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Double switch procedure
Congenitally Corrected Transposition of the Great Arteries (CCTGA, CCTGV, L-TGA, or L-TGV)
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Anatomy and pathophysiology
Congenitally corrected transposition of the great arteries (CCTGA) or L-Transposition of the great arteries (L-TGA) occurs when there is atrioventricular discordance as well as ventriculoarterial discordance. Systemic venous return enters the right atrium and traverses a morphological mitral valve and left ventricle, which in turn gives rise to a pulmonary valve and pulmonary artery. Pulmonary venous return enters the left atrium and traverses a morphologic tricuspid valve and right ventricle, which in turn gives rise to an aortic valve and aorta. Although this arrangement results in blue blood going to the pulmonary artery and red blood going to the systemic circulation (physiologically “corrected”), it is complicated by poor long-term performance of the morphologic right ventricle acting as the systemic pumping chamber. CCTGA is also associated with other congenital cardiac defects, such as ventricular septal defect, pulmonary stenosis, and single ventricle.
The traditional approach to patients with CCTGA is to correct the associated defects, leaving the tricuspid valve and right ventricle in the systemic circulation. Long-term outcomes using this approach are predict- ably marginal. Like patients who have undergone the Mustard or Senning procedures for d-TGA, patients managed with the traditional approach to CCTGA often go on to develop right (systemic) ventricular failure and tricuspid insufficiency. A procedure known as the “double-switch” operation has been applied to some of these patients. The procedure involves an atrial-level re-routing procedure (Mustard or Senning) and either an arterial switch or a Rastelli-type ventricular level re-routing procedure.
Application of the arterial switch versus Rastelli depends primarily on the condition of the pulmonary valve. When the pulmonary valve is normal, the arterial switch is applied; when the pulmonary valve is stenotic and a ventricular septal defect is present, the Rastelli is applied. The atrial level re-routing procedure requires that the mouths of the superior and inferior vena cavae be baffled across to the opposite atrioventricular valve. This results in the systemic venous return being directed to the tricuspid valve and right ventricle. Pulmonary venous return is directed to the mitral valve and left ventricle. This atrial level re-routing procedure (Mustard, Senning) is sometimes called an “atrial-level switch.” The arterial switch or Rastelli procedure is then performed. The arterial switch involves switching the great vessels and reimplanting the coronary arteries into the root of the neo-aorta. The Rastelli procedure involves directing left ventricular output to the orifice of the aortic valve with a patch closing the ventricular septal defect and creating right ventricle to pulmonary artery continuity with a valved tube graft or homo- graft. The advantage of the double-switch procedure is that the mitral valve and left ventricle can perform in the systemic circulation, and the tricuspid valve and right ventricle can perform in the pulmonary circulation. The disadvantage is that the operation is technically challenging. Both the traditional repair of associated defects and the double-switch procedure in patients with CCTGA require median sternotomy, cardiopulmonary bypass, and aortic cross-clamping. When the double-switch procedure is chosen, a more extensive operation can be anticipated.
The postoperative course following traditional repair of associated defects in patients with CCTGA is predict- ably similar to repair of those defects in patients with otherwise normal cardiac anatomy. Closure of the ventricular septal defect may be complicated by the development of complete heart block, as the course of the conduction system is frequently abnormal in these patients. When the double-switch procedure is chosen, a more complex postoperative course is the rule. Extensive suture lines predispose these patients to postoperative bleeding and arrhythmias. Long cross-clamp time can result in myocardial dysfunction and the need for significant inotropic support. Invasive monitors used include arterial and central venous catheters. An LA line is used when needed for hemodynamic management. LA pressure acts as a surrogate for left ventricular end diastolic pressure, an excellent indicator of left ventricular performance. Non-invasive monitors include NIRS (near infrared spectroscopy) probes to assess adequacy of regional and global perfusion and traditional pulse oximetry. Vasoactive agents might include epinephrine and/ or milrinone. Numerous other agents are available and are tailored to the specific needs of the patient, targeting adequate oxygen delivery to the tissues of the body and optimization of cardiac output. Intracardiac pressures following repair should be normal. Arterial oxygen saturation should be normal. Length of hospital stay following traditional repair of associated defects averages 3 to 6 days. Following the double switch procedure, hospital stay is likely to be somewhat longer.