Myocarditis (Acute)
Background Information
Definition
Myocarditis refers to any inflammatory disease of the myocardium.
Aetiology
The causes of myocarditis can be grouped as following: [Ref]
| Category | Causes |
|---|---|
| Viral infection – most common cause | Most commonly implicated viruses:
|
| Bacterial infection |
|
| Parasitic infection |
|
| Autoimmune disorders |
|
| Toxin / drugs |
|
Complications
Acute complications: [Ref]
- Heart failure (most commonly causes systolic heart failure / HFrEF) – leading independent predictor of death and need for transplantation
- Arrhythmias
- Sudden cardiac death
Chronic complications: [Ref]
- Recurrence (up to 11.5% over 2 years)
- Progression to dilated cardiomyopathy
Diagnosis
Clinical Features
The typical setting is a young male patient with a preceding viral prodrome / recent infection / exposure to cardiotoxins. [Ref]
Classic triad of: [Ref]
- Chest pain
- Arrhythmias (can present as palpitations, syncope etc.)
- Heart failure
Other possible features: [Ref]
- Fever – common
- Dyspnoea
Clinical features are important in distinguishing acute myocarditis from STEMI:
- Absence of cardiovascular risk factors (e.g. non-smoker, normotensive etc.)
- Younger patients (often male)
- Viral prodrome
- Chest pain is typically sharp, central, and pleuritic (but also possible to be pressure-like / constricting, mimicking ischaemic chest pain)
Also, take the investigation findings (see below) and the general presentation into account.
Investigation and Diagnosis
The ACC guidelines emphasise that no single test can definitively diagnose myocarditis; diagnosis is based on a combination of clinical features, tests, imaging and exclusion of other causes. The work-up and diagnosis of myocarditis is complicated, often undertaken by a cardiologist.
In undergraduate exams (e.g. UKMLA), history is key to distinguishing between myocarditis and other causes of chest pain. The history is often very stereotypical: young patient with recent viral infection + ACS-like presentation.
Initial workup for suspected acute myocarditis: [Ref]
| Test | Interpretation |
|---|---|
| 12-lead ECG | Most commonly show non-specific changes:
A normal ECG does NOT exclude myocarditis. |
| Cardiac biomarkers |
|
| FBC | Non-specific findings:
|
| Trans-thoracic echocardiography |
|
| Coronary angiography (invasive / CT) | Angiography is performed to exclude ACS, not to diagnose myocarditis
|
Gold standard non-invasive test: cardiac MR [Ref]
- If initial tests suggest myocarditis, cardiac MR should be conducted routinely
- The presence of myocardial oedema, hyperaemia, necrosis or fibrosis is highly specific for myocarditis
Endomyocardial biopsy is NOT routinely performed; it is reserved for cases with severe presentation or to identify a specific underlying cause that may require targeted therapy. [Ref]
Management
The management of myocaditis is complicated, guided by severity, aetiology and clinical stage. A student-friendly version is summarised below, based on the severity of the disease.
Uncomplicated myocarditis is defined by the presence of ALL of the following: [Ref]
- Preserved left ventricular function (no heart failure)
- No significant arrhythmia
- Haemodynamically stable
Mild, Uncomplicated Myocarditis
Key management principles: [Ref]
- Advise that mild myocarditis tend to resolve spontaneously
- Stop any causative agents / treat any reversible underlying causes
- Activity restriction for 3-6 months
- Reassessment before return to activity
- Avoid strenuous physical activity and competitive sports
- NSAIDs / colchicine for pericardial-type chest pain
- Follow up with ECG, echo, cardiac MR
NSAIDs should be avoided if there is any evidence of heart failure or shock.
Corticosteroids should be avoided in the management of mild, uncomplicated myocarditis; unnecessary immunosuppression may increase the risk of infection without improving outcomes.
Severe / Complicated Myocarditis
Admit to hospital for management: [Ref]
- Stabilise the patient and treat any complications
- Endomyocardial biopsy is recommended to identify specific aetiologies that may require targeted immunosuppressive therapy (e.g., giant cell, eosinophilic, or sarcoid myocarditis)
- Imunosuppression (such as corticosteroids) may be initiated in biopsy-proven, noninfectious, immune-mediated cases or in fulminant presentations after exclusion of active infection