Cardiomyopathy and Myocarditis

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Cardiomyopathies

Cardiomyopathies are diseases primarily affecting heart muscle Once cases of ischaemic heart disease, valvular heart disease, and hypertensive heart disease have been excluded, there remains a group of patients who have presented with abnormal cardiac
function due to primary disease of the myocardium.

These disorders, termed cardiomyopathies, can be considered together, as the diseases have a primary impact on cardiac muscle function.

Many have a defined cause and can be classed as secondary cardiomyopathies.
Other diseases have, as yet, no defined cause and are classed as idiopathic primary cardiomyopathies.

The cardiomyopathies usually cause progressive development of cardiac failure.
The time scale varies according to the cause of disease; development may occur over weeks or years.
In some instances, sudden cardiac death is the first manifestation of disease.

Diseases that infiltrate the myocardium causing abnormal rigidity are termed restrictive cardiomyopathies, e.g. amyloid.

Primary cardiomyopathies are classified according to myocardial dysfunction

Primary cardiomyopathies follow two main patterns according to the dysfunction of the myocardium.

In hypertrophic cardiomyopathy the heart walls (especially the left ventricle) are enormously thickened and hypertrophied, often in an asymmetrical pattern, particularly affecting the interventricular septum.
Catheter studies show an abnormal pressure gradient along the left ventricular cavity. Histologically there is disorganized branching of hypertrophied muscle fibres, which show loss of the normal parallel orientation.
In about 50% of cases,  hypertrophic cardiomyopathy is inherited as an autosomal dominant disorder; it occurs most often in young adults and juveniles, and may present with sudden, unexplained death on exertion.
Less dramatic presentations include angina and breathlessness on exertion in a young person, or repeated fainting attacks.
In some kindreds this is due to a point mutation in the gene coding for heavy myosin.

Hypertrophic cardiomyopathy

In hypertrophic cardiomyopathy there is marked left ventricular hypertrophy. This often preferentially affects the septum.

Dilated cardiomyopathy

In Dilated (congestive) cardiomyopathy the ventricles are dilated, the chamber walls stretched thin, and the muscle is poorly hypocontractile.
Typically, there is  an elevated ventricular end-diastolic pressure.
The cause is not known, but some cases may follow viral myocarditis.


Myocarditis

Myocarditis is a rare disease in which diffuse inflammation of the myocardium occurs

Inflammation of the myocardium, termed myocarditis, is generally rare.
Although it is considered by many to be grouped best as a cardiomyopathy, others categorize this pattern of disease separately.

The myocardium shows interstitial oedema and infiltrate with lymphocytes and macrophages.

The disease can be caused by direct infection, e.g.Trypanosoma cruzi (Chagas' disease), Coxsackie A and B viruses, HIV, influenza, Epstein-Barr virus, and fungi; toxin-mediated damage, e.g. diphtheria, typhoid and septicaemic states; and immune hypersensitivity,
e.g. acute rheumatic fever.
There are also idiopathic causes, such as giant-cell myocarditis.

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