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Archives of cardiovascular diseases
Volume 110, n° 4
pages 223-233 (avril 2017)
Doi : 10.1016/j.acvd.2016.09.004
Received : 30 May 2016 ;  accepted : 15 September 2016
Cliinical research

Vascular anatomy in children with univentricular hearts regarding transcatheter bidirectional Glenn anastomosis
Anatomie vasculaire chez les enfants avec des cœurs univentriculaires concernant la dérivation cavopulmonaire partielle par voie percutanée
 

Aleksander Sizarov a, Francesca Raimondi a, b, Damien Bonnet a, c, Younes Boudjemline a, c,
a Cardiologie pédiatrique, centre de référence malformations cardiaques congénitales complexes, hôpital universitaire Necker-Enfants–Malades, Assistance publique des Hôpitaux de Paris, 75015 Paris, France 
b Service de radiologie pédiatrique, hôpital universitaire Necker-Enfants–Malades, Assistance publique des Hôpitaux de Paris, 75015 Paris, France 
c Université Paris V Descartes, 75006 Paris, France 

Corresponding author. Cardiologie pédiatrique, hôpital universitaire Necker-Enfants–Malades, 149, rue de Sèvres, 75015 Paris, France.
Summary
Background

Transcatheter stent-secured Glenn anastomosis, aiming to reduce the invasiveness of palliation in patients with univentricular heart defects, has been reported in large experimental animals. The advent of biodegradable stents and tissue-engineered vascular grafts will make this procedure a reality in human patients. However, the relationship between the superior vena cava (SVC) and the right pulmonary artery (RPA) is different in humans.

Aim

To characterise vascular anatomy in children with univentricular hearts, regarding technical aspects and device design for this procedure.

Methods

Retrospective analysis of 35 thoracic computed tomography angiograms at a mean age of 18.1±22.4 months.

Results

Two types of arrangement between the SVC and the RPA were identified: anatomy convenient for immediate wire passage and stent deployment between the two vessels (60%); and pattern of early RPA branching, requiring the perforation wire to traverse the intervascular space to avoid entrance into the upper RPA branch (40%). In patients with the convenient vascular arrangement, the vessels were nearly perpendicular, having immediate contact, with the posterior SVC aspect partially “wrapping” the adjacent RPA in most patients. In patients with early RPA branching, the mean shortest SVC-to-central RPA distance was 4.3±2.7mm. For the total population, the mean length of proximal SVC that allowed stent deployment without covering the brachiocephalic vein was 15.6±5.1mm.

Conclusions

A trumpet-shaped covered stent in a craniocaudal orientation reaching from the SVC into the prebranching RPA seems most suitable for achieving bidirectional Glenn anastomosis percutaneously in humans. However, the short length of the proximal SVC and the presence of early RPA branching pose challenges for optimal design of the dedicated device.

The full text of this article is available in PDF format.
Résumé
Contexte

La dérivation cavopulmonaire partielle (DCPP) par un stent couvert, visant à réduire le caractère invasif de palliation chez les patients avec des malformations cardiaques univentriculaire, a été rapportée expérimentalement chez l’animal. Cependant, la relation spaciale entre la veine cave supérieure (VSC) et de l’artère pulmonaire droite (APD) est différente chez l’homme.

Objectif

Caractériser l’anatomie vasculaire chez les enfants avec des cœurs univentriculaires.

Méthodes

Nous avons analysé rétrospectivement 35 scanners thoraciques à l’âge moyen de 18,1±22,4 mois.

Résultats

Deux types d’arrangement entre l’APD et VSC ont été identifiés : une anatomie favorable pour le passage d’un guide et le déploiement du stent entre les deux vaisseaux (60 %) ; et une division précoce de l’APD induisant un trajet plus long pour une éventuelle perforation (40 %). Chez les patients ayant une anatomie favorable, les vaisseaux sont presque perpendiculaires et sont étroitement en contact, avec la partie postérieure de la VCS enroulant partiellement de l’APD dans la grande majorité des patients. Chez les patients avec une division précoce de l’APD, la plus courte distance moyenne entre la VCS et l’APD centrale était de 4,3±2,7mm. Pour la population totale, la longueur moyenne entre la partie proximale de la VCS et le tronc veineux innominé était de 15,6±5,1mm.

