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Draw It to Know It: Step-by-Step Double Switch Procedure for Congenitally Corrected Transposition of the Great Arteries
In this video, the authors discuss congenitally-corrected transposition of the great arteries. In order to describe a congenital heart defect adequately, the relationships between heart chambers and great vessels are defined according to the so-called “segmental approach,” thus identifying:
- atrioventricular connection
- ventriculoarterial connection
- and, indeed, cardiac position, atrial arrangement, and the presence of one or two completely or partially developed ventricles.
The ccTGA is a complex congenital heart defect defined by atrioventricular and ventriculoarterial discordance. In its simplest form, it presents without any other structural abnormalities in S, L, L configuration: the atria are in normal position with the left ventricle on the right side, the great vessels are L-malposed with the aorta anterior and to the left of the main pulmonary artery. The interventricular septum lies in a straight anterior plane with side-by-side ventricles.
When choosing a surgical approach to perform the repair, it is always important to be aware of two features:
- the anatomy of coronary arteries, which usually originate from the two aortic sinuses that are adjacent to the pulmonary trunk but can have different courses, steps possibly complicating the surgical repair;
- the location of the conduction system.
In ccTGA with usual atrial arrangement, the atrioventricular conduction axis arises from an anteriorly located atrioventricular node, rather than from the typical AV node, located at the apex of the triangle of Koch. This is important when closing a VSD associated with ccTGA to avoid any damage to the conduction system itself.
Given the presence of both atrioventricular and ventriculoarterial discordance, the circulation is still physiologically normal in ccTGA. Deoxygenated blood is pumped to the lungs to be oxygenated, and oxygenated blood is pumped out to the body.
However, the morphologically right ventricle (RV) is pumping blood to the body in place of the morphologically left ventricle (LV), and this can typically lead to heart failure over time. The video demonstrates the connection between the morphologically right atrium (systemic collecting chamber) connected to the morphologically left ventricle and the pulmonary artery and the morphologically left atrium (pulmonary venous collecting chamber) connected to the morphologically right ventricle and the aorta. This arrangement results in physiologically corrected but not anatomic circulation. The ccTGA is also often associated with other defects impacting the decision of the strategy for surgical repair. The indication for surgery is generally driven by the presence of symptoms or, in asymptomatic patients, by the evidence of declining right ventricular function and worsening tricuspid regurgitation.
The atrial switch-arterial switch operation or double switch aims to perform an anatomic repair for ccTGA when there is no valvular PS and a VSD is associated. The double-switch procedure has been designed to allow the RV to pump deoxygenated blood to the lungs and the LV to pump oxygenated blood to the body. This complex operation is made of three basic steps:
- VSD closure
- Atrial switch procedure
- Arterial switch procedure
Step1: VSD closure
VSD in the subpulmonary area is closed first either through the mitral valve, the right atrium, a right ventriculotomy, or the transaortic approach.
Once VSD closure is accomplished, the atrial switch is the following step.
The atrial septum is completely excised, creating a new common atrium. This step includes the resection of the ovalis fossa, with special care to avoid any injury to the conduction system. Some surgeons remove a portion of the septum secundum in order to facilitate the creation of the superior portion of the pericardial baffle.
A baffle is created so that the systemic venous flow is redirected to the tricuspid valve, while the pulmonary venous return is redirected to the mitral valve: one edge of the baffle is sutured over the opening of the four pulmonary veins and continues with superior and inferior vena cava, while the final edge is secured to the anterior end of the atrial septum.
In the classic atrial switch operation, Senning utilized autologous atrial tissue for all the steps of the venous reconstruction. In situations where the autologous tissue is not sufficient to provide unobstructed venous baffles, Mustard proposed his modification of autologous pericardium. The autologous pericardium is harvested as free patches and then used to create the baffle. An alternative to this approach entails using foreign material, for example, Goretex, to construct the baffle and redirect only the systemic venous return from the inferior caval vein to the tricuspid valve, performing the so-called hemi-Mustard procedure. Indeed, a bidirectional Glenn shunt is, in this case, necessary to direct the venous return from the superior caval vein directly into the right pulmonary artery. The following step is the arterial switch procedure, even if some surgeons prefer to do this step before the baffle suturing if the hemi-Mustard approach with BDG is used.
In the drawing, the paths of great artery transection, coronary artery button formation, and reimplantation sites on the pulmonary artery (neoaorta) are shown. The great arteries are transected to allow the reanastomosis of the distal aortic segment to the proximal pulmonary artery (neoaortic root). Linear incisions in the pulmonary artery are made in preparation for a “trap door” type re-implantation of the coronary artery when their anatomy is the usual arrangement for ccTGA. The “trap door” technique aims to optimize the coronary flow pattern, as the coronary arteries need to be mobilized for a considerable distance in this operation. Transfer of the coronary arteries to the pulmonary root is facilitated by their excision from the aortic sinus with a cuff of the adjacent aortic wall. The proximal aortic segment (neopulmonary root) can be connected to the distal pulmonary artery segment by an end-to-end anastomosis. Depending on the relationship between the great arteries, the Lecompte maneuver can be used to move the pulmonary bifurcation in front of the aorta.
- Mavroudis C, Backer CL (Eds). Atlas of Pediatric Cardiac Surgery. Springer-Verlag London;2015. DOI 10.1007/978-1-4471-5319-1_1
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