What is Myocarditis

Myocarditis is an inflammatory disorder of the myocardium (the heart muscle). It is usually caused by a viral infection, particularly adenovirus (a virus that contains DNA) and enterovirus (a group of viruses that infect the gastrointestinal tract and can spread to other areas) infections, although many infectious organisms commonly seen in infants and children have been implicated.

Statistics on Myocarditis

Internationally: Myocarditis is a rare disease. Incidence varies greatly among countries and is related to hygiene and socioeconomic conditions. Availability of medical services and immunizations also affect incidence. Occasional epidemics of viral infections have been reported with an associated higher incidence of myocarditis.

Mortality/Morbidity: Studies give a wide spectrum of mortality and morbidity statistics. With suspected coxsackievirus B, the mortality rate is higher in newborns (75%) than in older infants and children (10-25%). Complete recovery of ventricular function has been reported in as many as 50% of patients. Some patients develop chronic myocarditis (ongoing or resolving) and/or dilated cardiomyopathy and may eventually require cardiac transplantation.

Race: No racial predilection exists.

Sex: No sex predilection exists in humans, but some research in laboratory animals suggests that the disease may be more aggressive in males than in females. Certain strains of female mice had a reduced inflammatory process when treated with estradiol. In other studies, testosterone appeared to increase cytolytic activity of T lymphocytes in male mice.

Age: No age predilection exists. Younger patients, especially newborns and infants, and immunocompromised patients may have increased susceptibility to myocarditis.

Risk Factors for Myocarditis

These include:

1) Viral infections: Coxsackie, Influenza, Rubella, Polio, Adeno and HIV have all been implicated.
2) Bacterial infections with agents such as Corynebacterium, Rickettsia, Chlamydia and Coxiella.
3) Protozoal infections: Trypanosoma Cruzi which causes Chagas’ disease and is common in South America and Toxoplasma Gondii are both known to cause myocarditis.
4) Radiation and poisoning can cause myocarditis (agents such as lead).
5) Rarely, autoimmune processes may cause myocarditis.

Progression of Myocarditis

The disease usually develops acutely and may be linked to a causative agent (rarely is a single agent identified). A generalised inflammatory illness ensues and heart failure may develop. Recovery may be spontaneous or intractable heart failure may develop.

Heart blocks and ventricular tachyarrhythmias are associated with some of the more aggressive types of myocarditis.

How is Myocarditis Diagnosed?

Chest x-ray: there may be some cardiac enlargement depending on the aetiology and stage.

ECG: arrhythmias may be seen as well as ST segment and T wave abnormalities.

Prognosis of Myocarditis

This is usually good and depends somewhat on the underlying causes and origins of the disease. Chronic heart failure or cardiomyopathy may result with poorer outlook.

How is Myocarditis Treated?

Treatment is supportive and includes bed rest and treatment of identified causative factors (eg. eradication of infection).

Cardiac failure and arrhythmias should be mangaged appropriately.

Myocarditis References

[1] eMEDICINE Online.
[2] Hurst’s The Heart 8th Edition, McGRAW-HILL 1994.
[3] Kumar and Clark, Clinical Medicine 4th Edition, W.B SAUNDERS 1998.