Comparing Normal and Abnormal Findings in Three-Vessel Trachea View

Enhancing Fetal Cardiac Assessment: Inclusion of 3VTV Views

Fetal cardiac screening plays a key role in identifying potential abnormalities and facilitating early detection of congenital heart diseases. Recent advancements have highlighted the significance of specific views, including the left and right ventricular outflow tract (LVOT and RVOT) views, and the three-vessel (3VV) and three-vessel-trachea (3VTV) views. These views not only detect anomalies within the fetal heart but also provide valuable insights into the aortic arch, systemic veins, and thymus. By incorporating these essential views into fetal cardiac screening, clinicians can comprehensively assess potential abnormalities, such as arterial connections, size, position, and valve appearance. This enables early identification of conditions and appropriate interventions to ensure optimal fetal cardiac health.

The 3VV and 3VTV were initially introduced as a valuable addition to the four-chamber view, thereby enhancing the sensitivity of cardiac screening examinations. In the context of prenatal screenings, the grayscale 4-chamber heart view has demonstrated an accuracy rate of 47.8% in identifying cases of congenital heart disease (CHD). However, when combined with the grayscale 3VTV, the detection rate significantly increases to an impressive 71.7%. This clearly indicates that utilizing both views in tandem is an exceptionally effective method of identifying CHD cases, ensuring that no severe instances of the condition go unnoticed. These findings underscore the immense value of these tools, particularly in situations where resources may be limited.

Anatomical Exploration

To obtain a more comprehensive examination of the fetal heart, especially the aortic and ductal arches, the transducer is moved from the 4-chamber view towards the upper mediastinum and fetus head to capture the 3VTV. The acquisition of the 3VV/3VT can be achieved by initially obtaining a 4CV and subsequently moving the transducer in a cephalad/superior direction towards the fetal head while ensuring a transverse view of the fetal chest. It is important to note that the left side of the image corresponds to the fetal left, and the right side corresponds to the fetal right, with the spine being positioned posteriorly.

In this view, the aortic and ductal arches merge into the descending aorta at an acute angle. The pulmonary artery is the largest visible vessel in the 3VTV, followed by the slightly smaller Aorta, and finally, the smaller superior vena cava (SVC) situated posteriorly.

A satisfactory 3VTV is defined as demonstrating the main pulmonary trunk in direct communication with the ductus arteriosus (DA). To the right of the main pulmonary artery (MPA) and DA, a transverse section of the aortic arch should be visible. The image should also show a cross-section of the SVC and, posterior to it, a cross-section of the trachea. Both arches are located on the left side of the trachea. During a three-vessel trachea view scan, it is common to observe the azygos vein draining into the SVC, which can be identified by adjusting the color scale to a velocity of below 20 cm/s.

The azygos vein is frequently misidentified as the aberrant right subclavian artery. It is situated posterior to the trachea and ultimately drains into the superior vena cava. It is important to have a thorough understanding of the origin and accurate positioning of the aberrant right subclavian artery, and to consider its relationship with the aortic arch rather than the superior vena cava.

The thymus gland, an integral part of our immune system, is located in the middle anterior region of the chest, positioned above the great vessels and between the lungs. In imaging, the thymus gland may appear less bright compared to the lungs. A lack of development or absence of the thymus gland could indicate a higher risk of 22q11.2 deletion syndrome. When the color scale is adjusted to below 20 cm/s, the "Thy-Box" view can be obtained, providing a clearer image of the mammary arteries surrounding the thymus gland.

Sweeping upward past the three-vessel trachea view and slightly to the left, you will find the left brachiocephalic vein (LBCV) also known as innominate vein, which is another essential landmark. The normal blood flow in the left brachiocephalic vein is from left to right, always opposite to the aorta, as shown in the image. The absence of the brachiocephalic vein in the presence of bilateral SVC is a common anomaly. A dilated brachiocephalic vein is observed in cases of AV malformations or total anomalous pulmonary venous connections (TAPVC).

Color Doppler Assessment

One of the most beneficial methods for evaluating the fetal heart is through the use of color Doppler imaging in the three-vessel trachea view. It is highly recommended to become familiar with this approach and include it in standard screening procedures for examining the fetal heart. This useful technique offers insights into size differences, turbulence, reverse flow patterns, and even the presence or absence of a vessel. The color Doppler imaging in both arches should indicate laminar flow towards the fetus's spine, with the same direction in both great vessels. Accurate diagnosis requires careful monitoring and examination of flow patterns, and color mapping is an effective tool for this purpose. It's essential to ensure that the color map is perfectly aligned with the image before making any diagnosis. On a color map, the flow color above the baseline signifies flow towards the transducer, while the flow color below the baseline represents flow away from the transducer. Both examples demonstrate forward flow towards the fetal spine and descending aorta.

