One of the most striking features about subaortic stenosis is the diversity of lesions that it encompasses and the inconsistency of terms used in its classification. Authors use the same terminology to denote different conditions and a variety of names for identical lesions. Some terms are descriptive, others histological or anatomical. Choi and Sullivan1 suggested a classification based on morphological features that can be determined on cross sectional echocardiography (table 1).

Short segment obstruction is defined as subaortic stenosis with a length of less than one third of the aortic valve diameter, and consists of types previously termed membranous, diaphragm, discrete, fixed, fibrous or fibromuscular. The advantage of the term “short segment” is that it avoids descriptions that are inaccurate, and does not imply a histological diagnosis for that seen on echocardiography. Long segment subaortic obstruction is defined as stenosis that has a length of more than one third of the aortic valve diameter. This is sometimes called “tunnel” obstruction, but this term is confusing as it is applied to a number of different conditions. Subaortic stenosis can also be caused by deviation or malalignment of structures in the left ventricular outflow tract in association with a ventricular septal defect2 or atrioventricular valve tissue in the subaortic area.

Short segment obstruction is caused by a complex fibromuscular structure a short but variable distance below the aortic valve with extension onto the anterior leaflet of the mitral valve and occasionally to the right coronary cusp of the aortic valve. In addition to being the most common type of subaortic stenosis, controversy surrounds both its cause and management.

A genetic predisposition has been suggested as there are reports of a familial incidence and a similar condition in Newfoundland dogs. Coarctation of the …