Hypertrophic Cardiomyopathy

What is Hypertrophic Cardiomyopathy (HCM)?

Hypertrophic cardiomyopathy (HCM) is a heart condition where the heart muscle becomes thickened and stiff. The thickening of the heart muscle makes it harder for the heart to contract and pump blood out and around the body. HCM is usually caused by a genetic change. It is often inherited and can be passed down from parent to child.

HCM is the most common type of inherited cardiomyopathy.

The heart has four chambers. The top two chambers are called atria and the bottom two are called ventricles. HCM typically thickens the muscular walls of the left ventricle, which is the main pumping chamber of the heart. 

The thickening of the muscle makes it harder for the heart to relax and fill with blood, and then contract to pump blood out and around the body. 

Depending on the location and the thickness of the muscle, the blood flow out of the heart can be affected. This is known as the hypertrophic obstructive cardiomyopathy (sometimes referred to as HOCM). 

Changes to the heart muscle can disrupt the electrical activity of the heart, leading to irregular or unusual heart rhythms (arrhythmias). 

    • In unaffected hearts, the thickness of the muscle in the left ventricle is 7 to 10 mm in adults. In people with HCM, the thickness can be 15 mm or more. 
    • Often, the heart appears normal early in life, but the heart muscle thickens over time.
Family members are at-risk of developing HCM, so it is important to monitor the heart in these individuals.
Comparison of a healthy heart and a heart with hypertrophic cardiomyopathy. The healthy heart on the left has four chambers: 2 atria and 2 ventricles. Each chamber of the heart is surrounded by muscle which has a healthy size and structure. The heart on the right indicates a heart with hypertrophic cardiomyopathy, the heart has 4 chambers surrounded by muscle. However, the muscle towards the bottom of the heart is thickened.

HCM has a range of symptoms that will differ from person to person. Even people in the same family may experience different symptoms. Some people may experience no symptoms, while others may experience any combination of the following:

  • Shortness of breath (dyspnoea)
  • Swelling (oedema) in the feet, legs, or abdomen (belly)
  • Dizziness or lightheadedness (presyncope
  • Chest pain (angina)
  • Fainting or loss of consciousness (syncope)
  • Fluttering / pounding in the chest (palpitations)
  • Abnormal heartbeats (arrhythmias)
  • Fatigue (lethargy)

In serious but rare cases, HCM can lead to heart failure, or sudden cardiac death. There can be no obvious symptoms prior to a sudden death.

HCM can be diagnosed by a cardiologist (heart doctor), and is usually diagnosed through testing that checks how well your heart is working. Your cardiologist may also repeat these tests as part of your on going management.

Testing may include, but is not limited to:

Image describes the different test types to diagnose cardiomyopathy. Taking a family history: Usually a three generation family history will be taken to find any clues to whether your cardiomyopathy runs in your family. You will typically be asked about family members' age, their health and if they have died at what age and the cause of death. Electrocardiogram (ECG): An ECG is a recording of the electrical activity of your heart, and can identify any unusual heart rhythms or extra heartbeats. The test involves placing ECG nodes (stickers) across your chest, arms and legs, and takes 5 minutes to complete. Echocardiogram (Echo): An echocardiogram (Echo) looks at the structure, size, and function (contraction and blood flow) of your heart. An echo uses wave sounds (ultrasound) to make a picture of your heart. This test takes around 30-40 minutes. Exercise stress test (Stress ECG): This test is done while exercising to see how your heart responds when it has to work harder than normal. For this test you will have an ECG while either on a treadmill or a bike. You will start the exercise test at an easy pace and increase the level of exertion. This test takes about 30-40 minutes to complete. Holter Monitor: A Holter monitor is a small device that records the heart’s electrical activity over a few hours or days. The device can be carried around your neck or waist and is connected to ECG electrodes (small patches that will stick to your chest). The monitor will take approximately 15 minutes to fit and will need to be returned at the completion of the test. Cardiac Magnetic Resonance (CMR) Imaging: CMR imaging takes detailed pictures of your heart structure and can see any changes to the tissues that make up the heart muscle. CMR looks at parts of the heart that may not be clearly visible on other tests such as an echocardiogram. You will lie very still on a bed that moves into a large cylinder (MRI machine). The scan takes approximately 45 minutes.

Our bodies are made up of millions of cells. Each cell contains a copy of our genetic information. Our genetic information is the instructions for our body deciding how we will grow and function. Each instruction is called a gene. We have two copies of all our genes.

We share our genetic information with our families as we receive half our genetic information from each of our parents.

In HCM, one copy of a gene that is involved in your heart function may contain a genetic change (variant) that stops the heart from working as it should. The genetic variant changes the instructions sent out to the body and may cause your cardiomyopathy.

Example of gene changes leading to cardiomyopathy. Left example shows two copies of the same gene one has a change which leads to cardiomyopathy. This is what the genetics of someone with cardiomyopathy would look like. Right hand side shows two genes without a cardiomyopathy gene change. Showing what the genetics of someone unaffected by cardiomyopathy would look like.

HCM is best managed by a team of healthcare professionals. This may include your GP, a cardiologist, a psychologist, and a cardiac genetic counsellor. Each member of your healthcare team plays a different and important role in caring for you, and your family. Management of your cardiomyopathy is very personal, your management plan will likely be different from other members of your family with the same diagnosis. There are a number of factors that go into personalising your management plan. Some of these are: age, current symptoms, how severe your disease is, your family history, and your specific type of cardiomyopathy.