Conclusions

Un stent en forme de trompette dans une orientation cranio-caudale allant de la VSC à l’APD paraît être la forme la plus appropriée pour réaliser la DCPP bidirectionnelle par voie percutanée chez l’homme. Cependant, la courte distance entre la partie proximale de la VCS et le tronc veineux innominé mais également la présence d’une division précoce de l’APD posent des challenges pour l’élaboration la plus optimale d’un dispositif dédié.

The full text of this article is available in PDF format.

Keywords : Cardiac computed tomography, Vascular anatomy, Transcatheter Glenn anastomosis

Mots clés : Scanner cardiaque, Anatomie vasculaire, Dérivation cavopulmonaire partielle par voie percutanée

Abbreviations : 3D, CT, PA, RA, RPA, SVC, TCPC


Background

Bidirectional Glenn anastomosis has become an essential part of the palliation of congenital heart defects, where biventricular repair is impossible or unfeasible [1]. Technically, it is a relatively simple procedure. It can, nonetheless, be associated with morbidity and mortality [2, 3], largely related to slow or absent adaptation to passive blood flow through the pulmonary vasculature in some patients. The adverse effects of intrathoracic surgery and cardiopulmonary bypass can also play a role [4]. The development of the minimally invasive technique establishing bidirectional Glenn anastomosis will help to reduce morbidity related to the extracorporeal circulation and surgical exploration. The proximity of the superior vena cava (SVC) and the pulmonary artery (PA) branch creates the attractive possibility of applying the technique of percutaneous stent-secured intervascular anastomosis. Several animal experiments have already demonstrated the feasibility of percutaneous perforation of adjacent right atrium (RA) and right pulmonary artery (RPA) walls, followed by deployment of long straight covered stents reaching from the SVC cranially into the RPA caudally [5, 6, 7, 8]. This technique allows simultaneous elimination of upper body venous blood flow towards the heart and occlusion of the azygos vein. The availability of biodegradable stents [9] and tissue-engineered vascular grafts [10] will make this procedure a reality in human patients, by eliminating the disadvantages of permanent stenting at a young age. A detailed insight into the relationship between the vessels to be anastomosed is crucial for development of the device design. Differences in vascular anatomy between large experimental animals and humans preclude the direct translation of experimental results and device design to humans [11].

In this study, we analyse vascular anatomy regarding procedural planning and device design for transcatheter bidirectional Glenn anastomosis in children with univentricular heart defects.

Methods
Patients

The database at our institution (Necker Hospital for Sick Children, Paris, France) was reviewed to identify patients with univentricular heart defects who had undergone thoracic computed tomography (CT) evaluation at age>2 months and before the Glenn procedure. The local ethics committee gave its approval for the retrospective review of patient data.

Morphometric measurements

To obtain morphological and morphometric insights into the region of adjacent SVC and RPA regarding transcatheter Glenn anastomosis in humans, all measurements were performed on all included scans, independent of the patient's eventual suitability for the procedure in the clinical setting. Analysis of tissue surrounding the vessels, and measurement of the vessel diameters, distances and angles considered to be important for device design and procedural planning, were done using the Volume Viewer 8.5 (GE Healthcare, Chicago, IL, USA). Two parallel oblique coronal planes were produced along the longitudinal axis of the central RPA – one through the centre of the SVC and the second through the middle of the RPA and its branching point, defined as the crossing of the longitudinal axes of its branches (Figure 1C*, Figure 2C*) – and used to assess the type of vascular arrangement. Patients with scans in which the middle of the SVC projection was lateral to the RPA branching point were defined as having an early RPA branching pattern.



Figure 1


Figure 1. 

