Myocarditis

Aetiology

• Infectious

  • Viruses (e.g. Coxsackie, influenza, adenovirus)

  • Bacteria (e.g. Streptococcus)

  • Fungi (e.g. Aspergillus)

  • Spirochetes (e.g. Leptospira)

• Non-infectious

  • Autoimmune diseases (e.g. sarcoidosis, giant-cell myocarditis)

  • Hypersensitivity reactions (e.g. certain antibiotics)

  • Toxins (e.g. alcohol, cocaine)

  • Drugs (e.g. anthracyclines)

Pathophysiology

• Inflammatory infiltrates lead to myocyte necrosis and dysfunction

• Cytokine release and immune-mediated injury contribute to impaired cardiac contractility

• Can result in systolic heart failure and dilated cardiomyopathy if severe or persistent

Clinical Features

• Variable presentation, from asymptomatic to acute heart failure

• Common symptoms

  • Chest pain (often pleuritic or similar to pericarditis)

  • Flu-like prodrome (fever, myalgia)

  • Fatigue, dyspnoea, orthopnoea, paroxysmal nocturnal dyspnoea

  • Palpitations (arrhythmias)

  • Signs of fluid overload (peripheral oedema)

• Pericardial involvement

  • Myopericarditis can present with pericardial rub or effusion

Differential Diagnosis

• Pericarditis

• Acute coronary syndrome

• Pulmonary embolism

• Dilated cardiomyopathy from other causes (e.g. ischaemic, alcoholic)

Investigations

• ECG

  • Conduction abnormalities, ST/T wave changes, possible arrhythmias

• Cardiac enzymes

  • Elevated troponins and CK-MB suggest myocardial injury

• Blood tests

  • Raised inflammatory markers (ESR, CRP, leukocytosis)

  • BNP elevation if heart failure is present

• Echocardiography

  • Global or regional wall motion abnormalities

  • Potentially dilated ventricles or reduced ejection fraction

  • Can detect pericardial effusion

• Cardiac MRI

  • Late gadolinium enhancement indicative of active inflammation or fibrosis

  • Useful for diagnosis and assessment of myocardial involvement

• Endomyocardial Biopsy (gold standard)

  • Considered in severe, fulminant, or unclear cases

  • Limited sensitivity but can confirm specific aetiologies (e.g. giant-cell myocarditis)

Diagnostic Criteria

• Combination of clinical presentation (e.g. chest pain, dyspnoea), ECG and imaging abnormalities, elevated cardiac biomarkers, and sometimes biopsy confirmation

• MRI can confirm suspected myocarditis when clinical and standard investigations are inconclusive

Management

• Supportive Care

  • Rest and reduced physical exertion during acute phase

  • Inpatient telemetry if arrhythmias or significant cardiac dysfunction are suspected

• Treat Underlying Cause

  • Targeted therapy for identifiable infectious agents (e.g. antivirals)

  • Immunosuppression (e.g. corticosteroids) in autoimmune or giant-cell myocarditis, guided by cardiology advice

  • Discontinue any offending drug or toxin

• Heart Failure Management

  • ACE inhibitors/ARNI, beta-blockers, mineralocorticoid receptor antagonists for systolic dysfunction

  • Diuretics if volume overloaded

• Arrhythmia Control

  • Antiarrhythmics if needed

  • Consider temporary pacing or implantable devices in severe conduction disturbances

• Physical Activity Restriction

  • Avoid intense exercise for at least 3–6 months, with specialist review before resuming sports

  • Follow-up echocardiography or MRI to ensure resolution of inflammation

• Fulminant or Refractory Cases

  • May require mechanical circulatory support (e.g. ECMO)

  • Urgent transplant evaluation if not responsive to medical therapy

Complications

• Dilated cardiomyopathy and chronic systolic heart failure

• Life-threatening arrhythmias and sudden cardiac death

• Cardiogenic shock in fulminant myocarditis

Notes:

• Myocarditis can mimic acute coronary syndrome and pericarditis

• Consider in otherwise healthy adults with new-onset heart failure, chest pain, or significant arrhythmias

• Cardiac MRI is increasingly central in diagnosis and follow-up

• Early detection and restriction of strenuous activity improve outcomes

• Ongoing follow-up is essential to monitor for progression to chronic heart failure