Comparison of left ventricular outflow tract obstruction in interruption of the aortic arch and in coarctation of the aorta, with diagnostic, developmental, and surgical implications

A morphometric comparison of the anatomic causes of left ventricular (LV) o utflow obstruction in interruption of the aortic arch and in coarctation of the aorta with ventricular septal defect (VSD), based on 30 postmortem cas es of each, revealed that posterior malalignment of the conal septum with a conoventricular VSD was significantly more prevalent with interruption (93 %) than with coarctation (47%) (p <0.001). The ratio of the aortic valve di ameter-ta-the pulmonary valve diameter, which provided a quantitative index of the degree of posterior canal septal malalignment and of the consequent LV outflow tract obstruction at and immediately below the level of the aor tic valve, was significantly smaller with interruption (less than or equal to 0.50 in 67%) than with coarctation (less than or equal to 0.50 in 17%) ( p <0.001), A bicuspid or unicuspid aortic valve, both with interruption and with coarctation, was more prevalent with posterior canal septal malalignm ent (74%) than with normal canal septal alignment (42%) (p <0.05), Posterio r canal septal malalignment was associated with LV outflow tract obstructio n at 3 different sites: subvalvar, annular, and leaflet, The anatomic findi ngs explain the incidence of postoperative LV outflow tract obstruction in patients with interrupted aortic arch after simple VSD closure, and may sup port a surgical strategy of elevating or otherwise removing the posteriorly malaligned canal septum from the LV outflow tract at the time of VSD closu re. (C) 2000 by Excerpta Medica, Inc.