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Myocarditis

Myocarditis encompasses non ischemic inflammatory diseases of the myocardium. Pathologically, the current standard for diagnosis are the Dallas Criteria. On a first biopsy, active myocarditis is diagnosed if inflammatory infiltrates are seen with necrosis or degeneration of adjacent myocytes myocarditis, miocarditis.

The epidemiology of myocarditis depends on the method of ascertainment. In viral epidemics, there is a 5% carditis rate. Autopsy series overall show a 1-4% incidence, but this rises to 15-20% in young subjects with sudden death. Males predominate. Presentations tend to be subacute - fulminant presentation is more common in young infants and neonates. The latency for clinical disease is usually long - most cases of dilated cardiomyopathy are attributed to 

Most cases of myocarditis are idiopathic. Infectious etiologies have been identified involving virus, rickettsia, fungi, protozoans (Chagas disease), bacterial, and spirochetes. Non infectious etiologies include system illnesses, cardiotoxic drugs, hypersensitivity drug reactions, and

The pathogenesis of tissue injury begins with an initial insult. In murine models of viral myocarditis, initial viral infection produces contraction band necrosis, myocyte vacuolization. The viral phase is short lived. Subsequently, an inflammatory response is induced with further tissue injury occurring over a protracted period. This may involve cytolytic T cells, B cells, and cytokines.

Clinically, the typical myocarditis presents in individuals without previous history of heart disease as new onset congestive heart failure, tachycardia, chest pain, syncope, or presyncope (manifestations of arrhythmias). A history of preceding flu like illness occurs in approximately half. Examination may reveal soft heart tones, muffled S1, S3 gallop, systolic murmurs, pericardial friction rub. The patient may be hypoperfused or congested.

Laboratory assessment may disclosed leukocytosis and elevated ESR; elevated liver and myocardial enzymes. EKG can show AV block, ST changes, Low voltage, sinus tachycardia, atrial fibrillation. Echo/MUGA scans will demonstrate global depression of all chambers without regional wall motion abnormalities. Radionuclude scans with gallium or antimyosin labeled pharmaceuticals will reveal myocardial uptake. Serological studies are valuable if a specific infective agent is suspected; a fourfold or greater rise of titer from acute to convalescent sera is needed to prove the agent is responsible.

Endomyocardial is the definitive step in making a histological diagnosis. However, prospective studies have shown a low diagnostic yield for specific etiological agents at the time of presentation of dilated cardiomyopathy. Given the risk of the procedure in DCM, it should be "routinely" reserved for evaluation of known myocarditis, such as heart transplantation or doxorubicin therapy.

The natural history of myocarditis has been likened to that seen in hepatitis (Lieberman, JACC 1991: 19:1617-1626). Acute cases can span fulminant disease ending in complete recovery or death to acute self limited disease with complete recovery or a chronic state. Chronic states may either have features of chronic active inflammation or chronic persistent inflammation. The variety of outcomes has led to prognostic difficulty in determining the natural history.

Evidence for success of definitive therapy with immunosuppressive agents is lacking. Spontaneous improvement occurs in approximately 29%. Non randomized trials had shown a 56% response to immunosuppressives, but a multicenter NIH trial showed NO benefit. A consensus does exist that therapy for fulminant presentations is unwise.

Withdrawal of offending toxins in non infectious cases does appear beneficial. This is most valuable in the circumstance of ethanol.

Supportive therapies are the bulwark of management. These include sodium restriction, activity limitation, diuretics, anticoagulation in the setting of arrhythmias and thrombus, antiarrhythmics and/or pacemakers for symptomatic electrical complications, prophylactic ACE inhibition, digitalis for Class III and IV patients, and intravenous inotropes, mechanical support and transplantation for Class IV patients admitted to the hospital.

True myocarditis is something that is uncommonly encountered. Itís consequences, however, in terms of dilated cardiomyopathy, are very, very common. On biopsy, myocarditis appears as myocytes in a sea of inflammatory cells reflecting an active inflammation with destruction of myocardial tissue. Myocarditis is a nonischemic inflammatory disease of the myocardium. Myocarditis and myocardial infarction will cause inflammation. But here thereís no evidence of epicardial or even penetrating vessel obstruction. Instead there is a primary inflammation.

The current state of the art has been defined in 1987 in a conference in Dallas. Active myocarditis is an active inflammatory infiltrate with necrosis or degeneration of adjacent myocytes not typical of ischemia. You can also classify a sample initial biopsy as borderline or negative and then subsequent biopsies can be performed with a new to determine if the disease is ongoing, resolving or resolved.

The epidemiology of myocarditis in the true clinical sense of an active inflammatory disorder is as follows. First there is male predisposition. Secondly, itís rare to be able to actually isolate virions in the myocardium. Third, in young individuals the presentation is often fulminant whereas in adolescent and adults itís subacute.

The symptoms of myocarditis, however, using the argument that dilated cardiomyopathy of unclear etiology is generally the outcome of myocarditis, the symptoms donít appear for years often. Weíll talk, however, about the fulminant presentations in adults that you might see that are different than this.

Now, if you look at viral epidemics such as influenza epidemics and ask how often the heart is involved, the average rate is said to be approximately 5%. Evidence of nonischemic inflammation, and that is indicative of myocarditis, can be seen in autopsy series as high as 4%. But this is rather remarkable. For young individuals who have sudden death, myocarditis may be found in 15-20% and this is important to remember unfortunately as an explanation after the fact, not in a way of accounting for whatís to follow.

If one looks at infectious agents that can produce myocarditis you can generate this long list but the top line is the key one. Most cases are idiopathic which is to say weíve been unable to identify the causative agent but itís valuable to look through and to see which viral illnesses are associated with cardiac disorders. The classic, of course, at this time of the year is the Enterovirus Coxsackie A and B but even common viruses such as hepatitis, mumps and herpes can be involved. In the AIDS era, HIV has been clearly implicated as a cause of myocarditis although there are questions as to whether itís an opportunistic infection thatís been involved.

Now, other infectious agents have roles and the rickettsia, in this area of the country we think about Lyme disease, we also think about Q fever, Rocky Mountain Spotted fever, fungal infections can be involved. Protozoan infections outside of the United States are the leading cause of myocarditis in South America. Chagasí disease due to trypanosomiasis. Schistosomiasis is