Myocarditis

Myocarditis

In medicine (cardiology), myocarditis is inflammation of heart muscle (myocardium). It resembles a heart attack but coronary arteries are not blocked.

Myocarditis is most often due to infection by common viruses, such as parvovirus B19, less commonly non-viral pathogens such as Borrelia burgdorferi (Lyme disease) or Trypanosoma cruzi, or as a hypersensitivity response to drugs.

The definition of myocarditis varies, but the central feature is an infection of the heart, with an inflammatory infiltrate, and damage to the heart muscle, without the blockage of coronary arteries that define a heart attack (myocardial infarction) or other common non-infectious causes.

Myocarditis may or may not include death (necrosis) of heart tissue. It may include dilated cardiomyopathy.

Myocarditis is often an autoimmune reaction. Streptococcal M protein and coxsackievirus B have regions (epitopes) that are immunologically similar to cardiac myosin. After the virus is gone, the immune system may attack cardiac myosin.

Because a definitive diagnosis requires a heart biopsy, which doctors are reluctant to do because they are invasive, statistics on the incidence of myocarditis vary widely.

The consequences of myocarditis thus also vary widely.

It can cause a mild disease without any symptoms that resolves itself, or it may cause chest pain, heart failure, or sudden death. An acute myocardial infarction-like syndrome with normal coronary arteries has a good prognosis.

Heart failure, even with dilated left ventricle, may have a good prognosis. Ventricular arrhythmias and high-degree heart block have a poor prognosis. Loss of right ventricular function is a strong predictor of death.

Signs and symptoms

The signs and symptoms associated with myocarditis 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:

  • Chest pain (often described as "stabbing" in character)
  • Congestive heart failure (leading to edema, breathlessness and hepatic congestion)
  • Palpitations (due to arrhythmias)
  • Sudden death (in young adults, myocarditis causes up to 20% of all cases of sudden death)
  • Fever (especially when infectious, e.g. in rheumatic fever)
  • Symptoms in infants and toddlers tend to be more non-specific with generalized malaise, poor appetite, abdominal pain, chronic cough. Later stages of the illness will present with respiratory symptoms with increased work of breathing and is often mistaken for asthma.
  • Since myocarditis is often due to a viral illness, many patients give a history of symptoms consistent with a recent viral infection, including fever, rash, diarrhea, 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.

Therapy

As most viral infections cannot be treated with directed therapy, symptomatic treatment is the only form of therapy for those forms of myocarditis.

In the acute phase, supportive therapy including bed rest is indicated.

For symptomatic patients, digoxin and diuretics provide clinical improvement.

For patients with moderate to severe dysfunction, cardiac function can be supported by use of inotropes such as Milrinone in acute phase followed by oral therapy with ACE inhibitors (Captopril, Lisinopril) when tolerated.

Patients who do not respond to conventional therapy are candidates for bridge therapy with left ventricular assist devices (LVADs).

Heart transplantation is reserved for patients who fail to improve with conventional therapy