Myocarditis

What is myocarditis?

Myocarditis is acute or chronic inflammation of the myocardium - and may present similarly to myocardial infarction. Myocardial destruction may lead to dilated cardiomyopathy.

How common is myocarditis? (Epidemiology)

The exact incidence of myocarditis is unknown. A primary diagnosis of myocarditis accounted for 0.04% (36.5 per 100,000) of all hospital admissions in England between 1998 and 2017, although this is likely to be an underestimate of the true burden of myocarditis.

Myocarditis symptoms¹

This is very variable, from asymptomatic changes seen on ECG to fulminant myocarditis, which is characterised by a rapid progressive decline in cardiac function and a high mortality rate.²

• Patients may be asymptomatic with ECG abnormalities.

• Others may have severe heart failure and left ventricular dysfunction (LVD).

Patients commonly complain of:

• Fatigue (>50% of patients).

• Chest pain (35% of patients).

• Fever (20% of patients).

• Dyspnoea.

• Palpitations.

• Tachycardia (may occur).

• Heart sounds - soft S1 or S4 gallop rhythm.

• Signs of heart failure.

What causes myocarditis? (Aetiology)

Infection

• Viral infection is the most common cause of acute myocarditis.³

• Coxsackievirus is the most common viral cause in Europe and the USA; however, most viruses are potential agents, including adenovirus, parvovirus B19, enteroviruses, HIV, Epstein-Barr virus and hepatitis A and hepatitis C.⁴

• Worldwide the most common bacterial cause is diphtheria.

• There are also spirochetal, fungal, parasitic and rickettsial causes.

• The protozoal Chagas' disease is a common entity worldwide.⁵

Immune-mediated

• Sarcoidosis.

• Systemic lupus erythematosus.

• Scleroderma.

• Chlamydophila pneumoniae (chlamydial pneumonia).

• Churg-Strauss syndrome.

• Inflammatory bowel disease.

• Giant cell myocarditis.

• Type 1 diabetes mellitus.

• Kawasaki disease.

• Myasthenia gravis.

• Polymyositis.

• Thyrotoxicosis.

• Granulomatosis with polyangiitis.

• Heart transplant rejection.

Drugs causing hypersensitivity reactions
Clozapine, acetazolamide, amitriptyline, cefaclor, colchicine, furosemide, isoniazid, lidocaine, methyldopa, penicillin, phenytoin, streptomycin, tetracycline, thiazides and tetanus toxoid.

Eosinophilic myocarditis is a rare form of myocardial inflammation with variable aetiology. In developed countries, the most common causes are hypersensitivity or allergic reactions, as well as various conditions leading to eosinophilia.⁶

Toxic myocarditis

• Drugs: ethanol, cytotoxic antibiotics (anthracyclines - eg, doxorubicin), amfetamines, cocaine, cyclophosphamide, fluorouracil, lithium, interleukin-2 and trastuzumab may exert a direct cytotoxic effect.

• Heavy metal poisoning: lead, copper, iron.

• Others: arsenic, insect stings and bites, phosphorus, carbon monoxide and inhalants.

Physical agents

• Electric shock

• Hyperpyrexia

• Radiation/radiotherapy

Investigations^{1 7}

• ECG: changes may include ST-segment elevation/depression, T-wave inversion, atrial arrhythmias, transient atrioventricular (AV) block.

• Blood tests: FBC (leukocytosis in 25%), U&E, creatine kinase (often elevated, as are other markers of myocardial cell damage, including troponin I and troponin T), ESR or CRP (elevated in 60%), LFT.

• CXR:
  

  • Normal cardiac silhouette but pericarditis or overt clinical congestive heart failure is associated with cardiomegaly.

  • Vascular redistribution.

  • Interstitial and alveolar oedema.

  • Pleural effusion.

• Viral or Chagas' serology may be helpful occasionally, as may autoantibodies (to screen for systemic autoimmune disease - eg, scleroderma).⁸

• Endomyocardial biopsy (the gold standard test) is sometimes performed - but has only limited sensitivity and specificity.⁹

• Cardiac MRI can differentiate transient and permanent tissue damage. Therefore, cardiac MRI is clinically useful to differentiate acute myocarditis from infarction.

Differential diagnosis

• Acute coronary syndrome.

• Myocardial infarction.

• Congestive heart failure.

• Pulmonary oedema.

• Pneumonia - bacterial or viral.

• Aortic dissection.

• Pulmonary embolism.

• Oesophageal perforation, rupture and tears.

• Kawasaki disease.

Myocarditis treatment and management^{1 7}

Treat the underlying cause. Patients with signs of acute myocarditis (fever, WCC, flu-like illness and haemodynamic compromise) should be transferred to ITU, as ventricular support may become necessary. For an outline of appropriate supportive measures, see the separate Heart Failure Management article.

Patients may recover or progress to intractable heart failure (mechanical support devices may be needed, as precipitous cardiac decompensation can occur).

• Treatment of acute myocarditis is still mainly supportive, except for giant cell myocarditis where steroids have been shown to improve survival.³

• In patients with severe myocarditis and symptomatic hypotension, parenteral inotropes, including phosphodiesterase inhibitors (eg, milrinone) or adrenergic agonists (eg, dobutamine or dopamine) may be required.⁵

• The use of anticoagulation is similar to that in patients with non-ischaemic dilated cardiomyopathy; anticoagulation is usually indicated for patients with concomitant atrial fibrillation or arterial or venous thromboembolism.⁵

• Corticosteroids do not reduce mortality for people diagnosed with viral myocarditis and low left ventricular ejection fraction (LVEF). There is some evidence that corticosteroids may improve cardiac function but only from small, low-quality studies.¹⁰

• There is currently insufficient evidence to support the routine use of intravenous immunoglobulin for presumed viral myocarditis in children or adults.¹¹

After recovery from acute myocarditis, patients should be advised to limit activity for several months.⁵

Complications

• Congestive cardiac failure.

• Pulmonary oedema.

• Cardiogenic shock.

• Dilated cardiomyopathy.

• Dysrhythmias.

• Recurrent myositis.

Prognosis

The prognosis for patients with acute myocarditis is very variable and depends on clinical presentation, LVEF and pulmonary artery pressure.⁵