Definition of the morphometric measurements for the convenient vascular arrangement. A, B, C and C*. Regular axial, oblique sagittal and oblique coronal planes transecting the superior vena cava (SVC) and the right pulmonary artery (RPA) from a representative patient, as described in the text. D, E, F and F*. Performed measurements by numbers: the diameters of the RPA (1) and the SVC (8); the shortest distance between the two vessels (3 & 5); the width of the tightest intervascular contact (2); the length of the proximal SVC cranial to the level of the RPA (9); and the distance between the RPA branching point (star in C* and F*) and the level of the SVC (10). Additionally, the angle between the anteroposterior plane and the line perpendicular to the RPA wall adjacent to the SVC (4), as well as two angles formed by the line passing the RPA centre and the SVC-RPA contact area's most cranial border and the longitudinal SVC axis (7) or the transverse plane (8), respectively, were measured. br.v: brachiocephalic vein; DAo: descending aorta; LA: left atrium; LPA: left pulmonary artery; mPA: main pulmonary artery; RA: right atrium; r.b: right bronchus.

Zoom



Figure 2


Figure 2. 

Definition of the morphometric measurements for the vascular arrangement with right pulmonary artery (RPA) early branching. A, B, C and C*. Oblique axial, oblique sagittal and oblique coronal planes transecting the superior vena cava (SVC) and the prebranching RPA in a representative patient, as described in the text. The star indicates the RPA branching point, defined as a crossing point of the longitudinal axes of the RPA branches. D, E, F and F*. Performed measurements by numbers: the shortest distance between the SVC and the RPA without interposition of its branches (3 & 5), and the width of the intervascular space free of adjacent structures (2). The remaining measurements are as described in Figure 1. AAo: ascending aorta; br.v: brachiocephalic vein; DAo: descending aorta; LA: left atrium; LPA: left pulmonary artery; mPA: main pulmonary artery; RA: right atrium; r.b: right bronchus.

Zoom

In patients without such a pattern, the regular axial plane through the middle of the RPA, followed by the oblique sagittal plane through the middle of the SVC and perpendicular to the adjacent RPA wall were produced (Figure 1). For patients in whom an early RPA branching pattern was identified, the oblique axial and oblique sagittal planes were prepared through the branching point of the central RPA and the middle of the SVC (Figure 2). Care was taken that the oblique axial plane transected the origin of the upper RPA branch. For both types of vascular arrangements, the resulting planes were used to perform the measurements illustrated and defined in Figure 1 and Figure 2. To determine intra- and interobserver variability, all the above-mentioned measurements were repeated by two investigators independently (A. S. and F. R.).

Three-dimensional reconstruction

CT angiographic images from a representative patient with a univentricular heart defect judged as a suitable candidate for transcatheter Glenn anastomosis were used to prepare a three-dimensional (3D) reconstruction of the vessels. After loading the serial images into the 3D reconstruction software (Amira, version 5.2), label-fields were created manually for the walls of the SVC and part of the RA (colour-coded as blue) and PAs (colour-coded as purple). The tracheobronchial lumen was colour-coded as light green. After correcting label-field deformities, the 3D surface was generated, simplified and further smoothed to obtain the final 3D model of the vessels. By reconstructing the space between the adjacent labels for the RPA and SVC walls, we obtained the borders of the intervascular contact with the shortest constant distance between these two vessels.

Statistical analysis

Mean values±standard deviations were calculated where appropriate. Differences between samples were tested using Student's t distribution two-tailed test, with a P value<0.05 considered significant.

Results
Clinical data

Thirty-five thoracic CT angiograms from 34 patients with different cardiac defects of the univentricular type, taken before the Glenn procedure, were analysed. One patient with two scans separated by 6.5 years was included. The mean age of the patients at the time of the scan was 18.1±22.4 months (range: 2.5–90 months); 66% of the scans were from patients aged<12 months. Overall, 90% of the whole population had undergone different types of surgical palliation before CT evaluation. In particular, 48% of patients had a systemic-to-PA shunt (some in the context of a Norwood procedure), while 39% had received PA banding as initial palliation. After the CT scan, 80% of the children underwent bidirectional Glenn anastomosis. Seventy-five percent of the whole analysed population had indications for concomitant surgical interventions at the moment of creation of the cavopulmonary connection, such as Damus-Kaye-Stansel anastomosis, patch-plasty of PAs or transection of systemic-to-PA shunts. However, as the CT scan is not a part of the routine evaluation before the Glenn procedure at our institution, patients with hypoplastic PAs needing patch-plasty at the time of Glenn anastomosis were overrepresented in the study population. This did not allow adequate assessment of the proportion of patients who were eventually unsuitable for transcatheter Glenn anastomosis in the clinical setting.

