PATENT DUCTUS ARTERIOSUS (PDA)

 

What is Patent Ductus Arteriosus (PDA)?
Normal anatomy of the heart: The normal heart consists of 4 chambers - the right & left atrium (These are the chambers that receive the blood - the right atrium receives impure blood from the rest of the body and left atrium receives pure blood from the lungs.) and the right & left ventricles (These are the chambers that pump the blood from the heart – right ventricle pumps the impure blood to the lungs via the pulmonary artery and left ventricle pumps the pure blood to the rest of the body via another artery called as the aorta).

To understand what is PDA, one has to first understand the circulatory system in the baby while in the mother's womb. While the baby is in the uterus, it does not breathe. Hence, the lungs do not require the blood from the right ventricle. Thus, nature provides a "bypass"- a small blood vessel called DUCTUS ARTERIOSUS that connects the pulmonary artery directly to the aorta. Thus blood that enters the pulmonary artery bypasses the lungs and goes to the aorta to supply blood to other parts of the body.

At birth, when the child taken the first breath, the lungs begin to function. Thus, now the blood from the right ventricle goes to the lungs to get oxygenated and the bypass or DUCTUS ARTERIOSUS closes. When the ductus does not close and remains open, then a condition called as Patent Ductus Arteriosus or PDA develops.

What happens if a child has PDA?
If the ductus arteriosus remains open, shunting of blood takes place as in the fetal life but now in the opposite direction. Soon after birth, the pressure in aorta rises. So blood flows from the aorta (high pressure area) to the pulmonary artery (low pressure area). As a result, more blood flows into the lung than it normally does. This extra blood flow to the lungs can cause frequent chest infections. The blood vessels in the lung due to exposure to constant high lung blood flow become hard and thick leading to pulmonary hypertension (high pulmonary blood pressure) and subsequent heart failure.
If the PDA is left untreated, due to heart failure the child will not grow normally and is not able to feed adequately. If the pulmonary hypertension becomes severe it will lead to irreversible lung and heart damage - a condition called as EISENMENGER SYNDROME.

How is PDA diagnosed?
On examination, a child with PDA will have a soft thrill on the chest like a cat purring due to forceful blood flow across PDA. Echocardiography is diagnostic.

Should PDA always be closed?
When PDA is the single heart defect it needs to be closed.
However in presence of other heart disease where PDA is the only route of blood flow into the lungs or the rest of the body (DUCT DEPENDENT CIRCULATION) PDA should be kept patent till repair of the associated condition is performed. A medicine called prostaglandin is then used to keep the ductus open.

Last created on 6-05-2003
Last updated on 18-11-2006