlet; (E) Right outlet.

FIGURE 4.2 (A) The entire heart seen by superimposition of transparent images. (B) Complete left outlet. (C) Complete right outlet.

A fast glance

Before going into the details of the examination we begin by taking a quick preliminary look round the entire area. This is done to avoid finding unexpected major cardiac anomalies later on, well after the morphological examination is underway. It is advisable to make these observations at the very beginning of the examination.

We move upwards and parallel towards the cephalic pole, beginning from the transverse abdominal view (after lateralization, with the stomach on the left), and then pass to the four-chamber view, from this point rapidly continuing along the beginning of the aorta to arrive at the pulmonary trunk (PT). Continuing the movement, we see the horizontal portion of the aortic arch using the three-vessel view. We can, with great benefit, do the same examination in the color mode (Figs 4.3 and 4.4).

FIGURE 4.3 Cranial translation from the TAD. (A, B) Lateralization of the fetus with the stomach; axis of the heart (green arrow). (C, D) Position of the four chambers related to the TAD. (E, F) LV–Ao related to the four chambers. (G, H) RV–PT related to the four chambers. (I, J)Three-vessel view related to be four chambers (Ao, DA, SVC).

FIGURE 4.4 These rapid observations allow us to locate certain important features—at least one of these four signs are implicated in most cardiac diseases. (A) Axial deviation of the heart (green arrow) from the median axis (white arrow) found in situs anomalies, four-chamber asymmetries, and diaphragmatic hernia. (B) Important defects: aspect of a heart with a large central defect (red arrows) in a complete AVSD. (C) A great vessel (red arrows) crosses right through the thorax due to an anterior insertion of the aorta, which is a suspicious sign of TGV. (D) Asymmetries of the great vessels, the outlet. Here, the PA (green arrow) is much greater in size compared to the aorta (red arrow), which implies cardiac anomalies. In a normal situation, the PA is only slightly larger than the aorta.

This rapid observation allows us to locate certain important features such as:

• Situs anomalies.

• Large (volume) defects, e.g., the aspect of a heart which has a large central hole points to a complete atrioventricular septal defect (AVSD).

• The great vessel crossing directly through the thorax with bifurcation, which testifies to an anterior insertion of the aorta leading us immediately to suspect transposition of the great vessels (TGV).

• The outlet and diameter of the great vessels, if abnormal, will imply cardiac anomalies in most cases.

These swift observations, performed at the very beginning of the examination, will influence what we say to the parents by observing their reactions before directly announcing a problem. Not only will this allow us the time to complete the specific screening required for determining our approach to the findings themselves, observing the reactions of the parents will give us the psychological basis to approach them at the end of the examination. Never make an announcement too early or brutally—take your time.

This dynamic and rapid examination can sometimes, if the technical conditions are favorable, extract those referential views that can demonstrate and affirm the elements we are searching for. The possibility of cineloop allows an easier acquisition of the reference scans.

Contrary to what we might believe, the real difficulty is not in the actual acquisition of these images, but rather in the choice and identification of the best view which highlights these structures.

The first part of the examination is limited to a simple sweep. New possibilities of acquisition in the 4D mode automatically interpret this sweep to acquire volume. We can thus obtain a view in the three spatial planes, avoiding difficulties linked to the handling of the probe when passing from one view to the next. This volume corresponds to a specific given instant but until recently it was not possible to use this technique for the fetal heart because the acquisition time was too long (especially for a heart beating at 145 beats per minute). With the arrival of the spatiotemporal image correlation (STIC) technique²^,³ we now have the added information of morphological variations as a function of the cardiac cycle. Increasingly we are seeing in the literature that authors consider this technique sufficient,² satisfying the needs of our examination for the screening of the heart itself. Based on the same principle of rapid acquisition, some authors have proposed applying this method to the whole exploration of the fetus.⁴ They would use this for “diagnosis at a distance” or for teaching using videoconferencing.⁵ Another technique, the “inversion mode”,⁶^,⁷ provides the possibility of combining different techniques such as STIC, “inversion mode”, and “B-flow” imaging.⁸

We should never forget that a 3D, 4D, STIC, or inversion mode can never mitigate the mediocrity of the initial image.

As mentioned previously, no matter what the method of acquisition, the real difficulty lays in acquiring a good image and not on the identification of these structures themselves. The quality of the acquisition centers on avoiding the bones: the ribs, the spine, and limbs. Remember if the position of the fetus is not favorable to our examination, temporarily abandon a detailed examination of the heart and the aortic arch, then concentrate on other organs that are, for the moment, more approachable. If the back is to the front, we can examine, for instance, the kidneys or the spine, going back to the heart when it is in a more favorable position for the quality views that we desire.

Different Views That Verify The 10 Key Points, Their Pathways, And Their Pitfalls

After this fast glance, as a general rule, for each view we choose the most favorable pathway to approach it. In short, we look for a perpendicular approach to the structures we are examining.

