Preparatory Mindset
Myocarditis is "heart failure/arrhythmia after a viral illness" — the classic vignette is a young adult with a recent flu-like or GI infection who presents with chest pain, dyspnoea, palpitations, or cardiogenic shock with elevated troponin and a non-ischaemic pattern. The exam skills: (1) suspect it in young patients with new heart failure/arrhythmia (not ischaemia), (2) know the causes ladder (viruses first — Coxsackie B, influenza, parvovirus B19, COVID; then giant-cell, autoimmune, drug-induced hypersensitivity), (3) remember endomyocardial biopsy (EMB) is the gold standard (Dallas criteria) but is reserved for specific cases, and (4) treat with heart-failure therapy + no routine corticosteroids (except giant-cell/eosinophilic/autoimmune forms), arrhythmia management, and exercise restriction. The HKHA handbook has no dedicated myocarditis chapter — it is managed under heart failure, arrhythmia, and acute coronary workup.
Core Concepts
Definition & etiology
- Myocarditis = inflammation of the myocardium, with necrosis/degeneration of myocytes and an inflammatory infiltrate (Dallas criteria on biopsy).
- Infectious: viral (most common) — Coxsackie B (classic), echovirus, influenza, adenovirus, parvovirus B19, CMV, EBV, HIV, SARS-CoV-2; bacterial (diphtheria — toxin, Lyme disease — Borrelia), fungal, protozoal (Chagas — Trypanosoma cruzi, common worldwide).
- Non-infectious: autoimmune/systemic (SLE, RA, sarcoidosis, giant-cell myocarditis, eosinophilic myocarditis), drug-induced hypersensitivity (sulphonamides, penicillins, clozapine, doxorubicin/anthracyclines — toxic), radiation, toxic (catecholamines, cocaine).
- Pathophysiology: viral entry (coxsackie-adenovirus receptor, CAR) → direct myocyte injury + immune-mediated damage (T cells, cytokines) → myocyte necrosis, oedema, fibrosis → dilated cardiomyopathy (chronic sequel), arrhythmias, heart failure.
Clinical manifestations
- Prodrome: recent viral illness (fever, myalgia, URTI/GI symptoms) days–weeks before.
- Cardiac: chest pain (pleuritic/ischaemic-like), dyspnoea, fatigue, palpitations; new-onset heart failure (young patient), cardiogenic shock (fulminant myocarditis); arrhythmias (VT, AV block, AF); syncope; sudden cardiac death.
- Signs: tachycardia out of proportion, S3 gallop, murmur (mitral regurgitation), signs of heart failure/congestion, low-grade fever.
- Subclinical: many cases asymptomatic with transient troponin rise.
Diagnosis
- ECG: non-specific ST/T changes, diffuse ST elevation (mimics pericarditis/MI), conduction blocks, arrhythmias.
- Cardiac biomarkers: elevated troponin ± CK-MB (non-ischaemic pattern).
- Echocardiography: global or regional LV dysfunction, dilated LV (not explained by CAD), wall thickening (oedema), pericardial effusion; normal in mild cases.
- CMR (cardiac magnetic resonance): Lake Louise criteria — oedema (T2), hyperaemia/early gadolinium enhancement, late gadolinium enhancement (LGE) — non-ischaemic (subepicardial/mid-myocardial) pattern — the key non-invasive tool.
- Endomyocardial biopsy (EMB) — gold standard (Dallas criteria: inflammatory infiltrate + myocyte necrosis; viral PCR): indicated in rapidly progressive HF, ventricular arrhythmias/AV block, suspected giant-cell/eosinophilic myocarditis, suspected sarcoidosis, or failure to respond to therapy.
- Coronary angiography to exclude ischaemia (young patients with ACS-like presentation).
- Bloods: inflammatory markers, viral serology/PCR (blood, throat), autoimmune screen (ANA, etc.), HIV.
Treatment
- Supportive care (mainstay): heart-failure therapy — ACEi/ARB, β-blocker, diuretics; inotropes/MCS (IABP, ECMO) for cardiogenic shock; antiarrhythmics (amiodarone) ± temporary pacing for AV block; oxygen.
- Exercise restriction during acute illness and recovery (avoid strenuous activity for ~3–6 months; arrhythmia risk).
- Antivirals: generally not indicated (except specific — e.g., influenza oseltamivir, HIV therapy).
- Immunosuppression: NOT routine (most viral myocarditis is self-limited); indicated for giant-cell myocarditis, eosinophilic myocarditis, sarcoidosis, autoimmune/systemic causes (corticosteroids ± azathioprine/cyclosporine); IVIG in some paediatric/acute settings (evidence limited).
- Treat the underlying cause (diphtheria antitoxin + penicillin, doxycycline for Lyme, antiparasitics for Chagas).
- Follow-up: repeat echo (recovery vs progression to DCM), monitor for arrhythmias; transplant evaluation for end-stage disease.
HKHA Handbook (LMCHK) — Key Points
- Chronic Heart Failure (C 27–28) and Acute Pulmonary Oedema (C 22): acute myocarditis causing LV dysfunction is treated with GDMT (ACEi/ARB/ARNi, β-blocker, MRA, SGLT2i once stable) and acute decompensation management (frusemide, nitrates, inotropes, NIV). - Arrhythmias (C 4–11): myocarditis-related VT/AV block managed per the arrhythmia protocol (amiodarone, temporary pacing for high-grade block). - CPR (C 1–3): fulminant myocarditis with arrest → BLS/ACLS.
- The handbook has no dedicated myocarditis chapter — myocarditis is managed through:
- Endomyocardial biopsy (Pr 9–10) is listed as a procedure — recognise it as the gold standard for diagnosing myocarditis (and its indications).
- LMCHK message: new heart failure + arrhythmia in a young patient post-viral illness = myocarditis until proven otherwise; CMR (Lake Louise) and EMB are the diagnostic tools; steroids only for giant-cell/eosinophilic/sarcoid forms.
High-Yield Points
- Viral myocarditis: Coxsackie B (classic), influenza, parvovirus B19, COVID; Chagas (worldwide), diphtheria (toxin).
- Young patient + new HF/arrhythmia + recent viral illness + raised troponin → myocarditis.
- ECG: diffuse ST changes (mimics MI/pericarditis); CMR — Lake Louise criteria (oedema + LGE non-ischaemic pattern).
- EMB = gold standard (Dallas criteria) — for rapidly progressive HF, giant-cell/eosinophilic suspicion, arrhythmia, therapy failure.
- Treatment: HF therapy (ACEi/β-blocker/diuretics), antiarrhythmics, MCS for shock; exercise restriction.
- Steroids NOT routine — only giant-cell/eosinophilic/autoimmune/sarcoid.
- Sequel: dilated cardiomyopathy.
Topic Summary
Myocarditis is myocardial inflammation — usually viral (Coxsackie B, influenza, parvovirus B19, COVID) — presenting after a prodromal illness with chest pain, new heart failure, or arrhythmias in young patients. Diagnosis integrates ECG, elevated troponin, echo and especially CMR (Lake Louise criteria with non-ischaemic late enhancement), with endomyocardial biopsy as the gold standard for severe/specific forms. Management is supportive heart-failure therapy with antiarrhythmics and mechanical circulatory support for fulminant shock; immunosuppression is reserved for giant-cell, eosinophilic, sarcoid and autoimmune myocarditis. Exercise restriction and follow-up echo are essential; progression to dilated cardiomyopathy is the main long-term risk.