Pathology of Left Ventricular Outflow Tract Obstruction.

THE anatomic sites at which obstruction to the egress of blood from the left ventricle may occur are three in number, as follows (fig. 1): the aorta, the aortic valve, and the subaortic region of the left ventricle. Obstruction in the aorta may involve one of two general areas, namely, (1) the arch or just beyond, the lesions taking the forms of classical coarctation, tubular hypoplasia, or interruption of the arch, or, (2) it may involve the ascending aorta. As the clinical manifestations of obstructive lesions in the vicinity of the aortic arch are not usually confused with obstruction in the region of the aortic valve, the author has chosen not to consider these conditions further in this symposium. Rather, consideration to obstructive lesions of the aorta will be confined to those that involve the ascending aorta, lesions which, while varied in appearance, are usually congenital in nature and, collectively, may be termed supravalvular stenosis of the aorta. Obstruction at the aortic valve itself, termed either aortic valvular stenosis or simply aortic stenosis, may be represented by a congenital malformation or may result from acquired disease affecting either an initially normal valve or one that is the site of a congenital malformation; the latter most commonly takes the form of a congenital bicuspid valve. Obstruction occurring proximal to the aortic valve in the outflow tract of the left ventricle is commonly known as subaortic stenosis. This condition is represented by a wide