In medicine (cardiology), myocarditis is inflammation of the myocardium, the muscular part of the heart. It is generally due to infection (viral or bacterial). It may present with rapid signs of heart failure.

Signs and symptoms

The signs and symptoms associated with myocardits are varied, and relate either to the actual inflammation of the myocardium, or the weakness of the heart muscle that is secondary to the inflammation. Signs and symptoms of myocarditis include:

• Sudden death (in young adults, myocarditis causes up to 20% of all cases of sudden death)
• Congestive heart failure (leading to edema, breathlessness and hepatic congestion)
• Palpitations (due to Arrhythmias)
• Chest pain
• Fever (especially when infectious, e.g. in rheumatic fever)

Since myocarditis is often due to a viral illness, many patients give a history of symptoms consistent with a recent viral infection, including fever, joint pains, and easy fatigueability.

Myocarditis is often associated with pericarditis, and many patients present with signs and symptoms that suggest concurrent myocarditis and pericarditis.

Diagnosis

Myocardial inflammation can be suspected on the basis of electrocardiographic results (ECG), elevated CRP and/or ESR and increased IgM (serology) against viruses known to affect the myocardium. Markers of myocardial damage (troponin or creatine kinase cardiac isoenzymes) are elevated.

The ECG findings most commonly seen in myocarditis are diffuse T wave inversions, without shifts in the ST segment.

The gold standard is still biopsy of the myocardium, generally done in the setting of angiography. A small tissue sample of the endocardium and myocardium is taken, and investigated by a pathologist by light microscopy and - if necessary - immunochemistry and special staining methods. Histopathological features are: myocardial interstitium with abundant edema and inflammatory infiltrate, rich in lymphocytes and macrophages. Focal destruction of myocytes explains the myocardial pump failure.

Causes

A large number of different causes have been identified as leading to myocarditis:

• Infectious:
  • Viral (e.g. Coxsackie virus, rubella virus, polio virus, cytomegalovirus, possibly hepatitis C)
  • Bacterial (e.g. brucella, Corynebacterium diphtheriae, gonococcus, Haemophilus influenzae, Tropheryma whipplei, and Vibrio cholerae).
  • Spirochetal (Borrelia burgdorferi and leptospirosis)
  • Protozoal (Toxoplasma gondii and Trypanosoma cruzi)
  • Fungal (e.g. actinomyces, aspergillus)
  • Parasitic: ascaris, Echinococcus granulosus, Paragonimus westermani, schistosoma, Taenia solium, Trichinella spiralis, visceral larva migrans, and Wuchereria bancrofti
  • Rickettsial
• Immunological:
  • Allergic (e.g. acetazolamide, amitriptyline)
  • Rejection after a heart transplant
  • Autoantigens (e.g. in Churg-Strauss syndrome, Wegener's granulomatosis)
• Toxic:
  • Drugs (e.g. anthracyclines and some other forms of chemotherapy, ethanol)
  • Toxins (e.g. arsenic, carbon monoxide, snake venom)
  • Heavy metals (e.g. copper, iron)
• Physical agents (electric shock, hyperpyrexia, and radiation)

Bacterial myocarditis is rare in patients without immunodeficiency. Myocardial damage due to chemotherapy, most notably the class of anthracycline drugs, is fairly common.

Epidemiology

The exact incidence of myocarditis is unknown. However, in series of routine autopsies, 1-9% of all patients had evidence of myocardial inflammation. In young adults, up to 20% of all cases of sudden death are due to myocarditis.

In South America, Chagas' disease (caused by Trypanosoma cruzi) is the main cause of myocarditis.

Therapy

Bacterial infections are treated with antibiotics, dependent on the nature of the pathogen and its sensitivity to antibiotics. As most viral infections cannot be treated with directed therapy, symptomatic treatment is the only form of therapy for those forms of myocarditis, e.g. diuretics and/or inotropes for ventricular failure.

Reference

• Feldman AM, McNamara D. Myocarditis. N Engl J Med 2000;343:1388-98. PMID 11070105.

External link

• Histopathology images of myocarditis