With each acquisition we must ask ourselves if the screen is showing us an image that is true or false, whether it is reassuring or a cause for concern. These questions must always be uppermost in our minds during the fetal examination. A precise idea of the potential pitfalls will help us avoid false leads, and possibly save us from making the wrong diagnosis.

In the greater part of fetal anomalies, at least one of these views is pathologic:

• The four-chamber view is not comprehensive if we have not observed the complete movement of the atrioventricular valves.

• The continuity LV–Ao.

• The continuity RV–PT.

• The aortic arch.

• The three-vessel view with the horizontal portion of the arterial duct, the aortic arch, and the transverse view of the superior vena cava (SVC), in 2D and Doppler.

Faced with an anomaly in one of these views, we add, according to the pathology we are looking for, one of the following views:

• The arterial duct view exploring: RV–PT–DA–Ao.

• The IVC–SVC (called bicaval incidence).

• The annular view.

• And eventually other more specific views.

For some practitioners the two views (the four-chamber view and the three-vessel view) may be sufficient in systematic screening, but others still feel we need to add the view that incorporates the LV outlet, without forgetting to study flow in color Doppler (Fig. 4.5).

FIGURE 4.5 Overview of the different reference views, positions of the probe and how to get them. (A) The fetus. (B) Different positions of the probe. (C) Four-chamber view. (D) LV–Ao. (E) RV–PT. (F) Three-vessel view.

Verification of lateralization and its pitfalls: the elevator

To be certain of the lateralization of the fetus we must begin by clearly determining the left side of the fetus which varies according to how it presents. This has been described in Chapter 3 (Fig. 4.6).

FIGURE 4.6 (A) Sagittal view demonstrating the technique of the elevator—parallel movements of the probe from the TAD to the four-chamber view (yellow arrows)—guided using the aorta (red arrow) and the IVC (blue arrow). (B) TAD; with the stomach (green arrow) we can determine the position and lateralization of the fetus. Using the red and blue lines as guides, we rise to the four-chamber view. Aorta (red arrow) and IVC (blue arrow). (C) Four-chamber view showing the arrival of the IVC (green arrow) into the right atrium and the aorta behind the left atrium. (D) Arrival of the elevator compared with the four-chamber view: IVC in the RA (blue point) and the aorta behind the LA (red point).

The Technique

In the fetus, the lungs are physiologically empty and the liver is large which causes the base of the heart to be horizontal and found in the same plane as that of the ribs and intercostal spaces.

First we should ensure that we have obtained a good view of the TAD with a centered umbilical vein, including the stomach and, if possible, the two adrenal glands. The position of the stomach will be interpreted as verifying the position of the fetus to ensure that it is definitely on the left. Then we go cranially parallel towards the head, continuing in a parallel movement finally reaching the heart using the aorta and the IVC (in the manner of the cables of an elevator). This cranial translation must rest axially, i.e., perpendicular to the axis of the fetal spine, and not necessarily to an imaginary straight cranial–caudal line. This point is of particular importance when the fetus is flexed.

In this way we ensure that the IVC exists and that the aorta is definitely to the left of the spine, on the same side as the stomach. The IVC is situated in front and on the right of the aorta, deviating towards the front in the cranial translation while still remaining in a median plane. The presence of a great vessel of an identical caliber to that of the aorta, which remains straight and parallel to the aorta, should make us suspicious of an azygos vein, and consequently look for the absence of the IVC. This is one of the easiest signs to detect of an important pathology which we will look at later: visceroatrial heterotaxia.

The movement of this caudal translation leads us to the view of a rib and the intercostal spaces which is that of the “optimal” four-chamber view. We have defined this view by the alignment of the apex of the heart and the two inferior pulmonary veins (PVs), a reference point for the four-chamber view.

Pitfalls

The position of the fetus: lateralization elements

These considerations are generally thought to be obvious, but are perhaps more difficult when the fetus is found to be in a transverse position. The fetus might also have moved between the stage of lateralization and that of the examination of the heart.

Organ position

It can be dangerous to be satisfied simply by observing that the stomach is on the same side as the heart.

Normally the stomach is to the left, while the gall bladder is to the right. But what is to the right passes to the left (for the same back position) depending on whether the presentation of the fetus is cephalic or breech. The position of the stomach should be understood as verifying this presentation, i.e., in relation to the position of the head and not of the heart. Forgetting to do this can make us mistake a stomach that is to the right with a gall bladder that is actually to the left.

Abdominal vessel position

It is important to remember to verify that the aorta is truly to the left and that the IVC is present, and comes out into the RA. It is also extremely useful to use the aorta and the IVC as our guides for the “elevator” between the TAD and the four-chamber view. To do this we must search for them, knowing that we will always find the aorta to the left of the spine, and the IVC on the right side of the TAD view of a normal fetus.

A vessel remaining close to the aorta without separating towards the front during a cranial translation—and which has an appearance similar to the barrel of a rifle—should not be taken to be the IVC. It is most probably a voluminous azygos venous return which is confirmed by the absence of a normal image of a vessel in front and on the right of the aorta, the IVC. These elements are easily seen in the TAD view, and also on the parasagittal view of the aortic arch, as long as the fetus is in a neutral position.

