(See also Overview of Heart Defects.)
Hypoplastic is a medical term for underdeveloped. Hypoplastic left heart syndrome (HLHS) accounts for 2 to 4% of birth defects of the heart. Because the left side of the heart is underdeveloped, oxygenated blood coming into the left heart from the lungs is diverted into the right side of the heart through the atrial septal defect, where it mixes with deoxygenated blood returning to the heart from the body. This relatively deoxygenated blood exits the right heart to the lungs and through the ductus arteriosus to the body. The ductus arteriosus is a blood vessel connecting the two great arteries leaving the heart, the pulmonary artery and the aorta (see Normal Fetal Circulation). In the womb and during the first few days of life, the ductus is open. Blood flow to the body is maintained only because the ductus arteriosus remains open. Once the ductus closes, as it normally does after birth, very little blood flows to the body. If the defect is not repaired immediately, the infant will die.
Symptoms of hypoplastic left heart syndrome appear when the ductus arteriosus begins to close during the first 24 to 48 hours of life. Subsequently, signs of heart failure, including rapid breathing, shortness of breath, weak pulse, pale or bluish skin, cool body temperature, lethargy, and a decreased number of wet diapers, rapidly develop. When blood flow to the body is reduced, the heart, brain and other vital organs do not receive sufficient blood flow. Unless blood flow is re-established, the infant will die.
Many infants are diagnosed before birth when hypoplastic left heart syndrome is detected on a prenatal ultrasound examination done on the mother or on echocardiography (ultrasonography of the heart) done on the fetus.
Diagnosis is suspected when doctors notice symptoms during an examination of the infant. Diagnosis is confirmed by emergency echocardiography.
Because most affected children with hypoplastic left heart syndrome are identified before birth, doctors begin giving a drug to keep the ductus open immediately after birth.
All affected infants are treated in a neonatal intensive care unit or pediatric cardiac intensive care unit. Prostaglandin is given by vein to prevent closure of the ductus arteriosus or to reopen a narrowed ductus. Newborns, particularly those that are critically ill, usually require assistance with breathing (mechanical ventilation). Severely ill newborns may require drugs to improve heart function.
Survival ultimately requires a series of surgical procedures that enable the right ventricle to take over the work of the underdeveloped left ventricle.
Surgery is done is several stages:
In some infants, heart transplantation is considered the procedure of choice for hypoplastic left heart syndrome. Infants must be given an infusion of a prostaglandin to keep the ductus arteriosus open until a donor heart is available. Because availability of donor hearts is very limited, about 20% of infants die while awaiting transplant. The 5-year survival rates after transplantation and after multistage surgery are similar.
After heart transplantation, drugs to suppress the activity of the immune system (immunosuppressants) are required for the rest of the child's life. These drugs make people more susceptible to infections and increase the risk of developing certain tumors. Immunosuppressants may also damage the coronary arteries of the transplanted heart. The only known treatment for coronary artery damage is retransplantation.
Some children need to take antibiotics before visits to the dentist and before certain surgeries (such as on the respiratory tract). These antibiotics are used to prevent serious heart infections called endocarditis.
Most children will take aspirin or a blood thinner such as warfarin or enoxaparin to help prevent clots from forming in the heart. Many affected children will need to take one or more other drugs to help their hearts continue to function optimally.