Cardiomyopathy

Summary

• The term cardiomyopathy means a disorder of the heart muscle. Often the cause is unknown, but several underlying causes/associations have been identified.
• Whatever the root cause, the disorder often manifests in one of four ways, and this largely determines the treatment approach and outcome. A common presenting pattern is heart failure, but sudden death is well documented.
• The condition cannot be cured, but can be managed, usually medically, though surgery may be necessary for hypertrophic obstructive cardiomyopathy (HOCM), and transplantation considered for some intractable forms. The longterm outcome is dependant on the underlying cause, with the best prognosis being for peripartum cardiomyopathy.
• Prevention is not really possible, though lifestyle modification could theoretically prevent the onset and advance of coronary artery disease, which, if untreated, becomes one of the common causes of cardiomyopathy.

In plain language, the term "cardiomyopathy" simply means "something wrong with the muscle of the heart" - in other words, the cardiomyopathies are disorders or diseases of heart muscle.

Two main classification systems are used: one system classifies according to known causes; the other sorts cardiomyopathies into categories according to anatomy and physiology. This second system is much more useful, as it links to treatment, and is internationally accepted.

This system will be used here, and recognises five main categories:

1. Dilated cardiomyopathy – (DCM)

In this condition there is enlargement of one or both ventricles, and the thickness of the muscle wall can vary from excessively thick to very thin. In extreme cases, all four chambers of the heart may be enlarged. The incidence of DCM seems to vary widely, but some studies suggest that more than 14% of the elderly population have some degree of DCM.

2. Hypertrophic cardiomyopathy (HCM)

Here 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, which is the 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, and 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 every 500 persons.

3. Restrictive cardiomyopathy (RCM)

In this condition, the ventricles are not dilated, but show impaired filling. While this is not as common a condition as HCM, it is a common cause of death in Africa, Asia and South/Central America, and is mainly linked to the high incidence of endomyocardial fibrosis in these regions.

4. Arrhythmogenic right ventricular cardiomyopathy (RVCM)

This is an unusual condition in which part or all of the right ventricular wall muscle is replaced with fatty or fibrous tissue. As little or no normal heart muscle remains, the ventricle cannot function normally.

5. Unclassified cardiomyopathies 

This category exists for types that do not fit into any of the above categories, and the two best-known examples are:

• Endocardial fibroelastosis (EFE): this occurs mainly in infants under one year, often together with other congenital heart disease. Survival is poor, and transplantation is often required.
• Left ventricular compaction: a rare entity, due to problems arising in the foetus.

Causes

1. Dilated cardiomyopathy

In this condition there is enlargement of one or both ventricles, and the thickness of the muscle wall can vary from excessively thick to very thin. In extreme cases, all four chambers of the heart may be enlarged.

The commonest causes of DCM are:

• Ischaemia (coronary artery disease).
• Heart valve disease.
• Viral CM.
• Genetic CM: a late manifestation of hypertrophic obstructive cardiomyopathy.

2. Hypertrophic cardiomyopathy (HCM)

This is a fairly common genetic condition, and can happen in varying degrees of severity. The heart muscle is thickened, often only in parts, and there may be dysfunction of the mitral valve as well. There are non-genetic causes of hypertrophy, notably hypertension and aortic stenosis. Fabry’s disease is a storage disease which may lead to HCM, however this is an extremely rare condition.

3. Restrictive cardiomyopathy (RM)

Often the cause of RM is not known, although it may have a familial tendency. It may be caused by infiltrative diseases, like amyloidosis and haemochromatosis. Chemotherapy and radiotherapy have also been implicated. A large number of cases have scarring of the heart muscle, such as with endomyocardial fibrosis (EMF) and Loeffler’s endocarditis. EMF is associated with extreme poverty and persistent parasitic infestations. Loeffler's is associated with persistently raised levels of specific white cells in the blood.

4. Right ventricular cardiomyopathy (RVCM)

In this unusual condition, there is replacement of heart muscle by fibrous or fatty tissue. The cause is often not known, but it may run in families, implying some form of genetic cause. Up to 30 percent of cases have a familial component. A number of specific gene abnormalities linked to this condition have been identified.

The term "athlete’s heart" is often used to describe the normal response to intensive exercise shown by all muscle (including heart muscle): here the heart muscle thickens at the expense of the cavity size, which may be markedly decreased. Under these conditions, there's an increased risk for rhythm disturbances. If an athlete has an underlying cardiomyopathy, heavy physical exertion carries a high risk of lethal arrhythmias. Many sports organisations now advise screening of serious athletes to exclude underlying cardiomyopathies to prevent sudden death during activities.