Four-Chamber View: Verification Of The Outlet And Its Pitfalls

The technique

As described earlier, examination of this view is obtained from the TAD view, after having gone up in parallel until reaching the heart, the “elevator” guided by the Ao and IVC (Fig. 4.7). Like this we have a four-chamber view (see Figs 4.7H–J) which is “optimally” aligned with these three reference points and the following structures:

FIGURE 4.7 (A, B) Position of the four-chamber view compared with the heart including the pitfalls of this view, a small LV or RV (red lines in B). (C) Going from the red position to the yellow we need to slide the probe on the skin (yellow arrows) turning around the apex (yellow point) and not simply turning the probe without moving it on the skin, as shown on this diagram (red point). (D) The position of the fetal organs can be better understood if we superimpose the four-chamber view on the TAD and compare the two. In doing this we can easily determine the best path to take, whether axial–apical (red arrow), axial–transverse (green arrow), or crux of the heart (blue arrow). (E) The four-chamber view and its pathways. (F) Here we see the parallelism between the plans of the TAD and the four-chamber view. (G) Position of the probe in a sagittal view. We can visualize the consequences of the loss of parallelism due to the curved back of the fetus. (H) Definition of the three points that confirm the four-chamber view. On the same image we have the apex (red arrow) and the two pulmonary veins (blues arrows), with an entire rib (yellow). (I) Same view as in H, but unmarked. (J) Posterior view of PVs: inferior (blue arrows) and superior (white arrows). This view explains the importance of the inferior PVs. Visualization to get an axial view and why they are one of the criteria for the four-chamber view to avoid lateral or anteroposterior swing. (K) The curved spine lost the parallelism between the TAD (white line) and the four-chamber view (yellow line).

• The apex of the heart.

• The two inferior pulmonary veins.

• The ideal level for examining the crux of the heart, and the insertion of the atrioventricular valves.

Due to the position of the fetal heart (empty lungs and large liver), this view is on the same plane as that of the ribs and the intercostal spaces.

One rib in front and one in the back are excellent criteria in obtaining the optimal four-chamber reference scan (see Figs 4.7H–J; see also Fig. 4.10).

!!! Attention !!!

It becomes impossible to obtain the three reference points by a parallel translation if the spinal curvature of the fetus is important. In this case, the incidences of the TAD and the four-chamber view are not strictly parallel.

In fact, the movement has to follow the curvature of the spine and remain always perpendicular to it. The movement won't be a parallel translation at all, but a curved movement in the same way that the spine of the fetus itself is curved.

In every case the cranial translation from the TAD should remain axial, i.e. perpendicular to the axis of the fetal spine and not that of the probe.

If the four-chamber view is not strictly axial, it will be impossible to find the three reference points, but we can also experience pitfalls due to the wrong swing, as shown in Figure 4.8. For instance, in this particular situation it happens when we pass along the apex and the superior—and not the inferior—PVs.

FIGURE 4.8 (A) These views demonstrate how a lateral swing can produce false small ventricles (RV or LV) shown with red arrows. Yellow arrows indicate several ribs instead of the usual one in axial views. (B) Anteroposterior swing. Small ventricles (red arrow) or false AVSD seen in the case of a dilated CS (green arrow).

To correct our views, we have a tendency of pivoting the probe around a fixed point on the surface of the skin. What in fact should be done is to move the probe along the skin, keeping as a fixed point a chosen interior reference of the view which thus serves as our axis of rotation (see Fig. 4.7C).

The choice of different access pathways for the four-chamber view will at first be determined by the position of the fetus and then the pathway. We must make use of three different pathways.

The Axial–Apical Pathway

This is shown in Figure 4.9.

FIGURE 4.9 (A) Position of the four-chamber view superimposed on the TAD. (B) Four-chamber view by the apex with the criteria for a reference view: the apex (red arrow) and inferior PVs (blue arrows). With this incidence the limits of the septum are not well defined (green arrow). (C) The same view with the valves open.

Why

This is the preferred pathway in pediatric cardiology. Free of any bone obstacles, it is usually easy to obtain in a fetus with a posteriorly positioned back. We can also use this with a fetus with an anterior back by passing by the paraspinal window. This is often possible with a transverse view as early as the first trimester. Especially useful in cases of a bad echogenicity it allows us, by its perpendicular approach, to visualize the closed atrioventricular valves demonstrating their symmetry and offsetting.

How

It is obtained by a cranial translation beginning with the TAD, perpendicular to the axis of the spine with a slight angulation.

!!! Attention !!!

The longitudinal approach to the muscle fibers of the interventricular septum (IVS) generates tangential shadow cones which make it appear thinner than it really is. This can also get in the way of apical visualization of the crux of the heart.

The apical view is never used in measuring the IVS for diabetic pregnancies.

The Axial–Transverse Pathway

This is shown in Figure 4.10.

