Totally anomalous pulmonary venous drainage - supracardiac type: ultrasound assessment of anatomically determined stenosis of the vertical vein collecting pulmonary venous return.

The diagnosis of the congenital heart defects, among others totally anomalous pulmonary venous drainage, is based on echocardiography. While the visualization of intracardiac structures rarely causes significant difficulties, the vessels positioned outside the heart, e.g. the pulmonary veins, are often hidden behind tissues impermeable to ultrasounds, which may necessitate the use of other imaging methods, such as computer tomography, nuclear magnetic resonance or angiocardiography. The serious limitation of these techniques, especially in pediatric age, is the necessity to administer general anesthesia and contrast media. In order to obtain clear images, the appropriate concentration of a contrast agent in the vessels is necessary, which is not always possible in a patient with severe circulatory failure. Therefore, every effort should be made to obtain as much information necessary for treatment determination as possible from echocardiography, in spite of its limitations. A significant morphological factor of totally anomalous pulmonary venous drainage is the connection between the pulmonary and systemic veins, which in the supracardiac type is the vertical vein draining into the left brachiocephalic vein. The narrowing of this connection impedes the return of the blood from the lungs, which leads to the secondary edema and severe, abrupt cardiorespiratory insufficiency. Such a narrowing should be sought for in every case of totally anomalous pulmonary venous drainage since it constitutes an indication for an urgent surgery. On the basis of own experience and information obtained from the pertinent literature, the authors describe the rules and criteria of the diagnosis of this rare supracardiac form of the heart defect with the presence of the vertical vein which may undergo stenosis due to a phenomenon called the anatomical or bronchoarterial vise. It is formed when the vessel "pushes through" a narrow opening bordered by the left pulmonary artery from the inferior side as well as the left main bronchus and the arterial duct or ligament from the superior side. This article describes a technique of echocardiographic test enabling the precise visualization of the vessel's course and the differentiation from a more common variant of the defect - without external stenosis.

The totally anomalous pulmonary venous drainage (TAPVD) belongs to relatively rare (less than 1%)( but highly fatal congenital cardiac disorders(. Due to the complex developmental process of pulmonary veins during the prenatal period, there are many anatomical variants of this defect. In most cases, the pulmonary veins form their confluence, which is located beyond the proper left atrial cavity and connected to the systemic veins by a single venous channel. The location of the ostium of this vein, which collects the pulmonary return, constitutes the basis of the division (important from the point of view of a cardiac surgeon) into the supracardiac, intracardiac, infracardiac and mixed types. The medical literature reports various numbers connected with the incidence of individual types(. In the case of the supracardiac type (43–57%), the pulmonary venous return is most frequently directed to the left brachiocephalic vein through the left vertical vein (about 37% of TAPVD) and more rarely to the superior vena cava or the azygos vein (14%). In the intracardiac type (15–21%) the connection place is the coronary sinus or directly the right atrium. In the infracardiac type (23–35%), in its supradiaphragmatic form, it is the inferior vena cava and in the subdiaphragmatic form – the inferior vena cava or one of the veins belonging to the portal system. The mixed type occurs much more rarely (about 6–10%). Here, individual pulmonary veins drain into the systemic veins in various anatomical configurations.

Due to the lack of connection between the pulmonary veins and the left atrium, the blood returning from the lungs is again directed to the systemic venous circulation and/or the right atrium and the only way to fill the left ventricle is the interatrial communication. Each obstacle which narrows the elongated tract leading the blood from the lungs to the left atrium, on the one hand, causes stasis and raises the pressure in the pulmonary circulation, and on the other hand, decreases the left ventricular output as well as systemic perfusion and thus, constitutes a direct threat to life. The prolonged impairment of the pulmonary drainage increases the risk of permanent remodelling of the walls of the pulmonary vascular bed. It also affects the long-term prognosis in patients who survived the postoperative period. The incidence of stenosis in patients with TAPVD is estimated in various reports to 22–79%(. The stenosis may affect the pulmonary veins, their confluence and the venous canal which connects the confluence of the pulmonary veins with the systemic veins as well as the region of the interatrial septum. The stenosis may result from both a pathology of the vascular walls and the external compression(. A special form of stenosis in the supracardiac type is the anatomic variant of the left vertical vein's course in which it has to cross a narrow window bordered inferiorly by the left pulmonary artery, the left main bronchus posteriorly and by the ductus/ligamentum arteriosus superomedially (so-called anatomical vise or bronchoarterial vise)(. It happens when the vertical vein originates from the confluence of the pulmonary veins more medially than usual and heads in the cranial direction, travelling beyond the pulmonary trunk – between its branches. Above the pulmonary trunk branching, the vein turns left at a nearly right angle and, running almost horizontally, crosses the left pulmonary artery. In the region of this crossing, the vein must “push through” the aforementioned structures. Next, it turns again and heads in the anterosuperior direction to finally connect with the left brachiocephalic vein.

