Hypertrophic cardiomyopathy (HCM) is a condition where the heart muscle becomes thickened.
Traditionally, the term HCM was used for disease caused by abnormalities in genes which make the proteins responsible for contraction of the heart (sarcomeric contractile proteins). More recently the definition of HCM has been broadened to include a number of other conditions that result in thickened heart muscle. It is a hereditary disease i.e. it is passed on from parents. In the majority of cases the condition is inherited from a defective gene of one of the parents in such a way, that if a parent has an abnormal gene then each child has a 50% chance of inheriting the disease.
It is a disease that can affect both men and women of any ethnic origin. The condition is present from conception and excessive growth of the muscle may begin before birth when the foetal heart is developing. In a healthy adult heart, the muscle fibres are arranged in an organised fashion and their thickness does not exceed 12mm. In the HCM heart, however, the muscle becomes excessively thick and the fibres are arranged haphazardly making the heart vulnerable to some dangerous heart rhythms (ventricular fibrillation or ventricular tachycardia). The heart muscle also may thicken in individuals who have high blood pressure or who participate in prolonged athletic training, but in HCM patients the muscle thickens without an obvious cause.
What are the symptoms?
Symptoms and severity can vary from person to person. They may begin in infancy, childhood, middle or elderly life. No particular symptom or complaint is unique to HCM sufferers. Most patients never experience any symptoms, thus affected individuals are often diagnosed during ECG screening or family screening.
The most common symptoms of HCM are:
shortness of breath
chest pains (usually brought on by physical exertion)
palpitations (rapid, irregular heart beat)
If you suffer from any of these symptoms it does not mean that you necessarily have HCM but if you visit your GP, he or she may suggest that you undertake some tests or may refer you to a cardiologist (a heart specialist).
How is it diagnosed?
Diagnosis involves having an ECG and an ultrasound scan of the heart (echocardiogram). The great majority (up to 98%) of individuals with HCM have an abnormal ECG, alerting the physician to the possibility of underlying heart disease. Although the echocardiogram is the gold standard test in the diagnosis of this condition, occasionally the ECG may become abnormal long before the excessive thickening of the heart can be observed in the echocardiogram. In individuals with a diagnosis of HCM or high index of suspicion, further tests with an exercise treadmill test and a 24-Holter is required. In some cases further imaging of the heart may be necessary using a magnetic resonance imaging scan (MRI).
Genetic testing can identify carriers of the HCM gene. Unfortunately, this form of testing is limited at the moment, as 3 in every 10 people who are known to have HCM do not have mutations of the genes known to be associated with HCM. An additional problem is that many families who do have the mutations appear to have a specific change to the DNA code which is not found in other families (known as a ‘private’ mutation). This sometimes makes it difficult to decide whether a mutation is causing the disease or not. Things are further complicated because people with the same mutation can have effects of varying severity. However, when a well known HCM gene is identified, it can be used after the clinical evaluation to confirm the diagnosis or in the context of family screening
Treatment and advice
There is no cure at present for HCM. Treatment is aimed at preventing complications and improving symptoms. Treatment can be obtained through lifestyle modification advice, drugs, specialised pacemakers, or in some cases, surgery.
If your tests prove positive your specialist will advise you on lifestyle modifications. You will probably be advised not to participate in competitive sport and strenuous activities.
Watch CRY’s myheart cardiologist, Dr Michael Papadakis talk about things to avoid with cardiomyopathy below.
For many people the condition should not significantly interfere with their lifestyle and can be controlled by drugs. Drugs are given initially when a patient presents with symptoms. A variety of drugs are used in the treatment of HCM and the choice of treatment will vary from patient to patient. However, in patients with severe symptoms, who do not respond to medical treatment, surgery may be suggested. A surgical myomectomy, where muscle is removed, is usually successful in the relief of symptoms. The operation involves removing a portion of the thickened muscle, which relieves the obstruction.
There are other forms of treatment, which are occasionally recommended for people with HCM.
- Electrical cardioversion– This is for sufferers of atrial fibrillation (irregular heart beat), which is quite common in HCM patients. It is carried out under general anaesthetic and involves the patient being given a small electric shock to the chest which restores the normal heartbeat.
- Pacemaker– In HCM sufferers the normal electric signal may fail, and if so a pacemaker can be fitted. This is a small box containing a battery which is placed in the chest under the skin and ensures the heart receives the necessary electrical signals.
- Implantable cardiac defibrillator (ICD) – In cases where a rapid heart beat is seen that could potentially cause cardiac arrest, and cannot be controlled by drugs, an ICD may be fitted. This is similar to a pacemaker where a box is implanted under the skin in the chest. The box has a fine wire which is attached to the heart to record and deliver electrical impulses in the presence of an abnormal heart rhythm.
What should you do if you are diagnosed with HCM?
If your tests prove positive your specialist will advise you on lifestyle modifications. You will probably be advised not to participate in continuous strenuous activities e.g. competitive sports. For many people the condition should not significantly interfere with their lifestyle and can be controlled by drugs. It will be necessary for you to have at least annual check-ups. However, the severity of the disease varies from person to person and even if you have been diagnosed with HCM you may not necessarily present any symptoms and can live a fairly normal life. Since the disease runs in families, all first degree relatives of the affected patients have to be screened with ECG and an echocardiogram.