characterized by dense diffuse fibrosis of the ventricular endocardium and subendocardium, often involving the tricuspid and mitral valves. The fibrous tissue markedly diminishes the volume and compliance of affected chambers, resulting in a restrictive physiology. Endomyocardial fibrosis has been linked to nutritional deficiencies and/or inflammation related to helminthic infections (e.g., hypereosinophilia); worldwide, it is the most common form of restrictive cardiomyopathy.
• Loeffler endomyocarditis also exhibits endocardial fibrosis, typically associated with formation of large mural thrombi. It has no geographic or population predilection. It is characterized by peripheral hypereosinophilia and eosinophilic tissue infiltrates; release of eosinophil granule contents, especially major basic protein, probably engenders endocardial and myocardial necrosis, followed by scarring, layering of the endocardium by thrombus, and finally thrombus organization. Of interest, some patients have an underlying hypereosinophilic myeloproliferative neoplasm driven by gene rearrangements that lead to expression of constitutively active tyrosine kinases (Chapter 12). Treatment of such patients with tyrosine kinase inhibitors can result in hematologic remission and reversal of the endomyocardial lesions.
MORPHOLOGYInrestrictivecardiomyopathy,theventriclesareofapproximatelynormalsizeoronlyslightlyenlarged,thecavitiesarenotdilated,andthemyocardiumisfirm.However,bothatriaaretypicallydilatedasaconsequenceofrestrictedventricularfillingandpressureoverloads.Microscopicexaminationrevealsvariabledegreesofinterstitialfibrosis.Althoughgrossmorphologicfindingsaresimilarforrestrictivecardiomyopathyofdisparatecauses,endomyocardialbiopsyoftencanrevealaspecificetiology.
Myocarditis encompasses a diverse group of clinical entities in which infectious agents and/or inflammatory processes target the myocardium. It is important to distinguish myocarditis from conditions such as IHD, where the inflammatory process is secondary to some other cause of myocardial injury.
In the United States, viral infections are the most common cause of myocarditis, with coxsackieviruses A and B and other enteroviruses accounting for a majority of the cases.
Cytomegalovirus (CMV), human immunodeficiency virus (HIV), influenza virus, and others are less common pathogens. Offending agents can be identified by serologic studies that show rising antibody titers or through molecular diagnostic techniques using infected tissues. While some viruses cause direct cell death, in most cases the injury results from an immune response directed against virally infected cells; this is analogous to the damage inflicted by virus-specific T cells on hepatitis virus–infected liver cells (Chapter 16). In some cases, viruses trigger a reaction against cross-reacting proteins such as myosin heavy chain.
The nonviral infectious causes of myocarditis run the entire gamut of the microbial world. The protozoan Trypanosoma cruzi is the agent of Chagas disease. Although uncommon in the northern hemisphere, Chagas disease affects up to one half of the population in endemic areas of South America, with myocardial involvement in the vast majority. About 10% of the patients die during an acute attack; others can enter a chronic immune-mediated phase with development of progressive signs of CHF and arrhythmia 10 to 20 years later. Toxoplasma gondii (household cats are the most common vector) also can cause myocarditis, particularly in immunocompromised individuals.
http://ebooksmedicine.net
Trichinosis is the most common helminthic disease associated with cardiac involvement.