Myocarditis

Also called heart inflammation, endocarditis or pericarditis

Myocarditis is inflammation of your heart. Most people with this rare condition have mild illness and recover without complications.

Key points about myocarditis

  1. Viral infection is the most common cause of myocarditis. It can also be caused by infection from bacteria or fungi, some medicines or from autoimmune diseases. 
  2. In rare cases when inflammation is severe, myocarditis can damage your heart.
  3. There have been very rare reports of myocarditis occurring after vaccination with the Comirnaty Pfizer COVID-19 vaccine
  4. However, you are more likely to get myocarditis from COVID-19 (along with a lot of other symptoms) than from the vaccine.
  5. Treatment for myocarditis depends on the cause and how severe it is. It can involve close monitoring and medication.
  6. Most people with myocarditis recover without any complications.

What is myocarditis?

Myocarditis is inflammation (swelling) of your heart. It can affect the whole heart or just part of it. Myocarditis is a rare disorder. Each year about 100 people in Aotearoa New Zealand have myocarditis. 

What is the difference between myocarditis, endocarditis and pericarditis?

These terms all refer to inflammation of your heart, but differ depending on which part of the heart is affected.

  • Myocarditis is inflammation of the heart muscle.
  • Endocarditis is inflammation of the inner lining of your heart’s chambers and valves.
  • Pericarditis is inflammation of the tissue that forms a sac around your heart.

These conditions can occur separately or together (myopericarditis).

What causes myocarditis?

Viral infection is the most common cause of myocarditis. It can also be caused by infection from bacteria or fungi, some medicines or from autoimmune diseases. Autoimmune diseases can also cause inflammation in other parts of your body. 

When you have an infection, your immune system produces special cells to fight off disease. If the infection affects your heart, the disease-fighting cells enter your heart. However, the chemicals made by these cells can also damage the heart muscle. As a result, your heart can become thick, swollen and weak. Symptoms of myocarditis usually occur 1–2 weeks after a viral infection. 

Myocarditis and the COVID-19 vaccine

There have been very rare reports of myocarditis and pericarditis occurring after vaccination with the Comirnaty Pfizer COVID-19 vaccine. Note that infection by COVID-19 is far more likely to cause myocarditis than vaccination.

 This is what we know so far about myocarditis and the COVID-19 vaccine:

  • Myocarditis has affected fewer than 1 person in 1 million people who have had the Pfizer 19 vaccine in the European Union countries.
  • Cases are typically occurring in men under the age of 30 within days of receiving of the second dose (generally within a week).
  • Cases typically occur in older adults around 21 days after their first or second dose.
  • In most cases, the myocarditis was mild and is not expected to have any long-term effects.
  • When hospitalised the average stay is 2 days.
  • The Pfizer vaccine is highly effective in protecting people from COVID-19 infection.
  • COVID-19 can also cause myocarditis. Infection by COVID-19 is far more likely than vaccination to cause myocarditis. COVID-19 infection is very dangerous to your body in many ways, and vaccination is a key part of protecting yourself and your family.
  • Read more: Myocarditis and pericarditis Medsafe, NZ, 2021 
In the first few days after your vaccination seek medical attention if you experience new onset chest pain, shortness of breath or an abnormal heartbeat. These are potential signs of myocarditis.

What are the symptoms of myocarditis?

The symptoms are different on each person, and depend on the type of myocarditis and the cause.

Symptoms of myocarditis include:

  • chest pain
  • fast heart beat (palpitations) or feeling like the heart is skipping a beat
  • difficulty breathing (either ongoing, only when active or when lying down)
  • tiredness and less ability to exercise
  • swelling of the feet and legs.

See your doctor or nurse if you have had any of the above symptoms. Let them know if you have had cold symptoms, had a vaccine or started on a new medicine.

How is myocarditis diagnosed?

Often symptoms are mild and go away on their own and so can be undiagnosed. This is not a problem if the symptoms have cleared. Some of the tests you may be recommended include:

  • blood tests to check for heart muscle damage and inflammation
  • an electrocardiogram (ECG) to check for problems in the electrical signals of your heart
  • a chest X-ray, to check for fluid in your lungs or around your heart, or whether your heart is bigger than normal.

There are other more specialised tests that are normally only available in hospital. For example an echocardiogram (echo) is sometimes done. This uses sound waves to create a moving picture of your heart. It checks how well your heart is pumping and how well the valves are working.

How is myocarditis treated?

Treatment for myocarditis depends on the cause and how severe it is. It can involve close monitoring and medication.

  • There are medicines to help with breathing, fluid build up, keeping your heart pumping normally and with preventing blood clots.
  • Your doctor will also suggest rest or reduced activity.
  • Some people need oxygen.
  • It is important to avoid drinking alcohol while recovering, as this can further damage your heart.
  • People with mild myocarditis may only need rest and medicine.
  • If you have severe myocarditis, you will need more intensive treatment, which might include surgery.

Your doctor will generally recommend having a check-up after recovering to make sure there are no further problems.

What is the recovery after myocarditis?

Most people with myocarditis recover without any complications. Sometimes recovery is several months after you receive treatment. In some rare cases, the myocarditis can recur later. 

References

  1. Heart inflammation National Heart, Lung and Blood Institute, US
  2. Myocarditis Patient Info, UK
  3. Myocarditis and the COVID-19 vaccine in New Zealand Immunisation Advisory Centre, NZ

Reviewed by

Jeremy Steinberg is a GP with special interests in musculoskeletal medicine, evidence-based medicine and use of ultrasound. He's been reviewing topics for Health Navigator since 2017 and in his spare time loves programming. You can see some of the tools he's developed on his website.

Credits: Health Navigator Editorial Team. Reviewed By: Dr Jeremy Steinberg, FRNZCGP, Auckland Last reviewed: 06 Sep 2021