NORD gratefully acknowledges Leslie T. Cooper Jr., MD, Chair, Cardiovascular Department, Mayo Clinic in Florida; Professor of Medicine, Mayo Clinic, for assistance in the preparation of this report.
Myocarditis is a rare cause of cardiovascular disease primarily manifest as sudden death, chest pain or heart failure. The symptoms of heart failure from myocarditis include shortness of breath, fatigue and ankle swelling. The cause is an inflammation of the heart muscle, most often following a viral infection. Between 0.5 and 3.5 percent of heart failure hospitalizations are due to myocarditis. Most cases of myocarditis are identified in young adults with males affected more often than females. The diagnosis should be considered in any young adult with unexplained cardiac causes of shortness of breath or loss of consciousness. Many authorities recommend the diagnosis be made by heart biopsy, but imaging with magnetic resonance is growing as an accepted diagnostic method. Specific causes of myocarditis vary by world region, which mandates region-specific diagnostic and management strategies.
The symptoms of myocarditis are not specific to the disease and are similar to symptoms of more common heart disorders. A sensation of tightness or squeezing in the chest that is present with rest and with exertion is common. Not infrequently chest pain is improved with leaning forward and worse with lying back when the inflammation affects the outer lining of the heart or pericardium as well as the heart muscle. If the heart pacing or conduction tissues become inflamed, a slow heart rate may cause fatigue or lightheadedness. Inflammation can also cause extra beats that feel like a flutter in the chest. Sustained runs of extra beats in quick succession may lead to lightheadedness or even loss of consciousness. Sudden death resulting from a myocarditis-related arrhythmia is an important cause of death in children and young athletes.
In a majority of cases, the symptoms of myocarditis are preceded a few days to weeks by a flu-like illness. Specific viruses and even multiple virus infections may be seen in immunocompromised patients such as persons infected with HIV. Rarely myocarditis may result from an adverse drug reaction. In this setting, a temporal association between a new medication and myocarditis symptoms can suggest the cause.
Most cases of myocarditis are mild and improve with standard medical therapy directed at improving heart function or correcting abnormal heart rhythms. In a minority of cases the symptoms do not improve or become recurrent. In these circumstances referral to a medical center with expertise in myocarditis management is useful. The evaluation and management of chronic or recurrent myocarditis is not standardized.
Most cases of myocarditis are of unknown cause (idiopathic). When a cause is identified, it is usually the result of an infection. In North America and Western Europe, viral infections are the most common identified causes of myocarditis. In specific world regions, other important causes include myocarditis following a streptococcal bacterial infection and HIV related infections. In specific Eurasian groups bacteria such as diphtheria, rubella, and even scorpion bite have been reported.
The heart injury may result directly from a toxic effect such as a toxin or a virus. More commonly myocarditis is a result of the body’s immune reaction to the initial heart damage. Most immune reactions are helpful and serve to clear infections, but sometimes the scar tissue resulting from the inflammation can lead to long term decline in heart function or chronic abnormalities in heart rhythm. Sometimes the immune reaction fails to clear an infection which can lead to chronic viral myocarditis. Myocarditis can also accompany systemic inflammatory disorders such as lupus or Kawasaki disease.
Myocarditis is not inherited. There are no known genes associated with human myocarditis. When multiple family members are affected, the cause is usually due to common infection or environmental exposure. For example, experimental studies suggest that low blood levels of selenium and high levels of mercury may worsen viral myocarditis.
Myocarditis is most frequently diagnosed in younger adults between the ages of 20 and 40 years. Children seem to have a more severe presentation than adults with a greater proportion requiring temporary mechanical circulatory support. Men are generally more frequently affected than women, possibly due to effects of testosterone on the immune reaction to infection. The relative frequency of more common age related cardiovascular diseases such as coronary artery disease may lead to under diagnosis in the elderly. Certain forms of myocarditis, such as cardiac sarcoidosis, are more common in black than white persons in the US. However, most forms of myocarditis have no known ethnic predisposition.
