Myocarditis is an inflammatory disease of the heart muscle, which mostly arises due to infections with cardiotropic viruses, especially infections with the coxsackie virus. The course of myocarditis, in contrast to endocarditis, is usually slower and less distinct.
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Histopathology of viral myocarditis

Picture: „Histopathology of viral myocarditis” by KGH. License: CC BY-SA 3.0

Definition of Myocarditis

Myocarditis is an inflammation of the heart muscle.


Picture: “Graphic of a Myocardiocyte (Heart Muscle Cell), including organelles and cell membrane functions” by OCAL. License: Public domain

Epidemiology of Myocarditis

Coxsackie Virus

Picture: “Coxsackie Virus” by Angusmclellan. License: Public Domain

In cases of infections with the coxsackie B virus, it can be assumed that in about 4 % of all cases, the heart will be affected as well. For other cardiotropic viruses, this number goes down by about 1 % of all cases. When young adults die from a sudden cardiac arrest, in about 10 % of the cases, the autopsy will reveal myocarditis.

Etiology of Myocarditis

Causes of myocarditis

A distinction is made between infectious and non-infectious forms. The coxsackie B virus is often the trigger of the infectious form. Other entero-, adeno-, and influenza viruses, or for example EBV, CMV, HCV, or HIV can also lead to myocarditis. Bacteria are able to induce myocarditis as well. This includes primarily staphylococci and streptococci, and also enterococci and Borrelia burgdorferi. Fungi, protozoa and parasites may also be the cause.

In rare cases, chronic systemic diseases, such as rheumatoid arthritis, vasculitis and collagenoses can be triggers of non-infectious myocarditis. Medications may cause the so-called hypersensitivity myocarditis. An idiopathic Fiedler’s myocarditis or myocarditis following radiation therapy to the mediastinum are also possible.

Classification of Myocarditis

Myocarditis can be classified according to its course or its pathogenesis. Regarding its course, an acute and chronic myocarditis are to be distinguished. According to its pathogenesis, infectious myocarditis, toxic myocarditis, idiopathic myocarditis and autoimmune myocarditis must be distinguished from each other.

Pathophysiology of Myocarditis

Histopathology of viral myocarditis

Picture: “Histopathology of viral myocarditis” by KGH. License: CC BY-SA 3.0

First, the virus damages myocardial cells, which triggers an immune reaction. This can cause the destruction of other myocardial cells or cause cross-reactions between viral and myocardial structures, which produces antibodies.

Symptoms and Clinical Presentation of Myocarditis

Typically, the onset and progress is slow and non-specific, involving symptoms such as fever, fatigue, or chest pain. During the course of the disease (days to weeks), signs of heart failure and arrhythmia as well as tachycardia develop. Rarely, the course may be fulminant and similar to an infarction.

Diagnostics of Myocarditis

Laboratory diagnostics of myocarditis

The patient’s medical history often reveals evidence of a previous infection. Clinical signs can be combined with laboratory values, such as a possibly elevated ESR, raised CRP, troponin, and CK-MB, as well as with bacteriological and viral diagnostics. ECG may show non-specific changes. A diagnosis is confirmed after detection of the pathogen in a myocardial biopsy.

Pathology of Myocarditis

Initially, viral infections typically present with a serous exudate and hypereosinophilia. Later, the fibrotic replacement of cardiac muscle cells can be found. In infections caused by bacteria, microabscesses that are rich in granulocytes and bacteria are present.

Differential Diagnosis of Myocarditis

Similar diseases to myocarditis

A distinction must be made between post-myocardial cardiomyopathy, viral myocarditis as well as virus-positive myocarditis and inflammatory dilated cardiomyopathy (DCM).

Treatment of Myocarditis

Therapeutic approaches for myocarditis

Initially, the treatment of myocarditis is symptomatic. Physical rest, abstinence from alcohol, thromboembolism prophylaxis and the treatment of complications such as heart failure are indicated. Moreover, the therapeutic approach may be causal, being directed at the causative disease, for example diphtheria or Chagas disease. As part of research studies, anti-viral and immunosuppressive treatments are also performed.

Complications of Myocarditis

Complications of myocarditis include cardiac insufficiency and cardiac arrhythmias.

Review Questions

The answers can be found below the references.

1. Which is the most common trigger of infectious myocarditis?

  1. Staphylococci
  2. Streptococci
  3. Cardiotropic viruses
  4. Fungi
  5. Parasites

2. How can the diagnosis of myocarditis be confirmed?

  1. Measurement of troponin
  2. Increased ESR
  3. Myocardial biopsy
  4. Determining the CK-MB level
  5. Changes in the EKG

3. Which of the following is least likely to be part of the clinical manifestation of myocarditis?

  1. Serous exudate
  2. Hypereosinophilia
  3. Fibrotic replacements
  4. Hypertrophic myocytes
  5. Microabscesses rich in bacteria


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