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Hypertrophic Cardiomyopathy (HCM)

What is hypertrophic cardiomyopathy?

Cardiomyopathy is a form of heart disease where the heart muscle is enlarged and is not able to pump as effectively.  In hypertrophic cardiomyopathy (HCM), the heart’s lower chambers (ventricles) are thickened, and the heart cannot fully relax between heartbeats.  

Who is affected by HCM?

HCM affects about 1 in 500 people, but milder forms often go undiagnosed. It is the most common cause of sudden cardiac death in individuals under the age of 30, and can be diagnosed anywhere from infancy to old age.

Genetics and HCM

The majority of idiopathic (no known reason for developing the condition) forms of HCM appears to be genetic, even if a person does not have any affected relatives. Childhood forms of HCM can sometimes be associated with inborn errors of metabolism or other genetic syndromes, but other inherited forms are thought to be caused by a genetic mutation in one of several genes responsible for the building of proteins in the heart’s muscle fibers.  These genetic mutations result in the heart’s muscle fibers growing in a disorganized fashion. 

HCM can be inherited in a variety of ways, although the most common follow what is called an autosomal dominant pattern. This means that for those individuals who have a genetic mutation associated with HCM, all of his/her children will have a 50% chance of inheriting this mutation as well. For this reason, it is important that all first-degree relatives (sibling, children, and parents) of a peron diagnosed with HCM be checked for signs of this condition. 

To date, at least 18 genes associated with HCM have been identified and several more are being investigated.

What are the symptoms of HCM?

The symptoms of HCM are extremely variable.  They can appear at any time from infancy to old age, or perhaps not until a sudden cardiac death episode occurs.  They can appear suddenly and worsen quickly, or remain stable for a long time before worsening.  Because of this variability, it is important to maintain regular checkups with a cardiologist if you are determined to be at risk.   Symptoms associated with HCM are often the same as those seen with heart failure and include:

-    Shortness of breath

-    Swelling or accumulation of fluid in ankles, belly, or other areas

-    Fatigue

-    Heart palpitations (often described as a feeling of fluttering)

-    Fainting of loss of consciousness (syncope)

-    Chest pains

How is HCM diagnosed?

A careful assessment of a family history, a thorough physical exam, and several heart tests can be used to make the diagnosis of HCM.  There are also certain diagnostic criteria that must be met, based on the results of these tests.

Some of the tests used to diagnose HCM include:

-        Electrocardiogram (ECG):  This test is performed by placing electrodes on the body and measuring the electrical signal through the heart as it beats.  By reviewing the pattern of this electrical signal, the doctor can determine if the heart is beating normally.

-  Echocardiogram (ECHO):  This test is an ultrasound of the heart.  It is performed by placing a wand on the chest that transmits sound waves; these waves create a picture of the heart.  This picture can be used to determine whether or not the heart is enlarged.

-  Blood tests:  Some blood tests can be used to tell how the heart is functioning or if there is muscle damage.  These tests alone cannot be used to diagnose cardiomyopathy, but they may be used in conjunction with the tests listed above.

Additional testing may be necessary if the results of the above tests warrant closer investigation.  Additional testing options include:

-    Chest X-ray:  May be used to see enlargement of the heart or fluid in the lungs.

-    Magnetic Resonance Imagining (MRI):  Provides a more detailed picture of the heart than an ECHO.

-    Holter monitor:  Measures heart rhythm over a 24-hour period.

Is there any treatment for HCM?

Treatments focus on managing the wide range of symptoms of HCM. Treatment plans are tailored to each individual and can cover a range of options from drug therapy (i.e. beta-blockers) to surgical intervention (i.e. septal ablation or myectomy to physically remove part of thickened heart muscle). For some individuals with symptoms of arrhythmia, a pacemaker or implantable cardioverter defibrillator (ICD) can be inserted to help maintain a normal rhythm of the heart. A heart transplant is optional if symptoms are severe and no other form of treatment helps to lessen the symptoms. Individuals with HCM should establish a personalized management plan with his or her cardiologist that involves regular checkups and maintenance. A discussion about participation in strenuous activities and sports should also be considered, due to the possible risk of sudden cardiac death. Currently there is no known cure for HCM.

Genetic testing options

Of the genes that are currently known to be associated with HCM, a few are available for clinical testing at this time. For more information regarding current clinical testing options, contact your local doctor to find out where genetic counseling services are available in your area. 

Genetic testing is currently available as part of a research protocol through the University of Colorado Denver Cardiovascular Institute. For more information, please go to our Familial Cardiomyopathy Study section.