Obstruction of the left ventricular outflow tract: anatomical observations and surgical implications.

Obstruction within the outflow tract from the left ventricle can take several anatomic forms. To understand better these substrates, we reviewed the anatomy in the normal heart and, with this background, focused on the malformations observed at each level of the outflow tract which produce stenosis. We examined 75 malformed hearts and reviewed the literature pertinent to surgical aspects of obstruction. Close study of the normal aortic valve shows the lack of any discrete fibrous structure which can be described in terms of a ring-like annulus. The semilunar attachment of the leaflets makes a crown-shaped arrangement at the ventriculo-arterial junction rather than a strict ring. In the pathological study, valvar abnormalities were found in 45 cases. The valve had three leaflets in 20 cases, two leaflets in 24 cases and one leaflet in to the other. In two cases, additional obstruction was found at the sinutubular junction. Subvalvar stenosis was found in 30 hearts, the aortic valve being trifoliate in 28 and bifoliate in 2. The main substrate of subvalvar obstruction was posterior malalignament of the outlet septum (40%), followed by muscular septal hypertrophy (23%); obstruction was also an intrinsic feature in association with atrioventricular septal defects (14%). Although rare in our material, it can also be due to a fibrous or fibromuscular shelf. In our review of the literature, we have highlighted the various forms of valvar malformation and commented on the surgical options. Clear analysis of both the level of obstruction, and its precise anatomic substrate are essential for optimal surgical intervention.