What is hypoplastic left heart syndrome (HLHS)?

What is hypoplastic left heart syndrome (HLHS)?


(gentle music) – Hypoplastic left
heart syndrome is a type of congenital heart
disease where the left side of the heart is underdeveloped. So in the normal heart, the
blood that’s been to the body comes back through two
veins to the right atrium, or right upper chamber,
goes through a valve to the right ventricle,
which pumps out to the lungs. Blood picks up oxygen in the lungs and comes back to the left
upper chamber, the left atrium, goes through the mitral
valve to the left ventricle, which pumps the blood
across the aortic valve out to the aorta, which
supplies the entire body. In hypoplastic left heart syndrome, the left-sided heart
structures are underdeveloped. So the mitral valve, left
ventricle and aortic valve, as well as the aorta, are all small. And because of that,
there’s not enough blood that can go through the
left side of the heart to meet the baby’s demands. Before the baby’s born,
the fetus takes advantage of two normal structures in
the heart, in the fetal heart. One is a hole between
the two upper chambers, called the atrial septal defect. And the second is called
the ductus arteriosus. It’s a blood vessel that allows
blood to bypass the lungs, while the mom is providing
oxygen for the fetus. Because of that, blood
that has gone to the lungs and come back to the left atrium, does not have to go through
the left side of the heart. Instead, it can go across
the atrial septal defect, into the right ventricle,
be pumped out the artery that usually goes to the
lungs, the pulmonary artery, and across the ductus
arteriosus and supply the body. And for that reason, in many cases, babies with hypoplastic
left heart syndrome are born without this diagnosis
being made prenatally. So after a baby is born, the ductus arteriosus usually closes. If that happens in a baby with hypoplastic left heart syndrome, there’s no way for an
adequate amount of blood to get out to the body.

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