Viral Myocarditis: More often, the heart tries to heal itself. The heart muscle heals by changing the damaged or dead heart muscle cells into scar tissue. Scar tissue is not like heart muscle tissue because it does not contract and it cannot help the heart to pump. If enough scar tissue forms in the heart, it can lead to congestive heart failure or dilated cardiomyopathy.

What is Myocarditis?
Myocarditis is a non-ischemic inflammation of the heart and is a common cause of dilated cardiomyopathy. Although most cases of myocarditis resolve on their own, some result in heart failure and death in one to two years for 50% of these patients. It can be caused by almost any infectious agent however viral infections are considered the most common cause.

Viruses Responsible?
Coxsackievirus B is the most common viral culprit of myocarditis (in Europe and North America). Coxsackieviruses are enteroviruses and are divided into two classes, A and B. Enteroviruses are viruses that multiple in the gut and are transmitted via the fecal-oral route and spread throughout the body by the blood stream. The infections can range from a minor cold to myocarditis or meningitis in some people. As the prevalence of enteroviruses decreased, the prevalence of adenovirus increased after 1995. More recently, parvovirus BI9 has been the most commonly detected viral genome. Other viruses that may lead to myocarditis include adenovirus, poliovirus, echovirus, influenza viruses, erythroviruses, human herpesvirus type 6 (HHV6), HIV, cytomegalovirus, herpes simplex type 2 virus and hepatitis C virus.


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Fig. 1 Evolution of viral causes of myocarditis over time.
(CVA=coxsackievirus A;CVB=coxsackievirus B; EBV=Epstein barr virus; HCV=hep C virus;
HHV6= human herpesvirus6; PVB19=parvovirus B19)

Can I catch this from my patient?
Viral myocarditis is not directly contagious however the organism that can lead to myocarditis can be spread by coughing, sneezing or through the fecal-oral route. According to IPAC, those infected with a virus require the use of standard precautions. These patients do not require isolation.

Who Gets Myocarditis?
It is unclear why myocarditis develops in some people and not in others. Studies show that the pathogenesis of viral myocarditis involves genetics (host and virus) and the environment in which they interact. Most studies indicate a slight male dominance. Although the cause in individual cases of myocarditis often is unidentified, specific and treatable causes that should be investigated include infections, systemic auto immune diseases, and hypersensitivity to certain medications.

What Happens in Myocarditis?
Myocarditis can affect both the heart muscle and the electrical system leading to reduction in pumping function and irregular heart rhythms. Initially, interstitial tissue is infiltrated by lymphocytes, and neutrophils and there is necrosis of individual muscle fibres. Later lymphocytes and histiocytes predominate and some degree of connective tissue proliferation occurs. Myocarditis generally results in a decrease in myocardial function, with enlargement of the heart and an increase in the end-diastolic volume caused by increased preload. Normally, the heart compensates for dilation with an increase in contractility (Starling law), but because of inflammation and muscle damage, a heart affected with myocarditis is unable to respond to the increase in volume. In addition, inflammatory mediators, such as cytokines and adhesion molecules, as well as apoptotic mechanisms are activated. The progressive increase in left ventricular end-diastolic volume increases left atrial, pulmonary venous, and arterial pressures, resulting in increasing hydrostatic forces. These increased forces lead to both pulmonary edema and congestive heart failure. Without treatment, this process may progress to end-stage cardiac failure and death.

How to Treat Myocarditis?
In many cases the swelling that causes myocarditis improves on its own or with treatment leading to a complete recovery. The focus of treatment is to treat the underlying cause. Medications to remove excess fluid and to reduce the work of the heart are prescribed. In severe cases inotropes, VAD, balloon pump or heart transplant may be necessary. For those who suffer permanent damage life-long medications and heart failure lifestyle modifications are required.
References:
Schultz JC; Hilliard AA; Cooper LT Jr;
Rihal CS; Mayo Clinic Proceedings, 2009 Nov; 84 (11): 1001-9
Mayoclinic.com