Hypertrophic cardiomyopathy classification

Editors-In-Chief: C. Michael Gibson, M.S., M.D. [mailto:mgibson@perfuse.org]

Overview
There are two variants of hypertrophic cardiomyopathy: an obstructive variant, and a non-obstructive variant.

Obstructive Variant
About 25% of individuals with HCM demonstrate an obstruction to the outflow of blood from the left ventricle during rest. In other individuals obstruction only occurs under certain conditions. This is known as dynamic outflow obstruction, because the degree of obstruction is variable and is dependent on the amount of blood in the ventricle immediately before ventricle systole (contraction). If left ventricular outflow obstruction is present, then this syndrome has been known as wide variety of terms including: Hypertrophic cardiomyopathy or HCM, Asymmetric septal hypertrophy or ASH, Hypertrophic obstructive cardiomyopathy, HOCM, Idiopathic hypertrophic subaortic stenosis or IHSS, familial isolated hypertrophic obstructive cardiomyopathy, familial isolated hypertrophic subaortic stenosis, familial or idiopathic hypertrophic subaortic stenosis, familial or idiopathic hypertrophic obstructive cardiomyopathy, primitive hypertrophic obstructive cardiomyopathy, primitive hypertrophic subaortic stenosis.

Non-Obstructive Variant
A non-obstructive variant of HCM is known as apical hypertrophic cardiomyopathy ,which is also known as nonobstructive hypertrophic cardiomyopathy and Japanese variant hypertrophic cardiomyopathy or the Yamaguchi variant (since the first cases described were all in individuals of Japanese descent).