THE DIAGNOSIS OF CORRECTED TRANSPOSITION OF THE GREAT VESSELS

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Abstract
Ten patients with corrected transposition have been reported. This was associated with a ventricular septal defect in 6, and in 3 of them there was also pulmonary stenosis, in one pulmonary hypertension, and in one probable pulmonary regurgitation. Two had a single ventricle, one with and the other without pulmonary stenosis the remaining 2 had mitral regurgitation, with a left-sided Ebstein type of anomaly in one. The association of any degree of heart block, particular when this is complete, with features suggesting mitral regurgitation, or of either or both of these with a congenital heart lesion, particularly ventricular septal defect (with or without pulmonary stenosis), is very suggestive of corrected transposition. Clinical examination is not often helpful, but suspicion may be aroused when pulmonary systolic murmurs are maximal low down or to the right of the sternum, when the pulmonary component of the 2nd sound is inaudible in the pulmonary area, but can be heard or recorded elsewhere, or when there are auscultatory signs of pulmonary hypertension without evidence of right ventricular hypertrophy. The chest radiograph may provide valuable information if the ascending aorta gives a straight or convex smooth contour to the left upper portion of the heart shadow normally occupied by the pulmonary artery, or if the arrangement of the great vessels is such that the vascular pedicle appears unusually narrow. In the ecg there may be, in addition to heart block, a Q wave in right chest leads (Qr, QR, or qR, with or without S, qrS, or QS) and an absence of q from the left chest leads; an abnormally prominent Q in leads III and a VF; or deep S waves in all the precordial leads in patients with hypertrophy of the right-sided ventricle. All of these clinical, radiological, and cardiographic features may, however, occur in other circumstances; and may all be absent in some patients with corrected transposition. Their presence, however, should lead to a search for further evidence from cardiac catheterization and particularly from angiocardiography. At cardiac catheterization, the pulmonary trunk is seen to be abnormally medial and it may be difficult to enter. When the tip is in the left pulmonary artery, the course of the catheter in the right-sided ventricle may even be concave to the left. The pulmonary valve is lower than normal. A lateral radiograph shows the catheter to be abnormally posterior. A catheter passed from the right-sided ventricle or retrogradely into the aorta shows that this is situated to the left of and anterior to the pulmonary trunk. Pulmonary arterial wedge or direct left atrial puncture records may provide evidence of mitral regurgitation. Selective angiocardiography shows the parallel great vessels, the aorta being anterior and to the left: the aorta fills from the left-sided ventricle and the pulmonary trunk from the right-sided ventricle. It may be necessary to perform left ventricular angiocardiography, preferably through a catheter passed retrogradely through the aortic valve; and this may show the coronary artery inversion in addition to the abnormal position of the aorta. The differentiation of corrected transposition with an associated cyanotic form of congenital heart disease from complete uncorrected transposition may be difficult. The O2 saturation in a systemic artery is above that in the pulmonary artery, unless there is complete mixing of the pulmonary and systemic venous returns. If no pulmonary arterial sample is obtained, the angiocardiogram should be diagnostic.