The myocardium is the muscular wall of the heart, or the heart muscle. It contracts to pump blood out of the heart and relaxes as the heart refills with blood. The myocardium's smooth outer membrane is called the epicardium. Its inner lining is called the endocardium.
Myocarditis is an inflammation of the myocardium. When the heart becomes inflamed, it cannot pump well because of swelling and cell damage. The heart muscle may be further damaged if the immune system sends antibodies to fight the cause of the inflammation, because the antibodies sometimes attack the heart tissue during the process. If too much heart tissue is damaged, the heart muscle weakens. If this process happens very quickly, it results in heart failure or sudden death. When weakened, the heart tries to heal itself. It heals by changing damaged or dead heart muscle cells into scar tissue. Scar tissue is not like heart muscle tissue because it does not contract--it cannot help the heart pump. If enough scar tissue forms in the heart muscle, congestive heart failure or dilated cardiomyopathy is the result.
What Causes Myocarditis?
Myocarditis is a rare condition. The initial inflammation of the heart muscle may be caused by:
• A viral, bacterial, parasitic, or fungal infection
• Diphtheria, rheumatic fever, or tuberculosis
• Toxic drug or chemical poisoning
• Connective tissue diseases, such as lupus or rheumatoid arthritis
A mild case of myocarditis will produce no symptoms, and it will usually resolve on its own without any lasting damage.
A moderate case of myocarditis will produce symptoms that are similar to a bad cold or flu, including fever, achy chest pain, and severe fatigue. Some patients will develop an arrhythmia or difficulty breathing.
Severe cases of myocarditis may not be diagnosed until heart failure symptoms begin to develop. These cases can also resolve without intervention, but they cause ongoing and irreversible damage to the heart muscle.
Myocarditis is difficult to diagnose because it can resemble many other diseases. It may be suspected if symptoms appear within six months of having an infection. A number of tests are used to confirm the diagnosis, including:
• Physical examination for heart sounds and heart rate.
• Blood tests for infection and signs of inflammation.
• Chest x-ray for pulmonary edema.
• Electrocardiogram (ECG) for heart rhythm, size, and function.
• Echocardiogram for heart wall motion and size.
• Endomyocardial biopsy with a bioptome to test for signs of infection.
Depending on the level of damage to the heart, medicines and follow-up visits to the doctor may be all that is needed. Myocarditis is treated with pain relievers and anti-inflammatory medicines. If myocarditis is part of another illness (such as rheumatoid arthritis), treating that illness will also treat the heart. If myocarditis is caused by a bacterial infection, antibiotic medicines are prescribed. In some cases, diuretics, digitalis, angiotensin-converting enzyme (ACE) inhibitors, angiotensin II receptor blockers, or vasodilators may be prescribed to help the heart pump while it heals. Antiarrhythmic medicines may be prescribed for patients who have an associated arrhythmia. Patients with a higher level of heart muscle damage may need to limit activities and take medicine for the rest of their lives. A heart transplant may be necessary for those rare patients who suffer severe damage.
Texas Heart Institute www.texasheartinstitute.com/HIC/Topics/Cond/myocard.cfm
Medline Plus www.nlm.nih.gov/medlineplus/ency/article/000149.htm
American Heart Association www.americanheart.org/presenter.jhtml?identifier=4729