Disorders of the myocardium
Myocarditis
An acute or chronic inflammatory disorder of the myocardium.
Myocarditis is often a feature of a systemic infection but occasionally septicaemia may lead to focal suppurative lesions. Known causative factors:
· Viruses: Coxsackie, cytomegalovirus.
· Protozoa: Trypanosoma cruzi (Chagas’ disease), Toxo-plasma gondii.
· Radiation chemicals and drugs, e.g. cytotoxic agents. Bacterial infection, e.g. Corynebacterium, Coxiella.
· Myocarditis is an important feature of rheumatic fever.
Myocarditis may arise by direct effect, toxin or immunopathology.
Myocarditis is an acute illness characterised by fever and cardiac failure. Patients often experience chest pain due to an associated pericarditis. Signs include soft heart sounds, third sound, tachycardia and often a pericardial friction rub. Myocarditis may be complicated by arrhythmias.
The myocardium shows an acute inflammatory reaction with interstitial oedema and cellular infiltration.
· Chest X-ray may show cardiac enlargement.
· ECG may show ST and T wave abnormalities and arrhythmias.
· Cardiac enzymes are elevated.
· Cardiac biopsy shows acute inflammation. Viral IgM antibody titres may be increased.
Bed rest and eradication of the acute infection, i.e. supportive therapy. Cardiac failure and arrhythmias may need treatment.
Depending on the aetiology the prognosis is usually good, although a chronic cardiomyopathy may occasionally result.
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