Myocarditis and pericarditis have been thrust into the spotlight due to risks associated with COVID-19 disease, and as a potential side effect of mRNA COVID vaccines. These conditions represent inflammatory effects on the myocardium, or pericardium, and can co-exist. Severity ranges from minimally symptomatic and very low risk through to life-threatening cardiac decompensation and tamponade.

Dr Steve Gordon, Cardiologist, Subiaco

COVID vaccine-related myocarditis is recognised as a rare complication (2.7 cases per 100,000 patients) of mRNA vaccination. The risk complicating COVID-19 infection is much higher at approximately 11 cases per 100,000 patients. To date there has not been definite evidence of an increased risk after non-mRNA vaccines.

The majority of cases have occurred in younger (under age 30) patients, with the highest risk between 16 and 19 years. Most occur in the first week post vaccination, are more common after the second dose (versus first,) and substantially more common in males. Some evidence suggests a higher risk with Moderna than Pfizer, but this remains unproven, with no difference in disease severity.

The commonest presenting symptom of myocarditis (and pericarditis) is chest pain. Myocarditis-related chest pain is generally reported as pressure, aching, or squeezing. Pericarditis pain in contrast is generally sharper, pleuritic, and better sitting forward than lying flat. Other common presenting symptoms include dyspnoea, general fatigue, and palpitations.

Physical signs (if any) associated with myocarditis may be tachycardia, arrhythmia (atrial or ventricular ectopy, AF, VT). In severe cases typical manifestations of CCF may be present. The physical sign of pericarditis is
the pericardial rub.

In suspected myocarditis or pericarditis, the essential initial investigations include an urgent troponin level, inflammatory markers (CRP, ESR), 12 lead ECG, and semi-urgent echocardiogram. ECG changes associated with myocarditis are often non-specific (non-specific ST-T wave changes, Q waves, atrial and/or ventricular ectopy, and arrhythmia). 

Widespread ST elevation and depression of PR segments accompanies pericarditis. Some guidelines recommend CXR though the diagnostic yield will be low if timely echocardiogram can be obtained. CXR be useful in excluding other causes of chest pain and dyspnoea or to assess cardiac size where access to echocardiogram is delayed. The possibility of the patient having COVID-19 disease as a cause should also be considered.

Inflammatory markers and troponin are commonly raised. A normal troponin does not completely exclude myocarditis. The echocardiogram may show LV dysfunction and wall motion abnormalities, and extent of any pericardial effusion. A normal echocardiogram may not completely exclude the diagnosis where very focal cases can occur which can be diagnosed with cardiac MRI. 

This is only (temporarily) subsidised by Medicare when requested by a consultant physician, and where the investigations above have been inconclusive.

In primary care, the result of troponin, ECG, and echo should allow a management decision. Patients who are clinically very unwell, have elevated troponin, ECG or echo manifestations suggesting myocarditis, or concern regarding significant pericardial effusion should be referred to hospital. Patients with just pericarditis without large effusion can be managed with NSAIDs +/- Colchicine in standard doses.

Consider cardiology referral for patients discharged from hospital with myocarditis, or monitoring of pericardial effusions, or where there remains a high suspicion of myocarditis with inconclusive investigations described above. Remain alert for other serious causes of chest pain including acute coronary syndrome, pulmonary embolus, and aortic dissection. If in doubt refer to ED.

The vast majority of cases tend to be mild and self-limiting, even in hospitalised patients. Recent reported experience from Royal Melbourne Hospital of 61 patients with post-vaccine myocarditis indicated 90% had early symptom resolution and median hospitalisation stay of four to six days. Patients discharged following a diagnosis of myocarditis should probably restrict physical activity for six months.

Our experience with patients experiencing chest pain post vaccination is that most do not have myocarditis or pericarditis. Many are very anxious. A significant number have chest wall pain and costochondritis, also exacerbated by anxiety. Palpitation symptoms are also common, often correlating with mild sinus tachycardia, usual degrees of atrial or ventricular ectopy, or even normal sinus rhythm. A Holter monitor may be useful.

Many patients referred to ED with normal investigations and chest pain leave with a diagnosis of pericarditis often without specific diagnostic features of it.

Diagnosis of these conditions has implications with regards to the choice of further vaccination options. Patients with diagnosed myocarditis should likely avoid further mRNA vaccines. Astra Zeneca or Novavax are options. The decision on further vaccines following diagnosis of pericarditis will vary according to patient age and sex in different situations and is best assessed by reference to the Australian government guidelines available at: www.health.gov.au/COVID19-vaccines.

Key messages
  • Myocarditis (and pericarditis) are uncommon common complications of mRNA COVID vaccines
  • Appropriate investigation of suspected cases in primary care can triage those requiring hospitalisation
  • Remain wary of other serious causes of chest pain.

Author competing interests -nil