Spatial relationship between the adjacent RPA and SVC

Two types of arrangement between the SVC and RPA with its branches were identified. Twenty-one (60%) scans demonstrated an anatomy convenient for immediate wire passage and stent deployment between the two vessels (Figure 3). Fourteen (40%) scans showed a pattern of early RPA branching, where the SVC was in contact with the branches of RPA, which required an SVC-to-RPA wire passage through the extravascular space to avoid entrance into the upper RPA branch (Figure 4). Patients with the early RPA branching pattern, compared with those with the convenient vascular arrangement, tended to have a higher prevalence of systemic-to-PA shunts (64% vs. 40%; P =0.17) and fewer PA bandings (21% vs. 55%; P =0.05). In patients with the convenient vascular arrangement, the SVC and RPA were in immediate contact, and nearly perpendicular to each other, with the dorsal SVC aspect partially “wrapping” the adjacent RPA. Figure 5 illustrates further the spatial relationship between the RPA and the SVC, and demonstrates the two possible orientations of the SVC-to-RPA anastomosing stent, using different views of the 3D model based on the representative thoracic CT angiogram of a patient aged 5.5 months with a univentricular heart defect and a tight SVC-RPA contact.



Figure 3


Figure 3. 

Morphology of the region with adjacent right pulmonary artery (RPA) and superior vena cava (SVC) in three representative patients with vascular anatomy convenient for immediate SVC-to-RPA wire passage and stent deployment. A, C and E are the oblique ventral views and B, D and F are the left lateral views of the maximum-intensity projections, with the SVC being immediately anterior to RPA. Images in A and B are from a patient with the typical arrangement of the SVC posterior aspect partially “wrapping” the adjacent RPA. Dotted circles point to the orifice of brachiocephalic vein (br.v), while dashed lines represent the contours of the posteriorly-located RPA and its branches, which are clearly visible lateral to the SVC. Double arrows point to the range of different lengths of the proximal SVC (7–21mm) allowing deployment of the stent without covering the brachiocephalic vein orifice. AAo: ascending aorta; LA, left atrium; p.v., pulmonary vein; RA: right atrium.

Zoom



Figure 4


Figure 4. 

Morphology of the region with adjacent right pulmonary artery (RPA) and superior vena cava (SVC) in three representative patients with the RPA early branching pattern. A, C and E are oblique dorsal views and B, D and E are oblique cranial views of the maximum-intensity projections, with the SVC being in contact with RPA branches. Asterisks indicate the systemic-to-RPA shunt, while dashed lines represent the contours of the anteriorly-located SVC. The dotted lines refer to the trajectory of the perforation wire through the extravascular space between the SVC and the central RPA, to avoid entrance into its upper branch. Note that passage of the wire and, thus, SVC-to-RPA stent deployment, would be still possible even in the presence of the early RPA branching pattern. AAo: ascending aorta; DAo: descending aorta; LA: left atrium; LPA: left pulmonary artery; mPA: main pulmonary artery; p.v., pulmonary vein.

Zoom



Figure 5


Figure 5. 