The incidence and prevalence of myocarditis are not known from population-based studies because there is no widely available test that can be applied at a population level. The global burden of myocarditis has been estimated from population-based studies of heart muscle disease (heart disease not related to blocked arteries or abnormal heart valves). In 2010, approximately 400,000 people died of heart muscle disease (cardiomyopathy that includes myocarditis) world wide, including 160,000 women and 240,000 men. Expert consensus opinion extrapolating from regional clinical registries and treatment trials estimates that up to 40% of dilated cardiomyopathy results from myocarditis.
Myocarditis should be suspected in people who have recent onset cardiac symptoms, such as chest pains or trouble breathing, and who have no evidence of more common disorders such as coronary artery disease, heart valve damage or severe high blood pressure. In mild cases characteristic features on cardiac magnetic resonance imaging (MRI) strongly support the diagnosis and heart biopsy is not usually required. In more severe cases or if patients fail to respond to standard medical care, a heart biopsy may be needed to confirm the diagnosis and guide therapy. There are no specific blood tests to confirm the diagnosis of myocarditis; however, an otherwise unexplained elevation in troponin (a blood test that indicates heart muscle damage) and/or electrocardiographic features of cardiac injury are supportive. Similarly new heart wall motion abnormalities or a fluid around the heart seen on echocardiography are not specific but support the diagnosis once other more common disorders have been excluded.
In mild cases of myocarditis, particularly with normal heart pump function and evidence of inflammation of the adjacent pericardium, cardiac MRI is a reasonable confirmatory test. The diagnostic MRI features of acute myocarditis are often transient and evolve from a focal to a more diffuse pattern of injury. Over months these diagnostic features may resolve.
In more severe cases of myocarditis a heart biopsy should be performed when the information will uniquely impact prognosis or guide treatment. Heart biopsy should be done at centers with expertise in the technique so as to minimize risk of procedure-related complications. Centers performing heart biopsy should have access to cardiac pathologists to examine the heart tissue. In general the diagnostic strategy to confirm myocarditis should balance probable clinical impact with safety.
Persons diagnosed with myocarditis often require follow up physician visits and cardiac testing to ensure the disease is responding to treatment. The specific tests and the intervals and duration of follow up depend on the presentation and severity of the initial illness.
Myocarditis that presents with heart failure symptoms and decreased heart pump function should be treated according to the current national society guidelines for “systolic” heart failure. Drugs that block the immune system are generally not indicated for the management of the most common forms of myocarditis in adults. However, in specific forms of myocarditis such as giant cell myocarditis, cardiac sarcoidosis or eosinophilic myocarditis, medications that modify the immune response should be considered. These specific forms of myocarditis are diagnosed by heart biopsy. Sports participation during acute viral myocarditis may cause sudden death. Thus high levels of physical activity following the diagnosis of myocarditis should be avoided for at least 3 to 6 months. Non-steroidal anti-inflammatory drugs such as ibuprofen should be avoided due to a risk of increased inflammation.
Some patients with severe myocarditis develop low blood pressure despite optimal medical care. These patients may require a temporary heart pump (a kind of mechanical circulatory support device) to survive the acute injury. Some of these patients with myocarditis can be bridged to recovery and have the pump removed. The survival after heart transplantation for adult patients with myocarditis is similar to that for other causes of cardiac failure. Patients with severe myocarditis should be seen by cardiologists with expertise in heart failure and heart rhythm disorder management.
Specific forms of myocarditis may require tailored therapy aimed at clearing viral infections or inhibiting select arms of the immune system. People with complex or refractory cases of myocarditis may seek expert opinion for advice regarding investigational therapies. Research trials directed at increasing viral clearance are underway.
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Cooper, L.T., Keren, A., Sliwa. K, and Matsumori, A., The Global Burden of Myocarditis. Part 1: A Systemic Literature Review for the Global Burden of Diseases, Injuries, and Risk Factors 2010 Study. Global Heart. 2014; 9(1):121-9.
El Amm, C, Fairweather, D and Cooper, LT Pathogenesis and Diagnosis of Myocarditis. Heart. 2012; 98(11): 835-40.
Blauwet, LA and Cooper, LT. Myocarditis. Progress in Cardiovascular Diseases 2010; 52(4): 274-288.
Cooper LT, Jr. Myocarditis. New England Journal of Medicine 2009; 360:1526-38.
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