Introduction 

Myopericarditis is a rare condition marked by simultaneous inflammation of the pericardium, the heart's protective lining, and the myocardium, the heart muscle.¹ This interplay between pericarditis and myocarditis complicates diagnosis and treatment. Various factors contribute to myopericarditis, including viral and bacterial infections, autoimmune disorders, and post-myocardial infarction inflammation.

Understanding its aetiology is crucial for effective management and improving patient outcomes. This article explores the causes of myopericarditis, highlighting the importance of early diagnosis and intervention.

Pericarditis

The pericardium is essentially the heart’s lining, it is a sac with two layers that surrounds the heart.² Pericarditis refers to when the sac around the heart becomes inflamed. Parts of your body become inflamed when trying to fight off things that could be harmful, such as infections. 

So, although relatively rare, if the pericardium is exposed to something like an infection, its most common response is inflammation.³ This inflammation can sometimes allow blood or fluid to leak into it. In most cases, it is not serious, but it can potentially cause more serious problems. 

According to the NHS, the most common symptom of pericarditis is chest pain. Usually, this pain is: 

• Stabbing or sharp
• Can spread to your stomach, arms, shoulders
• More intense when you are lying down, swallowing, or breathing deeply
• Less intense when you are leaning forward

It is also possible to have a fever, cough, or joint pain. 

Myocarditis

The myocardium is the heart muscle and makes up the thickest layer of the heart wall.⁴ Similar to pericarditis, myocarditis is when this heart muscle becomes inflamed, usually in response to fighting something such as an infection. Again, people usually make a full recovery, however, if the extent is severe enough it can leave lasting damage, such as the heart becoming bigger and weaker from overworking.

Common symptoms of myocarditis can include: 

• Chest pain 
• High temperature
• Fatigue 
• Cold/flu-like aches 

Whilst rare, it is also possible to experience: 

• Irregular heartbeats 
• Difficulty breathing
• Fainting
• Swollen stomach/ankles

Myopericarditis

When an individual suffers from both pericarditis and myocarditis, the terms are often linked. The condition is most commonly referred to as ‘myopericarditis’ when the issues with the pericardium are more pronounced.¹ Conversely, if the myocardium is more affected, the term ‘perimyocarditis’ may be used. However, it is important to note that these terms are frequently used interchangeably and do not always reflect which condition is more predominant.

From a clinical perspective, both pericarditis and myocarditis share many common causes, which is why they often coexist.⁵

‘Idiopathic’ myopericarditis 

In many cases of myopericarditis, determining a specific cause can be challenging, even after extensive testing.⁵ This uncertainty can be distressing for those affected. If you find yourself in this situation, it’s crucial to seek support for managing your symptoms.

Consider reaching out to resources like the British Heart Foundation’s Heart Helpline, where you can connect with a cardiac nurse via phone, email, or online chat for guidance and support.

Types of myopericarditis

When the cause of myopericarditis is identified, it is generally classified into two categories: infectious and non-infectious.¹

Infectious myopericarditis is often linked to viral infections, such as those caused by enteroviruses, adenoviruses, and even the influenza virus. Bacterial and fungal infections can also lead to this condition, though they are less common.

On the other hand, non-infectious myopericarditis can arise from autoimmune disorders, post-myocardial infarction syndromes (Dressler's syndrome), or exposure to certain medications and toxins. In some cases, myopericarditis may also develop after a heart attack or as a result of radiation therapy.

For a more detailed overview of the causes of myopericarditis, you can refer to resources like the American Heart Association or the British Journal of Cardiology.

Infectious causes of myopericarditis 

Viral causes of myopericarditis 

Across developed countries, clinicians most often find viral infections to be the cause of myopericarditis.¹ The presence of the virus, if affecting the heart, can cause the myocardium and pericardium to become inflamed. 

In North America and Europe, the most common viruses that are found to be a cause of myopericarditis are: 

• Human parvovirus B19
  • The most common cause of myocarditis in children and infants⁶
  • Is usually a mild infection, which can result in a rash
• Human Herpesvirus 6
  • Two closely related herpes viruses can infect approximately 70% of children 
  • Usually leads to a fever and/or diarrhoea
• Epstein-Barr virus
  • The virus usually causes glandular fever
• Enteroviruses
  • Usually causes several mild illnesses
• Cytomegalovirus
  • A mostly harmless, common virus
• Adenovirus
  • A virus that often causes respiratory infections and cold/flu-like symptoms
• SARS-CoV-2 (COVID-19)
  • Multiple studies have found that the incidence of myocarditis/pericarditis increased by over 15 times compared with pre-COVID⁷

Whilst these have been identified as the most common viral causes of myopericarditis across North America and Europe, most people who catch these viruses will not develop myopericarditis as a result – this is a rare outcome. 

