Summary
Completion of the total cavopulmonary connection and creation of the majority of vascular anastomoses are currently usually performed surgically. The major disadvantage of the surgical approach, however, is its invasiveness, as patients undergoing cardiac surgery generally need sternotomy and cardiopulmonary bypass – often with cardiac arrest – commonly resulting in a prolonged and complicated postoperative intensive care period. Transcatheter procedures, in contrast, have a lower risk of complications, shorter intensive care and total hospital stays, and do not need a cardiopulmonary bypass or sternotomy. The second part of our review focuses on new advances in transcatheter technology, which will allow safe and effective percutaneous management of patients requiring the creation of an intervascular anastomosis and completion of the total cavopulmonary connection. It will create a therapeutic alternative able to reduce the surgical burden on this group of patients.
Résumé
La totalisation d’une circulation de Fontan et la création de la grande majorité des anastomoses sont actuellement réalisées par voie chirurgicale. Cette technique est cependant invasive nécessitant sternotomie et circulation extracorporelle avec ou sans arrêt circulatoire avec comme résultante un séjour prolongé en soins intensifs. Les procédures percutanées au contraire sont moins invasives sans besoin d’abords chirurgicaux complexes ni circulation extracorporelle avec comme résultant un séjour plus court en soins intensifs. La deuxième partie se concentre sur les nouvelles techniques percutanées de création d’anastomoses vasculaires et de totalisation de la dérivation cavopulmonaire. Ces approches devraient apporter une alternative thérapeutiques élargissant le champs d’application du cathétérisme interventionnel.
Background
Most congenital defects of the heart and great vessels require intervention, either corrective or palliative, to increase survival, relieve symptoms and/or improve quality of life. Interventions can be performed either surgically or transcatheter percutaneously. The major advantages of surgery include:
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working under direct vision with the ability to cut, suture, relocate and remove tissues;
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the opportunity to add various patches and valved or non-valved conduits.
The superiority of the surgical approach is the presumed durability of the repair performed in small children destined to grow. The major disadvantage, however, is its invasiveness, as cardiac surgery generally requires sternotomy, cardiopulmonary bypass and cardiac and/or circulatory arrest, often resulting in a prolonged and complicated postoperative intensive care period. Furthermore, the results of surgical repair on long-term outcomes remain suboptimal, especially in small patients, for complex lesions and after use of grafts. Multiple surgeries, which are often required in complex cases, further increase of the above-mentioned disadvantages.
Various transcatheter techniques and devices have been developed in order to create less invasive alternatives that can – similarly to surgery – alter the intra- or extracardiac flow patterns. In carefully selected patients, closing simple atrial and ventricular defects, occluding or stenting the arterial duct, relieving valvular and vascular stenoses and replacing an arterial valve can now be performed via catheter, without the need for opening the chest and without arresting the heart, thus eliminating the risks and disadvantages of open-heart surgery. However, most of the currently available materials and devices date from the late 1990s and early 2000s, with only slight modifications extending their applicability. They are also only suitable for a small proportion of children with congenital heart disease. In stark contrast, there is currently a continuous flow of new commercialized percutaneous techniques and transcatheter devices in the field of adult structural heart diseases, which provide less invasive management options for conditions not amenable to surgical repair or for which surgical results are unsatisfactory.
The situation in the field of interventions for congenital heart diseases is markedly different. On one side, there is a plethora of case reports and case series describing novel and out-of-the-box applications of existing devices that extend the spectrum of patients treated percutaneously. However, such “off-label” applications of the currently available devices are mostly probing the limits of safety rather than providing true novelty. On the other hand, there are numerous new transcatheter biomaterials, devices and technologies that have the potential to expand the percutaneous approach to a much broader spectrum of congenital cardiovascular lesions and conditions, with safe and durable results in children as well as adults. Nonetheless, virtually all of the current developments in the transcatheter device technology and biomaterials for congenital heart diseases do not go beyond the stage of design or initial animal testing. As a result, the majority of young patients with cardiac defects currently still require surgery, as no transcatheter alternatives exist. We focus here on new advances in transcatheter technology in the field of the creation of vascular anastomosis and completion of the total cavopulmonary connection.