FIGURE 4.10 (A) The lateral pathway (green arrows) showing the four-chamber view on the TAD by superimposition. (B) Despite an insufficient zoom this incidence allows us to better visualize the septum. (C) A correct zoom emphasizes the good visualization of the endocardium (green arrows) because of its perpendicular incidence.

Why

This approach, often obscured by the ribs, makes viewing the walls easier, especially those of the IVS. Indispensable in measuring the IVS in the diabetic, it is equally of great interest in the study of a complete AVSD where the IVS appears short and squat (Fig. 4.11).

FIGURE 4.11 (A) Diagram of the four-chamber view with the valves and their situations. (B) A large central defect is a sign of an AVSD. (C) This diagram shows the modifications which occur causing the septum to be large and stubby.

View Of The Crux Of The Heart

This is shown in Figure 4.12.

FIGURE 4.12 (A, B) This preferred approach allows a perpendicular approach to the fibers that cross the septum creating a hyperechogenicity due to the mirror effect (blue arrow). (C, D) The correct zoom improves our ability to identify hyperechogenic fibers. The greater the zoom, the easier it is to differentiate the fibers of the myocardium. This depends on optimum settings. (D–F) Demonstration of the importance of the choice of US angle (white arrow). When it is perpendicular the intramyocardial fibers are hyperechogenic, instead of those in E and F where the US is not perpendicular (red arrow); this portion of the fibers is ignored. Very echogenic in “D”, when the angle of indicence is changed in F the fibers become anechogenic. Note the usefulness of a large zoom in better visualizing interseptal fibers.

Why

This appearance allows us to emphasize the offsetting of the septal atrioventricular leaflets by underlining the obliquity of the fibers linking these valves in their intraseptal section.

How

We must approach the fibers perpendicularly by using the zoom; in this way the fibrous portion (non-muscular), which is normally oblique in relation to the IVS (muscular), appears very echogenic and well differentiated from the muscle tissue. To emphasize the difference of echogenicity a very high contrast setting can be used.

To be absolutely clear, the study of the offsetting of the atrioventricular valves can only be performed using the “optimal” four-chamber view, i.e. the view defined by the apex and the two inferior PVs.

We understand the heart as having two parts: inlet and outlet. The part concerning inlet corresponds to the four-chamber view.

!!! Attention !!!

The offsetting of the valves may appear difficult to highlight if access to the fibers has not been accomplished in a perpendicular fashion.

The reason for using a hard-contrast setting is to emphasize the difference between the myocardium and the fibers in continuation with the two atrioventricular valves crossing the septum. This setting can lead to not being able to recognize part of the septum, but this problem can be avoided by changing the trajectory (Fig. 4.13).

FIGURE 4.13 (A) Although specific settings can reassure us about the offsetting of the valves, these settings can lead to false images of a defect (red arrow). (B) In case of doubt it is necessary to change the incidence to be perpendicular showing the septum as normal (green arrow). Notice that by modifying the angle parallel, the fibers are hyperechogenic and seem to “disappear”.

Pitfalls Of The Inlet Or Four-Chamber View

The axis of the heart and the aorta to the left

The lateralization of the heart should be noted in relation to the fetal position, not simply in relation to the abdominal organs. The position of the aorta at the level of the four-chamber view is in the back and to the left where we find the left atrium in front and to the left of the spine. In conotruncal cardiopathy (CTC) the arch can be to the right, most often going off with a descending aorta to the right as well. This marker—which is very easy to see and is an element of our key points—is a powerful warning sign of a fetal pathology.

The axis of the heart

Normally situated between 30° and 60°, the axis is generally seen to fall around 45°. Values found at either limit should make us suspicious of an asymmetry and lead us to consider an inlet pathology. If the angle is less than 30° it is most likely a hypoplasia of the right ventricle. If the angle is more than 60° it suggests a left hypoplasia.

!!! Attention !!!

The “boot” form—well described in tetralogy of Fallot—also causes a deviation of the axis to the left.

Swings in the four-chamber view

The axis of the four-chamber view is confirmed by visualization of a whole rib; the optimal level of this view is ensured by visualization in the same plane as the apex of the heart and the inferior PVs. The absence of these criteria is due to a swing, which could be lateral or anteroposterior.

Lateral swings: asymmetries

Lateral swings create false asymmetries either to the right or to the left due to the direction of the swing, whether it is to the left or right (Fig. 4.14).

FIGURE 4.14 (A) A optimal four-chamber view (yellow line). The lateral swings are shown by a red line. Notice that there are several cut ribs (yellow arrows) in this view, but in the wrong position. (B) Angled towards the left, the LV appears falsely small. (C) Angled towards the right, the RV appears falsely small.

This view gives the impression of a right or left ventricular hypoplasia. The diagnosis needs to be reconsidered using our criteria to verify the horizontal nature of the view. On these images we cannot see one single complete rib but several. Continuing with the examination, a balanced outlet tract was seen, which would be illogical if a right or left hypoplasia actually existed.

