Congenitally Corrected Transposition of the Great Arteries
Congenitally corrected transposition of the great arteries (ccTGA) is a complex congenital heart defect that is defined by atrioventricular and ventriculoarterial discordance. Figure 15.1 shows a coronal view of a heart with ccTGA and ventricular septal defect (VSD). The morphologic right atrium (systemic collecting chamber) is connected to the morphologic left ventricle through a mitral valve, connected to the pulmonary artery. The morphologic left atrium (pulmonary venous collecting chamber) is connected to the morphologic right ventricle through a tricuspid valve connected to the aorta. This arrangement results in physiologically corrected but not anatomically corrected circulation. Associated lesions are generally responsible for circulatory aberrations; these include VSDs, pulmonary stenosis (PS) or atresia, and tricuspid valve abnormalities. Congenitally corrected TGA may also occur in association with situs solitus (normal atrial situs) or situs inversus. In addition, the conduction system in patients with ccTGA is notably atypical. Furthermore, the incidence of spontaneous heart block is high, even without surgical correction. Figure 15.2a shows a patient with ccTGA, VSD, and situs solitus undergoing aortobicaval cardiopulmonary bypass with aortic cross clamping and cardioplegic arrest. The relevant right atrial and morphological left ventricular anatomy is depicted, with retraction of the mitral valve for transatrial perimembranous VSD closure. The location of the normally positioned atrioventricular node is included to emphasize the abnormal location of the aberrant atrioventricular node (also shown) and the pathway of the bundle of His as it passes anterior to the pulmonary annulus along the morphologic left ventricular crest of the ventricular septum. The conduction system can be avoided during VSD closure by anchoring interrupted, pledgeted sutures on the right ventricular side of the VSD over the course of the conduction system (Fig. 15.2b). Sutures can be placed on the left ventricular side of the septum at the inferior margin of the VSD, which is safely away from the conduction system. The sutures can then be taken through a prosthetic patch and individually tied to effectively close the VSD.