CORRECTED TRANSPOSITION OF THE GREAT VESSELS

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Abstract
Corrected transposition without associated defects can usually be diagnosed only at necropsy. When attention is drawn to the heart in life because of associated defects, certain features raise the possibility of coexisting corrected transposition. Thus, splitting of the second heart sound may be better heard at the right sternal border than on the left and an unusually loud aortic component can sometimes be heard at the second left intercostal space. In the presence of large shunts or pulmonary hypertension however, these signs become obscured. Signs of concomitant "mitral" valve disease may also arouse suspicion. An important clue in some patients is the unusual appearance of the left upper cardiac border in the anterior X-ray due to inversion of the aorta and pulmonary trunk as they arise from the ventricles. Perhaps the most suggestive feature of all is the presence of some degree of atria-ventricular block on the electrocardiogram. The diagnosis can be established at cardiac catheterization. If the catheter can be advanced into the main pulmonary artery (often difficult or even impossible) the anomalous position of the pulmonary trunk can frequently be identified in the anterior X-ray film and with more certainty in the lateral projection. The most certain method of establishing the diagnosis is by angiocardiography which clearly demonstrates the anomalous position of the great vessels. The peculiar anatomy of the ventricles may also be identified. The surgical treatment of the associated defects, particularly ventricular septal defect, is complicated by the difficulty of opening the "right" ventricle due to the abnormal course of the coronary arteries. The presence of uncorrectable "mitral" valve disease also adversely affect the surgical results. The frequent occurrence of heart block following surgical intervention is probably the major reason for advocating a conservative policy in the management of these cases.