Health Library

Myocarditis in Children

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

There are many causes of myocarditis including:

• Infections
• Medications
• Chemicals
• Radiation
• Certain diseases that cause inflammation in 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 myocarditis. The severity of disease depends on many factors like age, sex, and the genetic makeup of the immune system.

Treatment for myocarditis is changing as the disease is better understood. Many children recover completely, but some may develop serious heart failure and need chronic care by a cardiologist (heart doctor).

Causes of Myocarditis

In children, viral infections are the most common cause for myocarditis. Certain drugs and autoimmune disorders may also cause myocarditis. The most common viruses involved are:

• Parvovirus
• Influenza virus
• Adenovirus and coxsackie virus
• 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, or fungus or parasites can cause myocarditis. If a child has one of these infections, it is rare for them to develop myocarditis.

When myocarditis is caused by an infection, the germ enters the body and travels through the bloodstream to the heart. It grows and reproduces within the heart. It may cause some cell damage as it spreads.

Normally, the immune system will go to the infection to get rid of the germ. In some children, this response is over-aggressive so that not only the germ is destroyed, but the heart cells also may be damaged.

Most of the damage to the heart is caused by the body’s immune reaction to the germ, and not by the germ 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. Often, the more heart muscle that is damaged, the more severe the symptoms. 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 reason for getting an abnormal immune response under these conditions is not as well understood.

Myocarditis and the Heart

The inflammatory process begins when the body's immune cells (the cells that fight infection) penetrate the heart tissue. These immune cells become activated and make 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 heart may have trouble pumping blood.

When this happens, important organs and tissues in the body do not get the oxygen and nutrients they need and cannot get rid of waste products. This is often called congestive heart failure.

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

Signs and Symptoms of Myocarditis

The symptoms of myocarditis may be subtle, making the diagnosis difficult, or the child may have clear symptoms of heart failure. Clinical experience has shown that 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.

A child may get an infection during pregnancy (rubella, for example) when it travels from mother to baby. Babies are often breathing fast and have trouble feeding. They can be very fussy and difficult to console, or very tired and sleep more than normal.

Blood will not travel through the body as well. Infants may have cool, pale hands and feet. The kidneys may also not work properly and there will be less urine (pee) made.

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

Older children may have fewer symptoms. They may complain of a flu-like illness with fatigue, malaise and fever.

They may not be able to tolerate exercise or may complain of chest pain or palpitations (skipped or extra heartbeats). They may develop a cough. Some children who experience congestive heart failure may also have swelling in the face, feet or legs. There may be belly pain and nausea due to swelling of the liver.

The kidneys may be injured because of poor blood flow. The signs and symptoms of myocarditis are subtle early in the illness, so it is not unusual for myocarditis to go unrecognized.

Myocarditis is sometimes diagnosed later 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.

Diagnosis of Myocarditis

There is no specific test for myocarditis. It is mostly a clinical diagnosis where the doctor must rely on the history given by the family and a physical examination of the child.

There are many tests that can be done to help with the 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 bigger, and fluid may enter the lungs.
• An electrocardiogram can give helpful clues if the diagnosis is suspected. But, the findings may be non-specific. There may also be abnormal heartbeats that can occur with myocarditis.
• An echocardiogram or heart ultrasound can be used to look at heart size and overall function, which helps confirm the clinical diagnosis as well as rule out blood clots inside the heart. Blood clots can form when the blood does not move easily through the heart.
• Additional blood tests may help to see how well the liver and kidneys are working. A blood count and specific tests for infections will be done.
• The most precise way to make the diagnosis of myocarditis is by doing a heart biopsy 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 taken and sent to the pathologist to look at under the microscope.

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

Treatment of Myocarditis

The inflammation in the heart muscle will usually go away on its own. There is no cure for myocarditis. Usually, the goal 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.

Medicines to help the heart work better, either by controlling 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 medicines may be used, depending upon the severity of the myocarditis. A diuretic can also help clear extra fluid from the lungs or other body tissues.

There are medicines currently being researched that help decrease the abnormal immune response.

One drug often used is called intravenous immunoglobulin (IVIG), which consists of purified antibodies, the substances that the body's immune cells produce to fight infection. Although it is not understood exactly how this works, it has been shown to slow down the inflammatory process. Patients treated with IVIG appear to have fewer long-term heart complications.

Medicines to prevent the formation of blood clots in the heart may be given. These medicines are used since a clot may form when the heart does not pump well.

Medicines to get rid of the virus are not typically used because this rarely changes the course. Most of the damage from the infection occurs early. Antibiotics are not helpful because viruses cause most myocarditis. Treating autoimmune disorders, typically with steroids, is helpful when this is the cause of the muscle inflammation.

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 on 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.

Long-Term Outlook

About two-thirds of children, with the right medical management, will have a complete recovery.

If untreated, only 10% to 20% will recover on their own, and 80% will develop chronic heart disease. For most children, recovery usually happens within two to three months from the onset of the illness.

Of the remaining one-third who are treated, 10% to 20% 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 need long-term follow-up by a cardiologist. Sometimes these children will develop progressive heart failure and need a heart transplant.

Other children may be at risk for having heart rhythm problems. These can often be treated with medicine.

The population that is at the highest risk for serious disease is newborns. The mortality rate is as high as 50% to 70%. 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.