A Comprehensive Checklist Approach

The following items are on the NORMAL three-vessel trachea view checklist:

Only 3 vessels present (P-PA, A-AoA, S-SVC), In descending order
The DA converges into a "V shape" with the descending aorta.
Position of vessels: (P-PA, A-Ao, S-SVC, T-Trachea)
DA and AoA are directed to the trachea's left side (anterior to the spine).
Thymus is present, normal in size anterior to the great vessels (PA and Aortic arch) and behind the sternum.
Forward flow: Color Doppler (Both) Great Vessels
LBCV present/flow direction opposite of aorta (L-R)

An Innovative Diagnostic Approach

Recognizing the clues observed with the three-vessel trachea view (3VTV) is of utmost importance when it comes to distinguishing congenital cardiac defects on ultrasound. The distinct characteristics that can be identified in this particular view, such as an abnormal number of vessels, unusual positioning and sizes of the great arteries and other vessels, as well as a misalignment between the systemic and pulmonary circulations, play a pivotal role in ensuring accurate diagnosis and differentiation of various congenital heart defects. By adeptly identifying these clues and comprehending the typical ultrasound findings associated with congenital heart defects in the 3VTV, healthcare professionals are empowered to make precise diagnoses and differentiate these conditions more effectively.

Abnormal Number of Vessels

In normal circumstances, the 3VTV typically shows three vessels: the main pulmonary artery, the aorta, and the superior vena cava. However, if there is a left superior vena cava (LSVC) or total anomalous pulmonary venous connection (TAPVC) present, an additional vessel will be seen, making a total of four vessels visible. It should be noted that in some cases of LSVC, the right superior vena cava (RSVC) may not be present, resulting in only three visible vessels that may appear in a different order. This can be identified by locating the LSVC to the left of the pulmonary artery (yellow star).

In patients with both left superior vena cava (LSVC) and right superior vena cava (RSVC), there is an additional vessel to the left of the pulmonary artery (PA) on grayscale imaging. The 4-chamber view shows an enlarged coronary sinus, and the left brachiocephalic vein (LBCV) is absent. Color Doppler demonstrates flow towards the heart in both the right and left superior vena cava. In contrast, in total anomalous pulmonary venous connection (TAPVC) of the supracardiac type, grayscale shows 4 vessels but with a normal-sized LBCV, and the coronary sinus has a normal size on the 4-chamber view. Color Doppler shows opposite flow in the vertical vein compared to the right superior vena cava, and left-to-right flow in a prominent LBCV.

Solitary Great Vessel

When dealing with Transposition of the Great Arteries (TGA) and Common Arterial Trunk, a diagnostic difficulty arises when there are only two visible vessels instead of the usual three. In the case of D-TGA, grayscale imaging typically shows a single great vessel - Ao (normal size) to the left of SVC & Trachea, forming an L-shaped or bent to the right, with a reverse boomerang sign. Color Doppler usually reveals antegrade flow in the Ao, either straight or curved, occasionally showing Ao & PA flowing in a parallel-side by side arrangement. For C-TGA, grayscale imaging typically displays a single great vessel - Ao (normal size) with an extra space in between followed by SVC to the left of the Trachea, forming a J-shaped or bent towards the left. Color Doppler typically shows antegrade flow in the Ao with a left curvature. In the case of Common Arterial Trunk (CAT), grayscale imaging typically shows a single great vessel - Ao (enlarged) to the right of the trachea and left of SVC, with branching of the left Pa (small). Color Doppler usually demonstrates aliasing due to a dysplastic valve. Accurate diagnosis of the specific cardiac anomaly is essential, and it is crucial to determine which vessel is being demonstrated. The combination of color Doppler and grayscale imaging provides complementary information that can aid in identifying the correct cardiac defect with precision. By employing both imaging techniques, one can enhance their ability to make an accurate diagnosis in cases involving TGA and Common Arterial Trunk, ensuring prompt implementation of appropriate treatment plans.

Solitary Great Vessel - Double Outlet Configuration

The main objectives of grayscale ultrasound in diagnosing double outlet right ventricle (DORV) are to illustrate the abnormal ventriculoarterial connections and the anatomical relationship of the great vessels. The four-chamber view typically appears normal, except in the presence of a ventricular septal defect (VSD). By adjusting the transducer between the five-chamber view and the three-vessel trachea view (3VTV), the parallel alignment of the great vessels can be visualized. In cases where a single convex-shaped vessel is observed in the 3VTV, it is most commonly indicative of malposition of the great vessels. The pulmonary artery is situated posteriorly and inferiorly to the aorta and is not visible in the 3VTV. Additionally, in the specific case described, the absence of the right superior vena cava (SVC) and the persistence of the left SVC are confirmed by the presence of a dilated coronary sinus observed in the four-chamber view.

