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. Hypertrophic Cardiomyopathy 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 Hypertrophic Cardiomyopathy has typically been recognized by its structure – hypertrophy, the electrical function of the heart is 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 Hypertrophic Cardiomyopathy, 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 Hypertrophic Cardiomyopathy.

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

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.

Myocardial Disarray

History and Other Names

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 Hypertrophic Cardiomyopathy 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.

What Symptoms Does Hypertrophic Cardiomyopathy Cause?

There is no particular symptom or complaint which is unique to Hypertrophic Cardiomyopathy. Symptoms may occur at any stage in a person’s life even though the condition may have been present for some time. The reason for the onset of symptoms is often not clear.

Shortness of Breath

Exercise capacity may be limited by breathlessness and fatigue. Most individuals experience only mild exercise limitations, but occasionally limitation is severe and a minority may have shortness of breath at rest.

Chest Pain

Chest pain is a common symptom. It is usually brought on by exertion and relieved by rest, but pain may occur at rest or during sleep and may persist. The cause of the pain is thought to be insufficient oxygen supply to the myocardium. In Hypertrophic Cardiomyopathy the main coronary arteries are usually normal, but the greatly thickened muscle demands an increased oxygen supply which cannot be met in some circumstances.


Palpitation is an uncomfortable awareness of the heart beat. People may occasionally feel an extra beat or a skipped beat and this is usually normal. Sometimes an awareness of the heart beating does suggest an irregular heart rhythm. In this case, palpitation may start suddenly, appear to be very fast and may be associated with sweating or light-headedness. The cause of such episodes should be determined and treated.

Light-Headedness and Blackouts

Persons with the condition may experience light-headedness, dizziness and more seriously, blackouts. Episodes may occur in association with exercise, with palpitations or without any apparent provocation. The reasons for these episodes are not always clear. They may be due to an irregularity of the heart beat, or fall in blood pressure. Episodes of light-headedness and certainly a blackout should be reported to one’s doctor and investigated.

Most commonly seen “misdiagnosis” associated with HCM?

Most commonly seen is asthma, specifically athletically induced asthma as a first sign or symptom. This is likely due to transient shortness of breath often seen in Hypertrophic Cardiomyopathy. It is also common to have a diagnosis of mitral valve prolapse prior to a proper diagnosis of HCM. This often happens upon an audible murmur that is thought to be simply mitral valve prolapse a common condition. It is not uncommon to see people diagnosed with anxiety attacks, panic attacks or some forms of depression only to find that the underlying cause of the symptoms is Hypertrophic Cardiomyopathy.