Myocarditis

Myocarditis may present with a wide range of symptoms, ranging from mild dyspnea or chest pain that resolves without specific therapy to cardiogenic shock and death. Dilated cardiomyopathy with chronic heart failure is the major long-term sequela of myocarditis. Most often, myocarditis results from common viral infections; less commonly, myocarditis may result from other pathogens, toxic or hypersensitivity drug reactions, giant-cell myocarditis, or sarcoidosis. Cardiac MRI is increasingly used as a diagnostic test in suspected acute myocarditis, and may be used to localize sites for endomyocardial biopsy.

Clinical Pearl Biomarkers and Myocarditis
Biomarkers of cardiac injury are elevated in a minority of patients with acute myocarditis but, if present, may help confirm the diagnosis. Troponin I has high specificity (89%) but limited sensitivity (34%) in the diagnosis of myocarditis. Clinical and experimental data suggest that increased levels of cardiac troponin I are more common than increased levels of creatinine kinase MB in acute myocarditis.

Clinical Pearl Causes of Myocarditis
Viral and postviral myocarditis remain the major causes of acute and chronic dilated cardiomyopathy; viruses associated with myocarditis include coxsackievirus B, adenovirus, parvovirus B19, Epstein–Barr virus, cytomegalovirus, and human herpesvirus 6. Other infectious causes of myocarditis include Borrelia burgdorferi (Lyme disease), with or without coinfection of ehrlichia or babesia, and Trypanosoma cruzi infection. Numerous medications including some anticonvulsants, antibiotics, and antipsychotics, have been implicated in hypersensitivity myocarditis. Eosinophilic myocarditis may occur in association with Churg–Strauss syndrome, Löffler's endomyocardial fibrosis, cancer, parasitic, helminthic, or protozoal infections.

How helpful is an EKG in diagnosing myocarditis and what kinds of EKG changes might you see in a patient with myocarditis?
A: The sensitivity of the electrocardiogram for myocarditis is low (47%). In a patient with acute myocarditis, the electrocardiogram may show sinus tachycardia with nonspecific ST-segment and T-wave abnormalities. Occasionally, the changes on electrocardiography are suggestive of an acute myocardial infarction and may include ST-segment elevation, ST-segment depression, and pathologic Q waves. Pericarditis not infrequently accompanies myocarditis clinically and is often manifested in pericarditis-like changes seen on electrocardiography.

When should endomyocardial biopsy be performed?
A: Endomyocardial biopsy should be performed in patients with unexplained, new-onset heart failure of less than 2 weeks' duration in association with a normal-size or dilated left ventricle and hemodynamic compromise, for suspected fulminant myocarditis. Endomyocardial biopsy should also be performed in patients with unexplained, new-onset heart failure of 2 weeks' to 3 months' duration in association with a dilated left ventricle and new ventricular arrhythmias or Mobitz type II or second-degree or third-degree heart block in patients who do not have a response to usual care within 1 to 2 weeks, for suspected giant-cell myocarditis. (Cooper et al., Circulation, 2007.)

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New England Journal of Medicine - Vol. 360, No. 15, April 9, 2009