For an inferior–superior swing: false AVSD and VSD

By the same mechanism, if the view is too caudal towards the front, the ventricles will be visualized by their walls and not their chambers (Fig. 4.15A–C). This can increase our impression of hypoplasia if the view also has a lateral swing.

FIGURE 4.15 The four-chamber reference view is illustrated by a yellow line. (A) Anatomic view. An inferior swing (red arrow) uncovers the CS in such a way that it can be mistaken for an AVSD. (B) This section of the dilated CS gives a false image of AVSD, which disappears when we perform a cranial translation to look at the integral crux of the heart. Note that this CS can be dilated, especially if it receives a persistent SVC. (C) If there is an upward swing (red arrow), the four-chamber view elucidates the superior PVs and the beginning of the aorta. This view, which passes by the superior PVs and by the inferior portion of the beginning of the of the aorta, gives a false image of a VSD—a septal defect which is too cephalic and anterior. (D) Sonographic correspondence with the departure of the aorta creates a false image of a defect (red arrow) as the PV visualized is the superior one (blue arrow) not the inferior.

A view which is too caudal towards the back can present us with the following:

• When there is a right swing, we have distracting images such as the visualization of the Eustachian valve situated at the entry of the IVC. Of variable size, it can be seen on one view, even when situated at a good level. Another distracting image in the RA is the presence of Chiari network, an embryological remnant floating in the RA (Fig. 4.16).

FIGURE 4.16 (A) A double echogenic line due to the tricuspid (green arrow) and Chiari network (red arrow). (B) When the tricuspid is open, there is persistence of the echogenic line of Chiari network.

• When there is a left swing you can be confused by the following images.

The CS, especially if it is dilated by the arrival of a persistent LSVC receiving an abnormal pulmonary venous return, easily gives us a false image of the alignment of the atrioventricular valves, implying the existence of an AVSD. If the static image is disconcerting, dynamically we see that these “linear valves” are without any movement because in fact it is the wall of the coronary sinus. In addition, the absence of the arrival of the PVs in a small left atrium should be a warning of this pitfall and lead us to reconsider the level of this four-chamber view—as the absence of a complete rib (Fig. 4.15C, D).

A dilated CS can also be an obstacle to left flow leading us to consider a diagnosis of left hypoplasia or coarctation. Even a normal CS can be visualized on the axial plan of the four-chamber view if this plane is too low. Here as well, the PVs will not be seen arriving in the LA because they come out above the plane of this image. Looking for the ribs will allow us to confirm the absence of even one complete rib confirming the axiality.

On these two images, the presence of several ribs proves that the image has been taken obliquely. This puts in doubt a diagnosis of asymmetry, especially since the axis of the heart is normal, the opposite of a true asymmetry.

When the swing is towards the top, it is not the crux of the heart, but the membranous septum and the base of the aorta which are in the view, easily creating false images of VSD.

These pitfalls can be avoided if we respect the three reference points of the “optimal” four-chamber view, confirmed by seeing: a complete rib; the apex, and the two inferior PVs.

To avoid these pitfalls, we have a tendency to pivot the probe around a fixed point made of skin. On the contrary, it is indispensable to move the probe on the skin while keeping as a fixed point the references of the view which will serve as an axis of rotation; in this case the apex can be used to align the two inferior PVs and reach our three points (Fig. 4.17).

FIGURE 4.17 (A) To obtain the four-chamber view, using the skin as an axis of rotation (red point) makes it impossible to get an optimal reference scan. (B) On the other hand, one reference point (here the apex is shown as a green point) is an excellent axis of rotation (green point) to obtain the optimal four-chamber view.

Four-chamber view and concordance

One of the steps in the examination using the four-chamber view is the identification of each of the chambers, which will permit us to judge whether they are concordant or not. The LV has a smooth wall whose apical extremity constitutes the apex of the heart. If there is one left atrium characterized by the arrival of the PVs and then followed by a type of straight ventricle, that is to say having coarse trabeculations, we speak of an atrioventricular discordance. You must pay particular attention to the atrioventricular concordance to be sure not to overlook a double discordance (also called “corrected transposition”).

Aspect Of A False Echogenic Tumor Of The Right Ventricle

The apical approach can give us a very echogenic, bulky, and filled image of the back of the RV. This is due to the trabeculations formed by the numerous bridge-like fibers. These fibers give us a multitude of interfaces which are at the origin of the echogenicity that makes this such a distracting image. Color Doppler (ideally used in an apical path) allows us to immediately disprove the presence of a tumor by the total filling of the ventricle. This is accomplished through the visualization, in color Doppler, of blood passing between the muscular bridges and the trabeculations. Moreover, if this happens to be filling defect linked to a hypoplasia or a ventricle tumor, there will be a dilatation upstream with a valvular leak associated with hypoplasia downstream, that is to say of the pulmonary artery (Fig. 4.18).

FIGURE 4.18 (A) Hyperechoic structures occupying all the back of the right ventricular cavity (red arrow). (B) The flow in color mode completely fills the ventricle (green arrow), which rules out the possibility of a ventricular tumor. It is simply the tight chordae that result in numerous interfaces.

