Hypoplastic Right Heart Syndrome

Definition

Hypoplastic right heart syndrome (HRHS) is the underdevelopment of the right side of the heart, particularly the ventricle. The ventricle is the muscular lower chamber of the heart.

Normally, the right ventricle pushes blood out of the heart and to the lungs where it can pick up oxygen. The blood with oxygen then moves to the left side of the heart which pumps the blood to the rest of the body.

HRHS makes it difficult or impossible to pass blood to the lungs. This decreases the amount of oxygen for the rest of the body. The underdeveloped muscle of the right ventricle can also be easily exhausted by normal heart functions.

Other structures of the right side of the heart may also be underdeveloped and decrease the flow of blood from the heart to the lungs. Structures that may be affected include:

• Tricuspid valve—Tissue that manages blood flow between the upper and lower chambers of the heart. If the valve does not exist or does not open it is called tricuspid atresia.
• Pulmonary valve—Tissue that manages flow of blood out of the heart to the pulmonary artery. If the valve does not exist or does not open it is called pulmonary atresia.
• Pulmonary artery—Blood vessel that carries the blood from the right ventricle to the lungs. The artery may be underdeveloped as well.
• Atrium—The top chamber of the heart.

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Causes

Problems with heart development occur before birth, often early in the pregnancy. It is unclear why the heart does not develop as expected. It may be a combination of genetic and environmental factors.

Risk Factors

A family history of similar heart defects is only potential risk factor.

Symptoms

A fetus does not need to rely on their lungs for oxygen so blood flow to the lungs is not important. The mother’s blood will provide all the oxygen they need. However, after birth the lungs provide oxygen and poor blood flow to the lungs will begin to cause:

• Blue tint to skins and lips
• Rapid breathing
• Feeding problems

Certain structures of the heart and related blood vessels are present before birth. These structures decrease blood flow to the lungs. After birth, the baby will need to supply its own oxygen through the lungs. These structures gradually close over the first few weeks of life to increase the flow of blood to the lungs. Structures include:

• Ductus arteriosus—a connection between the pulmonary artery and the aorta (a large blood vessel that carries blood with oxygen away from the heart to the body)
• Foramen ovale—opening between the right and left side of the heart

These structures can decrease the efficiency of a normal heart. However, these structures actually help compensate for shortcomings created by HRHS. Symptoms of HRHS may worsen over the first few weeks of life as these structures close.

Diagnosis

HRHS may be diagnosed before birth with prenatal ultrasound. The doctor may notice a size difference between the right and left side of the heart. A fetal echocardiogram may be done to confirm the diagnosis. An echocardiogram takes images of the heart in motion and can show structural and functional abnormalities.

After birth, HRHS may be suspected based on the baby’s symptoms. The doctor may also hear a heart murmur, which is the sound of turbulent blood flow. Your baby may be referred to a pediatric cardiologist. An echocardiogram may be used to examine the heart.

Treatment

Babies with HRHS will need treatment shortly after birth. If HRHS was detected before birth, a team of specialists will help monitor and treat the baby immediately after birth. The course of later treatment will depend on the baby’s overall health and parental choice.

Medication may be given shortly after birth to help keep the ductus arteriosus open. This and other openings will provide some relief until surgery can be done.

Blalock-Taussig Shunt

This procedure is often done within the first few days of life. It will help to increase the flow of blood to the lungs.

A tube, called a shunt, is attached from the pulmonary artery to the aorta (major blood vessel that carries blood from the left side of the heart to the body). Some blood can then move from the aorta to the pulmonary artery which carries the blood to the lungs. This increases the amount of blood that passes the lungs. The oxygen available for the body will increase as a result.

The shunt is a temporary measure to improve oxygen supply to the body and relieve symptoms such as blue tint to skin.

Glenn and Fontan Procedures

As the child ages, the shunt will not be able to provide enough blood flow to the lungs. Glenn and Fontan procedures may be done once the child is around 3 months of age. The procedures are often split into two separate surgeries.

Blood returns from the body to the right side of the heart through major blood vessels called inferior and superior vena cava. The Glenn shunt creates a connection between the superior vena cava and the pulmonary arteries. This allows blood returning to the heart from the upper part of the body to bypass the right side of the heart and go directly to the lungs.

The Fontan or Fontan completion is done when the child is 3-5 years of age. It creates a connection between the inferior vena cava and superior vena cava. This means all the blood returning from the body will go directly to the lungs and bypass the right side of the heart.

Heart Transplant

The shunts will help improve the amount of oxygen in the blood and reduce symptoms. However, surgery cannot repair the damaged right ventricle. Eventually, the left side of the heart will have difficulty keeping up with the extra workload. The heart will eventually need to be replaced with a heart transplant.

A heart transplant may be done early in childhood instead of the Glenn and Fontan procedures or late in adulthood when the heart is no longer able to properly function.

Prevention

There are no current guidelines to prevent HRHS because the cause is unknown. If you are pregnant, proper prenatal care may help decrease the risk of having a baby with a heart defect.