Transcatheter creation of intervascular anastomoses
Right ventricular outflow tract obstructions – often in context of univentricular cardiac malformations – constitute the majority of the cyanotic congenital heart diseases, where interventions are needed early in life to ensure survival beyond infancy. For patients with severe cyanosis and an underdeveloped pulmonary vascular bed, several palliative interventions are possible to increase the critically diminished pulmonary blood flow and allow the growth of the pulmonary arteries. The most frequently used intervention is still the modified Blalock-Taussig shunt using a polytetrafluoroethylene graft between the systemic and pulmonary arteries. Additionally, stenting of the arterial duct and stenting of the right ventricular outflow tract have recently become popular alternatives to surgical shunts in small infants, allowing the postponement of surgical restoration of the right ventricular to pulmonary artery connection. Patients with univentricular heart defects mostly undergo bidirectional superior cavopulmonary anastomosis (Glenn), as a halfway intervention to reduce ventricular volume load . Furthermore, a clinical interest in the descending aorta to left pulmonary artery (Potts) anastomosis recently emerged as palliative management in cases of therapy resistant suprasystemic pulmonary arterial hypertension . All of these types of intervascular anastomoses are currently performed surgically and are often associated with substantial morbidity and even mortality, especially in high-risk patients. Transcatheter procedures, in contrast, have a lower risk of complications, shorter intensive care and total hospital stays, and do not require a cardiopulmonary bypass or sternotomy. While arterial duct stenting is largely restricted to the neonatal period, placement of a rigid bare-metal stent in the non-atretic but severely stenotic right ventricular outflow tract can also be safely performed in older children at high risk for complete surgical repair. There is, however, an issue of stent extraction during corrective surgery at a later stage, which can be a technically demanding procedure . Furthermore, there are some complex patients with atretic or anatomically complicated right ventricular outflow, where neither surgical aortopulmonary shunt nor outflow tract stenting are attractive options. In the search for safer, less invasive and easier techniques for establishing aortopulmonary and cavopulmonary anastomoses, the percutaneous placement of the stent between the lumens of two vessels – creating an intervascular communication – has been proposed . In the case of aortopulmonary anastomosis, a transcatheter approach in the setting of unaltered anatomy allows the avoidance of the problems of surgically induced pulmonary artery deformities, while a stent of an appropriate and fixed size regulates the volume of additional blood flow to the lungs. Transcatheter creation of a Potts shunt potentially carries a smaller risk in comparison to a surgical procedure in patients with therapy resistant suprasystemic pulmonary hypertension and right ventricular failure. In analogy, the transcatheter placement of a stent between the pulmonary venous confluence and the left atrium in uncomplicated cases of total anomalous pulmonary venous connection – together with percutaneous embolization of the vertical vein – can be applied instead of a surgical procedure to establish normal pulmonary venous blood flow to the left atrium and, thus, correction of the defect .
Inspirations for the technical improvement of the concept of stent-enhanced anastomosis between two vessels can be taken from gastrointestinal interventional endoscopy, where several spool-shaped self-expanding covered lumen-apposing stents are already commercially available ( Fig. 1 A–D). Using endoscopic placement of the covered spool-shaped stents, this technique has been successfully used in patients for the drainage of pancreatic pseudocysts and gall bladders, and for creating intestinal bypass in cases of inoperable cancer . Similarly, in cardiovascular interventions, perforating the walls of two adjacent compartments and placing the anastomosing stent endovascularly allows the creation of different intervascular communications. Using this principle, the transcatheter placement of custom-made diabolo-shaped stents has been successfully applied to create atriopulmonary communications as fenestration of the total cavopulmonary connection . The close proximity of the central pulmonary arteries with the different parts of the aorta, and the most distal parts of the superior vena cava creates an attractive possibility of establishing aortopulmonary and cavopulmonary anastomoses through stent deployment between two vessels by an endovascular approach. This technique consists of perforating the adjacent vascular wall by a wire passing from one vessel to the neighbouring one, followed by placement of a covered stent between them. Perforation can be performed either mechanically using a trans-septal needle or the sharpened end of stiff wire, or by means of radiofrequency energy. Either custom-made spool-shaped covered stents ( Fig. 1 E–G) or a commercially available straight covered stent have been used in several experimental studies in animals and human patients . No commercially available specially designed spool-shaped stents exist for cardiovascular interventions, and there is only one – the self-expanding InterAtrial Shunt Device (IASD ® ) (Corvia Medical, MA, US) ( Fig. 1 H) – for reducing left atrial pressure in patients with diastolic heart failure, which closely resembles the configuration of the lumen-apposing stent . As with gastrointestinal interventions, the spool-shaped covered stents facilitate the successful creation and patency of the anastomoses, with the flaring ends of the stent ensuring proper fixation of the stent with the approximation of two adjacent vessels without stent protrusion into the lumen ( Fig. 2 ) . Intuitively, endovascular perforation of the walls of two adjacent vessels and passing the catheters between them seems to be prone to bleeding and vessel damage. It has been shown, however, that in the case of appropriate performance, bleeding is minimal or absent, with no vascular rupture. The proper fixation of both ends of the stent within the two adjacent vessels plays a more crucial role in the safe outcome of transcatheter intervascular anastomosis procedures, as demonstrated very recently in adult patients with severe pulmonary hypertension , and previously in dogs . The long-term consequences of prolonged dilation and apposing effects exhibited by the spool-shaped stents on the vascular walls, as well as the probability of erosion of the flaring flanges of the stent through the wall of smaller vessels, are not known and need to be investigated.
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