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

Epidemiology

Because there are many cases which remain subclinical, and are therefore undiagnosed, the true number of cases is hard to estimate.
The male-to-female ratio is 1.5:1.
In the documented cases the average age of patients is 42 years.¹

Presentation

This is very variable:

• Patients may be asymptomatic with ECG abnormalities.
• Others may have severe heart failure and left ventricular dysfunction (LVD).

Patients commonly complain of:

• Fatigue (>50% patients)
• Chest pain (35% of patients)
• Fever (20% of patients)
• Dyspnoea
• Palpitations
• There may be a tachycardia
• Heart sounds - Soft S1 or S4 gallop rhythm
• Signs of heart failure

Postmortem studies suggest myocarditis is a major cause of sudden unexpected death in adults, implicated in approximately 20% of those aged <40 years.²

Aetiology

Infection

• Coxsackievirus is the most common viral cause in Europe and the USA, but most viruses are potential agents including HIV, Epstein-Barr virus and hepatitis A and hepatitis C.³
• 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.

Immune-mediated

Autoantigens:

• Sarcoidosis
• Systemic lupus erythematosus
• Scleroderma
• Chlamydophila pneumoniae (Chlamydial pneumonia)
• Churg-Strauss syndrome
• Inflammatory bowel disease
• Giant-cell myocarditis
• Type 1 diabetes mellitus
• Kawasaki's disease
• Myasthenia gravis
• Polymyositis
• Thyrotoxicosis
• Wegener's granulomatosis

Toxic myocarditis

• Drugs: ethanol, cytotoxic antibiotics (anthracyclines, e.g. doxorubicin), amfetamines, cocaine, cyclophosphamide, fluorouracil, lithium, interleukin-2 and trastuzumab may exert a direct cytotoxic effect.¹
• 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

ECG:

• ST segment elevation/depression
• T-wave inversion
• Atrial arrhythmias
• Transient AV block

Blood tests:

• FBC (leucocytosis in 25%)
• U&E
• Creatine kinase (CK)
• ESR or CRP (elevated in 60%)
• LFT

CXR:

• Normal cardiac silhouette, but pericarditis or overt clinical congestive heart failure (CHF) is associated with cardiomegaly
• Vascular redistribution
• Interstitial and alveolar oedema
• Pleural effusion

CK levels are often elevated, as are other markers of myocardial cell damage (troponin I and troponin T).
Viral or Chagas' serology may be helpful occasionally, as may autoantibodies (to screen for systemic autoimmune disease, e.g. scleroderma).⁴
Endomyocardial biopsy (the gold standard test) is sometimes performed - but has only limited sensitivity and specificity.
MRI scanning is capable of showing abnormal signal intensity in the affected myocardium.
It has been shown to have sensitivities and specificities approaching 100% for diagnosis.⁵

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's disease

Management

• Treat 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.
• Supportive measures (see separate article Heart Failure Management). Patients may recover or progress to intractable heart failure (mechanical support devices may be needed as precipitous cardiac decompensation can occur).
• There are ongoing trials on the use of antiviral agents or viral specific vaccines.
• Immunomodulating agents. The most promising research addresses the immune response in myocarditis. It involves immune modulators that target particular steps in the immune cascade without eliminating the ability of the body's defenses to shed virus. The role of tumour necrosis factor appears to be central in these approaches. Although studies have failed to show any immediate improvement in left ventricular ejection fraction with immune globulin therapy,^6,7 there is some data showing more long-term benefit in patients with dilated cardiomyopathy and HLA upregulation on biopsy specimens.⁸
• There is no evidence base for the use of corticosteroids.⁹

Recovering patients should have activity limitations for approximately 6 months, as animal models have shown permanent injury from a rapid return to activity.

Complications

• Congestive heart failure
• Pulmonary oedema
• Cardiogenic shock
• Cardiac failure
• Dilated cardiomyopathy
• Dysrhythmias
• Recurrent myositis

Prognosis

• Most cases are believed to be subclinical. They resolve spontaneously without sequelae.
• Patients presenting with congestive heart failure (CHF) experience morbidity and mortality in proportion to the degree of LVD.
• Elderly patients and patients with giant cell arteritis, who present with cardiogenic shock, have a poor prognosis.
• 50% of patients presenting with new-onset CHF, improve their cardiac function with treatment.
• 25% of patients presenting with CHF stabilise with compromised cardiac function.
• The condition of the remaining 25% of patients continues to deteriorate.
• Patients requiring transplantation have an increased risk of recurrent myocarditis and graft rejection.

Document references

1. Howes MD et al, Myocarditis in Emergency Medicine, Medscape
2. Feldman AM, McNamara D; Myocarditis.; N Engl J Med. 2000 Nov 9;343(19):1388-98.
3. Dennert R, Crijns HJ, Heymans S; Acute viral myocarditis. Eur Heart J. 2008 Jul 9. [abstract]
4. Frishman WH, Zeidner J, Naseer N; Diagnosis and management of viral myocarditis. Curr Treat Options Cardiovasc Med. 2007 Dec;9(6):450-64. [abstract]
5. Laissy JP, Messin B, Varenne O, et al; MRI of acute myocarditis: a comprehensive approach based on various imaging sequences.; Chest. 2002 Nov;122(5):1638-48. [abstract]
6. McNamara DM, Holubkov R, Starling RC, et al; Controlled trial of intravenous immune globulin in recent-onset dilated cardiomyopathy.; Circulation. 2001 May 8;103(18):2254-9. [abstract]
7. Mason JW, O'Connell JB, Herskowitz A, et al; A clinical trial of immunosuppressive therapy for myocarditis. The Myocarditis Treatment Trial Investigators.; N Engl J Med. 1995 Aug 3;333(5):269-75. [abstract]
8. Wojnicz R, Nowalany-Kozielska E, Wojciechowska C, et al; Randomized, placebo-controlled study for immunosuppressive treatment of inflammatory dilated cardiomyopathy: two-year follow-up results.; Circulation. 2001 Jul 3;104(1):39-45. [abstract]
9. Chen H, Liu J, Yang M; Corticosteroids for viral myocarditis. Cochrane Database Syst Rev. 2006 Oct 18;(4):CD004471. [abstract]

Acknowledgements