Hypoplastic left heart syndrome (also referred to as HLHS), is a congenital heart condition in which the left heart structures are excessively small or undeveloped. In the normal heart, the left side of the heart takes blood returning from the lungs and pumps it to the rest of the body. In the hypoplastic left heart this does not occur. The normal size right heart must pump blood for the lungs as well as the body. In HLHS, blood from the right heart supplies the aorta(the main artery to the body) through a structure called the patent ductus arteriosus. Normally the patent ductus arteriosus closes shortly after birth. In HLHS, the blood in the right heart gets oxygen from a hole between the right and left atria called an atrial septal defect.

The baby may appear normal at birth, but within a day or two after birth the ductus closes and the infant becomes very ill. Babies with hypoplastic left heart sydrome will become extremely pale, breathing is fast and shallow and they have difficulty feeding. Hypoplastic left heart sydrome is usually fatal within the first days of life unless it's treated.

Hypoplastic left heart sydrome is not correctable, but babies can be treated with a series of complex operations, or possibly heart transplantation. The ductus is kept open by intravenous medication(Alprostadil=prostaglandin E1), until surgery is performed, . These operations are extremely complex and are slightly different for each patient.

If surgery is to be performed, it is done in several stages. The first stage, is known as the Norwood procedure. The Norwood procedure makes the right ventricle pump blood to both the lungs as well as to the body. It is performed soon after birth. The final stages have many names, including Fontan procedure, bi-directional Glenn shunt, and the lateral tunnel. These surgical procedures connect the veins returning deoxygenated (blue blood) to the heart move it to the pulmonary arterywhere it goes to the lungs to pick up more oxygen. The goal of the series of procedures is to have the right ventricle to pumping only oxygenated (red) blood to the body and to minimize mixing of the red (oxygenated) and blue (deoxygenated) blood. Most infants require several intermediate surgeries to reach this final goal.

Heart transplantation to treat hypoplastic left heart sydrome is another option. While it does provide the infant with a heart which is normal in structure, the child will require somewhat toxic anti rejection medications to prevent organ rejection for the remainder of their life. Numerous, transplant associated diseases may develop.

Patients with hypoplastic left heart syndrome must have lifelong cardiologist care for repeated checks of how their heart is functioning. All the children will require heart medications. Infection of the heart's valves (endocarditis) is a major concern and patients need antibiotics prior to dental work and other surgeries to help avoid getting endocarditis.

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