The course of the left vertical vein described above is different from the one which is observed more frequently – analogical to the persistent left superior vena cava. In this situation, it originates in the confluence of the pulmonary veins at its left side and does not run between the pulmonary trunk branches. Instead, in its initial fragment, it crosses the left pulmonary artery from the anteroinferior side and then heads directly to the cranial direction and drains into the brachiocephalic vein. Thanks to this, there is no anatomical structure on its way which could compress it. It needs to be emphasized that stenosis resulting from the intrinsic pathology of the vertical vein wall is also possible in this case. Nevertheless, it is not obligatory while the anatomically determined stenosis always causes flow disorders and dramatic hemodynamic consequences.

Early diagnosis of TAPVD (during neonatal or even prenatal period) and, in particular, determining the type of the highest risk enables a prompt surgical correction before the irreversible changes appear(. Thorough and systematic echocardiographic analyses of the course and mutual spatial relations of the vessels enable the establishment of the accurate diagnosis without the need for invasive tests or angiotomography, which require general anesthesia and constitute additional stress for the failing circulatory system(.

As has already been mentioned, in the supracardiac form of TAPVD with anatomically determined stenosis, the vertical vein is winding which practically makes it impossible to fully visualize it in one plane – on one echocardiogram. Therefore, it is necessary to trace its course from the beginning to the end – i.e. from the confluence of the pulmonary veins – to the left brachiocephalic vein. The achievement of this goal is facilitated by “tomographic” views, in which the section plane corresponds to the basic planes: transverse, coronal and sagittal ones. By means of the transducer orientation according to the main directions (down-up, front-back, leftright) we are able to precisely determine the spatial relations between individual anatomical structures. The gradual and smooth movement of the ultrasound beam in the specified directions enables us to trace the course and identify the vessels appearing in the image. High, transverse parasternal views with the ultrasound beam directed from left to right in the intermediate plane between the transverse and coronal ones, are the most helpful. Figs. 1–4 present an example of such a maneuver conducted during the examination of a 5-week old infant suffering from supracardiac TAPVD with anatomical stenosis of the vertical vein presenting with cardiogenic shock.

Fig. 1

High parasternal view. The ultrasound beam in the intermediate plane between the transverse and coronal ones, placed nearly horizontally. The direction indicator of the transducer (V) is pointed specifically to the left. In the center, four pulmonary veins are visible draining into the confluence which is marked with an asterisk (*); in front of the confluent, the transverse sections of the superior vena cava (+), ascending aorta (#) and pulmonary trunk below the branching site (@); directly behind the confluence – the transverse section of the descending aorta (%)

Fig. 4

Slightly above, the vertical vein turns left and crosses the invisible left pulmonary artery from the cranial side; after this crossing, it again turns to the anterosuperior direction in order to drain into the left brachiocephalic vein. In this region, one may also observe the highest part of the pulmonary trunk and, above all, the stenosis of the vertical vein in the place of crossing with the left pulmonary artery. The remaining structures which form the bronchoarterial vise that compresses the vertical vein, i.e. the left main bronchus and the arterial ligament, are impossible to visualize directly in the echocardiographic exam. Nevertheless, their location and course can be determined. The arterial ligament stretches between the descending aorta and the apex of the pulmonary trunk (X symbol in the figure). In the case of the retained patency of the ductus arteriosus, this vessel would of course be visible. The left main bronchus is located right behind the vertical vein and crosses the aorta from the ventral side forming the dorsal bordering for the stenosis. The ultrasound tests do not show the airway, but acoustic shadows appearing in its vicinity may be detected. In presented case the image is not clear enough

