[Myocardial imaging in patients with transposition of the great arteries: comparison between Mustard and Rastelli operations].

Thallium-201 myocardial imaging was performed in 21 patients with transposition of the great arteries (TGA). Thirteen patients were studied before operation, eight patients after Mustard operation and five patients after Rastelli operation. Five patients were studied sequentially before and after the surgery. Each image was compared with hemodynamic and angiographic findings in order to assess the usefulness of this method. In the 13 patients with preoperative TGA, it was possible to differentiate TGA with the intact ventricular septum from TGA with associated anomalies such as patent ductus arteriosus or ventricular septal defect, and also TGA with pulmonary hypertension or pulmonary stenosis from TGA without them by evaluating the degree of thallium uptake in the free wall of the pulmonary ventricle (anatomical left ventricle). The degree of thallium uptake was well correlated with systolic pressure of the pulmonary ventricle (r = 0.98). In the 13 patients with postoperative TGA, it was less correlated with the pulmonary ventricular systolic pressure (r = 0.83). Four cases sequentially studied showed a marked decrease in thallium uptake in the pulmonary ventricle 10 to 16 months after Rastelli operation. But the corrected thallium uptake (thallium activity/ventricular systolic pressure) was more increased compared with the uptake of the systemic ventricle after the surgery. This was probably related to a decrease of the pressure load to the pulmonary ventricle following the surgery and to the fact that there should be some delay of a decrease of the ventricular mass. An increased lung uptake of thallium was noted in the cases of tricuspid regurgitation after Mustard operation, but the degree of regurgitation was not clearly correlated with the increase of thallium uptake in the lung. In five cases after Rastelli operation, one patient showed a high degree of thallium uptake of the pulmonary ventricle (anatomical right ventricle), and the conduit valve calcification and severe pulmonary stenosis were confirmed by cardiac catheterization and angiography. Thus myocardial imaging provides a reliable mean for the qualitative and quantitative assessment of TGA before and after operation.