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Myocarditis is an inflammation of the heart muscle. There are many causes, but problem is even greater when the body causes damage on its own. This is a serious condition when the heart becomes so weak that patient could even die.
The myocardium is the muscular wall of the heart, or the heart muscle, which contracts to pump blood out of the heart. After pumping, it relaxes as the heart refills with returning blood. The myocardium’s smooth outer membrane is called epicardium, while its inner lining is endocardium. Myocarditis is an inflammation of the myocardium, or middle lining. When the heart becomes inflamed, it cannot pump as well because of the damage done to its cells and swelling. The heart muscle may damage even more if the body’s immune system sends antibodies to try and fight whatever started the inflammation. Sometimes these antibodies attack the tissues of heart instead the cause of myocarditis. If too many heart muscle cells are damaged, the heart muscle weakens. In some cases, this process happens very quickly and results in heart failure or even sudden death. More often, the heart tries to heal itself; the heart muscle heals by changing the damaged or dead heart muscle cells into scar tissue. Scar tissue is not like heart muscle tissue because it does not contract and it cannot help the heart pump blood. If enough scar tissue forms in the heart, it can ultimately lead to congestive heart failure or dilated cardiomyopathy as a consequence of myocarditis.
What causes myocarditis?
- A virus causes one common form of myocarditis, which often occurs after a viral infection of the nose and throat. This myocarditis type often goes away on it own after it runs its course. Although many different viruses can cause myocarditis, coxsackie virus B is the most common in the United States.
- Other viruses that can cause myocarditis include echovirus, influenza, Epstein-Barr, rubella, chickenpox, mumps and hepatitis.
- HIV infection is also a common cause of myocarditis, because about 10% of people with HIV develop this disease. This might occur because HIV directly invades the heart muscle or because the patient's weakened immune system makes the heart muscle more susceptible to attack by other infections.
- Albeit rarely, bacteria can cause myocarditis as a complication of endocarditis, an infection of the heart valves and the lining inside the heart’s chambers. Some common bacteria responsible for myocarditis include Staphylococcus aureus, enterococci and Corynebacterium diphtheriae. In fact, about 25% of people with diphtheria, a toxin produced by C. diphtheriae bacteria, experience a form of myocarditis that leads to a flabby, stretched-out heart muscle. Because the flabby, enlarged heart cannot pump blood efficiently, severe congestive heart failure may develop within the first week of this illness.
- "Chagas" disease is an infection caused by the protozoan Trypanosoma cruzi, transmitted by insect bite. In the United States, myocarditis caused by Chagas’ disease is most common among travelers from Central and South America. In up to one-third of people with Chagas' disease, a form of chronic myocarditis develops many years after the first infection ends. This chronic myocarditis leads to a significant destruction of the heart muscle, with progressive heart failure as a serious consequence.
- Lyme myocarditis can also occur due to Lyme’s disease, an infection with tick-borne bacterium Borrelia burgdorferi. This disease causes myocarditis or other heart problems in about 10% of patients.
- Giant cell myocarditis is a rare form of myocarditis. It takes its name from large, abnormal giant cells found when a piece of the affected heart muscle is examined under a microscope. Giant cell myocarditis is most common among people who have thymoma, which is a growth of the thymus gland. This is a collection of immune-system tissues below the top of the breastbone.
- Other agents are also able to provoke myocarditis, such as alcohol, radiation, chemicals, and drugs, including doxorubicin, cyclophosphamide, emetine, chloroquine and sulfonamides. A recent study also showed that severe emotional stress could produce heart failure that starts abruptly, with evidence of inflammation of heart muscle as well.
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