Myocarditis

Abstract

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, specific forms of myocarditis may result from other pathogens, toxic or hypersensitivity drug reactions, giant-cell myocarditis, or sarcoidosis. The prognosis and treatment of myocarditis vary according to the cause, and clinical and hemodynamic data usually provide guidance to decide when to refer a patient to a specialist for endomyocardial biopsy. The aim of this review is to provide a practical and current approach to the evaluation and treatment of suspected myocarditis.

Figure 1. Lymphocytic and Histiocytic Infiltrate and T Lymphocytes in Heart-Tissue Sections from Patients with Acute Myocarditis

Panel A shows acute myocarditis with widespread lymphocytic and histiocytic infiltrate (arrow) and associated myocyte damage (arrowhead) (hematoxylin and eosin). Panel B shows CD3 immunostaining of T lymphocytes in a patient with acute myocarditis. Images provided courtesy of Dr. Dylan Miller.

Figure 2. Pathogenesis of Myocarditis

The current understanding of the cellular and molecular pathogenesis of postviral and autoimmune myocarditis is based solely on animal models. In these models, the progression from acute injury to chronic dilated cardiomyopathy may be simplified into a three-stage process. Acute injury leads to cardiac damage, exposure of intracellular antigens such as cardiac myosin, and activation of the innate immune system. Over weeks, specific immunity that is mediated by T lymphocytes and antibodies directed against pathogens and similar endogenous heart epitopes cause robust inflammation. In most patients, the pathogen is cleared and the immune reaction is down-regulated with few sequelae. However, in other patients, the virus is not cleared and causes persistent myocyte damage, and heart-specific inflammation may persist because of mistaken recognition of endogenous heart antigens as pathogenic entities. APC denotes antigen-presenting cell.

Figure 3. Contrast-Enhanced Magnetic Resonance Imaging (MRI) of the Heart of a 24-Year-Old Man with Acute Myocarditis

Cardiac MRI is being increasingly used to evaluate suspected acute myocarditis and to localize sites for endomyocardial biopsy, with additional detail shown with delayed gadolinium enhancement (Panel A, arrows), in a four-chamber view (Panel B, arrows), and in T₂-weighted three-chamber views (Panels C and D, arrows). Scans provided courtesy of Dr. Jeannette Schultz-Menger.