Hypertrophic Cardiomyopathy

Understanding the normal heart

The heart has four chambers - two atria and two ventricles. The walls of these chambers are mainly made of special heart muscle called the myocardium. During each heartbeat both of the atria contract first to pump blood into the ventricles. Then both ventricles contract to pump blood out of the heart into the arteries. There are one-way valves between the atria and ventricles and between the ventricles and the large arteries coming from the heart. The valves make sure that when the atria or ventricles contract, the blood flows in the correct direction.

What is cardiomyopathy?

Cardiomyopathy is a disorder of the heart muscle. There are four main types:

• Dilated cardiomyopathy - where the heart dilates (enlarges).
• Hypertrophic cardiomyopathy - where the heart muscle becomes thickened ('hypertrophied').
• Restrictive cardiomyopathy - where the heart muscle cannot relax properly between heartbeats. This is rare.
• Arrhythmogenic right ventricular cardiomyopathy - a rare type which mainly affects the right side of the heart.

The rest of this leaflet is only about hypertrophic cardiomyopathy.

What happens in hypertrophic cardiomyopathy

In hypertrophic cardiomyopathy (HCM) the heart muscle becomes thickened (hypertrophies) in parts of the heart. The cells of the heart muscle also become irregular and disordered rather than in the normal heart where the muscles cells are regular and patterned.

The muscle surrounding the left ventricle is the area commonly affected. Sometimes the muscle around the right ventricle is also affected. The degree of thickening may vary in different places. For example, the septum (the wall dividing the right and left ventricle) is often the area with the greatest thickening. In about 1 in 4 people the muscle thickening is evenly distributed throughout the walls of the left ventricle.

The thickened heart muscle usually contracts well to pump blood out of the heart. However, it may lead to problems which include the following:

• The affected heart muscle (usually around the left ventricle) may become 'stiff'. This can mean that your left ventricle may not fill as easily as normal, so less blood than normal is then pumped out from your heart each heartbeat.
• The thickening is often most marked in the upper part of the septum next to your aortic valve. This may partly obstruct the outflow of blood from your left ventricle into your aorta. This also results in less blood being able to be pumped out from your heart. The partial obstruction may also create turbulent flow of blood in this area of your heart.
• The thickened heart muscle may affect the function of your heart valves. In particular, the mitral valve may become 'leaky' if it does not close properly.
• In some people the abnormal heart muscle affects the electrical conducting system of the heart. This may cause abnormal heart rates and / or rhythms to develop (arrhythmias).

(Note: the heart muscle can thicken as a result of high blood pressure but with hypertrophic cardiomyopathy the heart muscle thickens without an obvious cause.)

What causes hypertrophic cardiomyopathy?

The muscle cells of the heart are 'disorganised' and not arranged in the normal way. It is not known why this occurs.

In most cases the condition is inherited. Men and women are affected equally. Children born to a couple where one parent has hypertrophic cardiomyopathy have a 1 in 2 chance of inheriting the condition. This pattern of inheritance is called autosomal dominant. It seems that affected people inherit defective genes which are involved in making parts of the heart muscle cells.

Who develops hypertrophic cardiomyopathy?

About 1 in 5000 people in the UK develop hypertrophic cardiomyopathy. It most commonly first develops in the teenage years or early adulthood. However, it can first develop in young children and is sometimes even present at birth.

What are the symptoms of hypertrophic cardiomyopathy?

If you only have mild thickening of the heart muscle then you may not have any symptoms. Symptoms can range from mild to severe. Even though you may have had the condition for a number of years, symptoms may not even develop until later. Possible symptoms include the following:

• Breathlessness (shortness of breath). This may develop only when you exercise if the condition is mild. When the condition is more severe you can be breathless at rest.
• Chest pain (angina). This may develop only when you exercise, but can also occur at rest when it is more severe. The pain occurs because the supply of blood and oxygen to the heart muscle is not sufficient to meet the demands of the thickened muscle.
• Palpitations. You may have an increased awareness of your heartbeat. Arrhythmias develop in some cases which can cause palpitations.
• Dizziness and fainting attacks. This more commonly occurs when you exercise, but may occur when you are resting. This may be due to a reduced output of blood from the heart or to bouts of arrhythmias.

How is hypertrophic cardiomyopathy diagnosed?

A doctor may suspect this condition from:

• Your symptoms.
• A family history of HCM.
• Changes on a heart tracing (ECG). This is a tracing of the electrical activity of the heart.
• Changes on a chest X-ray which may show your heart is large or may show some fluid in your lungs due to heart failure.
• An ultrasound scan of the heart called an echocardiogram. This is a painless test which can measure the thickness of your heart muscle.

Once the diagnosis is confirmed, other tests may be advised to assess the severity of the condition. Another type of ultrasound test called a Doppler ultrasound can detect blood flow through the heart chambers. This shows how well the heart ventricles are filling and contracting. A Doppler ultrasound can also show if there is any turbulent blood flow within the ventricles.

How does the condition progress?