Four-Chamber View And Foramen Ovale Valve

Beware of the pitfalls that involve the foramen ovale valve (FOV) and the LA. In the most severe hypoplasias of the left tracts, or if a left obstacle is important, an authentic FOV can be found in the right atrium. But we should be cautious because the Eustachian valve which sits over the arrival of the IVC could be confused in certain rare cases with the FOV. This valve can be identified especially when the four-chamber view is relatively low and/or the Eustachian valve is particularly large.

The FOV can also sometimes be seen to have an aneurism forming a sac looking like a spinnaker.

Verification Of The Outlet And Its Pitfall

The LV–Ao view

The aorta begins at the center of the heart above the inlet and under and behind the PT. Its ascending trajectory is followed by an arch which gives off the vessels of the neck before rejoining the descending Ao (Fig. 4.19).

FIGURE 4.19 (A) Diagram of the left outlet. Note the acute angle made with this and the four-chamber view. (B) The origin of the aorta is at the center of the heart (red arrow), close to the plane of the four-chamber view (yellow arrow). (C, D) Lateral view of the septum from the LV. Anatomic demonstration of the origin of the aorta, close to the center of the heart (red ring) as compared to the right tract, which is more anterior and superior (blue ring). (E) Description of the movement to go from the four-chamber view to the left outlet view. It seems natural to angle the probe, keeping it at the same place on the skin. In fact doing this makes reaching this frame impossible, as explained on this diagram, because the axis of rotation of this movement must be the apex and not the skin. The probe have to move on the skin keeping the apex on the screen. (F) Surrounding the left outlet. (G) Different pathways as a function of fetal position. Axial apical (red arrows), axial lateral (green arrows) and sagittal oblique (red curved arrows), axis of the rotation represented by the straight arrows). (H) How to get an axial view of the left track.

The technique

The LV–Ao view is obtained from the four-chamber views by a rocking movement of the probe with the apex for the axis. This can be compared to the opening of a “book”. The angulation of this four-chamber view, LV–Ao, is about 15°. It is in this zone that we find the membranous septum (MS), at the junction of the inlet and outlet. As in the four-chamber view, the close passage of the LV–Ao view to the MS should be avoided. This would indicate that the level is too caudal, the thinness of the MS easily producing a false image of a defect. It is thus important to produce an LV–Ao view at the level where the septal–aortic continuity is fibromuscular, i.e. more cranial.

There are three important principal pathways, as follows.

The Axial–Apical LV–Ao View

This is shown in Figure 4.20.

FIGURE 4.20 (A) Pathways. (B) Large field. (C) The zoom is always a good solution for easier analysis of the structures.

Why

This is easy to obtain in the continuity of the apical four-chamber view. It is used, above all, in the case where the positioning of the back is posterior.

If there remain any doubts, the use of color Doppler is especially efficient if the US beam is in the same axis as the supposed flow (Fig. 4.21). The systematic use of color Doppler can also allow the highlighting of small aortic valvular irregularities leading us to look for evidence of a bicuspid condition (Fig. 4.22).

!!! Attention !!!

This view can generate cones of shadow, in particular at the emergence of the aorta, which can suggest a VSD with misalignment. In order to verify the integrity of the septum, it is better to change the incidence angle and approach perpendicularly.

FIGURE 4.21 (A) There is some doubt about this septum (red arrow) due to the absence of echoes at this location. (B) Changing incidence angle often resolves this doubt (green arrow). (C) Use of color Doppler confirms that the aorta does not receive any flow from the right track at its origin. We can be sure of this because the US is perpendicular to the flow.

FIGURE 4.22 (A) Minor regurgitation of the aortic valve. (B) These data lead us to study the anatomy of the aortic valve more precisely and choose the best pathway to arrive in front of the junction of the valves when they are closed. This echogenic line crosses the valvular anuli demonstrating that there were only two valves instead of three.

The Preferred Axial–Lateral View

This is shown in Figure 4.23.

FIGURE 4.23 The preferred axial–lateral view. Lateral pathways (green arrows) are of interest in studying the vessel walls. Pathways compared to the (A) TAD and to the (B) four-chamber view. (C) There is evidence of a continuous septum on this view (green arrow). (D) As we look directly from “in front,” the defect of the wall (red arrow) cannot be explained by an artifact, but it can be confirmed with (E) color Doppler if we are in the axis of the supposed flow.

Why

This view gives the opportunity to explore the outlet VSD. The visualization of the aortic wall is optimal and the approach is perpendicular. It allows us to locate short and thick ventricular septa which are present in the larger defects.

The LV–Ao “SOS” View: Sagittal Oblique

This view is only acquired if the lateral axial approach to the emergence of the aorta is absolutely impossible (Fig. 4.24).

FIGURE 4.24 The LV–Ao “SOS” view. (A) Modification of the direction of the left outlet and its application to the pathway for observing the origin of the aorta. (B, C) Diagrams representing the orthogonal angle between the left outlet as explored by an axial–lateral view and a sagittal view. (D) Ultrasound perpendicular to the axis of the aorta.

