Myocarditis is an inflammation of the heart muscle. There are various causes but it is usually caused by a virus. Depending on the cause and severity, symptoms and possible problems can range from no symptoms at all, to life-threatening heart failure. Many people with myocarditis recover completely but it can cause serious problems and even death in some cases.
What causes myocarditis and whom does it affect?
Myocarditis means inflammation of the myocardium. The myocardium is the heart muscle. Myocarditis can affect anyone and occur at any age. There are various causes; many are mild and some are serious. Causes include the following:
Many types of viral infection can affect several parts of the body, including the heart muscle. Myocarditis may develop at the same time as, or more often just after, a viral throat or chest infection.
The body’s immune system can clear many types of virus. This means that many cases of viral myocarditis go away on their own within a week or so.
In the UK, the most common infections causing myocarditis are viruses called Coxsackie B and adenovirus. Other viruses which sometimes cause myocarditis include:
- Flu (influenza)
- Glandular fever (Epstein-Barr virus)
- German measles (rubella)
- Chickenpox (varicella)
- Yellow fever
- Dengue fever
- Polio (poliomyelitis)
- Viruses that cause hepatitis A and hepatitis C
Sometimes the inflammation in the heart lasts longer than other features of the infection. The virus may have gone but the immune system may over-react and cause inflammation which persists for a time in the heart.
Unknown cause (idiopathic myocarditis)
In many people with myocarditis, the cause is not found. However, for the majority of these people it is likely to be caused by a virus that could not be confirmed by a test.
What are symptoms of myocarditis?
Myocarditis can be mild and cause virtually no noticeable symptoms. The most frequent symptom of myocarditis is pain in the chest.
When myocarditis is more serious, it leads to weakening of the heart muscle. Myocarditis can then cause heart failure (with symptoms of shortness of breath, fatigue, fluid accumulation in the lungs, etc.) as well as heart rhythm irregularities from inflammation and/or scarring of the electrical system of the heart.
How is myocarditis diagnosed?
Myocarditis is diagnosed by detecting signs of irritation of heart muscle. Blood tests for heart muscle enzymes (CPK levels) can be elevated. Electrical testing (EKG) can suggest irritation of heart muscle and demonstrate irregular beating of the heart. Nuclear heart scan testing can show irregular areas of heart muscle.
What are the possible complications?
Complications may develop if the inflammation damages the heart muscle or the fibres that conduct the electrical impulses in the heart. Complications develop quickly in some cases following sudden-onset (acute) symptoms listed above.
Some cases of myocarditis develop gradually (such as in Chagas’ disease) and have no acute symptoms. It may be that the complications are the first indication that you have had myocarditis in the past.
Possible complications include:
- Sudden loss of consciousness (syncope).
- Abnormally fast, slow or irregular heartbeats (cardiac arrhythmias).
- Heart failure which can cause shortness of breath, swelling of the legs and tiredness. (See separate leaflet called Heart Failure.)
What is the prognosis (outlook) for patients with myocarditis?
The prognosis for long-term damage is not predictable and only becomes evident as the patient is followed by the doctor over time.
After the initial phase of myocarditis, some patients can experience complete recovery, others may develop chronic heart failure due to injured heart muscle. Infrequently, some patients develop fulminant heart failure, a fatal condition without heart transplantation.
Patients who have had myocarditis are at some risk for sudden unexpected, potentially fatal, heart rhythm abnormalities. These can often be prevented with implantable defibrillators if the heart muscle damage is severe.
How is myocarditis treated?
Except in systemic sarcoidosis and immune inflammation (such as from systemic lupus erythematosus) where myocarditis can respond to corticosteroids, no proven effective medications are currently available for treating active myocarditis.
Treatment measures mainly involves alleviating heart failure (salt restriction, water pills, ACE inhibitors, beta blockers, etc.) and treating as well as monitoring heart rhythm abnormalities.