Abnormal Vessel Size

Obstruction of the right ventricular outflow tract can lead to cardiac irregularities, including an enlarged appearance of the pulmonary artery when viewed through 3VTV imaging. Assessing pulmonary artery size is crucial for diagnosing and managing obstructive lesions in this area, as stenosis narrows or obliterates the artery, enlarging the proximal portion. A range of congenital heart defects, including pulmonary stenosis with poststenotic dilation, pulmonary atresia with or without VSD, Tetralogy of Fallot, and absent pulmonary valve syndrome, can cause abnormal pulmonary artery dilation. In pulmonary stenosis and TOF, grayscale shows a narrow pulmonary artery and color Doppler shows antegrade flow in the pulmonary artery and aorta. The ductus arteriosus connects to the descending aorta in a Y-shaped arrangement. In poststenotic dilation, grayscale shows mild pulmonary artery dilation and color Doppler shows aliasing and antegrade flow. In pulmonary atresia with intact septum, grayscale shows a narrow or invisible pulmonary artery and color Doppler shows retrograde flow in the ductus arteriosus and pulmonary artery with antegrade flow in the aorta and a straight ductus arteriosus. In pulmonary atresia with VSD, grayscale again shows a narrow or invisible pulmonary artery and color Doppler shows retrograde flow in the ductus arteriosus and pulmonary artery with antegrade flow in the aorta and an invisible or tortuous ductus arteriosus. In absent pulmonary valve syndrome, grayscale shows extreme dilation of the pulmonary artery and branches and color Doppler shows aliasing in systole and regurgitation in diastole. In ductus arteriosus aneurysm, grayscale shows a dilated, tortuous ductus arteriosus left of the spine and color Doppler shows aliasing in the ductus arteriosus.

Pulmonary stenosis and TOF are indicated by a narrowed pulmonary artery in grayscale imaging, while color Doppler shows forward flow in both the pulmonary artery and aorta. The ductus arteriosus is observed connecting to the descending aorta in a Y-shaped pattern. When poststenotic dilation occurs, grayscale imaging shows a small enlargement of the pulmonary artery, while color Doppler reveals atypical flow patterns and forward movement. In cases of pulmonary atresia with intact septum, grayscale imaging displays a narrow or undetectable pulmonary artery, while color Doppler shows reversed flow in both the ductus arteriosus and pulmonary artery, as well as forward flow in the aorta and a straight ductus arteriosus.

In cases of pulmonary atresia with VSD, the grayscale imaging reveals a constricted or absent pulmonary artery. Color Doppler shows backward flow in the ductus arteriosus and pulmonary artery, along with forward flow in the aorta. The ductus arteriosus may appear invisible or twisted.

Absent pulmonary valve syndrome is identified by a significant enlargement of the pulmonary artery and its branches as visualized through grayscale imaging. Furthermore, color Doppler imaging during systole demonstrates aliasing, while evidence of regurgitation is apparent during diastole. Conversely, in cases of ductus arteriosus aneurysm, grayscale imaging reveals a dilated and tortuous ductus arteriosus located to the left of the spine. Additionally, the application of color Doppler imaging to this condition allows for the observation of aliasing within the ductus arteriosus.

A small or absent aortic arch raises concerns about a narrowing or constriction in the aorta, called aortic coarctation. This condition reduces blood flow and increases the risk of cardiovascular complications. Aortic coarctation shows a narrow arch on grayscale ultrasound and antegrade flow in both the pulmonary artery and aorta on color Doppler (A). The aortic isthmus, located before where the arterial duct enters the descending aorta, is the narrowest part typically affected by aortic coarctation. Comparing the sizes of the aortic and ductal arches using the three-vessel trachea view allows easy assessment of the fetal aortic isthmus. Notably, a dilated transverse arch may indicate aortic valve stenosis and resulting post-stenotic dilation of the aorta. Aortic stenosis with poststenotic dilation shows dilation of the ascending aorta on grayscale and aliasing with antegrade flow in the dilated poststenotic aorta on color Doppler. Hypoplastic left heart syndrome (B), with or without aortic atresia, shows a hypoplastic or absent arch on grayscale and antegrade pulmonary artery flow with retrograde aortic flow on color Doppler. The integration of grayscale and color Doppler ultrasound offers a powerful diagnostic tool for identifying and assessing abnormalities in aorta size, enabling effective treatment strategies. By employing these techniques collectively, accurate diagnoses and tailored care plans can be established.

Left atrial isomerism is a rare congenital condition that affects the cardiovascular system, leading to various abnormalities. One potential complication of this condition involves the blockage of the inferior vena cava (IVC), causing the azygos vein to drain into the superior vena cava. This unique anatomy can be visualized through the 3VTV, where the SVC may appear similar in size to the transverse arch of the aorta. This distinctive feature not only aids in diagnosing left atrial isomerism but also helps identify other cardiac conditions like Supracardiac-type Total Anomalous Pulmonary Venous Connection and can be a complementary finding with Vein of Galen aneurysms.

