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 who is affected by it?
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.
Other causes of myocarditis are much less common. They include:
- Other types of infection. The heart can sometimes become infected by various bacteria, fungi, parasites and other germs. For example:
- Chagas' disease. This is an infection caused by a protozoan called Trypanosoma cruzi. You can catch this infection from an insect bite in certain tropical countries. Worldwide, this is a common cause of myocarditis (but is rare in the UK). With this infection a form of myocarditis develops many years after the initial infection. This leads to a gradual destruction of heart tissue, which can cause severe heart failure.
- Lyme disease. This is an infection caused by a germ (bacterium) called Borrelia burgdorferi. You can catch this infection by a bite from an infected tick.
- Giant cell myocarditis. This is a very rare condition and gets its name from abnormal cells which develop in the heart. The cause is not known but it tends to develop in some people who have a growth on the thymus gland (a thymoma), systemic lupus erythematosus (SLE) - also known as lupus - or an overactive thyroid (thyrotoxicosis).
- A rare side-effect of some medicines and a rare complication of various diseases.
- Other damaging agents. For example, inflammation in the heart can be caused by excess alcohol, radiation, certain chemicals and certain poisons.
- Rejection following a heart transplant.
What are the symptoms of myocarditis?
The symptoms depend on the cause and severity of the inflammation. Many people with viral myocarditis do not have any heart-related symptoms. The heart inflammation may be suspected by some changes on a heart trace (electrocardiogram, or ECG) - see 'How is myocarditis diagnosed?', below. If symptoms do develop they can include:
- Chest pain.
- Raised temperature (fever).
- A fast heartbeat - faster than usual for a normal high temperature.
- An irregular heartbeat.
- Shortness of breath.
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 for more details.
How is myocarditis diagnosed?
Your symptoms are likely to lead your doctor to make the possible diagnosis of myocarditis. A heart trace of your heart's electrical activity (an electrocardiogram) may be done.
A chest X-ray may show that your heart is larger than normal. It is also likely you will have some blood tests to test for some of the viruses that can cause myocarditis. An ultrasound scan of the heart (an echocardiogram) may also be arranged. You may also have an MRI scan to show how your heart is being affected.
Some people need to have an endomyocardial biopsy. This involves taking a very small tissue sample of the heart to investigate for the cause of myocarditis. Newer tests which are more sensitive at diagnosing some of the viruses are currently being developed.
What is the treatment of myocarditis?
The treatment of myocarditis will depend on the cause and severity of your myocarditis. Bed rest is usually recommended at the onset of myocarditis and athletic activities should be avoided for six months. This aims to avoid putting undue strain on the heart muscle. Painkillers will help to ease chest pain and high temperature (fever).
There is no treatment that will cure a viral infection. However, for most people with viral myocarditis, the virus clears away on its own without any treatment, often within a week or so.
In the past, the use of medicines called steroids has been tried. However, there are no clinical studies which demonstrate steroids as being beneficial other than for giant cell myocarditis.
Different treatments for myocarditis are currently being investigated in other clinical studies.
For the more uncommon causes, or if complications develop, a range of treatments may be needed. For example:
- Medication to treat heart failure or irregular heartbeats.
- A pacemaker if certain irregular heart rhythms develop.
- Antibiotic medicines if the cause of the myocarditis is a germ (a bacterial infection).
- Steroid medication if the cause is giant cell myocarditis.
- Stopping alcohol if alcohol is the cause.
What is the outlook (prognosis)?
In most cases of viral myocarditis, the illness goes away on its own and there are no complications. Symptoms may last only a few days or weeks. However, some types of viral infection are more serious and can cause more severe or persistent inflammation and complications.
Complications are more likely with the more uncommon causes of myocarditis. Sometimes the inflammation clears but the heart is left with some permanent damage. You may be left with a degree of heart failure which may require long-term medication.
In some cases, the inflammation and heart damage are so severe that the only treatment option is a heart transplant.
Myocarditis is fatal in some cases. In some cases death occurs some time after the diagnosis is made if the condition becomes worse and unresponsive to treatment. Also, some cases of sudden death in a previously healthy person are due to an acute myocarditis that develops rapidly.
Further help & information
Dr Tim Kenny
Dr Colin Tidy
Dr John Cox