Pulmonary atresia

Pulmonary Atresia with Intact Ventricular Septum

This defect is associated with complete obstruction of the Pulmonary Artery. However, as there is no associated Ventricular Septal Defect, blood is diverted from the right atrium to the left atrium via the ‘Foramen Ovale’ or a defect in the Atrial Septum (ASD). The right ventricle (RV) is usually small (Hypoplastic), though its wall may be thickened (Hypertrophied).

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Survival depends on the ductus remaining open in the early days of life (in order for blood to reach the lungs). Affected infants usually become blue soon after birth (as the ductus closes). Early surgery often involves opening the Pulmonary Valve and a ‘Shunt’ operation.  Corrective surgery is carried out later in childhood if the right ventricle is adequate. In some infants the RV is too small to allow complete repair and other forms of surgery may be required (e.g. Fontan operation)

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Hypoplastic Left Heart Syndrome

Hypoplastic Left Heart Syndrome (HLHS) is a condition in which the left side of the heart is underdeveloped.  Usually, the left ventricle, the left atrium, the mitral valve and the aorta are affected.  It is called a syndrome because it can encompass several different variations and varying degrees of development of these parts of the heart.

To understand HLHS, it is helpful to understand how a normal baby’s heart works.  The heart is comprised of four chambers: the upper chambers are called the left and right atria, and the lower chambers are called the left and right ventricles.

Very simply, in a healthy heart blood flows from the right atrium to the right ventricle where it is then pumped through the pulmonary artery to the lungs to be oxygenated.  Blood then flows back to the heart via the left atrium to the left ventricle, which pumps this oxygenated blood through the aorta out to the body.  This is how the body’s organs and tissue receive oxygen, which is vital.  When a baby has HLHS, the left side of the heart is underdeveloped so it cannot sufficiently pump the oxygenated blood out to the body.

Babies with HLHS do not have problems while in the womb – it is only after birth that the heart fails to work properly.  This is because all babies receive oxygen from the placenta while in the womb, so blood does not need to go to the lungs.  In addition, there is an opening between the pulmonary artery and the aorta, called the patent ductus arteriosus (PDA) that is present in all babies.  It allows the blood to go from the right ventricle out to the body, bypassing the left side of the heart.

The PDA usually closes a few days after birth, separating the left and right sides of the heart.  It is at this time that babies with undetected HLHS will exhibit problems as they experience a lack of blood flow to the body.  They may look blue, have trouble eating, and breathe rapidly.  If left untreated, this heart defect is fatal – usually within the first few days or weeks of life.

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