Why

While SOS highlights the infundibular part of the septal–aortic continuity, it leaves certain outlet VSDS untouched especially because it does not explore the wall under the aorta where misalignment defects are situated.

How

As it is impossible to pass from the four-chamber view to an axial or lateral LV–Ao view, we begin by placing ourselves on the LV–RA axis, and then make a 90° rotation. The LV–Ao axis is then approached with a vertical orientation that is slightly oblique (see Fig. 4.22).

Pitfalls Of The LV–Ao View

The same problems are encountered with this view as with the four-chamber view (Fig. 4.25). They are due to the incident tangent of the US which can be produced on the LV–Ao view with an approach by the apex. These phenomena will be increased when the axial view is too caudal or where the MS is so thin that it is easy to mistake it for a false VSD. Changing the incidence to arrive perpendicularly into this questionable zone will allow us to find another image of the septum, eventually reduced to an image of interfaces which are composed of the atrioventricular section of the MS. If changing the incidence does not clarify this artifact, we can further sensitize the examination by investigating the flow with color or energy Doppler.

FIGURE 4.25 Pitfalls of the LV–Ao view. (A) True VSD. (B) False VSD. Correcting the pitfall by changing incidence. (C) No defect (green arrow). (D) Real defect (red arrow). Doppler provides the diagnosis. Pitfalls of the mLV–Ao view. (E) No flow coming from the RV (green arrow) in contrast to. (F) This illustrates where the connection does exist (red arrow).

We should note that the sagittal approach to the LV–Ao view—which really deserves its reputation as the “SOS” view when the fetal position limits other approaches—can, at the same time, lead us to mistake a VSD caused by misalignment because this view only examines the wall anterior to the aorta, as well as the infundibular region, but not at all any misalignment under the aorta.

The RV–PT View

The PT, with its practically rectilinear and axial trajectory, arises in the RV in the anterosuperior part of the heart (Fig. 4.26). After having produced the two PAs on its posterior inferior side, where the right artery wraps round the aorta, it continues its straight route by the ductus arteriosus before joining the descending aorta.

FIGURE 4.26 RV–PT view. (A, B) Situation of the axial RV–PT and sagittal RV–PT views as placed in the heart. (C) Anatomic and (D) US correlations. (E) How to get it: as many different pathways as possible. The transverse path (red arrows) is preferable in 2D because it arrives perpendicularly to the PA wall. The axial pathway (green arrows) is preferable in color Doppler because the US is in the direction of flow. (F, G) Movements of the probe.

Its early bifurcation is the only pathognomonic criteria of the PA (Fig. 4.27).

FIGURE 4.27 Axial transverse view. (A) Ventricular–arterial concordance RV–PT. (B) Discordance is illustrated by the fact that the vessel with an early bifurcation (red arrows) is a PT coming out of the LV in a TGV.

A vessel with an early bifurcation is a pulmonary artery. If it comes from the left ventricle it is the very definition of a ventricular arterial discordance, something which is always seen in transposition of the great vessels.

Axial Transverse View

This is shown in Figure 4.28.

FIGURE 4.28 (A) Transverse path perpendicular to the PT wall. (B) Good echogenicity of the wall. The meeting point of the pulmonary valves (blue arrow) in the center of the vessel confirms the normality of their movements.

Why

This view allows us to be perpendicular to the PA wall which, because of the nature of the approach, appears little echogenic. It is very useful when conditions are difficult.

How

This is ideally from the axial lateral four-chamber view. It is sufficient to effect a cranial translation to make appear a tubular image whose bifurcation rapidly guarantees that this is the PA. A perpendicular view of the PA where the sigmoid valves are shut is preferably chosen as a recorded frame because they generate a small median, which underlines their normal mobility.

View Of The Right Tract, Small Axis

This view is close to the anatomic view called the ductus arteriosus (DA) (Fig. 4.29).

FIGURE 4.29 View of the right tract, small axis. (A) Movements of the probe turning around the PT axis. (B) The right outlet opening is “unrolled.”

Why

More complete, yet difficult to produce, it allows us to see all of the right tract with a single view: RA, RV, PT, and DA.

How

Beginning with the four-chamber view, we manage a cranial translation of the probe, by making an oblique movement to the left.

Pitfalls Of The RV–PT View

At the level of the great vessels there is a serious risk of confusing the aorta for a PA, creating the false diagnosis of a TGV by mistaking a ventricular arterial discordance.

If we recognize an Ao by three vessels emerging from its arch, it is the early bifurcation of the PA that confirms that we are in effect dealing with the trunk of the PA.