The thickening of the heart muscle does not tend to progress once you stop growing. This means that for many people, the symptoms that develop remain stable over many years in adulthood. However, for some people, the symptoms gradually become worse as the heart muscle becomes more 'stiff'. Sometimes the function of the heart gradually deteriorates and heart failure may develop (see separate leaflet called 'Heart Failure').

Complications may occur and include the following:

Arrhythmias

An arrhythmia is an abnormal rate or rhythm of the heartbeat. There are various types of arrhythmia, some more serious than others. Sometimes an arrhythmia develops intermittently and can cause bouts of palpitations, dizziness and other symptoms. Some arrhythmias become permanent. Arrhythmias can usually be treated. See separate leaflet called 'Arrhythmias'.

Endocarditis

This is a rare complication. Endocarditis is an infection of the inside lining of the heart chambers and heart valves. Unless promptly treated, endocarditis can cause serious illness. See separate leaflet called 'Endocarditis - Infective'.

Sudden Death

Sudden collapse and death without any warning occurs in a small number of people with HCM. This is probably due to a severe arrhythmia which may develop suddenly. People most at risk are those with more severe disease, especially those who have had a previous serious arrhythmia. Some people at high risk may be advised on treatments which aim to prevent or treat arrhythmias.

What is the treatment for hypertrophic cardiomyopathy?

There is no treatment which can reverse the changes of the heart muscle. Treatment aims to ease symptoms if they occur and to prevent complications. If you do not have any symptoms or only mild symptoms then you may not need any treatment. Treatment which may be required includes the following:

Medication

The medicines advised depend on what symptoms or complications develop. For example:

• Beta-blockers (such as propranolol) and calcium antagonists (especially verapamil) are the commonly used medicines. These can slow the heart rate, make the heart contract less forcefully and can allow more time for the ventricle to fill each heartbeat. These medicines may be used to treat chest pain, breathlessness and palpitations.
• Various other medicines called 'anti-arrhythmic' medicines (for example, amiodarone) are used to treat and to prevent arrhythmias. They work by interfering with and helping to correct the electrical impulses in your heart.
• Warfarin may be advised if you develop atrial fibrillation (a common arrhythmia). With this arrhythmia a blood clot is a possible complication. Warfarin is an anticoagulant which means it helps to prevent blood clotting by thinning the blood.

Antibiotics are now no longer advised before you have dental treatment or other procedures such as cystoscopy or colonoscopy. This is because taking antibiotics in this way has not been shown to reduce the risk of developing infective endocarditis.

Other types of treatment for arrhythmias

Other treatments may be an option if you develop arrhythmias. For example:

• Cardioversion is an option for some types of arrhythmia. Whilst under anaesthetic, you are given an electrical shock over the heart. This may revert the rhythm back to normal.
• Artificial pacemakers are used in certain types of arrhythmia where the heart beats abnormally slowly (complete heart block) and in certain other situations. An artificial pacemaker is a small device which is inserted just under the skin on the upper chest. Wires from the pacemaker are passed through veins into the heart chambers. The pacemaker can then stimulate the heart to maintain a regular normal heartbeat.
• Implantable cardioverter defibrillators (ICDs) are sometimes used in certain situations - especially if you are at risk of developing serious and life threatening arrhythmias. They are small devices which are similar to pacemakers and are inserted under the skin in the upper chest. Wires are passed through a vein to the heart. The device monitors the heartbeat. If it detects a change to an abnormal rhythm, the device can send a small electrical shock to the heart to stop the abnormal rhythm.

Surgery

An operation may be option if your HCM is severe.

• Myectomy. This is an operation done via open heart surgery to remove a segment of thickened muscle from the septum. It is not a cure, but can help if the thick septum is causing obstruction to the flow of blood through the aortic valve.
• Alcohol septal ablation. This is a fairly new technique in which alcohol is injected into the small arteries which supply the thickened area of heart muscle. This then destroys that part of muscle, which then becomes thinner.
• Valve replacement may be needed if the mitral valve is affected and does not work properly.
• A heart transplant may be needed in a small number of people.

Some other general points

• Family testing (screening). Your first degree relatives (mother, father, brother, sister, child) should have tests such as a heart tracing and an echocardiogram. Some people with hypertrophic cardiomyopathy do not have any symptoms which is why close relatives should be screened. People with hypertrophic cardiomyopathy, with or without symptoms, have a 1 in 2 chance of passing the condition on to their children who may develop symptoms. In some centres it may be possible to have a genetic blood test.
• Exercise. Depending on the severity of the condition, some people are advised not to take part in strenuous sports or jobs. Your doctor can advise you about this.
• Weight. Try not to become overweight which can put an extra strain on your heart.
• Alcohol. Normal social drinking in moderation should not affect your heart. However, too much alcohol can affect the heart muscle and should be avoided.

Further help and information

Cardiomyopathy Association

Unit 10, Chiltern Court, Asheridge Road, Chesham, Bucks, HP5 2PX
Freephone: 0800 018 1024 or Tel: 01494 791224
Web: www.cardiomyopathy.org