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Hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a common disorder of the heart muscle which affects people of any age. About 1 out of every 500 people has HCM. It is a disorder in which the normal arrangement, or 'architecture' of the heart muscle is disrupted. Rather than arranging themselves in neat well-aligned layers, the heart muscle fibres become misaligned and entangled. The result is thickening of the heart muscle, blockage of the small blood vessels that penetrate the heat muscle and disturbances of electrical conduction.

Although hypertrophy may be present at birth or in childhood, it is much more common for the heart to appear normal at this time. Occasionally, Hypertrophic Cardiomyopathy is the cause of a stillbirth. The condition can also develop during infancy, and if this is present with congestive heart failure, it may be fatal. However, hypertrophy more commonly develops in association with growth and is usually apparent by the late teens or early twenties. After this time it appears that there is no significant change in muscle thickness in the years of adult life.


Children and adolescents with the condition are usually identified when family screening is performed after an adult in the family is found to be affected. Of these adults approximately 50% will have experienced symptoms. In the remainder the diagnosis is made during family screening or following the detection of a murmur or an abnormality on routine electrocardiogram (ECG) and echocardiogram (ECHO).


There are various forms of HCM, depending on the pattern of wall thickening:

  • Asymmetrical septal hypertrophy: This mainly affects the wall that separates the ventricle (interventricular septum).​

  • Concentric hypertrophy: This affects the entire wall of the heart in an uniform fashion.

  • Apical hypertrophy: This affects the tip, or 'apex' of the heart.

​When the wall thickening blocks the outlet of the left ventricle, the condition is termed hypertrophic obstructive cardiomyopathy. 

HCM is the commonest cause of sudden cardiac death in young people. It is often the cause of sudden cardiac death in sports men and women.


HCM may not give rise to any symptoms and may not affect people's lives at all. It may have been detected incidentally after a visit to the doctor. It can, however, present with sudden cardiac death in young people, including young athletes. Sometimes, HCM can cause chest pain chest pain, breathlessness, dizziness or fainting. Physical exertion can be the precipitating factor of sudden cardiac arrest.


These are geared towards characterising the type of HCM, its severity and the risk factors for sudden cardiac death. These investigations may include:

  • ECG: This is usually abnormal

  • Echocardiogram: This usually shows thickening of the neart muscle. Sometimes, it also shown abnormal movement of the mitral valve (systolic anterior motion) and left ventricular outflow tract (LVOT) obstruction.

  • Cardiac MRI scan: This very sensitive test gives a very accurate picture of the heart and may reveal features of the disease that echocardiography does not provide.

  • Exercise testing: Failure to increase blood pressure on exercise is a risk factor for SCD in patients with HCM.

  • Ambulatory ECG monitoring: Ventricular tachycardia (fast heart rhythms from the main pumping chambers) is a risk factor sudden cardiac death.

Risk factors for sudden cardiac death (SCD)

Once HCM is diagnosed, the second step is to assess the risks of developing fatal heart rhythm problems. Typical risk factors for SCD include:

  • Family history of sudden cardiac death

  • History of loss of consciousness

  • Septal (interventricular wall) thickness of 3 cm or more

  • Ventricular tachycardia on ECG monitoring

  • Failure to increase blood pressure on exercise testing

Other clinical features may be considered in risk assessment. Generally, in the UK, ICD therapy would be recommended if there are 2 risk factors for SCD. In the US, 1 risk factor suffices for implantation of an ICD. 

The risk of SCD is calculated using the following risk calculator:  

Family screening

The majority of patients with Hypertrophic Cardiomyopathy have at least one other affected first degree relative, i.e. a parent, brother, sister or child. When a person is diagnosed as having Hypertrophic Cardiomyopathy it is strongly advised that all first degree relatives are screened for the condition. It is important to remember that family evaluation is recommended because Hypertrophic Cardiomyopathy may be present without any symptoms. Evaluation involves a physical examination, an ECG and an ECHO.


In most adults where the results of the above tests show no abnormality a diagnosis of Hypertrophic Cardiomyopathy may be excluded. In a small number of patients where there is no physical evidence of the disease, the abnormal gene may still be present. In this situation, the gene carrier will be normal, but may still pass on the gene for Hypertrophic Cardiomyopathy to the next generation. In children, however, regular clinical evaluation is required until full growth spurt is completed at around 20 years of age, as symptoms may not show until adulthood. While undiagnosed, children of an affected parent are advised to be screened every 3 years until puberty and then on an annual basis until around 20 years. ECG and ECHO should be used each time.



Clearly, the main concern of an affected parent is the risk of passing on the condition to their children. It is not possible to make a general statement about the risk and every case will need to be considered individually. For instance, in a family which has shown a dominant pattern of transmission from one generation to the next, the likelihood of a parent passing on the abnormal gene to a child is one in two. In other cases where there is no inheritance pattern in the family, the offspring of an affected individual probably also have a one in two risk of inheriting the condition.


Even if a child inherits the abnormal gene, the degree to which he or she might be affected is very variable. There is no definite method of predicting how severe the condition might be. In general it is recommended that children are screened regularly until adulthood. If there is no evidence of Hypertrophic Cardiomyopathy by early adulthood it is extremely unlikely that the condition will develop in later life.



For many people the condition should not interfere with their lifestyle in any way. Some individuals may have symptoms related to exertion and find that they cannot undertake as much physical work or recreation as other people of their age. Medical advice should be sought before undertaking physically demanding activities. Some persons may be advised not to take part in competitive sports or other strenuous physical effort.


Life Insurance

Clearly, as with many heart conditions, difficulties may be encountered in acquiring insurance cover and/or premiums may be high. The offices of the Cardiomyopathy Association carry a list of the names of agents who are prepared to act for sufferers (UK only).

Pregnancy and Childbirth

Pregnancy in Hypertrophic Cardiomyopathy is usually well tolerated and safe and for the majority of women with Hypertrophic Cardiomyopathy, pregnancy and delivery should be entirely normal. 


However, as for women with any heart condition, pregnancy carries a slight additional risk for women with Hypertrophic Cardiomyopathy. This is because pregnancy imposes an increased demand on the heart.


Women may find that they develop symptoms for the first time in pregnancy or that their usual symptoms are increased. Also, the question of taking drug treatment around the time of conception or during pregnancy arises in many cases. For all these reasons it is best to plan pregnancy in advance and discuss all aspects at an early stage with your doctor. 


It is best to avoid epidural anaesthesia at delivery as this may cause an excessive fall in blood pressure.



There is no treatment for HCM itself. The following treatments may be appropriate in certain circumstances:

  • An implantable cardioverter defibrillator (ICD) if there are risk factors for SCD.

  • Medications such as beta-blockers and amiodarone, can be used to control rhythm abnormalities.

  • Alcohol septal ablation: This catheter procedure can be used to get rid of the bulge of muscle that causes left ventricular outflow obstruction. It involves injection of alcohol to remove the bulge.

  • Surgical myectomy: This operation consists of surgically removing the muscle bulge causing left ventricular outflow obstruction.

Lifelong follow-up by a cardiologist is required.


HCM links:

Information leaflet on HCM

Information leaflet on living with cardiomyopathy

Thee Cardiomyopathy Association:

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