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 ± 2.7 mm. For the total population, the mean length of proximal SVC that allowed stent deployment without covering the brachiocephalic vein was 15.6 ± 5.1 mm.
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.
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 ± 2,7 mm. Pour la population totale, la longueur moyenne entre la partie proximale de la VCS et le tronc veineux innominé était de 15,6 ± 5,1 mm.
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.
Background
Bidirectional Glenn anastomosis has become an essential part of the palliation of congenital heart defects, where biventricular repair is impossible or unfeasible . Technically, it is a relatively simple procedure. It can, nonetheless, be associated with morbidity and mortality , 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 . 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 . 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 and tissue-engineered vascular grafts 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 .
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 ( Fig. 1 C *, Fig. 2 C *) – 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.
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 ( Fig. 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 ( Fig. 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 Fig. 1 and Fig. 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 ( Fig. 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 ( Fig. 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. Fig. 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.