Spatial relationship of the vascular walls in a patient with univentricular heart, transposition of the great arteries, pulmonary artery banding and the representative convenient vascular arrangement. A. Cranio-right lateral view of the whole reconstruction. B and C. Ventrocranial and dorsocaudal views of the oblique transverse cuts through the superior vena cava (SVC) and right pulmonary artery (RPA), respectively. The dashed circle schematically represents the cross-section of the presumably suitable ∼9mm stent, corresponding to the SVC diameter in this patient. Dotted arrows indicate the RPA branches being relatively close to the eventual stent. D and E. Left and right views of the sagittal cut through the SVC, respectively, to illustrate schematically the two methods of stent deployment to create an SVC-to-RPA connection: perpendicularly to the SVC blood flow, with a need to separately close off the SVC-right atrium (RA) junction (asterisk in D); and in a craniocaudal stent orientation through the cranial border of the SVC-RPA contact with the simultaneous RA-SVC junction occlusion (asterisk in E). Note, however, the short length of the proximal SVC, making it possible to avoid covering of brachiocephalic vein (br.v) orifice. F. Volume-rendered reconstruction of the vessels from the same patient, 7 months after surgical creation of the bidirectional Glenn anastomosis, which has a very similar SVC-RPA angulation (dashed line) to the eventual connection created by the craniocaudally oriented stent. LA: left atrium; LPA: left pulmonary artery; r.br: right bronchus; tr: trachea.

Zoom

Three angles related to procedural planning and stent deployment in a fashion as close to the surgical configuration of the Glenn anastomosis as possible were measured (Figure 6). These angles differed significantly between patients with the convenient vascular anatomy and those with an early RPA branching pattern (Table 1), eventually resulting in a more anteroposterior orientation of the SVC-to-RPA stent in the second group. The first angle corresponds to the rightward rotation of the angiographic lateral projection to produce a left anterior oblique view of the SVC and RPA walls next to each other, with minimal overlay of their shadows. The second angle corresponds to the cranial angulation of the angiographic anteroposterior projection, producing complete overlay of the wire perforation points on the SVC and central RPA walls at their contact's most cranial border. Finally, the third angle is the angle of the delivery catheter curved tip within the SVC, to promote the passage of the perforation wire exactly through the SVC-RPA contact's most cranial border, while taking the trajectory with the shortest distance to the central RPA, to avoid entrance into its upper branch. Figure 6 demonstrates the proposed angulations and rotations of the angiographic C-arms, and shows resulting views based on patient-specific 3D vascular anatomy.



Figure 6


Figure 6. 

A. Schematic representation of the posteroanterior C-arm position (12–68° of cranial angulation; α2), and the resulting angiographic projection for right pulmonary artery (RPA) and superior vena cava (SVC) visualization, with complete overlay at the most cranial border of their tight contact. B. Schematic representation of the lateral C-arm position (14–93° of leftward rotation; α1), and the resulting angiographic projection of the RPA and SVC, having minimal overlay. An introducer-sheath with a curved tip (104–180° of angulation relative to the SVC longitudinal axis; α3) is simulated within the SVC, with the end pointing to the SVC-RPA tightest contact area's cranial border. A ring with a dashed line schematically represents a snare within the RPA, in the vicinity of its contact with SVC. The profile and en face projections of the introducer-sheath within the SVC and the snare within the RPA in the posteroanterior and lateral views should give precise visualization of the course of the wire passing through the adjacent walls of the SVC and RPA at the cranial border of their tightest contact (or shortest distance between them), facilitating SVC-to-RPA stent deployment in a craniocaudal orientation. br.v: brachiocephalic vein; LPA: left pulmonary artery; mPA: main pulmonary artery RA: right atrium; tr: trachea.

