Summary
Background
The alliance between surgeons and interventionists has inspired creative techniques to surgically precondition the heart for subsequent transcatheter repair. The interest stems from the need to avoid repeated surgeries. Transcatheter Fontan completion of intracardiac pathway has been reported.
Aim
To report a new surgical preparation for transcatheter completion of extracardiac Fontan circulation.
Methods
The inferior vena cava (IVC) was cut and anastomosed end-to-end with the inferior end of a Gore-Tex conduit in 20 lambs. A ring was placed around the IVC near the anastomosis. The superior vena cava was cut and connected with the right atrium (RA) auricle. In group 1 ( n = 9), the Gore-Tex conduit was occluded at both ends by a polytetrafluoroethylene membrane. In group 2 ( n = 11), the upper segment of the Gore-Tex tube was opened and connected to the RA to allow free flow of IVC blood. Fontan completion was attempted 1–3 months following surgery. Animals were sacrificed just after or 3 months after completion.
Results
All lambs were successfully preconditioned. We failed to complete the pathway in all animals from group 1 – autopsy showed occlusion of the pathway. In group 2, there was one postoperative death, one elective sacrifice after 2 months to assess pathway integrity, and nine successful completions. Autopsies showed widely patent pathway and well-deployed covered stents completely occluding the fenestrations.
Conclusions
Circulating extracardiac conduit offers the best option to prepare for extracardiac Fontan completion. This surgical preparation opens new frontiers for transcatheter and hybrid techniques for extracardiac Fontan completion.
Résumé
Contexte
La réalisation de Fontan percutanée a été décrite dans la littérature.
Objectif
Rapporter la création d’un modèle pour la réalisation d’une circulation extracardiaque de Fontan par voie percutanée.
Méthodes
La veine cave inférieure de 20 animaux a été anastomosée avec l’extrémité inférieure d’un conduit de Gore-Tex. La veine cave supérieure a été coupée et reliée à l’auricule droite. Chez neuf agneaux (groupe 1), le conduit de Gore-Tex a été occlus aux deux extrémités. Dans le groupe 2, le tube de Gore-Tex a été largement fenêtré pour permettre la circulation du sang cave inférieur sans contrainte. L’extrémité supérieure était fermée. La totalisation du Fontan a été réalisée un à trois mois après la chirurgie. Les animaux ont été sacrifiés juste après et 3 mois après la totalisation.
Résultats
Tous les agneaux ont été pré-conditionnés avec succès avec un décès postopératoire (groupe 2). Aucune totalisation n’a été possible dans le groupe 1. L’autopsie a montré une occlusion complète des conduits extracardiaques. Dans le groupe 2, un animal a été sacrifié électivement après 2 mois pour évaluer l’intégrité du conduit extracardiaque. Les 9 autres ont eu leur totalisation percutanée avec succès. À l’autopsie, les conduits étaient largement ouverts; les stents couverts étaient parfaitement déployés, occluant le passage conduit-oreillette droit.
Conclusions
Le conduit extracardiaque circulant offre la meilleure option pour préparer à une totalisation percutanée d’un Fontan extracardiaque. Cette préparation chirurgicale ouvre de nouvelles perspectives pour des techniques percutanées et hybrides de totalisation de circulation de Fontan.
Background
Children with functionally univentricular hearts face remarkable struggles throughout their lives. The development of the classic Fontan operation has significantly improved their long-term survival, but repeated surgeries impact on survival and quality of life. The incidence of atrial arrhythmias secondary to atrial scarring after classic Fontan ranges from 4% to 35% at 5-year follow-up, and up to 40% at 10-year follow-up . Atrial arrhythmia may lead to reduced cardiac output and left ventricular dysfunction, both of which may detrimentally affect Fontan physiology. Extracardiac Fontan surgery deserves special attention as it reduces atrial scarring and thereby, the incidence of atrial arrhythmia. Furthermore, the incidences of obstruction of the cavopulmonary pathway, reoperation, thromboembolism and late death is reported low with extracardiac Fontan circulation .
The alliance between surgeons and interventional cardiologists during hybrid procedures has inspired some highly creative techniques to surgically precondition the heart for subsequent transcatheter repair. The interest for such procedures stems from the need to avoid repeated surgeries and accomplish Fontan completion with minimal invasion. The attributes of ideal surgical preparation for transcatheter completion of Fontan circulation include:
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achievement of a safe and viable preparation without the use of extracorporeal circulation and cardiac arrest;
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a minimal quantity of foreign material left in the systemic atrium;
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no interference with sinus rhythm;
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limited atrial scarring;
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the use of conduits of sufficient diameter to accommodate future cardiac growth and thus avoid surgical redo;
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most importantly, safe completion of Fontan circulation using transcatheter techniques.
