Myocarditis and pericarditis

Background

Myocarditis and pericarditis are rare but serious cardiac conditions. Myocarditis involves inflammation of the myocardium (the middle muscular layer of the heart wall). Pericarditis involves inflammation of the pericardium (the sac surrounding the heart). They can occur separately or together (myopericarditis). Complications of these conditions can include irregular heartbeat (arrhythmia), and/or enlargement and weakening of the heart – both of which can impair the ability to pump blood effectively.

Myocarditis and pericarditis can be inherited conditions, or can be caused by infections (such as influenza and COVID‑19), injury, taking certain medications (including illicit drugs) and autoimmune diseases. A small number of cases have been reported following receipt of some vaccines (COVID‑19 and mpox).

Diagnosis

Myocarditis and pericarditis present with a similar range of symptoms. In cases following vaccination, myocarditis symptoms have typically presented within 2 to 7 days, and pericarditis symptoms can occur within 2 to 3 weeks. Individuals may notice:

• chest pain, pressure or discomfort
• pain with breathing (pleuritic chest pain)
• shortness of breath
• palpitations
• syncope (faint)
• other non-specific symptoms such as fatigue, dizziness, abdominal pain.

Timely medical review by a GP or through a hospital emergency department is important. Investigations to support diagnosis might include blood tests (for cardiac biomarkers, e.g. troponin), ECG and imaging (e.g. chest X‑ray, cardiac MRI, ultrasound, echocardiogram).

Association and incidence

Myocarditis, from any cause, occurs more commonly in males than females. It is also more likely to affect younger adults, compared with children or older adults.

Pericarditis, from any cause, occurs in similar rates among males and females. It is more likely to affect adults, compared with children.

COVID‑19 vaccination

Most cases of COVID‑19 vaccine‑associated myocarditis and/or pericarditis were reported following receipt of a second dose of mRNA vaccine. However, they have been reported following any dose and any type of COVID‑19 vaccine.

Local and international data shows that pericarditis following COVID‑19 vaccination is more common in the 18- to 39‑year‑old age group for both males and females.  Rates of myocarditis occurring following COVID‑19 vaccination vary; however, they are above expected background rates for both sexes. The peak risk group for COVID‑19 vaccine related myocarditis is young adult males aged 16 to 17 years, with a smaller increased risk for males aged between 12 to 24 years.

Mpox vaccination

Myocarditis and/or pericarditis have been associated with administration of the smallpox vaccine ACAM2000, occurring at a rate of approximately 1 in 175 adults who receive the vaccine for the first time. A very small number of cases of myocarditis and/or pericarditis have been reported following receipt of JYNNEOS (MVA-BN), with no causal relationship established with this vaccine.

Treatment

Myocarditis and/or pericarditis (including arrhythmias, decreased cardiac function, congestive cardiac failure) are managed by a cardiologist. Treatment may include in-patient monitoring and pharmacological agents such as ACE-inhibitors and beta-blockers. 

Long‑term follow‑up of individuals who have experienced myocarditis and/or pericarditis following COVID-19 vaccines continues to be evaluated to determine long‑term prognosis and impact. One of the key, long-term follow-up issues post-myocarditis is late gadolinium enhancement (LGE) seen on cardiac MRI, indicating heart scarring and a risk of future arrhythmias. LGE can occur following both infection and vaccination, so longer term follow-up remains important.

Implications for future doses

All episodes of myocarditis and/or pericarditis occurring following vaccination should be reported to the adverse event reporting service in your jurisdiction. 

COVID-19 vaccination

Further vaccination should be withheld until review by a specialist immunisation service if the individual has experienced:

• suspected myocarditis following COVID-19 vaccination (with no clear alternate diagnosis)
• suspected pericarditis following COVID-19 vaccination with abnormal investigations (and no clear alternate diagnosis)
• suspected pericarditis where investigations were unable to be performed/unavailable (in those aged 39 years or younger).

Mpox vaccination

Individuals who have been diagnosed with myocarditis and/or pericarditis following mpox vaccination should be referred to a specialist immunisation service for follow–up and advice on future doses.

Precautions

If both COVID-19 and mpox vaccination are recommended and the timing is not urgent, an interval of 4 weeks is recommended to minimise the risk for developing myocarditis and/or pericarditis.

However, if mpox primary preventative vaccination (PPV) or post-exposure preventative vaccination (PEPV) is urgent, it should not be delayed or withheld in individuals who recently received a COVID–19 vaccine.

Resources

• Sexson Tejtel SK, Munoz FM, Al-Ammouri I, et al. Myocarditis and pericarditis: Case definition and guidelines for data collection, analysis, and presentation of immunization safety data. Vaccine. 2022;40(10):1499-1511. doi:10.1016/j.vaccine.2021.11.074
• ATAGI: COVID-19 vaccination – Guidance on myocarditis and pericarditis after COVID-19 vaccines
• MVEC: Mpox
• MVEC: COVID-19