Hypertrophic cardiomyopathy

Summary
- In plain language, the term 'cardiomyopathy' simply means that there's something wrong with the muscle of the heart. With hypertrophic cardiomyopathy (HCM) there is abnormal, often localised, thickening of the heart muscle.
- It is a fairly common genetic condition, which can occur in varying degrees of severity.
- HCM has been strongly linked to sudden, unexpected deaths occasionally seen in apparently healthy, young adults.
- Diagnosis can be made by means of physical examination; chest X-ray; e lectrocardiogram; echocardiogram; exercise testing; catheterisation; and other, more s pecific diagnostic tests.
- Few forms of therapy have been shown to alter the natural progression of this disease.
- The following signs are indications that you should consult your doctor: unexplained shortness of breath; chest pains; unexplained fainting; previous unexplained cardiac arrest; a family history of cardiomyopathy.
- Genetic testing in selected individuals (family members of affected persons) can lead to carrier detection (of the mutations) and early diagnosis.

Alternative names
Cardiomyopathy - hypertrophic; idiopathic hypertrophic subaortic stenosis; asymmetric septal hypertrophy; hypertrophic obstructive cardiomyopathy

What is hypertrophic cardiomyopathy?
In plain language, the term 'cardiomyopathy' simply means that there's something wrong with the muscle of the heart. In other words, the cardiomyopathies are disorders or diseases of the heart muscle.

With hypertrophic cardiomyopathy (HCM) there is abnormal, often localised, thickening of the heart muscle.

This is a genetic disorder, resulting in abnormal patterns of muscle cells in the heart, often affecting mainly the interventricular septum - the stout wall separating the two ventricles. The left ventricle is usually affected by this bulging septum, which takes up some of the cavity, thereby reducing the volume of blood the ventricle can hold and pump out.

The ventricle also may become stiffened, and unable to relax completely to permit normal filling. This can further reduce the volume of blood it can hold. When the upper part of the interventricular septum is affected, it often causes the mitral valve to leak.

HCM is estimated to affect 1 in 500 persons.

What causes it?
As already stated, this is a fairly common genetic condition, which can occur in varying degrees of severity.

There are non-genetic causes of hypertrophy, such as hypertension (high blood pressure) and aortic stenosis (narrowing of the opening of the aortic valve). These, however, lead to a cardiomyopathy only in extreme cases of longstanding neglect.

Fabry's disease, which is characterised by multiple, localised collections of thin-walled blood vessels covered by a cap of warty material, may also lead to HCM. However, this is an extremely rare condition, which causes generalized hypertrophy, rather than the more common, localised form.

What are the symptoms?
Symptoms of HCM include:
- chest pain (angina-like in origin);
- palpitations (awareness of an abnormal heart beat);
- syncope ( falls due to brief loss of consciousness );
- shortness of breath.

This form of cardiomyopathy has been strongly linked to sudden, unexpected deaths occasionally seen in apparently healthy, young adults. The classic scenario is that of a young, fit athlete collapsing and dying suddenly and unexpectedly on a sports field or even in a swimming pool.

How is it diagnosed?
Your doctor will ask about your symptoms and perform a physical examination. Certain physical signs (such as heart murmurs and chamber enlargement) should alert an examining doctor to the possible presence of cardiomyopathy.

The following special investigations may also help to make the correct diagnosis:
- Chest X-ray. This will point to any enlargement of the heart and major blood vessels in the chest. Accumulation of fluid in the lungs (indicating heart failure) will also be shown.
- Electrocardiogram (ECG). There are no changes diagnostic of cardiomyopathy, but rhythm disorders, coronary artery disease and muscle thickness may be identified.
- Echocardiogram. This form of ultrasound provides information on the functioning of the heart and its valves, and the thickness of the muscle walls. It can also be used to measure the cardiac output (pumping ability) and the pressures within the heart.
- Exercise testing can record how the heart functions during physical activity. If a patient cannot exercise, other methods can be used to simulate exercise.
- Catheterisation. This angiogram shows the chambers of the heart, as well as the flow through the coronary arteries. During the angiogram, accurate pressure readings can be made to assess heart function.
- Specific diagnostic tests for suspected underlying causes may include blood tests (e.g. to test for virus infection) or genetic tests.

How is it treated?
Few forms of therapy have been shown to alter the natural progression of this disease.

However, therapies used include:
- Beta-blockers. These drugs are the mainstay of treatment and are most useful in alleviating the chest pain associated with the disease.
- Calcium-blockers. This class of drugs alleviates symptoms in some people.
- Anti-arrhythmicdrugs. Low-dose amiodorone is used in some cases, especially if there is a moderate risk of sudden death. This may be used as an adjunct for patients with implanted cardioverter/defibrillators.
- Surgery. This includes septal myomectomy, which involves the surgical removal of parts of the thickened or hypertrophied septum or other thickened heart muscle. As a result of the thickening of the heart muscle, blood flow out of the heart may be obstructed and the surgical removal of the muscle may alleviate the obstruction. In the patient whose condition is severe enough to warrant this type of surgery, there is usually accompanying mitral valve dysfunction (leakage), so that the valve is also replaced at the same time. Heart transplantation is reserved for end-stage heart failure.
- Catheter interventions. In the past, alcohol was injected directly (via a catheter in the heart) into the arteries feeding the thickened septum. This caused the heart muscle to die (i.e. it induced a heart attack in the thickened part of the heart). This procedure is now discarded in favour of medical management plus corrective surgery, when appropriate.
- Implantable cardioverter defibrillators. These are beneficial for people who previously suffered a life-threatening dysrhythmia.

What is the prognosis?
The major concern is sudden cardiac death, which often occurs without warning. Unfortunately, it can be difficult to predict likely candidates.

The following factors, however, are important risk factors:
- Genetic factors. Certain mutations (e.g. troponin T) are associated with a high risk, even when little heart enlargement is evident. Other mutations (e.g. beta-myosin light chain) carry a relatively low risk, despite significant heart enlargement.
- A family history of sudden cardiac death.
- Previous cardiac arrest.
- Dangerous cardiac rhythm disturbances, as indicated via ambulatory ECG (ECG leads are attached to the patient and the heart rhythm is recorded over a period of 24 or 48 hours).
- Recurrent syncopal attacks (fainting).
- Pronounced cardiac enlargement.

Most deaths occur in young patients during strenuous physical exertion and in the early hours of the morning.

When to call your doctor
The following signs are definitely indications that you should consult your doctor:
- Unexplained shortness of breath.
- Chest pains.
- Unexplained fainting.
- Previous unexplained cardiac arrest.
- A family history of cardiomyopathy.

Family members of patients with documented HCM can be screened by either echocardiography and/or genetic testing. Echocardiography is usually repeated at regular intervals, especially in high-risk families.

How can it be prevented?
HCM is largely genetic and current measures cannot prevent the development of this affliction.

Genetic testing in selected individuals (family members of affected persons) can lead to carrier detection (of the mutations) and early diagnosis. A person may be diagnosed as having HCM many years before actual heart enlargement develops.