Myocarditis

Myocarditis is a condition where the muscular walls of the heart become inflamed. Myocarditis typically results in poor heart function.

There are many causes of myocarditis including infections, medications, chemicals, radiation, and certain diseases that cause inflammation in many different organs of the body. In most children, myocarditis is triggered by an infection, usually viral, involving the heart.

There are no known risk factors for developing myocarditis. The severity of disease seems to be dependent upon many factors such as age, sex, and the genetic make-up of the immune system.
Treatment for myocarditis is evolving as the disease process is better understood. Many children experience a complete recovery, but some may develop serious heart failure and require chronic care by a cardiologist.

In children, viral infections are the most common causes for myocarditis, but certain drugs and autoimmune disorders may also cause myocarditis. The most common viruses involved are Influenza virus, Adenovirus and Coxsackie virus although viruses such as Rubella, Rubeola and HIV may also cause myocarditis.

Rarely, bacteria such as those causing Lyme disease, Rocky Mountain Spotted Fever or toxic shock syndrome, fungus, or parasites can cause myocarditis. It is important to recognize that even though a child may have one of these infections, it is rare for them to develop myocarditis.

When an infectious organism is the causitive agent for myocarditis, the initial event that must occur is infection of the heart by that organism. The organism enters the body and travels through the blood stream to the heart. It grows and reproduces within the heart and may cause some cell damage in the process of spreading from one cell to another.

In normal individuals, the immune system is called upon to eliminate the infection. In some children, this response is over-aggressive so that in addition to destroying the infecting organism, the heart cells themselves may be damaged.

Most of the damage to the heart seen is a result of the body’s immune reaction to the infectious organism, not the organism itself. It is unclear why this happens in some children. The abnormal immune response may be confined to a small area or involve a large portion of muscle tissue. The severity of symptoms is often related to how much heart muscle is involved.

There are other triggers for myocarditis. Many drugs used for chemotherapy and certain antibiotics in rare cases can cause an immune response similar to what is seen with viral infections.

Children with diseases such as Lupus, Rheumatoid arthritis, Ulcerative Colitis, and Scleroderma (diseases that involve inflammation of many different organs of the body) may also develop myocarditis, but this is rare. The mechanism causing the abnormal immune response under these conditions is not as well understood.
The inflammatory process begins when the body’s immune cells (the cells that fight infection) actually penetrate the heart tissue. These immune cells become activated and produce chemicals that can cause damage to the heart muscle cells. There is thickening and swelling of the heart muscle. All four chambers of the heart may be affected and become enlarged.

Damaged muscle cells may heal over time or there may be cell death followed by scar formation. If this process is extensive and a large portion of the heart is involved, the ability of the heart to pump blood is impaired.

As a result, the important organs and tissues in the body are deprived of oxygen and nutrients and cannot eliminate waste products. This is often referred to as congestive heart failure.

It is not unusual for someone that has severe myocarditis to suffer from other problems such as liver or kidney failure, as well.

The symptoms of myocarditis may be subtle, making the diagnosis difficult, or the child may experience overt symptoms of heart failure. Clinical experience has shown the severity of symptoms or illness is dependent upon the age of the child.

Children over 2 years of age may be less symptomatic than newborns and infants who are usually more severely affected. This is thought to be due to the immaturity of a baby’s immune system.

Infections may be acquired during pregnancy (Rubella for example) via transmission of the infectious agent from mother to baby. In general, infants with myocarditis will appear anxious, listless and weak. They are often breathing fast and having difficulty feeding.

There is evidence of poor circulation manifested by cool, pale hands and feet. Due to poor circulation throughout the body, the kidneys may not be functioning normally; therefore, they may have decreased urine production.

There may be fever or other evidence of infection. In older infants, the findings are similar but there may be an associated weight loss due to difficulty with feeding.

Older children may be less symptomatic. They may complain of a flu-like illness consisting of fatigue, malaise and fever.

They may exhibit a decreased tolerance for exercise or complain of chest pain or palpitations (skipped or extra heartbeats). They may develop a cough. Some children who experience congestive heart failure may also exhibit swelling in the face, feet or the legs. There may be abdominal pain and nausea due to swelling of the liver.

