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What is Hypertrophic Cardiomyopathy (HCM)?

LAST UPDATED: 2008/06/24 13:48
 


 

What is Hypertrophic Cardiomyopathy (HCM)?

Cardiomyopathy is a condition in which the muscle of the heart is abnormal in the absence of an apparent cause. This terminology is purely descriptive and is based on the Latin deviation. HCM is a primary and usually familial cardiac disorder with heterogeneous expression, unique pathophysiology, and a diverse clinical course, for which several disease causing mutations in the genes encoding proteins of the cardiac sacomere have been reported. While HCM has typically been recognized by its structure ie., hypertrophy, the electrical function of the heart are also adversely affected. There are three types of cardiomyopathy: "hypertrophic", "dilated" and "restrictive". The main feature of hypertrophic cardiomyopathy is an excessive thickening of the heart muscle (hypertrophy literally means to thicken). Thickening is seen in the ventricular septal measurement (normal range .08-1.2cm), and in weight. In HCM, septal measurements may be in the range of 1.3cm to 6.0+cm. Heart muscle may also thicken in normal individuals as a result of high blood pressure or prolonged athletic training. Furthermore, there is a fine line between and athletic heart and a heart with HCM.

In Hypertrophic Cardiomyopathy (HCM), the muscle thickening occurs without an obvious cause. In addition, microscopic examination of the heart muscle in HCM is abnormal. The normal alignment of muscle cells is absent and this abnormality is called "myocardial disarray".

myocardial.gif

Myocardial Disarray

These diagrams contrast the regular, parallel alignment of muscle cells in a normal heart with the irregular, disorganized alignment of muscle cells or "myocardial disarray" found in some parts of the heart in hypertrophic cardiomyopathy.

History and Other Names

What's in a Name?

It is confusing. Remarkably, this disease (hypertrophic cardiomyopathy) has been given 75 separate names by individual investigators over the last 40 years. Literally, no other disease can make that claim. Why has this occurred? The principal reason for the proliferation of names has undoubtedly been the heterogeneity and diversity in which the disease is expressed. Few individual investigators have seen large numbers of patients with hypertrophic cardiomyopathy, and therefore individuals have come to regard the overall disease based on their own (sometimes limited) experience. Many of the names are somewhat misleading since they emphasize obstruction to left ventricular outflow which is a highly visible feature of the disease but is probably present in no more than about 25% of all patients. These names include IHSS (or idiopathic hypertrophic subaortic stenosis) which was the first popular term used in the United States; "stenosis" means obstruction. The same can be said for HOCM (hypertrophic obstructive cardiomyopathy) which is still used in the United Kingdom...largely out of habit and convenience.

Nevertheless, virtually all HCM experts and other cardiovascular specialists now regard as the best single name for this broad disease spectrum --- hypertrophic cardiomyopathy or HCM. This term emphasizes the hypertrophy which is the diagnostic marker in most patients and the fact that this disease is a form of cardiomyopathy -- or heart muscle disorder... without mentioning obstruction. Therefore, it is preferable to describe the disease as either "HCM with obstruction" or "HCM without obstruction."

"Cardiomyopathy" itself is a very general term referring to any condition (and there are many) importantly affecting the heart muscle itself while "hypertrophic cardiomyopathy" refers to a specific and genetic condition which usually shows a familial pattern. The most characteristic feature of HCM is a hypertrophied left ventricle (asymmetric thickening of the wall usually most prominently involving the ventricular septum) without abnormal enlargement of the ventricular cavities.

CREATED: 2004/11/23 LAST UPDATED: 2008/06/24