10th May 2025

Aetiology

Myocarditis is a result of inflammation of the heart which can result from several mechanisms, including direct toxic effects on the myocyte, production of a toxin and immunologically mediated cell damage.

Table 1: Aetiology of myocarditis, adapted from the ESC guidelines on heart failure

An accurate and in-depth history is important for suggesting the aetiology of myocarditis.

Viruses are the most common cause, accounting for around 50% of all cases and patients will often note a recent or concurrent illness associated with the onset of chest pain. In Western countries, enteroviruses (especially Coxsackie B) are the most common and usually mild and self-limiting, however, can be much more severe in neonates and young children. Recently myocarditis has become a well-recognised complication of COVID infections and there is growing evidence to suggest an association with the  COVID vaccination⁵.

Travel history can be helpful for those in which you suspect a parasitic cause or viruses less associated with the Western world, such as dengue or Zika virus.

Newly started drugs, including prescription, over-the-counter and recreational drugs, as well as recent vaccinations are important. Immunosuppressive medications are important for viruses which would not typically affect the immunocompetent.

Autoimmune disorders such as rheumatoid arthritis, systemic lupus erythematosus and sarcoidosis are important to rule out. Myocarditis can (although uncommonly) be the first presentation of these disorders and around 7% of patients with myocarditis have an associated autoimmune disorder. Expanding your history taking and investigations to consider systemic symptoms (such as a history of fatigue, lymphadenopathy, ocular manifestations etc.) and a family history is therefore important. Sarcoidosis especially can present predominantly with cardiac manifestations.