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What is Hypertrophic Cardiomyopathy (HCM)?

To better understand what Hypertrophic Cardiomyopathy (HCM) is let's first talk about how cardiomyopathies are described.

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 primarily 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. There are some forms of HCM that are currently being debated by the medical community regarding how they should specifically be defined because the cause of the hypertrophy in these cases is now understood to be from other mutations impacting either the storage of glycogen or lysosomal storage within the heart.

While HCM has typically been recognized by its structure ie., hypertrophy, the electrical functions of the heart are also adversely affected. There are four types of cardiomyopathy: “Hypertrophic”“Dilated”“Restrictive” and “Right ventricular”.

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 or wall measurements may be in the range of 1.3cm to 6.0+cm anywhere in the left ventricle. 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, hypertensive heart disease, 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”.

Figure 1:   A. Represents normal cell structure B. Represents abnormal structure known as myocardial disarray C. is a pathology slide of a heart with HCM, not the patter of cells show myocardial disarray. 
It is important to note that myocardial disarray may occur in patches throughout the heart and not be present in 100% of the muscle. 
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Citations:

Maron, B.J. and Salberg, L.  Hypertrophic Cardiomyopathy: For patients, their families and interested physicians.  Blackwell Futura:   1stedition 2001,81 pages; 2nd edition 2006, 113 pages; 3rd edition 2014
Gersh, B.J., Maron, B.J., Bonow, R.O., Dearani, J.A., Fifer, M.A., Link, M.S., et al. (2011). 2011 ACCF/AHA guidelines for the diagnosis and treatment of hypertrophic cardiomyopathy. A report of the American College of Cardiology Foundation/American Heart Asociation Task Force on practice guidelines. Journal of the American College of Cardiology and Circulation, 58, e212-260.


Sinagra G, Di Lenarda A, Moretti M, Mestroni L, Pinamonti B, Perkan A, Salvi A, Pyxaras S, Bussani R, Silvestri F, Camerini F.J The challenge of cardiomyopathies in 2007. Cardiovasc Med (Hagerstown). 2008 Jun;9(6):545-54
Yetman AT, McCrindle BW. Management of pediatric hypertrophic cardiomyopathy. Curr Opin Cardiol. 2005 Mar;20(2):80-3.