A slight cranial movement of the transducer and shift of the ultrasound beam to the horizontal plane presents the branching of the pulmonary trunk; in this region the vertical vein (VV) is visible as it originates from the confluence of the pulmonary veins and runs behind the trunk, between its branches. The remaining structures are localized and marked like in fig. 1

Further cranial movement of the transducer allows for the imaging of another fragment of the vertical vein – from the posterior side of the left pulmonary artery, the right branch is not visible. The remaining markings as above

The flow imaging with the color Doppler technique makes it easier to obtain a clear image of the vessels. This technique is exceptionally useful in the case of inappropriate course of veins. The flow in the vertical vein is presented in figs. 5 and 6 and the examination of a child with TAPVD without the stenosis of the vertical vein is pictured in figs. 7–9.

Fig. 5

Imaging of the vessels in the upper mediastinum by means of the color Doppler. Contraction phase – the flow in large arteries is visible. The intermediate plane between the transverse and coronal ones – closer to the coronal, presents the pulmonary trunk in the region of its branching. Two fragments of the vertical vein: proximal – between the branches of the pulmonary trunk, and distal – draining into the brachiocephalic vein

Fig. 6

The narrowed horizontal fragment of the vertical vein becomes visible after the ultrasound beam is moved a little bit to the anterosuperior direction

Fig. 7

Analogically to fig. 1. The pulmonary veins drain into the common confluence (*), before which the following are noticeable: the sections of the superior vena cava (+), ascending aorta (#) and the pulmonary trunk (@) in the region of branching (the initial fragments of both branches are respectively marked as L and P). The vertical vein (VV) exits the confluence below the left branch of the pulmonary trunk and runs in the anterosuperior direction. The section of the descending aorta (%) may be noticed behind the confluence. The lumen of the vertical vein does not show signs of stenosis at the site of crossing with the left pulmonary artery

Fig. 9

The section analogical to the one presented in fig. 6, i.e. the transverse one, obtained from the zygomatic notch in a plane similar to coronal. The color Doppler examination presents the vertical vein as a straight, wide vessel with its entire course visible – from the confluence of the pulmonary veins to its opening to the left brachiocephalic vein (brach). A highly intensive flow in these vessels draws attention. Moreover, the flow in the pulmonary ostium of the closing ductus arteriosus (^) is visible, which does not cause any deformation to the adjacent vertical vein

After moving the ultrasound beam even more cranially, both branches of the pulmonary trunk are visible. The vertical vein, which crossed the left pulmonary artery from the inferior side, can be found in the left anterior side, far from the structures which could cause a compression

Upon the analysis of the presented images, it may be concluded that during echocardiographic examination, it is possible to precisely trace the characteristic, winding course of the vertical vein, which runs between the main branches of the pulmonary artery and crosses the left branch from the posterosuperior side. This allows for the differentiation from other forms of supracardiac TAPVD. In this condition the compression of the vertical vein by structures forming the anatomical vise is invariably present and resulting stenosis always causes critical hemodynamic disturbances leading quickly to the patient's death(.

The 2D image presenting the pathognomonic anatomical details is frequently of greater diagnostic significance than measuring the flow speed by means of spectral Doppler, particularly in patients with intensified hemodynamic disorders, such as a low cardiac output, which make it difficult to obtain a flow spectrum of satisfactory quality. The maximum flow velocity above 2.0 m/s is considered the diagnostic criterion for pulmonary vein stenosis(. Therefore, the detection of the characteristic, abnormal course of the vertical vein in a child with TAVD in 2D examination, which might be supplemented with the flow imaging by the color Doppler, is equivalent with the diagnosis of significant hemodynamic stenosis and with the determination of urgent indications for the defect correction.