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) outflow obstruction in interruption of the aortic arch and in coarctation of the aorta with ventricular septal defect (VSD), based on 30 postmortem cases 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 diameter-to-the pulmonary valve diameter, which provided a quantitative index of the degree of posterior conal septal malalignment and of the consequent LV outflow tract obstruction at and immediately below the level of the aortic valve, was significantly smaller with interruption (</=0.50 in 67%) than with coarctation (</=0.50 in 17%) (p <0.001). A bicuspid or unicuspid aortic valve, both with interruption and with coarctation, was more prevalent with posterior conal septal malalignment (74%) than with normal conal septal alignment (42%) (p <0.05). Posterior conal septal malalignment was associated with LV outflow tract obstruction at 3 different sites: subvalvar, annular, and leaflet. The anatomic findings explain the incidence of postoperative LV outflow tract obstruction in patients with interrupted aortic arch after simple VSD closure, and may support a surgical strategy of elevating or otherwise removing the posteriorly malaligned conal septum from the LV outflow tract at the time of VSD closure.