Miocarditis

Myocarditis
Cooper LT Jr.
N Engl J Med. 2009 Apr 9;360(15):1526-38. Review. No abstract available.
PMID: 19357408 [PubMed - indexed for MEDLINE
Source: Content provided by the American College of Cardiology Foundation

Perspective: The following are 10 points to remember about myocarditis:

1. Epidemiology: The true incidence of myocarditis in the community is unknown. The greatest burden of pediatric myocarditis may not be apparent for 6-12 years after diagnosis, when children die or require orthotopic heart transplantation for chronic dilated cardiomyopathy.

2. Etiology: Viral and postviral myocarditis remain major causes of acute and chronic dilated cardiomyopathy. Seroepidemiologic data are difficult to discern because of the heterotopic effect of enteroviruses, which may result in an amnestic antibody response to other coxsackievirus B strains. The spectrum of viruses in endomyocardial biopsy samples has shifted from coxsackievirus B to adenovirus in the late 1990s and, in the past 5 years, to parvovirus B19 and other viruses, in the United States and Germany. Other viruses associated (but less frequently with myocarditis) include hepatitis C, Epstein–Barr virus, cytomegalovirus, and human herpesvirus 6 (HIV). Lyme myocarditis should be suspected in patients with a history of travel to regions where the disease is endemic or of a tick bite, especially when they have atrioventricular conduction abnormalities.

3. Etiology: In Central and South America, Trypanosoma cruzi infection can present as acute myocarditis, sometimes with right bundle branch block or left anterior fascicular block. Myocarditis is the most common cardiac pathological finding at autopsy of HIV patients (~50% of cases).

4. Etiology: Anticonvulsants, antibiotics, and antipsychotics, have been associated with hypersensitivity myocarditis. Eosinophilic myocarditis has been associated with the Churg–Strauss syndrome, Loffler’s endomyocardial fibrosis, cancer, and parasitic, helminthic, or protozoal infections and with vaccination for several diseases, including smallpox.

5. Etiology: Giant-cell myocarditis should be considered in acute dilated cardiomyopathy associated with thymoma, autoimmune disorders, ventricular tachycardia, or high-grade heart block.

6. Pathophysiology: In animal models, the progression from acute injury to chronic dilated cardiomyopathy is a three-stage process: 1) Acute injury leads to cardiac damage, 2) exposure of intracellular antigens such as cardiac myosin, and 3) activation of the innate immune system that results in mistaken recognition of endogenous heart antigens as pathogenic entities.

7. Clinical picture: Although a viral prodrome is classically associated with myocarditis, reported symptoms are highly variable. Children often have a more fulminant presentation.

8. Tests: Troponin I has high specificity (89%), but limited sensitivity (34%) in the diagnosis of myocarditis. The sensitivity of the electrocardiogram for myocarditis is low (47%). Fulminant myocarditis may be distinguished from echocardiography by acute myocarditis by a smaller left ventricular cavity size and increased wall thickness. Endomyocardial biopsy should be done in 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. In the future, analysis of messenger RNA and protein markers from peripheral-blood components may be able to detect a clinically meaningful inflammatory signal in high-risk populations without the risk of endomyocardial biopsy.

9. Diagnostic procedures: The Dallas diagnostic pathologic criteria are limited by variability in interpretation, lack of prognostic value, and low sensitivity, whereas criteria based on immunoperoxidase staining have greater sensitivity and may have prognostic value. Preliminary data suggest that noninvasive cardiac MRI is an alternative method for diagnosis without the risks of biopsy. Clinicopathological criteria may distinguish fulminant lymphocytic myocarditis from acute lymphocytic myocarditis and introduce prognostically useful data that are better than pathologic criteria.

10. Treatment: The mainstay of treatment for acute myocarditis is supportive therapy for left ventricular dysfunction. Most patients will improve with a standard heart failure regimen. Because most patients with acute myocarditis are diagnosed weeks after viral infection, it is unlikely that antiviral therapy would be provided early enough to be of benefit in acute viral myocarditis. Interferon beta may be effective in patients with viral persistence in chronic, stable dilated cardiomyopathy. The routine use of intravenous immunoglobulin (IVIG) for acute myocarditis in adults is not recommended because in the Intervention in Myocarditis and Acute Cardiomyopathy trial, patients with acute dilated cardiomyopathy with IVIG did no better than placebo. Studies suggest that immunosuppression is not beneficial in the routine therapy of acute lymphocytic myocarditis. Unlike lymphocytic myocarditis, transplant-free survival in patients with giant-cell myocarditis may be prolonged with a combination of cyclosporine and steroids. Patients recovering from acute myocarditis should refrain from aerobic activity for a period of months after the clinical onset of the disease, based on rodent studies. Ragavendra R. Baliga, M.B.B.S.