Pediatric Heart Disease Hypoplastic Syndrome

Hypoplastic left heart syndrome is a rare but extremely serious heart defect that is characterized by an underdeveloped left side of the heart at birth. This immaturity severely restricts blood flow to the body. Left untreated, hypoplastic left heart syndrome is invariably fatal, often within days of birth.

Hypoplastic Left Heart Syndrome Overview

The left side of the heart includes the:

  • aorta
  • aortic valve
  • left atrium
  • left ventricle
  • mitral valve.

In a healthy heart, oxygen-rich blood from the lungs fills the left atrium and flows through the mitral valve into the left ventricle. Blood then passes from the left ventricle through the aortic valve into the aorta, the major artery that transports blood to the rest of the body.

In cases of hypoplastic left heart syndrome, the mitral valve, aortic valve, left ventricle and aorta are seriously underdeveloped: The aortic and mitral valves are extremely small or even completely closed, while the left ventricle and first portion of the aorta is also significantly smaller than normal.

Although the right side of the heart pumps normally to transport blood to the lungs, the underdeveloped side of the heart is incapable of oxygenating blood for the rest of the body.

The Ductus Arteriosus and Foramen Ovale

Despite the severe heart defects associated with hypoplastic left heart syndrome, symptoms often develop a few days after birth. This is due to two characteristics of the newborn heart:

  1. The foramen ovale is a hole in the heart wall that separates the two upper chambers of the heart. Present in all newborns, the foramen ovale closes in the weeks following birth in healthy infants.
  2. Also present in all newborns is a fetal blood vessel, the ductus arteriosus, which connects the aorta to the pulmonary artery. The ductus arteriosus usually closes within two or three days of birth.

If a child has hypoplastic left heart syndrome, oxygen-rich blood is forced through the foramen ovale from the left atrium into the right atrium, where it mixes with unoxygenated blood bound for the lungs. If an atrial septal defect is present (an abnormal hole between the two atria), the same mixing of the blood occurs.

From the right atria, the mix of unoxygenated and oxygenated blood passes through the right ventricle into the pulmonary artery. If the ductus arteriosus is open, some of this blood is redirected through the ductus arteriosus, landing in the aorta where it is released back into the body.

Once the ductus arteriosus closes, this alternate blood route to the aorta is cut off, causing the infant to quickly go into shock.

Hypoplastic Left Heart Syndrome Symptoms

Once the ductus arteriosus closes, symptoms of hypoplastic left heart syndrome become apparent quickly. While symptoms may appear within hours of birth, they can also take several days to develop.

Hypoplastic left heart syndrome symptoms include:

  • ashen skin
  • cold hands and feet
  • cyanosis (blue skin)
  • enlarged liver
  • faint pulse
  • lethargy or extreme tiredness
  • poor feeding ability
  • pounding heartbeat
  • rapid breathing
  • shortness of breath.

Hypoplastic left heart syndrome symptoms can rapidly cause the body to go into shock. Seizures, liver failure, kidney failure and progressively worsening cardiac symptoms develop, potentially causing death if the patient doesn’t receive emergency treatment.

Diagnosing Hypoplastic Left Heart Syndrome

Occasionally, doctors can diagnose hypoplastic left heart syndrome before birth. Both fetal echocardiograms and routine fetal ultrasounds can detect the major defects caused by this heart condition. An echocardiogram, a test that uses sound waves to construct an image of the heart, effectively perceives the key features of hypoplastic left heart syndrome. In addition, echocardiograms can determine if any co-existing heart defects are present.

If hypoplastic left heart syndrome is detected or suspected before birth, the medical team can prepare for immediate intervention at birth, reducing the risk of serious shock. Even if hypoplastic left heart syndrome isn’t diagnosed before birth, echocardiograms are still effective diagnostic tools for detecting this condition in infants.

Hypoplastic Left Heart Syndrome Treatment

Because hypoplastic left heart syndrome is inevitably fatal without treatment, prompt surgical intervention is required to save the child’s life. However, before surgery is possible, blood flow to the body must be stabilized. Intravenous prostaglandin is administered to keep the ductus arteriosus open, ensuring some blood flow to the body. During this time, the infant is closely monitored, as the child’s condition can change rapidly.

The two possible surgical treatments for hypoplastic left heart syndrome are cardiac transplantation and the Norwood procedure. Both are complicated operations with variable results.

Cardiac Transplantation

Cardiac transplantation, or a heart transplant, replaces the newborn’s defective heart with a normal donor heart. While cardiac transplantation prevents further hypoplastic left heart syndrome complications, this procedure has some serious limitations.

The most obvious complication is the difficulty of finding a suitable donor heart for such a small patient. Because newborn donor hearts are rare, chances that a suitable heart will be available in time are slim.

A child who receives a cardiac transplantation will require lifelong medication to prevent organ rejection. There is also a high likelihood that another heart transplant will be required in the future: The average life of a transplanted heart is 15 years.

The Norwood Procedure

The Norwood procedure is a complex series of operations performed over the first three years of a child’s life. The Norwood procedure, sometimes referred to as “staged reconstruction,” is divided into three stages.

  • Stage I (Blalock-Taussig Shunt): Within the first days after birth, the right ventricle is surgically attached to the aorta, and a large chest artery is attached to the pulmonary arteries. This first step, known as the Blalock-Taussig shunt, ensures that enough blood reaches the lungs.
  • Stage II (the Glenn or Hemi-Fontan Procedure): Performed three to six months after birth, stage II attaches the superior vena cava to the pulmonary arteries. At this point the Blalock-Taussig shunt is removed. This step helps restore the functioning of the superior vena cava so it can effectively remove oxygen-poor blood from the arms and head.
  • Stage III (the Fontan Procedure): At 2 or 3 years of age, the inferior vena cava is attached to the pulmonary arteries. This final stage restores the inferior vena cava, allowing it to remove unoxygenated blood from the lower body.

Norwood Procedure Prognosis

Surgical reconstruction of hypoplastic left heart syndrome is one of the most complex heart operations. Survival rates for Stage I of the Norwood procedure range between 70 percent and 75 percent. After Stage I, survival rates for Stage II and III hypoplastic left heart syndrome reconstruction average over 90 percent.

Children who successfully undergo hypoplastic left heart syndrome surgery will require continual check ups by pediatric cardiologists. Most children also require medication to control heart function.

In some cases, the right ventricle loses the ability to function after hypoplastic left heart syndrome surgery. If this happens, cardiac transplantation is required. Older children are better candidates for heart transplants because they can withstand the surgery and recovery better than younger patients. Additionally, the older the child is, the more donor hearts there are available.

Resources

American Heart Association (n.d.). Hypoplastic left heart syndrome. Retrieved September 17, 2007, from the AHA Web site: www.americanheart.org/presenter.jhtml?identifier=1353.

Cincinnati Children’s Hospital Medical Center (n.d.). Hypoplastic left heart syndrome / norwood procedure. Retrieved September 17, 2007, from the Cincinnati Children’s Hospital Medical Center Web site: www.cincinnatichildrens.org/health/heart-encyclopedia/anomalies/hlhs.htm.

Texas Heart Institute Heart Information Center (n.d.). Hypoplastic left heart syndrome. Retrieved September 17, 2007, from the Texas Heart Institute Web site: www.texasheartinstitute.org/lefthear.html.