Zoom

Morphometry of the region with adjacent RPA and SVA

Six patients had bilateral SVCs without bridging brachiocephalic vein; in these children, only right-sided structures were measured. Table 1 summarizes the results of the morphometric measurements. On 64% of the scans showing an early RPA branching pattern, and on 33% of those demonstrating the convenient vascular anatomy (P =0.07), the central RPA diameter was under two-thirds of SVC diameter. No patient had discontinued or extremely hypoplastic PAs. The SVC diameter itself and the length of its proximal part were very similar in patients with both types of vascular arrangement. For infants aged<1 year, the mean length of the proximal SVC allowing covered stent deployment without closing off the brachiocephalic vein was 13.8±3.9mm (range: 7.4–20.4mm). The opposing walls of the SVC and central RPA were surrounded in all directions by mediastinal tissues to a variable extent. SVC-RPA contact was bordered by the left atrial wall caudally, and by the ascending aorta or pulmonary trunk, and the right-sided pulmonary veins, medially and laterally, respectively (Figure 3 and Figure 4). In no patient was the lung tissue or bronchial lumen identified between the two vessels or immediately cranial to the RPA. In patients with the convenient vascular anatomy, the branching point of the RPA was located lateral and close to the SVC, with a mean distance to its middle of 4.1±2.0mm (range: 1.3–8mm). The extension of the SVC-RPA contact medially, allowing vessel wall perforation maximally away from the upper RPA branch, was 4.7±1.9mm (range: 2.7–8.9mm). In patients with the pattern of early RPA branching, its point was located medial to the SVC, at a mean distance to its middle of 8.1±3.8mm (range: 1.8–15.2mm). In all but two patients with the early RPA branching pattern, mediastinal tissue filled the space of variable size between the non-contacting SVC and central RPA walls and surrounding structures. The shortest distance and width of space between these vessels that was free of adjacent structures varied widely between patients, without correlation with any variable, including age. In all patients where the azygos vein was visible on the scan, it arrived into the proximal SVC immediately below the brachiocephalic vein. However, this structure was clearly visible only in a minority of the scans, which did not facilitate accurate distance measurements.

Discussion

Development of the transcatheter alternative for creation of the bidirectional Glenn anastomosis will help to reduce palliation invasiveness and associated morbidity in patients with univentricular heart defects. There have been several reports of successful feasibility studies concerning transcatheter Glenn anastomosis in large experimental animals [5, 6, 7, 8]. The advent of biodegradable stents and tissue-engineered vascular grafts [9, 10] will also make this procedure a reality in human patients. However, differences in vascular anatomy preclude direct extrapolation of results from animal experiments to human patients [11], where systematic evaluation of the anatomical aspects related to such a procedure is presently lacking. With our study, we sought to fill this gap, and to provide discussion of the implications of the anatomical findings for device design and procedure planning.

Suitability for transcatheter stent-secured Glenn anastomosis

Application of the transcatheter technique to establish cavopulmonary anastomosis should exclude the need for preceding or concomitant surgical interventions. Patients undergoing Glenn anastomosis, however, often have adjoining intracardiac and vascular problems, only some of which can be addressed percutaneously. Thus, an undesired native or artificial additional PA flow can be eliminated using a variety of transcatheter occluders [12, 13, 14]. Similarly, stenosis of the PA branches can be safely relieved by stenting, which can also now be done in infants [15, 16]. However, permanent RPA stenting may complicate the transcatheter Glenn procedure or other consecutive interventions. Moreover, transection of shunts, patch-plasty of hypoplastic PAs and creation of the Damus-Kaye-Stansel anastomosis – surgical interventions performed in 75% of patients in our study – are not safely replaceable by the currently available transcatheter options. Although our study population, selected based on availability of preoperative cardiovascular imaging, allowed the comprehensive analysis of the anatomy related to the procedure, it did not accurately represent the real proportion of unsuitable transcatheter Glenn shunt candidates. Most probably, in the entire population of patients receiving Glenn anastomosis, this proportion is considerably smaller. Substitution of surgical shunts with arterial duct stenting [17], advances in biodegradable stents [18] and further improvements in transcatheter techniques will allow preceding and concomitant problems to be addressed percutaneously in the future, without interfering with the transcatheter creation of the Glenn anastomosis and, thus, further increasing the proportion of suitable patients.

