Myocarditis

Myocarditis symptoms

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 'Diagnosis', below.

If they do develop, the symptoms of myocarditis include:

• Chest pain.

• Raised temperature (fever).

• A fast heartbeat - faster than usual for a normal high temperature.

• An irregular heartbeat.

• Tiredness.

• Shortness of breath.

Myocarditis causes

Myocarditis means inflammation of the myocardium. The myocardium is the heart muscle. Myocarditis can affect anyone and occur at any age. There are many causes of myocarditis; many are mild and some are serious. The most common causes are:

Viral infection

In the UK, the most common infections causing myocarditis are viruses called Coxsackie B and adenovirus.

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.

  • Myocarditis can be a rare side-effect of some types of Covid mRNA vaccine - although the risk of getting myocarditis due to a Covid vaccine is less than the risk of getting myocarditis due to Covid infection.

• 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.

Myocarditis treatment

The treatment of myocarditis depends on the cause and severity of your myocarditis.

Treatment for myocarditis includes:

• Treatment of the cause of myocarditis, if possible. For example, if myocarditis is caused by an autoimmune problem like lupus (SLE), treatment to reduce the activity of your immune system may be given.

• Treating symptoms of myocarditis, such as pain and fever.

• Treating or preventing complications of myocarditis; for example, treatments for heart rhythm problems, or treatments for heart failure.

For myocarditis that is caused by viral infections or has an unknown cause, there is no specific treatment for the cause, and treatment involves controlling symptoms and treating or preventing complications, whilst waiting for the condition to improve on its own.

Common treatments include:

Bed rest

People with myocarditis are usually advised to avoid exercise and playing in competitive sports whilst they have it. They are also often advised to avoid sustained and high intensity exercise for three to six months after they have recovered. This aims to avoid putting too much strain on the heart muscle whilst it is recovering.

Painkillers

Chest pain and high temperature (fever) can be eased with the help of painkillers.

Other medication

If complications develop (see below), 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 bacterial infection).

• Steroid medication, in some types of myocarditis.

• Stopping alcohol if alcohol is the cause.

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 the separate leaflet called Heart Failure for more details.

Diagnosis

Your doctor may suspect that you have myocarditis based on your symptoms, and what they find when they examine you.

There are several different tests that are useful for diagnosing myocarditis, including:

• A heart trace of your heart's electrical activity (an electrocardiogram or ECG).

• Blood tests. These can include tests to look for damage to the heart, tests to look for inflammation, and tests to look for viral infections.

• An ultrasound scan of the heart (an echocardiogram), to see how well the heart is pumping.

• An MRI scan to show how your heart is being affected. This can sometimes show typical features of myocarditis in the heart muscle.

• An endomyocardial biopsy. This involves taking a very small tissue sample of the heart to investigate for the cause of myocarditis, and is sometimes recommended.

What is the outlook?

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.

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