Abnormal Alignment

The 3VTV is a diagnostic tool utilized in prenatal ultrasound for assessing the arrangement and alignment of the major blood vessels within the fetal heart. In a typical 3VTV, both the ductal and transverse aortic arch are observable in front of the spine, forming a distinct V shape alongside the trachea and superior vena cava positioned on the right. However, when these structures deviate from this anticipated pattern and do not form the characteristic V-shape configuration, it indicates the presence of an abnormality. This deviation serves as a significant indicator for further investigation and potential diagnosis of congenital heart defects such as right-sided aortic arch, double aortic arch, interrupted aortic arch, and aberrant right subclavian artery (ARSA) in the developing fetus. The various deviations of the right aortic arch with ductus arteriosus encompass several anomalies, including the presence of an aberrant left subclavian artery, mirror-image branching, double aortic arch, and isolation of the left subclavian artery. Specifically, the presence of a right aortic arch with an aberrant left subclavian artery and a double aortic arch may lead to the formation of a vascular ring, resulting in respiratory failure. Consequently, early prenatal identification of this vascular configuration could significantly improve postnatal care.

Right-sided aortic arch with left ductus arteriosus is a rare congenital heart condition in which the aortic arch is positioned to the right of the trachea, while the ductus arteriosus is located on the left side. Grayscale ultrasound imaging allows for visualizing this abnormality, showing the anatomical positions of both structures. However, it is through color Doppler that we can truly appreciate the blood flow patterns associated with this anomaly. With color Doppler, we observe antegrade flow in a U-shaped pattern, where the aortic arch and ductus arteriosus are seen on opposite sides of the trachea. This finding helps clinicians accurately diagnose and evaluate this particular cardiac anomaly. The ability to visualize blood flow using color Doppler not only aids in diagnosing right-sided aortic arch with left ductus arteriosus but also provides valuable information about its hemodynamics. In contrast, the right-sided aortic arch with right ductus arteriosus presents an alternate configuration. Grayscale ultrasound reveals both the aortic arch and ductus arteriosus situated to the right of the trachea. Color Doppler demonstrates antegrade flow in a V-shaped pattern, indicating that both structures are flowing in the same direction on the right side of the trachea.

Double Aortic Arch is a congenital vascular anomaly that can be visualized on grayscale ultrasound as two aortic arches encircling the trachea in a ring configuration. This condition occurs when both the right and left aortic arches persist during fetal development, leading to the formation of an abnormal vascular ring. On color Doppler imaging, antegrade flow can be observed in both the pulmonary artery and both aortic arches, with the left arch typically being smaller than the right. Interrupted Aortic Arch, on the other hand, presents as the absence of the typical V-shaped ductus arteriosus and aortic arch on grayscale ultrasound. This condition arises when there is a discontinuity or interruption in the aorta, resulting in non-continuous blood flow to the distal part of the body. Color Doppler examination reveals only antegrade flow in the proximal portion of the aorta, with no detectable flow distally.

Aberrant Right Subclavian Artery, another vascular anomaly, is best identified using color Doppler imaging. This condition appears as an aberrant vessel traveling inferior to the trachea, with low velocity blood flow directed toward the right shoulder. The anomaly can be detected by observing a low Pulse Repetition Frequency scale (PRF) <20cm/s, indicating slower blood flow through this anatomical variant. In conclusion, the study of blood flow patterns in these defects is essential for their proper identification and comprehension. This understanding has wide-ranging benefits, from more accurate diagnoses to improved treatment strategies and increased detection rates, ultimately advancing our knowledge of these intricate conditions.

Future Directions and Potential Developments

The implementation of the 3VTV in prenatal screening has revolutionized the way congenital heart disease is diagnosed through ultrasound. By incorporating these essential views into fetal cardiac screening, healthcare providers can now achieve a comprehensive assessment of potential abnormalities. This technique has significantly increased diagnostic accuracy and reduced false-positive results, providing relief for expecting parents who would otherwise be unnecessarily stressed. Furthermore, the use of the 3VTV allows for early identification of conditions, enabling healthcare providers to offer timely counseling and support tailored to each specific case. This facilitates informed decision-making regarding further investigations or interventions, ensuring that expectant parents have all the necessary information to make the best choices for their baby's health. As new techniques and technologies continue to evolve in fetal cardiac screening, it is crucial to recognize that the importance of these essential views remains paramount in providing optimal care for expectant mothers and their unborn babies. The 3VTV has made significant contributions to prenatal screening and will undoubtedly continue to play a pivotal role in diagnosing and managing congenital heart diseases effectively.

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Comparing Normal and Abnormal Findings in Three-Vessel Trachea View

Chapter 1