Hypertrophic Cardiomyopathy (HCM)

Hypertrophic cardiomyopathy (HCM) is an inherited condition. It leads to abnormal thickening of the heart muscle, most often of the left ventricle (the main pumping chamber of the heart). The thickened muscle creates problems because it causes the heart to work less efficiently. Therefore, some people may experience chest pain, shortness of breath, dizziness, fainting episodes or palpitations. Occasionally, the disease may cause sudden death.

In adults, the walls of the left ventricle are usually 7 to 10 mm thick (can be thicker at post mortem/autopsy). In hypertrophic cardiomyopathy the walls are 13mm or more in thickness. The wall thickening is often unevenly distributed, unlike in people with high blood pressure. This is illustrated in the diagram below. In about 25% (1 in 4) of people with hypertrophic cardiomyopathy there is obstruction to the blood being pumped out of the heart because of the thickened muscle. This is known as the obstructive form of hypertrophic cardiomyopathy (sometimes referred to as HOCM).

It is thought that about 1 in 500 people have hypertrophic cardiomyopathy, and many never have any symptoms. Tragically, in some cases the first sign of the disease is sudden death especially in young athletes. Therefore, it is very important that everyone with a family history of hypertrophic cardiomyopathy be screened by a cardiologist.

How it is inherited
Hypertrophic cardiomyopathy is inherited as an autosomal dominant disease (see section on Genetic Inheritance and Testing for more information).

Genetic testing
Genetic testing for hypertrophic cardiomyopathy is commercially available. It involves testing 10 genes commonly associated with causing HCM, and in about 50-60% of families the gene alteration (or “mutation”) will be identified. In the remainder, a gene alteration likely exists but in a gene that was not tested or is yet to be discovered. More research is required in this field.

If you would like to find out more about how genetic testing may be useful in your family, please contact one of the clinic coordinators below.

Common Treatments
Your cardiologist will decide what medications or treatments you may require. Many patients will not need any medications, particularly if they have no symptoms. Some common medications are:
Beta-blockers are very commonly used in the general population to treat high blood pressure. They are used in HCM patients to slow the heart rate and reduce the effect of sudden exertion or excitement on the heart. As beta-blockers make the heart beat slower, it allows blood to completely fill the chambers before it is pumped out, leading to improved heart function. Examples include Metoprolol, Atenolol, and Nadolol.
Sotolol (antiarrhythmic drug) is a type of beta-blocker but has additional effects of suppressing abnormal heart rhythms, particularly atrial fibrillation.
Warfarin is a common drug used in people who have atrial fibrillation. Approximately 25% of HCM patients will develop atrial fibrillation, and will require warfarin therapy. Warfarin is a blood thinning medication that prevents blood clots forming. When a heart is in atrial fibrillation, it does not effectively pump all of the blood out of its chambers, leading to clots which can then break away and travel to the lungs (pulmonary embolism) or brain (stroke).

Your risk of sudden death is also something that your cardiologist will assess. If your cardiologist believes you may be at increased risk of dying suddenly, he/she will often advise an automatic implantable cardioverter-defibrillator (AICD). This is a device (similar to a pacemaker) that is inserted in to the chest, with leads extending down in to the heart. The AICD monitors the hearts rhythm and if it becomes abnormal (the type of heart rate that occurs during a cardiac arrest), it will deliver an electric shock to revert the heart back to a normal rhythm. These devices have revolutionised the management of patients with HCM as it is the only therapy proven to stop people dying suddenly. As your cardiologist determines your level of risk based on certain criteria, you should report any new symptoms to your cardiologist immediately, including black-outs or if a family member passes away unexpectedly.

Exercise & Competitive Sports
One of the most difficult aspects of HCM is the advice to avoid high level, competitive sports. Competitive sports include those that require significant exertion, for example: touch football, basketball, netball, squash, running and even social games that you may not think are too strenuous. We recommend people avoid competitive sports because it has been observed that a large proportion of young people who die suddenly due to HCM, die during or just after exercise.

While high-level exercise should be avoided it is still important to maintain a healthy lifestyle. Regular light exercise such as walking is not only good for your heart, but also good for your general health.

Advice to family members
Direct relatives of someone who has been diagnosed with HCM should have their hearts checked by a cardiologist (see section on clinical screening). Direct family members include children, brothers and sisters, and parents. As HCM is an inherited heart condition, these family members are generally at a 1 in 2 (50%) risk of also carrying the gene and are termed at-risk relatives.

We rely on this information being passed on within a family, and would therefore ask you to encourage any at-risk relatives to arrange an appointment with a cardiologist. We know there is huge variability in the range of symptoms seen even within a family (with some family members having minimal symptoms, while others have the most serious outcomes of heart failure and sudden death). So even while an at-risk relative may feel healthy and well, it is possible they could have mild disease. If this was deemed to be the case, we would not necessarily start any treatments in this relative, but we would then know his/her children are now at-risk. Please talk to one of the clinic coordinators for more information or to organise a ‘heart check’.

National Genetic Heart Disease Registry
HCM is one of the diseases being investigated by the Registry. We aim to enrol every family in Australia with HCM. To enrol your family, or get more information please contact the Registry Coordinator or go to www.registry.centenary.org.au.

Registry contacts Registry Coordinator: Ms Jodie Ingles
QLD - Jodie Ingles, Royal Brisbane & Women’s Hospital 07 3636 3244
NSW - Laura Yeates, Centenary Institute & RPA Hospital 02 9565 6187
VIC - Vanessa Connell, Royal Children’s Hospital 03 9345 5724
VIC - Tina Thompson, Royal Melbourne Hospital 03 9342 7151
VIC - Ivan Macciocca, Genetic Health Services Vic, 03 8341 6201