**1. Introduction**

Myocarditis is a clinical syndrome characterized by inflammation of myocardium. It can be produced by a myriad of etiologies including infectious, autoimmune, myocardial toxins, hypersensitivity reactions and physical agents. Virtually any infectious agent can produce myocardial inflammation and injury. Human myocarditis is most frequently caused by viral infection. Ongoing viral infection, myocardial destruction, and adverse remodeling can lead to persistent ventricular dysfunction and dilated cardiomyopathy. The modern molecular techniques have facilitated new insights into inflammatory autoimmune processes that affect the myocardium and ultimately result in acute or chronic dilated cardiomyopathy.

The clinical manifestations are highly variable, ranging from asymptomatic electrocardiographic or echocardiographic abnormalities to acute myocardial infarction-like syndrome, overt congestive heart failure, fulminant condition with new atrial or ventricular arrhythmias or profound cardiogenic shock and death. Myocarditis is occasionally the unrecognized culprit in cases of sudden cardiac death. Autopsy series have reported much higher rates of myocarditis than expected with overt clinical manifestation from different etiological agents. The prospective postmortem data have implicated myocarditis in sudden cardiac death of young adults at rates of 8.6 percent to 12 percent (Doolan et al., 2004; Fabre & Sheppard, 2005). Furthermore, it has been identified as a cause of dilated cardiomyopathy in 9 percent of cases in a large prospective series (Felker et al., 1999).

The clinical history in patients presented with myocarditis remains essential to envelop a wide variety of etiologies in the clinical scenarios, many of which are infectious (Brodison & Swann, 1998). In the past 10 years, however, viruses, including adenovirus, parvovirus B19, hepatitis C, and herpes virus 6, have emerged as significant pathogens (Mahrholdt et al., 2006). The geographical distribution can be of relevance for some forms of myocarditis. In selected countries, Chagas disease, Lyme myocarditis, acute rheumatic fever and disorders associated with advanced human immune deficiency virus infection are significant causes. Other important infrequent clinicopathologic variants in the etiological spectrum are systemic disorders like giant cell myocarditis, cardiac sarcoidosis and eosinophilic myocarditis. Additionally, drugs, vaccinations, toxins, physical agents like radiation, heat stroke and hypothermia can be the key point for some rare clinical diagnoses. The physical examination in patients with myocarditis might be normal, but more severe cases frequently evident for significant physical findings. Although histological findings remains the gold standard for establishing the diagnosis of myocarditis, low risk patients are often given a

Clinical Presentation 5

transplant free 11 years following initial biopsy, compared with only 45 percent in those

Classically, patients with acute myocarditis presents with a less distinct onset of illness with nonspecific symptoms related to the heart. Viral prodrome occurs between 20 and 80 percent of the cases, can be readily missed by the patient, and thus cannot be relied upon for diagnosis. They present with an established ventricular dysfunction and may respond to immunosuppressive therapy or their condition may progress to dilated cardiomyopathy. In a series of 245 patients with clinically suspected myocarditis, the most common symptoms include fatigue (82 percent); dyspnea on exertion (81 percent); arrhythmias (55 percent, both supraventricular and ventricular); palpitations (49 percent); and chest pain at rest (26 percent), (Kuhl et al., 2005). The presentation can mimic acute coronary syndromes in view of troponin release, ST segment elevation on electrocardiogram, and segmental wall motion

This group of patients with chronic active myocarditis represents the majority of older adult with myocarditis. They are also presents with a less distinct onset of illness and often insidious with symptoms compatible with moderate ventricular dysfunction such as fatigue and dyspnea. Affected patients may initially respond to immunosuppressive therapy but often have clinical and histologic relapses and develop ventricular dysfunction associated with chronic inflammatory changes, and mild to moderate fibrosis on histological study

This group of patients with chronic persistent myocarditis, whom also presents with a less distinct onset of illness, is characterized by a persistent histological infiltrate, often with foci of myocyte necrosis but without ventricular dysfunction, despite other cardiovascular

The previously depicted four forms are still used to describe the clinical presentation and progression of myocarditis, particularly in the absence of ongoing histological evaluation. These categories may also provide some prognostic information and may suggest which

A new diagnostic criteria derived from limited data was proposed in 2009. The Lake Louise Consensus Criteria utilizes the cardiac magnetic resonance imaging (CMR) for the diagnosis of myocarditis (Friedrich et al., 2009). The CMR enhances the ability to detect myocardial inflammation through noninvasive means, as well as to improve diagnostic accuracy. In these criteria, four major domains are considered when making the diagnosis including, clinical presentation compatible with myocarditis, evidence of new or recent onset myocardial damage, increased T2 signal or delayed enhancement on CMR (compatible with myocardial edema and inflammation), and endomyocardial biopsy evidence of myocardial inflammation. The use of CMR appears suitable to identify patients with significant ongoing inflammation, which may be especially important for patients with recurrent or persisting symptoms and in patients with new onset heart failure. The awareness came out that the

with more classic forms of acute myocarditis.

**2.2 Acute myocarditis** 

abnormalities on echocardiogram.

**2.3 Chronic active myocarditis** 

**2.4 Chronic persistent myocarditis** 

symptoms such as chest pain or palpitation.

patients can or cannot benefit from immunosuppressive therapy.

including giant cells.

presumptive diagnosis if imaging studies and a compatible clinical scenario suggest new onset cardiomyopathy. The clinical manifestations of suspected patients with myocarditis will be discussed in details.
