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Myocarditis (Acute)
Acute myocarditis refers to inflammation of the heart muscle (myocardium), most commonly triggered by viral infection, autoimmune disease, toxins, or drug reactions, and can range from mild self-limiting illness to life-threatening cardiogenic shock or arrhythmias.
This article covers causes, complications, signs & symptoms, diagnosis & investigations and management.
Background Information
Definition
Myocarditis refers to any inflammatory disease of the myocardium.
Aetiology
The causes of myocarditis can be grouped as following: [Ref]
Myocarditis presents with a broad spectrum of symptoms, ranging from minimal symptoms to fulminant myocarditis (~3-9% cases). [Ref]
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:
Sinus tachycardia
ST segment / T-wave abnormalities (ST elevation, T wave inversion etc.)
Low QRS voltage
PR segment depression
Various arrhythmias (BBBs, QTc prolongation, AV blocks etc.)
A normal ECG does NOT exclude myocarditis.
Cardiac biomarkers
↑ Cardiac troponin (reflecting myocardial injury)
↑ BNP / NT-pro-BNP
FBC
Non-specific findings:
Leukocytosis / normal
Eosinophilia can occur in hypersensitivity / eosinophilic myocarditis
Trans-thoracic echocardiography
Mostly shows left ventricular dysfunction (typically systolic dysfunction + regional wall motion abnormalities, esp. in inferior and lateral walls)
Coronary angiography (invasive / CT)
Angiography is performed to exclude ACS, not to diagnose myocarditis
Both US and EU guidelines endorse that coronary angiography should be performed routinely to exclude ACS in suspected myocarditis cases
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)
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.
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
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