Bacterial causes of myopericarditis 

It is less common for myopericarditis to be caused by a bacterial infection. However, in the cases where it has been, the most common types of bacteria have been identified as: 

• Mycobacterium tuberculosis 
  • A bacteria causing tuberculosis
• Streptococcus (Strep A) infection
  • Usually a mild infection with cold/flu-like symptoms
• Staphylococcus 
  • Staph infections commonly lead to rashes or sores
• Legionella
  • Often referred to as ‘Legionnaires’ disease
  • Rare but can be treated with antibiotics
• Mycoplasma 
  • A bacteria that can cause respiratory illnesses

Fungal causes of myopericarditis 

Fungal infections have also been known to rarely cause myopericarditis. These include: 

• Fungal lung infections like histoplasmosis and coccidioidomycosis
• Aspergillosis 
  • An infection is caused by breathing in very small bits of mould
• Other fungal infections, such as Athlete’s foot

Parasitic causes of myopericarditis 

In some cases, infections caused by parasites have caused myopericarditis, these have included but are not limited to: 

• Toxoplasmosis
  • An infection is caused by the toxoplasma parasite, which you can catch from infected cat faeces or infected meat
• Amoebic dysentery/amoebiasis
  • An intestine infection caused by amoebic parasites
• Chagas disease
  • A disease caused by a protozoan parasite
  • Also known as American trypanosomiasis

Non-infectious causes of myopericarditis 

Medications/harmful substances

Sometimes, the use of certain medications or harmful substances can either produce a toxic effect on the heart, or the heart can be hypersensitive to them, and this can lead to myopericarditis.⁵

Some examples can include:

• Isoniazid
  • Antibiotics for tuberculosis
• Procainamide
  • A medication intended to manage arrhythmias (irregular heartbeats)
• Hydralazine
  • A medication used to treat hypertension (high blood pressure)
• Alcohol
• Cocaine 
• Carbon monoxide

Autoimmune diseases 

Many autoimmune diseases have been linked to myocarditis.⁸ An autoimmune disease is when the body damages its tissue due to a problem with its immune function. Imagine your immune system being a brigade that usually fights off unknown substances that can cause you harm but with an autoimmune disease, that same fighting brigade turns on you and attacks you instead, mistaking you for the harmful substance.

This can involve several different organs and systems in the body, and the heart is often one of those affected. Parts of the heart’s structure, like the myocardium and the pericardium, can become damaged as a result of these types of diseases, therefore causing myopericarditis in some cases.⁹

Examples of these diseases include: 

• Sarcoidosis
• Giant cell arteritis
• Eosinophilic myocarditis
• Lupus
• Rheumatoid arthritis

Post-myocardial infarction syndrome

Post-myocardial infarction syndromes, commonly known as Dressler's syndrome, is a type of pericarditis that occurs after a myocardial infarction (heart attack).⁹ Dressler's syndrome is therefore directly linked to myopericarditis as both conditions involve inflammation of the heart and its surrounding structures. 

After a heart attack, the body may mount an autoimmune response to the damaged heart tissue, leading to delayed inflammation often weeks to months post-infarction. This syndrome can contribute to the symptoms of myopericarditis, such as:⁹ 

• Chest pain
• Fever, and 
• Pericardial effusion

Management of myopericarditis and Dressler's syndrome often overlap, focusing on reducing inflammation with treatments like NSAIDs or corticosteroids. Understanding the connection between these conditions is crucial for effective diagnosis and treatment.

COVID-19 and mRNA vaccines 

mRNA vaccines for COVID-19 have been associated with a rare but notable risk of myocarditis and pericarditis, particularly after the second dose.¹⁰ This risk is especially pronounced in males under the age of 25, where incidents of myopericarditis following vaccination have been reported. However, it is crucial to note that the risk of myocarditis from Covid-19 infection itself is higher compared to the risk posed by the vaccines.

The British Heart Foundation emphasizes that while vaccine-associated myocarditis is concerning, the benefits of vaccination in preventing severe COVID-19 outweigh these risks, particularly since COVID-19 is a more likely cause of myocarditis. For more detailed information, you can explore sources such as the British Heart Foundation and the Centers for Disease Control and Prevention (CDC).

Summary 

Myopericarditis is characterised by the simultaneous presence of myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the heart’s lining). Often, the cause of myopericarditis remains unknown and is classified as idiopathic. When the cause is identified, it can be categorised as either infectious or non-infectious.

Infectious causes may involve viral, bacterial, fungal, or parasitic infections, while non-infectious causes can include medications, exposure to harmful substances, autoimmune diseases, post-myocardial infarction complications, and adverse effects from COVID-19 or its vaccines.

For those seeking advice on myopericarditis, the British Heart Foundation offers support through their cardiac nurses. More information can be found on their website here.