Due to poor circulation, there may be impaired liver and kidney function. The signs and symptoms of myocarditis are subtle early in the illness; therefore, it is not unusual for myocarditis to go unrecognized.
Myocarditis is sometimes diagnosed in retrospect when the child has an abnormal heart rhythm or is critically ill. It can also be diagnosed retrospectively in adulthood with abnormal heart rhythm or an enlarged heart.
Unfortunately, to the frustration of parents and doctors, there is no specific test for myocarditis. It is mostly a clinical diagnosis; therefore the physician must rely on the history provided by the family and physical examination of the child.

There are many tests that can be performed that help support a suspected diagnosis of myocarditis. The most common test is a chest X-ray. Often the heart size is enlarged, the blood vessels of the lungs are prominent, and fluid may enter the lungs.

An electrocardiogram can also give helpful clues if the diagnosis is suspected; however, the findings may be non-specific.

An echocardiogram or heart ultrasound can be used to assess heart size and overall function which helps confirm the clinical diagnosis as well as rule out the presence of blood clots within the heart chambers which can form due to poor heart function.

Other blood tests may by obtained to assess liver and kidney function. A blood count and specific tests for infections may also be obtained.

The most precise way to make the diagnosis of myocarditis relies on heart biopsy obtained during a cardiac catheterization. This involves the use of a long catheter that is passed up a large blood vessel in the leg. Once the catheter is in the heart, a tiny piece of heart muscle is obtained and sent to the pathologist for inspection under the microscope.

Results vary but the diagnosis of myocarditis is made by this method up to 65 percent of the time. The results of the biopsy are not 100 percent because the areas of the heart affected by the inflammation are often patchy and may be missed.

The inflammation that occurs is usually self-limiting, that is, it will resolve on its own. There is no cure for myocarditis. In general, the goal of medical therapy is to support the heart function so that adequate blood circulation is maintained. Most children diagnosed with myocarditis are admitted to an intensive care unit for initial management and careful monitoring.

Medications that are able to help the heart work more either by regulating the blood pressure or by improving the ability of the heart to pump blood are the first line of treatment.

One or more of these medications may be considered depending upon the severity of the myocarditis. In addition, a diuretic is commonly used to help clear excess fluid from the lungs or other body tissues.
There are also medications that are designed to decrease the abnormal immune response, which are currently under investigation.

One drug frequently used is called intravenous immunoglobulin (IVIG) which consists of purified antibodies, the substances that the body’s immune cells produce to fight infection. Its mechanism of action is unclear but it has been shown to slow down the inflammatory process. For those individuals who were treated with IVIG, there appear to be fewer long- term heart complications.

For those individuals who were treated with IVIG, there appear to be fewer long- term heart complications. Medications to prevent the formation of blood clots in the heart may be instituted.

Specific therapy for treatable infections such as antibiotics may be provided; however, this rarely alters the course of the myocarditis.

Most children diagnosed with myocarditis are admitted to an intensive care unit for initial management.
It is important for the child to be placed on bed rest. There is evidence to suggest that strenuous activity may be harmful to the heart during the recovery period.

Depending upon the severity of the myocarditis, this may mean that physical activity is restricted for weeks to months. The child’s physical activity should be slowly increased over time.

The good news is that approximately two-thirds of the children, with appropriate medical management, will have a complete recovery.

If untreated, only 10 to 20 percent will have a spontaneous recovery and 80 percent will develop chronic heart disease. For most children, recovery usually occurs within 2-3 months from the onset of the illness.
Of the remaining one-third who are treated, 10 to 20 percent will improve but have chronic residual heart problems called “dilated cardiomyopathy.”

This is a condition where the heart has become enlarged and may have diminished function or residual heart failure. In this case, the child will require long term follow-up by a cardiologist because sometimes these children will develop progressive heart failure and need a heart transplant.

Other children may experience problems with the electrical conduction system within the heart and are at risk for rhythm problems. These can often be treated with medication.

The population that is at the highest risk for serious disease is newborns. The mortality rate is as high as 50 to 70 percent. When this is the case, there is a high risk of sudden death and some children may need a heart transplant urgently. This severity of disease is rare and therefore represents a very small number of children.

Victoria & Tasmania