Myocarditis is the inflammation of the heart muscle and pericarditis is the inflammation of the lining outside the heart. In both cases, the body's immune system is causing inflammation either to try to get rid of the infection or in response to some other trigger. With rheumatoid arthritis and the other noninfectious diseases, the body is responding to some trigger with an abnormal or exaggerated response of the body's immune system.
The immune system sends white blood cells, called lymphocytes and macrophages, to respond to the trigger (infection or non-infectious trigger). The white blood cells may attack the heart muscle, sometimes destroying the heart cells when they try to destroy the invaders (viruses which live inside the heart cells, bacteria or fungi) or other trigger. Poison-like substances are released from the cells and interfere with the ability of the heart muscle to squeeze (contract). More importantly, damaged heart muscle cells may themselves become antigens, compounds that trigger more of an immune response. This response may result in even more damage to the heart muscle cells.
The severity and side effects of the inflammation depend on the exact cause. With some viruses, there is only a mild inflammation in the lining outside the heart muscle (pericarditis) causing some fluid to accumulate and symptoms such as sharp chest pain which may be worse while lying down. Occasionally, the fluid accumulation can be quite large so that the heart is unable to pump well. This is especially true if the cause of the pericarditis is a bacteria rather than a virus.
Sometimes inflammation is due to a virus which attacks the muscle of the heart (myocarditis). The heart muscle may be further injured when the body's immune system tries to get rid of the virus. When too many heart muscle cells are damaged, the heart muscle may become severely weakened so that the heart can't pump effectively. The process may be rapid and may result in death. More commonly, the heart begins to heal itself. If there are few dead cells, the heart may improve completely, or at least in part. Heart muscle heals by changing dead cells to scar tissue. Scar tissue does not contract and can't help the heart to pump. If enough scar tissue forms, congestive heart failure (the inability of the heart to pump enough blood to meet the demands of the body) may result.
Myocarditis or pericarditis may occur because of an inflammatory disease of the body such as rheumatoid arthritis (JRA), systemic lupus erythematosus, dermatomyositis, Kawasaki disease, rheumatic fever or other noninfectious diseases. They may also occur as a result of an infection (viral, bacterial or fungal) of the heart.
Diagnosis of myocarditis is hard because it looks like so many other diseases. The diagnosis is made first by the history and a physical examination by a doctor. A physical exam may show a fast heart rate, abnormal blood pressure, and fast breathing rate, an abnormal examination of the heart and lungs, and sometimes an enlarged liver.
Very few laboratory or blood tests will give a quick answer. Special tests such as an x-ray of the chest, electrocardiogram and echocardiogram may help with the diagnosis. Sometimes blood tests are obtained to help show the presence or cause of inflammation.
Myocarditis can best be diagnosed by examining a small piece of heart muscle under a microscope. Samples of the heart muscle are taken with a bioptome, a thin, flexible tube with small cutting jaws at its tip. The bioptome is inserted through a vein in the patient's neck and positioned in the heart. Once the bioptome is in position, it withdraws very small heart muscle samples for analysis.
Pericarditis can best be diagnosed with echocardiography showing fluid around the heart. Sometimes a needle is inserted into the area around the heart to obtain a sample of the fluid for analysis.
A doctor then looks at all of these things to make the diagnosis.
Symptoms of fever (a common symptom of inflammation) rash, diarrhea, fatigue, abnormal heart rhythms, shortness of breath, chest pain, and lightheadedness or fainting can occur. Some of these are symptoms of congestive heart failure; however, there may be other causes.
Sometimes, the inflammation is part of another illness such as rheumatoid arthritis and treating the primary illness will treat the heart as well. Other times, it is so mild that nothing needs to be done. In more severe cases, anti-inflammatory drugs such as aspirin or steroids are used. There are other medicines that may also be used but have not been truly shown to work. One of these medicines is intravenous gamma globulin.
Besides treating the inflammation, supportive care may need to be given such as medicines to make the heart pump better until it heals. In very severe cases of myocarditis with a very weak heart, machines may be required to help the heart pump. In pericarditis, if the amount of fluid that accumulates around the heart is quite large, it may need to be removed with a needle or surgery to open the lining around the heart and let it drain.
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With most types of pericarditis, the outlook is very good after the inflammation has resolved and the infection treated if needed to be. On some occasions, there is a recurrence of pericarditis, but this is more common with an underlying inflammatory disease.
With myocarditis, the outlook depends on the underlying cause. It is impossible to predict into which category a new case of myocarditis will fall. If it is due to an inflammatory disease of the body, the outlook for the heart is usually good as it responds to treating the inflammation. Some causes of myocarditis tend to resolve over time without treatment such as rheumatic fever or Kawasaki disease.
With certain types of viruses, damage can occur to the heart though usually, the heart improves partly if not completely. If the heart is left mildly damaged, very few restrictions in activity, medications or follow-up may be needed. If there is more severe damage, more medications may be required. If the heart has been severely damaged, multiple medications may be needed to help the heart pump better, but eventually, a heart transplant may be needed.