• Myocarditis is a challenging and potentially life-threatening condition that is underdiagnosed in the emergency department.
• Complications include cardiomyopathy, heart failure, arrhythmias, and fulminant myocarditis.
• It is more common in males and younger populations.
• Myocarditis is an inflammatory disease of the cardiac musculature as seen on biopsy.
• Causes include:
  • Infectious
    • Most commonly viral.
    • Consider bacterial, fungal, protozoal, and parasitic.
  • Immune-mediated and systemic disorders
    • Allergens including drug hypersensitivity, tetanus toxoid, vaccines, serum sickness.
    • Autoimmune such as IBD, giant cell, SLE, scleroderma, thyrotoxicosis, GPA, Kawasaki’s, rheumatic heart disease.
    • Alloantigens such as in heart transplant rejection.
  • Toxins
    • Alcohol, amphetamines, anthracyclines, heavy metals, carbon monoxide, catecholamines, radiation.

Clinical presentation

• Variable clinical presentation
  • Symptoms include dyspnea and chest pain (most common), as well as fatigue, palpitations, and edema.
  • Presentation may range from subclinical or mild symptoms to severe heart failure, cardiogenic shock, and sudden cardiac death.
  • Viral prodrome often present including fever, malaise, myalgia, cough, and diarrhea 2 weeks prior to cardiac dysfunction.
• Suspect myocarditis in patients with
  • Heart failure or cardiogenic shock with ventricular dysfunction and no clear etiology.
  • Signs of MI with minimal or absent cardiovascular risk factors or normal angiogram and no clear etiology.
  • Pediatric patient with signs of cardiac dysfunction, especially with viral prodrome.
  • Patient with suspected sepsis who worsens with IV fluids and has signs of volume overload.

• Gold standard for diagnosis is endomyocardial biopsy (EMB)
  • Limited role in emergency room setting as it is not readily available, has a high sampling error, and has relatively low yield in terms of impact on patient management.
• Recommended approach is based on 3 tiered classification as adapted from Sagar et al. 2012 when myocarditis is suspected.
  • Possible subclinical acute myocarditis
    • No cardiovascular symptoms but at least one of:
      • Elevated cardiac biomarkers.
      • ECG findings consistent with cardiac injury.
      • Abnormal cardiac function on echo.
      • CMRI findings.
    • Probable acute myocarditis
      • Cardiovascular symptoms AND at least one of:
        • Elevated cardiac biomarkers.
        • ECG findings consistent with cardiac injury.
        • Abnormal cardiac function on echo.
        • CMRI findings.
      • Definite myocarditis
        • Histological or immune-histological evidence of myocarditis.

• Recommended investigations
  • Labs: CBC, lytes, renal/liver function, CRP, troponin, BNP
    • Troponin levels are commonly elevated in myocarditis, but their absence is not sensitive in myocarditis and should not be used for prognosis.
    • Over 50% of patients will have elevated BNP, but the absence of BNP does not rule out myocarditis.
    • CRP positive in majority of patients, but is not specific for myocarditis.
    • CBC showing eosinophilia may suggest eosinophilic myocarditis.
  • ECG
    • Useful to evaluate for ST/T wave changes, AV blocks.
  • CXR
    • Abnormal in 50% of patients including cardiomegaly, pulmonary edema, and pleural effusions.
    • Not sensitive.
  • Echocardiogram
    • Assessing for global or regional ventricular dysfunction, wall motion abnormalities, and pericardial effusions.
    • If formal TTE unavailable, POCUS is useful to assess for gross signs of cardiac dysfunction or for pulmonary edema.
  • Consider cardiovascular MRI (CMRI)
    • Patients must be clinically stable.
    • Findings must be consistent with myocarditis according to Lake-Louise criteria (specialist interpretation recommended.)
    • Useful in low risk myocarditis to differentiate between myocarditis and ACS or in intermediate risk myocarditis for diagnosis.
    • Limited role in high risk myocarditis.

• Treatment should be tailored around the etiology of the myocarditis, risk stratification, and clinical presentation.
• For hemodynamically unstable patients
  • May require inotropic support, diuresis, and ventilator support.
  • Norepinephrine is the preferred vasopressor in myocarditis.
  • Avoid excessive IV fluids which may worsen symptoms.
• For hemodynamically stable patients
  • If heart failure is present, standard heart failure therapy may be used including ACEi/ARB and beta blocker with consideration of MRA.
• Immunosuppressive agents should only be considered for subgroups of patients with specific etiologies of myocarditis including giant cell myocarditis, sarcoidosis, or other systemic autoimmune diseases, which require EMB.
• Immunotherapy is not recommended as it has not been shown to affect outcomes and may have significant side effects.
• Antiviral therapy should not routinely be used.
• NSAIDs not recommended as it may worsen mortality in myocarditis, as seen in experimental models, although clinical trial data is lacking.
• Physical exercise should be restricted in the acute phase, which will require follow-up 6 months after onset of the disease (expert opinion.)
• Disposition
  • All patients with suspected acute myocarditis should be admitted to hospital and those requiring vasopressors or ventilator support require ICU admission.
  • 50% recover fully.
  • 30% will decompensate.
  • 20% require transplantation.

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