The potential for subpulmonary obstruction in complete transposition after the arterial switch procedure. An anatomic study

Increasing experience with the arterial switch procedure has revealedthat, in some instances, obstruction of the newly created sub-pulmonaryoutflow tract is a major problem. In this study, we examined the rightventricular outflow tract in 51 specimens of complete transposition, 18 ofwhich were associated with a ventricular septal defect. We focussed ourattention on the musculature which made up the outflow region andconsidered variations from that found in the normal right ventricle. Ourgross observations showed differences in morphology which produced asharper angulation between inflow and outflow when compared to the normal.Discrete outflow obstruction was found in 11 hearts (8 with ventricularseptal defect and 3 with an intact ventricular septum). The obstruction wasdue to deviation of the outlet septum in 5, and anomalous muscle bundle in1, hypertrophy of septomarginal and septoparietal trabeculations in 3 andcircumferential infundibular hypertrophy in 2 hearts. Coexistingobstruction of the left ventricular outflow was present in 3 hearts. Theanatomical substrates of discrete obstruction should be identified bypreoperative cross-sectional echocardiography and/or angiography.Modifications in surgical techniques or radical resection of theobstructing musculature could then be performed to avoid the problem ofsubpulmonary obstruction after the arterial switch procedure.