Written by Leslie T. Cooper, MD & DeLisa Fairweather, PhD
What is “chronic myocarditis”?
A: Chronic diseases are by definition diseases that develop or progress slowly and are difficult to treat. Acute diseases occur suddenly and last for a relatively short period of time. “Myocarditis” usu
ally refers to “acute myocarditis” and the term “chronic myocarditis” is used if acute myocarditis does not disappear quickly or if myocarditis symptoms reappear later after an episode of acute myocarditis.
What causes “chronic myocarditis”?
A: Many different environmental agents can trigger myocarditis including viral or bacterial infections, toxins, and drugs 7. The reasons why some persons recover and others do not is an area of active investigation.
Does everyone who has myocarditis progress to “chronic myocarditis”?
A: No, most patients with myocarditis resolve the disease relatively quickly. Only certain susceptible individuals progress from acute to chronic myocarditis and dilated cardiomyopathy 1. Research has shown that susceptibility to develop “chronic myocarditis” depends on the type of immune response an individual has in response to infections, chemicals or physical damage to the heart 2,3,8-10.
How is chronic myocarditis diagnosed?
A: Examination of heart tissue under a microscope is the only way to prove the diagnosis of chronic myocarditis. Up to 40% of patients with chronic dilated cardiomyopathy (large, poorly functioning hearts) who have symptoms of heart failure despite standard medical care can have myocarditis when special techniques are used to study heart tissue.
Magnetic resonance imaging (MRI) of the heart is under evaluation to aid in diagnosis of chronic myocarditis. The sensitivity and specificity of MRI for the diagnosis of myocarditis varies with duration of illness and the sequences used.
Blood tests that measure damage to heart muscle cells (e.g. troponin T) can also be elevated in chronic myocarditis, but the levels may be normal or only minimally elevated.
The electrocardiogram has nonspecific changes in the majority of myocarditis cases. There are also no specific echocardiographic features of chronic myocarditis.
How can “chronic myocarditis” occur later after “acute myocarditis”?
A: Research in animal models has shown that myocarditis can be a biphasic disease, meaning that acute myocarditis can resolve and then several weeks or months later it can reappear 1. Researchers have found that proteins called cytokines that are released from inflammatory cells during acute myocarditis begin to cause changes in heart structure that only appear several weeks or months later 2-5. This process is called “remodeling” and leads to fibrosis (i.e. scar tissue in the heart) and dilated cardiomyopathy (i.e. an enlarged heart). However, it is important to note that only some individuals progress from acute to chronic myocarditis, while most patients with acute myocarditis do not develop the chronic phase of disease.
Is chronic myocarditis associated with other diseases?
A: Non-infectious causes of myocarditis are uncommon, and include myocarditis associated with connective tissue disease such as systemic lupus erythematosis or rheunmatoid arthritis. Myocarditis can also develop in patients who have rare primary disorders of immune regulation.
Is “chronic myocarditis” an autoimmune disease?
A: In most cases, chronic myocarditis involves autoimmunity 16. An autoimmune response occurs when the immune system attacks the cells and tissues of our body. The immune system does this in an attempt to heal the damage induced by infections or chemicals, for example, but can end up causing damage itself. This results in chronic inflammation and may involve deposition of proteins called autoantibodies on cardiac tissue that can adversely affect heart function and further promote inflammation 16-18.
Is “chronic myocarditis” related to dilated cardiomyopathy and heart failure?
A: Yes, most patients with chronic myocarditis also have dilated cardiomyopathy, or an enlarged heart 6. Having an enlarged heart places the patient at a greater risk for developing heart failure. Because of this, and the difficulty of treating dilated cardiomyopathy, patients may need a heart transplant. However, there are other causes of dilated cardiomyopathy and heart failure besides myocarditis.
Am I at a greater risk of heart failure with “chronic myocarditis”?
A: Not necessarily. Patients are at a risk for heart failure during acute and chronic myocarditis, but for different reasons. For example, patients may be at heightened risk for heart failure during “acute myocarditis” because of the release of cytokines (which are immune signaling proteins) that adversely effect cardiac function, but at risk for heart failure during “chronic myocarditis” more because of poor cardiac function due to myocardial scarring 5.
How is chronic myocarditis treated?
A: There is no established treatment for chronic myocarditis. However, studies in patients with chronic heart failure that did not respond to usual care suggest a limited role for immunosuppression. Randomized trials of patients with chronic myocarditis (diagnosed by special stains of heart biopsy tissue) immunosuppression with azathioprine and prednisone resulted in an improvement in quality of life and left ventricular ejection fraction. This treatment strategy is now under evaluation in well-designed, multicenter trials. Other studies seek to evaluate antiviral therapy in patients with evidence of chronic viral heart infections.
Is there a sex difference in “chronic myocarditis”?
A: Yes. Chronic myocarditis, dilated cardiomyopathy, and heart failure occur more frequently in men than women. Recently two studies were published finding that myocardial recovery after acute myocarditis and transplant-free survival occurred much less frequently in men than women with myocarditis 6,11. Another study found that men are two-times more likely to develop myocardial fibrosis (i.e. scarring) following myocarditis than women 12. Fibrosis is a scar that develops in the cardiac muscle that makes it more difficult for the heart to pump efficiently and usually leads to dilated cardiomyopathy, or an enlarged heart, and may progress to heart failure. Researchers have found that elevated testosterone levels in males directly promote the type of inflammation that leads to increased myocarditis, fibrosis, dilated cardiomyopathy and heart failure 4,8,13-15.
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