Keeping these attributes in mind, we have developed new techniques of surgical preparation for further transcatheter completion. We have previously reported the creation of a model that mimics a Fontan circulation, thus allowing surgical conditioning and transcatheter completion to be tested . Both intracardiac and extracardiac pathways were tested in ewes . The extracardiac pathway initially consisted of a non-circulant pathway – an occluted Gore-Tex filled with saline was connected to create the Fontan-like circulation in a model of fully grown ewes. The aim was to test the non-circulant extracardiac pathway and a new circulating pathway in growing animals. In order to try to improve the pathway and see if the good results were sustained in a growing animal model of Fontan, we report here the evolution of a previously published extracardiac pathway in a population (growing animals) more closely related to clinical practice.
Methods
Animals
Twenty lambs weighing 20 ± 2.5 kg were included and divided into two groups: nine in group 1 (non-circulant extracardiac pathway) and 11 in group 2 (circulant extracardiac pathway). Experiments on all animals in group 1 were completed prior to those on animals in group 2. All animals received humane care in compliance with the standards of European Convention on Animal Care. The study was approved by the local institutional ethics committee (INRA, Paris, France). Qualified personnel supervised the procedures and adequate anaesthesia using inhaled isoflurane (1–5%) was used to minimize unnecessary pain.
Surgical preparation
Animals underwent endotracheal intubation and mechanical ventilation under sedation. Surgical preparation was performed without extracorporeal circulation using temporary vascular clamping. The heart was exposed through a right thoracotomy. A Gore-Tex conduit was interposed between the superior vena cava (SVC) and the inferior vena cava (IVC). No anticoagulation was given to animals during the study.
Group 1 (non-circulant)
Animals in group 1 underwent the non-circulant extracardiac pathway surgical technique ( Fig. 1 ) as has been previously reported . Briefly, a 20-mm Gore-tex conduit – de-aired and filled with heparinized saline – was anastomosed to connect the SVC and the IVC. The IVC end was anastomosed in a termino-lateral fashion and the SVC end in a termino-terminal fashion; both ends were occluded with a polytetrafluoroethylene (PTFE) membrane. Due to the latero-terminal connection of the IVC, the blood from the IVC could flow freely to the right atrium (RA) as normal. Metallic rings were placed around the superior and inferior connections at the level of the occluding membranes ( Fig. 1 B).
Group 2 (circulant)
In animals in group 2, the connections were modified to create a circulant pathway ( Figs. 2 and 3 ). At the IVC end, an end-to-end anastomosis was performed that directed all blood from the IVC into the conduit. A nitinol wire was used to create an open ring of diameter 16 mm. Using the property of memory alloy, after straightening and release of constraint, the wire regained its ring configuration. This ring was straightened, placed and fixed around the extracardiac conduit and the IVC just below the level of the anastomosis. In the middle section, a large connection (larger than “classical” fenestration) was created at the upper segment of the extracardiac Gore-Tex conduit. This was connected laterally to a similarly large opening in the RA to allow free flow and washout of the conduit by IVC blood. The SVC was cut and connected to the RA auricle in an end-to-end fashion. The upper end of the Gore-Tex conduit was occluded with a PTFE membrane. A venous segment harvested from a small Contegra conduit (Medtronic Inc., MN, USA) was connected between the Gore-Tex conduit and the SVC to reduce the diameter and allow a smooth connection with the SVC. An end-to-side anastomosis was performed between the venous segment and the SVC. A short stent (CP, Numed, NY, USA; 2 rows) was placed around or inside the venous segment as reported previously . The stent was secured with single stitches before suturing to the SVC. The chest was then closed and lambs were sent to the farm to recover and heal for subsequent transcatheter Fontan completion.
Interventional catheter completion
At 1–3 months after surgical preparation, cardiac catheterization was performed using both right femoral and internal jugular veins (8Fr). Using fluoroscopic guidance, a 7Fr long Mullins sheath (Cook, IN, USA) was placed from the right common femoral vein in the conduit. A paediatric trans-septal needle was advanced into the Mullins sheath and positioned in contact with the membrane separating the conduit and the SVC by tilting the needle clockwise. The position was verified in two planes.
In group 1, we expected to advance a wire in the non-circulant conduit to get contact with the inferior IVC membrane after puncturing the superior SVC membrane. The second membrane would then be perforated and vascular stents would be placed as reported previously .
In group 2, the stent used in the interposed venous segment served as an important radiological landmark to position the needle. When in position, the needle was pushed through the membrane. A 0.014” wire was then passed through the lumen of the needle and snared from the neck. Following the perforation of the membrane, balloons of increasing diameters were inflated at the level of the stent until complete disappearance of the waist. A 14-Fr sheath was advanced over a stiff guide wire into the IVC. A covered stent graft (CP covered, Numed Inc.) mounted on 22-mm BIB catheter (Numed Inc.) was placed to cover and exclude the opening of the conduit with the RA (i.e. large fenestration). Additional bare metal stents (uncovered CP stent, Numed Inc.) were placed at the SVC and IVC connections when required.
Selective angiographies ( Figs. 4 and 5 ) were performed at subsequent steps:
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initially, to confirm the competence of the occluding membrane;
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the patency of the SVC–RA connection;
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the patency of the fenestration;
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after re-establishment of the pathway between the SVC and the extracardiac conduit to confirm opening of the membrane;
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after placement of covered stents to confirm sealing of the covered stents.
