Hypoplasia is defined as underdevelopment of a tissue or organ, usually due to a deficiency in the number of cells. Hypoplastic left heart syndrome is the underdevelopment of the left side of the heart, including the left atrium and ventricle, the mitral valve, the aortic valve, and the aorta. In some cases an associated ASD allows blood returning from the lungs to flow through the opening in the septum from the left to the right atrium. The mixed blood enters the right ventricle and is then pumped into the pulmonary artery. The blood reaches the aorta through a patent ductus arteriosus, which is kept open by intravenous medication. This heart defect is fatal within the first days or months of life without treatment. Options for treatment include a series of three operations collectively known as the Norwood Procedure or heart transplantation.
The goal of the Norwood Procedure is to direct deoxygenated blood directly to the lungs and utilize the functional right heart to pump oxygenated blood to the body. The first stage, performed in the first week of life, is known as the Stage I Norwood Procedure. The connection between the right ventricle and the branch pulmonary arteries is broken and the main pulmonary artery and the small aorta are connected and augmented to create a new, larger aorta. Next, a small tube (shunt) is placed between the aorta and the right branch pulmonary artery to allow for blood flow to the lungs. The second procedure is performed at approximately six months of age. This involves connecting the superior vena cava to the right pulmonary branch artery. This connection allows the deoxygenated blood of the upper half of the body to flow directly to the lungs. The shunt placed during the first stage operation is also ligated at this time. The third and final stage is performed at approximately 12 months of age. During this procedure, the deoxygenated blood of the lower half of the heart is directed to the lungs. This is done by channeling the blood of the inferior vena cava through the right atrium to the right branch pulmonary artery.
View an animated heart with Hypoplastic Left Heart Syndrome