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

Increasing experience with the arterial switch procedure has revealed that, in some instances, obstruction of the newly created sub-pulmonary outflow tract is a major problem. In this study, we examined the right ventricular outflow tract in 51 specimens of complete transposition, 18 of which were associated with a ventricular septal defect. We focussed our attention on the musculature which made up the outflow region and considered variations from that found in the normal right ventricle. Our gross observations showed differences in morphology which produced a sharper angulation between inflow and outflow when compared to the normal. Discrete outflow obstruction was found in 11 hearts (8 with ventricular septal defect and 3 with an intact ventricular septum). The obstruction was due to deviation of the outlet septum in 5, and anomalous muscle bundle in 1, hypertrophy of septomarginal and septoparietal trabeculations in 3 and circumferential infundibular hypertrophy in 2 hearts. Coexisting obstruction of the left ventricular outflow was present in 3 hearts. The anatomical substrates of discrete obstruction should be identified by preoperative cross-sectional echocardiography and/or angiography. Modifications in surgical techniques or radical resection of the obstructing musculature could then be performed to avoid the problem of subpulmonary obstruction after the arterial switch procedure.