Procedural considerations and planning

In human patients, an SVC-to-RPA stent deployment through the centre of the intervascular contact necessitates separate closure of the SVC-RA junction, and probably hemodynamically disadvantageous anastomosis orientation perpendicular to the SVC blood flow (Figure 5D). By comparison, stent deployment through the most cranial border of the SCV-RPA contact will result in a more favourable communication along the SVC blood flow, with simultaneous occlusion of the SCV-RA junction, resembling the surgically created Glenn anastomosis (Figure 5E, F). The SVC posterior aspect partially “wrapping” the adjacent RPA, without interposed lung parenchyma, observed in most of our patients, should allow the safe introduction of the perforation wire and stent deployment in this haemodynamically more favourable orientation. Furthermore, a craniocaudally deployed covered stent will invariably result in attachment of the distal SVC to the intact caudal surface of the RPA, which, in turn, will facilitate the transcatheter completion of the total cavopulmonary connection (TCPC) at a later stage [19, 20]. However, blood flow patterns through the stent-secured anastomosis need to be carefully evaluated before the transfer to the patients.

In patients with early RPA branching, there is a slightly longer distance between the SVC and the central RPA, which will necessitate application of different angles of angiographic projections to ensure correct visualization of the perforation wire trajectory, avoiding the upper RPA branch. The longest SVC to central RPA distance was, however, only 9mm, and can be relatively easily traversed by an appropriately guided radiofrequency wire and the delivery sheath for covered stent deployment. We found that the mean length of the proximal SVC in infants that allowed stent deployment without covering the brachiocephalic vein, where the Glenn procedure is most frequently performed, did not exceed 15mm, and will probably pose an important challenge for the stable fixation of the rigid stent in the desired craniocaudal orientation without paraprosthetic leak.

Additionally, half of our patients had systemic-to-PA shunts. Besides the issue of shunt transection to avoid vascular complications as the patient grows, placement of the snare to indicate a direction and catch the perforation wire within the RPA, establishing a venovenous wire-loop for stent deployment, might be technically complicated and not tolerated haemodynamically in patients with a systemic-to-PA shunt as the main or only access to the RPA. These potential difficulties act as a further prompt for initial palliation strategies, avoiding shunt placements.

Dedicated device considerations

An ideal device for the transcatheter Glenn anastomosis should provide a haemodynamically favourable and hermetic SVC-to-RPA communication. At least for the period that is necessary for the healing of the anastomosed vascular walls, such a device should be covered, easily further dilatable and sufficiently rigid to maintain its orientation while firmly attached to the vascular walls. Furthermore, it should neither interfere with vessel growth nor impede TCPC completion at a later stage. Application of biodegradable materials, such as magnesium alloys, to design the stent [9], and use of rapidly endothelializing tissue-engineered vascular grafts [10] as the stent covering, are very attractive, as device remodelling in time will secure vascular growth and facilitate future interventions.

The trumpet-shaped covered stent, similar to the arterial ostial stenting system [21], would be of value as a prototype for such a dedicated device. The flaring end of such a device located within the RPA will minimize protrusion into the vascular lumen, and will secure the bidirectional pulmonary blood flow while leaving the caudal RPA surface intact for (transcatheter) TCPC completion. Obviously, excessive flaring of the device within the RPA should be avoided to minimize the risk of covering the orifice of its upper branch. The covered stent's straight part, resting within the SVC, will occlude the SVC-RA junction, while closing off the azygous vein. Very recently, a long trumpet-shaped self-expanding covered stent was used successfully to establish a transcatheter bidirectional Glenn shunt in pigs [7], thus confirming our earlier proposal [11].

Study limitations

The major limitations of our study were the small number of patients, and the biased study population selection, because of the availability of preoperative imaging virtually only in patients with suspected problems with PAs. However, our systematic analysis of vascular anatomy and morphometry in children with univentricular heart defects provides important insights into the most optimal design of the dedicated device, and into the experimental setup of further studies on transcatheter Glenn anastomosis.

Conclusions

A trumpet-shaped stent in a craniocaudal orientation reaching from the SVC into the prebranching RPA seems most suitable to achieve bidirectional Glenn anastomosis percutaneously in humans, with the short length of the proximal SVC and the presence of early RPA branching posing important challenges.

Disclosure of interest

The authors declare that they have no competing interest.


Acknowledgements

The authors thank the Association pour la Recherche en Cardiologie du Fœtus à l’Adulte (ARCFA) for financial support.

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