Hypoplastic left heart syndrome is the result of underdevelopment of the left heart structures and includes a tiny, or hypoplastic, left ventricle, complete closure or severe narrowing of the aortic and mitral valves, an abnormally small aorta, a patent foramen ovale and a large patent ductus arteriosus, or PDA. The severe underdevelopment of the left heart structures prevents oxygen-rich blood from flowing to the body normally. Thus, the right heart takes over and pumps blood to the body through the PDA. A patent foramen ovale is a hole between the upper chambers of the heart, or the atria, that allows oxygen-rich blood from the lungs to bypass the left heart by flowing from the left atrium to the right atrium. In this way, oxygen-rich blood reaches the right heart, PDA, and the aorta to supply the body with oxygen.
This condition can be improved by a series of three operations. The first operation, which is called the Norwood procedure, is done shortly after birth. After placing the baby on the heart-lung machine, the aorta is opened and the PDA is tied closed. The pulmonary artery is divided into two parts. The part of the pulmonary artery that is close to the heart is sewn to the small aorta with a patch to make it bigger. This allows blood from the right ventricle to flow easily into the aorta to pump blood to the body. In order to allow blood to flow to the lungs a small tube, known as a modified Blalock-Taussig shunt, is placed between a branch of the aorta and the pulmonary arteries. Sometimes, instead of a Blalock-Taussig shunt, a Sano conduit is placed between the right ventricle and the pulmonary arteries.
At the second operation, known as the bidirectional Glenn shunt or the hemi-Fontan, the shunt or conduit is closed off and the large vein draining the head and arm, known as the superior vena cava, is connected directly to the pulmonary arteries. At the third operation, or Fontan, the large vein draining the lower part of the body, known as the inferior vena cava, is connected to the pulmonary arteries. At the end of the three operations, the oxygen-poor blood from the veins flows directly into the lungs and the oxygen-rich blood from the lungs flows into the left atrium to the right ventricle and is pumped to the body.
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