The Three-Vessel View Or The Two Crosses

This is shown in Figure 4.30. This view, first described by Yoo in 1997 and 1999,⁹^,¹⁰ has been quickly developed and its increasing importance, due in part to the simplicity and quickness in obtaining it as compared to the long axis view of the aorta,¹¹ gives us a summary of more or less all outlet pathologies such as the aortic arch,¹² and often disorders of inlet. Normal values were established for each vessel.¹³

FIGURE 4.30 The three-vessel view or the two crosses. (A, B) Situation of the axial and sagittal views as placed in the heart. (C) How to get it: parallel translation from the TAD to the three-vessel view, meeting the four-chamber view. This shows a very short left outlet, then the right outlet arising to the three-vessel view. (D, E) Anatomic–US correlations.

Why

This view visualizes, from left to right, the ductal arch, the aortic arch, and then the SVC sectioned transversally. In this way we have reviewed all the outlets of the heart in one single view. Right and left outlet positions are seen and their diameters can be studied, and modified in cases of CTC. It also allows the exploration of the aortic arch, researching interruptions and its posterior diameter, which is particularly interesting in the diagnosis of coarctation at the end of pregnancy. These points were classically researched on the aortic arch sagittal view, but were sometimes very difficult to obtain. The three-vessel view, on the other hand, is almost always possible.

How

This view is, as we have described in the “A fast glance” section above, taken in the continuity of the cranial translation: the four-chamber view and RV–PA. By being placed in the axis of the vessels, the use of color Doppler can be a useful complement in difficult cases.

It is wise to finish the examination by color Doppler¹⁴ because verifying that the direction of the flow is in the same direction, as well as the respective speeds of this flow, is a very important element in determining normality.

In paying special attention to the aortic arch (which can already be studied in the three-vessel view in “A fast glance”), any acceleration in flow at the level of the isthmus should suggest the possibility of the formation of a coarctation. The study of flow can be completed by taking the measure in pulsed Doppler just downstream of the origin of the left subclavian artery.

In certain pathologies, it allows us to rapidly identify a retrograde flow, which is a serious element involved in ductal dependence.

Pitfalls Of A Normal Three-Vessel View

In reality there are few pitfalls with this view because it allows each outlet structure to be represented in the cardiac outlet architecture so that pathologically at least one of the elements can be seen as “abnormal”.

We should not neglect to study flow in the color mode; particularly in the third trimester, reassuring us that we have not picked up any signs of coarctation.

Sagittal View Of The Aortic Arch

This is shown in Figure 4.31.

FIGURE 4.31 (A) Axial view showing the different directions between the origin of the aorta and the aortic arch (in red) compared with the four-chamber view (in yellow) and the TAD. The aortic arch is viewed starting with an orthogonal translation (curved arrows) from the top of the arch on a three-vessel view. Note the position of the sigmoid valves: pulmonary (small blue arrow) and aortic (small red arrow), more posterior and inferior in the center of the heart. This gives us a narrow hooked cross (large red arrow) that will be enlarged of the aorta receives the RV flow. In this case the origin of the aorta would be at the RV outlet, shown with the large blue arrow. (B–D) Anatomic correlations. (E, F) Ductal arch showing its anterior and superior origin (large blue arrow), giving a normal enlarged cross compared to the aortic arch (B, F).

Why

Verification by this view gives us a clear “proof positive” of the normal outlet by visualizing:

• The emergence of the aorta in the center of the heart.

• Its regular diameter, without any obvious asymmetry between the anterior and posterior sections of the aortic arch.

• The emergence of the three vessels of the head and neck.

Flow forms the chambers: the diameter and the curve of the arch informs us also of its flow (and indirectly of that of the PA).

Visualization of the complete arch is, outside of this, useful in the diagnosis of pathologies: aortic interruption or coarctations of the aorta.

!!! Attention !!!

The aortic arch should not be confused with that which describes the RV–PT–DA or the ductal arch, for these two axes are only separated by about 10°. The trajectory of the ductal arch is practically axial, but it can be modified due the relative physiologic overload of the right tracts at the end of pregnancy. The ductal arch becomes more rounded and perhaps can be taken then for an aortic arch. Particular attention should be taken of the anterior and superior curve, which is absent in the case of interruption of the aortic arch.

How

The approach of the aorta is achieved in a slightly oblique sagittal plane by the anterior or posterior pathway. This is done using the left paraspinal window. The aortic arch appears in the form of a candy cane. Just as in the characteristic sign of PA with its bifurcation, only the departure of the vessels of the neck can ensure that this is the aorta. It is important to remember that this pathology occurs mainly after birth when the arterial duct closes.

Pitfalls Of The Aortic Arch View

The principal pitfall consists of confusing the aortic arch with the ductal arch. The origins of the aortic arch are posterior and inferior giving it the form of a candy cane, very regular and with a small radius.

Opposite to this, the origin of the ductal arch, more anterior and superior to the PA, leaves it appearing more horizontal.

The aortic arch is identified by the departure of three vessels from the arch.

The confusion between these two elements can be simplified, especially at the end of pregnancy when the relative overload of the right tract causes it to be elevated, often situated above the aortic arch. If there is the slightest doubt, you should concentrate on showing the existence of the origin of the vessels of the neck, thus identifying the aortic arch.

Only seeing the three vessels exiting from the superior section of the arch can confirm that this is indeed the aorta.

References

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