Myocarditis is inflammation of the myocardium, which is the muscular layer of the heart.
Etiology
Myocarditis has a diverse etiology, including a wide range of infectious and non-infectious causes:
Infectious Causes
Non-Infectious Causes
Idiopathic
No specific cause is identified in many cases, and these cases are classified as idiopathic myocarditis.
Pathophysiology
The pathophysiology of myocarditis involves three key stages: initial myocardial damage, immune response, and potential widespread myocardial damage.
Initial Insult and Immune Response: The causative agent, whether infectious or toxic, invades the myocardium, leading to direct cellular damage and necrosis. This initial damage activates the immune system, resulting in the release of cytokines and oxygen-free radicals. These inflammatory mediators are intended to combat the causative agent and contribute to further myocardial injury.
Autoimmune Response: In some cases, the immune system mounts an autoimmune response, where antibodies and immune cells target healthy myocardial cells in addition to the causative agent. This autoimmune response exacerbates myocardial damage.
Myocardial Inflammation and Necrosis: Inflammation can cause heart dilation, thrombi formation on the heart wall (mural thrombi), and the infiltration of circulating blood cells around coronary vessels and between muscle fibers. The inflammation and immune response lead to the degeneration of myocardial fibers.
Progression and Hemodynamic Impact: As the inflammation progresses, it can spread throughout the myocardium, leading to extensive myocardial necrosis and the destruction of interstitial collagen and elastin. This destruction impairs the myocardium's structural integrity and function, leading to reduced cardiac output and impaired hemodynamic function.
Long-Term Consequences: The severity of myocardial inflammation and necrosis determines the extent of myocardial dysfunction. Severe cases can result in chronic heart failure and significant structural heart changes.
Myocarditis is an inflammation of the myocardium, the heart's muscular layer, caused by various infectious and non-infectious factors.
Infectious causes include viruses like Coxsackievirus A and B, influenza A, and bacteria such as Streptococcus pyogenes and Mycoplasma pneumoniae.
Fungi like Aspergillus and parasites such as Trypanosoma cruzi can also cause myocarditis.
Non-infectious causes include autoimmune disorders such as systemic lupus erythematosus, radiation therapy, and chemotherapy drugs like doxorubicin.
Next, the pathophysiology of myocarditis involves a causative agent, such as a virus or bacteria, invading the myocytes and leading to cellular damage and necrosis.
This damage activates the body's immune response, releasing cytokines and oxygen-free radicals that attempt to eliminate the infectious agent but also contribute to myocardial damage.
As the infection progresses, an autoimmune response may mistakenly target the body's myocardial cells, leading to further destruction of myocytes and heart dysfunction.
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