Myocarditis Pathophysiology
Myocarditis is characterized by inflammation and necrosis of the
myocardium.
Myocardial damage can lead to
arrhythmias,
heart failure,
dilated cardiomyopathy, and sudden cardiac death.
Damage can be due to direct injury or to autoimmune reactions.
Inflammation can be diffuse or local, and acute or chronic; when the myocardium and pericardium are both inflamed, we call this myopericarditis.
Myocarditis is most common in children and young adults, and occurs more often in males.
Treatments often focus on the complications of myocarditis, including signs of heart failure and arrhythmias.
Myocarditis Signs & Symptoms
Signs and symptoms are often non-specific, often mimic
myocardial infarction or
ischemia.
Thus, myocarditis should be considered when other cardiac conditions can be ruled out and/or the patient's age and history suggest it.
Symptoms range from subclinical to sudden cardiac death; myocarditis may go undiagnosed until heart failure or death have occurred.
Many patients experience flu-like symptoms, dyspnea, and chest pain.
Biomarkers include elevated cardiac troponin, leukocytes, and C-reactive proteins.
ECG may show ST-segment and T-wave changes.
Imaging tests may be helpful, as they can show structural or functional abnormalities, such as systolic dysfunction, dilation, wall thickening, and changes in cardiac shape or motion.
Endomyocardial biopsy
Definitive diagnosis of myocarditis requires endomyocardial biopsy, which is recommended when other cardiac conditions have been excluded and a definitive diagnosis will impact treatment or prognosis.
Acute lymphocytic myocarditis is characterized by necrotic cardiomyocytes, T-cells and macrophages, and, in this example, virions (which would indicate a viral infection is responsible for the inflammation).
Chronic myocarditis, which occurs when inflammation is not resolved, is characterized by dead myocardial cells and fibrosis.
Eosinophilic myocarditis, which, as its name suggests, is associated with
eosinophil infiltrates; this form is often associated with hypersensitivity myocarditis.
Giant cell myocarditis is characterized by giant cells – recall that these are multinucleated macrophages.
Giant cell myocarditis often progresses quickly, and is typically fatal without cardiac transplant. This rare form of myocarditis is more common in women around 50 years of age, and is thought to be associated with autoimmune disorders.
Myocarditis Causes: Infectious & Non-Infectious
Infectious:
Viral infections are the most common cause of myocarditis, particularly in children.
–
Parvovirus B19,
Human-herpes Virus 6,
HIV,
Influenza,
Coxsackievirus, and
Adenovirus are the most common viral culprits.
Bacterial pathogens include Gram-negative bacilli,
Group A Streptococci,
Staphylococci, and
TB;
Parasitic and fungal infections include
Chagas disease, amebiasis,
toxoplasmosis, and
aspergillosis.
Non-infectious causes of myocarditis
Cardiotoxins, which include alcohol and cocaine.
Medications, which can cause hypersensitivity myocarditis; be aware myocarditis is a potential component of
DRESS – Drug Rash with Eosinophilia and Systemic Symptoms.
Examples of commonly used medications associated with this reaction include penicillin, thiazide diuretics, and clozapine.
Radiation therapy
Autoimmune and inflammatory disorders, such as systemic lupus erythematosus, are also associated with myocarditis.
Viral Myocarditis: Pathogenesis Details:*
Because viral infections are the most common causes of myocarditis, let's use them to learn about the pathogenesis of acute and chronic myocarditis stemming from a viral infection.
First, viral entry and replication cause direct damage to the cardiomyocytes.
Second, In response, the
innate immune system is triggered, and T-cells and Natural Killer Cells move in; we show these cells and the cytokines they release.
Third, we show that
adaptive immune system kicks in; we see continued necrosis, and clearance of infected cells and debris.
Lastly, resolution or chronic inflammation occur:
Resolution occurs if the virus is effectively cleared and systolic function is restored.
If viral clearance is ineffective, then chronic inflammation, fibrosis, and remodeling will occur, and cardiac functioning will be impaired. We show dilated cardiomyopathy as an example, because myocarditis is a common cause of this condition.
