Myocarditis
This is an
acute inflammatory condition that can have an infectious, toxic or autoimmune
aetiology. Myocarditis can complicate many infections in which inflammation may
be due directly to infection of the myocardium or the effects of circulating
toxins. Viral infections are the most common causes, such as Coxsackie (35
cases per 1000 infections) and influenza A and B (25 cases per 1000 infections)
viruses. Myocarditis may occur several weeks after the initial viral symptoms
and susceptibility is increased by corticosteroid treatment, immunosuppression,
radiation, previous myocardial damage and exercise. Some bacterial and
protozoal infections may be complicated by myocarditis; for example,
approximately 5% of patients with Lyme disease (Borrelia burgdorferi, develop
myopericarditis, which is often associated with AV block. Toxic aetiologies
include drugs, which may directly injure the myocardium (e.g. cocaine, lithium
and anticancer drugs such as doxorubicin) or which may cause a hypersensitivity
reaction and associated myocarditis (e.g. penicillins and sulphonamides), lead
and carbon monoxide. Occasionally, autoimmune conditions such as systemic lupus
erythematosus and rheumatoid arthritis are associated with myocarditis.
The clinical picture ranges from a symptomless
disorder, sometimes recognised by the presence of an inappropriate tachycardia
or abnormal ECG, to fulminant heart failure. Myocarditis may be heralded by an
influenzalike illness. ECG changes are common but non-specific. Biochemical
markers of myocardial injury (e.g. troponin I and T, creatine kinase) are
elevated in proportion to the extent of damage. Echocardiography may reveal
left ventricular dysfunction that is sometimes regional (due to focal
myocarditis), and if the diagnosis is uncertain it can be confirmed by endomyocardial
biopsy.
In
most patients, the disease is self-limiting and the immediate prognosis is
excellent. However, death may occur due to a ventricular arrhythmia or rapidly
progressive heart failure. Myocarditis has been reported as a cause of sudden
and unexpected death in young athletes. There is strong evidence that some
forms of myocarditis may lead to chronic low-grade myocarditis or dilated cardiomyopathy (see below); for example, in Chagas disease the patient
frequently recovers from the acute infection but goes on to develop a chronic dilated
cardiomyopathy 10 or 20 years later.
Specific
antimicrobial therapy may be used if a causative organism has been identified;
however, this is rare and in most cases only supportive therapy is available. Treatment for
cardiac failure or arrhythmias may be required and patients should be advised
to avoid intense physical exertion because there is some evidence that this can
induce potentially fatal ventricular arrhythmias. There is no evidence for any
benefit from treatment with corticosteroids and immunosuppressive agents.
