Written by Dimitrios Vrachatis, Specialist Cardiologist, PhD, National and Kapodistrian University of Athens.
What is myocarditis?
Myocarditis is inflammation of the heart muscle caused by infectious or non-infectious factors.
What are the symptoms?
Presentations range from:
- No symptoms
- Mild symptoms, such as palpitations, mild breathlessness, feeling faint or mild chest pain
- Severe, rapidly developing heart failure
A febrile infection often precedes the diagnosis.
How common is it?
Its exact frequency is difficult to establish because it is often asymptomatic. Global estimates suggest 10–20 cases per 100,000 people.
How is myocarditis diagnosed?
A definite diagnosis combines histological, immunohistochemical and immunological criteria, requiring a myocardial biopsy.
Most cases are assessed as probable myocarditis based on:
- Clinical signs and symptoms
- Blood markers of myocardial injury
- Imaging with echocardiography and cardiac MRI
- ECG findings
In practice, the main diagnostic examination is cardiac MRI, which can reveal a characteristic pattern.
What causes myocarditis?
Viral infections are the main trigger. Adenoviruses and enteroviruses, such as Coxsackie viruses, were previously the most commonly implicated agents.
Herpesviruses, including HHV-6 and CMV, and parvovirus B19 are now considered more frequent causes of viral myocarditis.
Coronaviruses, including SARS-CoV-2, can also cause myocarditis, although myocardial injury in COVID-19 can have several mechanisms.
Why does myocarditis develop?
The exact mechanism in viral myocarditis is not fully understood. The leading explanation involves the immune response to the infectious agent.
If the body completely clears the virus from the myocardium, the harmful processes gradually reverse.
If clearance fails, continuing inflammation may cause fibrosis, enlargement and remodelling of the left ventricle, resulting in dilated cardiomyopathy.
Only some people exposed to these viruses develop myocarditis, and familial clustering has been observed, suggesting a genetic predisposition.
Can it be prevented?
There are no specific prevention measures. Personal protection against infection, such as wearing a mask and avoiding close contact with people with active infections, provides an indirect approach.
Which tests will I need?
Your cardiologist decides after reviewing your history. Assessment includes examination, an echocardiogram, an ECG, blood tests such as troponin and possibly cardiac MRI.
Coronary angiography may be performed to exclude other causes of the symptoms.
How is it treated?
Rest is important. Failing to rest may increase viral load and mortality. Medication depends on the clinical picture and local hospital protocols.
If ejection fraction is reduced or heart failure is present, treatment includes beta-blockers, ACE inhibitors, diuretics and mineralocorticoid receptor antagonists.
When ejection fraction is normal, there is no consensus on the benefit of these medicines, with the possible exception of beta-blockers.
How long should I avoid exercise?
All patients are advised to avoid physical exercise for at least six months.
How do I return to activity?
Return requires confirmation that active inflammation has resolved and cardiac function has recovered, using ECG, echocardiography and/or MRI.
Residual arrhythmia risk is assessed at rest with 24-hour Holter monitoring and during exertion with a treadmill exercise test.
What long-term follow-up is needed?
If function is normal after this period, intermittent cardiology follow-up continues for up to three years to exclude late complications, including dilated cardiomyopathy or heart failure with preserved ejection fraction.
What is the prognosis?
In most cases, the heart returns to its previous state without further problems.
Some patients do not recover function fully or later develop problems such as dilated cardiomyopathy. A more dramatic initial presentation generally carries a higher risk of lasting or late complications.
Myocarditis, COVID-19 and Vaccination
mRNA vaccines against SARS-CoV-2 have been associated with very small rates of myocarditis, mainly in young men, with a good clinical outcome in the vast majority.
The risk of myocarditis from COVID-19 in unvaccinated people is several times higher than the risk associated with vaccination.