Patent Ductus Arteriosus – PDA

Patent Ductus Arteriosus - PDA

As you already know about the large blood vessels – the aorta and pulmonary artery – it’s easy to learn about the birth defect called Patent Ductus Arteriosus (or PDA).

What is a Patent Ductus Arteriosus?

As a child develops inside its mother’s womb, it is not able to “breathe”. So, even though the child’s lungs are well developed, they do not carry out their normal work.

The blood which flows through the right ventricle and pulmonary artery to the lungs has no function. It is “wasted” blood flow.

In an attempt to make use of this flow, nature provides man with a “shunt” or “bypass”. A small tube, or blood vessel, connects the pulmonary artery to the large artery called the aorta. This tube is the ductus arteriosus.

Through this tube, blood which enters the pulmonary artery, instead of going to the lungs, flows into the aorta. From the aorta, the blood reaches other parts of the body. It is now useful to these other parts, which get energy to do their work.

At birth, when the child draws its first breath, the lungs begin to work. Now, when blood flows into the lungs, it is mixed with oxygen and “purified”. At this time, the ductus arteriosus normally closes. At first, it closes by spasm or contraction of the muscle in its wall. Later, the tube becomes permanently blocked by a scar.

Sometimes, it does not close normally. It then remains open, and the condition is called Patent Ductus Arteriosus – or PDA.

What happens in a PDA ?

I have told you about the changes that happen in an Atrial Septal Defect (ASD) or Ventricular Septal Defect (VSD). A PDA is somewhat similar.

In a PDA too, more blood flows into the lungs than normal. The blood flow in the PDA is from the aorta to the pulmonary artery, and then to the lungs. This is in the opposite direction to flow that occurs before birth. The reason is that, soon after birth, the pressure in the aorta becomes very high. So blood, like any fluid, flows from a high pressure area (aorta) to a lower pressure area (pulmonary artery).

The extra blood in the lungs, like in ASD and VSD, causes frequent “chest colds”. It also increases the lung blood pressure, and over the years makes the blood vessels and thick – pulmonary hypertension.

When the PDA is large, and particularly in small children, the enormous blood flow may cause heart failure. The small ventricle is not able to pump out all the blood entering it, and “fails”. The child has fast shallow breathing, excessive sweating, inability to feed well, irritability, constant crying, and a failure to grow normally. Early repair may be needed in these cases.

An interesting fact about PDA is that, like in a VSD, when you place your palm over the patient’s chest, you feel a soft thrill, like a kitten purring! The reason for this is the forceful and turbulent blood flow across the PDA.

What happens if PDA is left untreated ?

The changes mentioned before become worse. Heart failure sets in. The child does not grow and develop normally. Due to the turbulent blood flow, there is an increased risk of infection inside the blood vessels – called Infective Endocarditis.

In late stages, the blood pressure in the lungs becomes very high – severe pulmonary hypertension – and at this time, even with surgery, there will be no improvement. The limit for “operability” has been crossed. The condition is called Eisenmenger Syndrome.

PDA as a part of other conditions

Sometimes a Ductus Arteriosus may remain patent (PDA) as a part of other heart diseases. In such a situation, the PDA may indeed be the only route of blood flow into the lungs or the rest of the body!

This is called a duct dependent circulation. The PDA then should remain open, until repair of the associated condition is performed. A medicine called Prostacyclin, a prostaglandin, is used to keep the ductus open in these patients.

When should a PDA be closed ?

When a PDA is the only heart defect, it needs to be closed. In duct dependent circulation, it is closed at the time of repair of the other heart defects.

In very small children with severe symptoms of heart failure, closure of the PDA is necessary immediately. It may be truly life-saving in these cases. If it does not produce serious problems, closure is not urgent. Still, it is better to close a PDA as early as possible, to avoid the risk of infection and pulmonary hypertension.

What are the methods to close a PDA ?

The earliest and most common method to close PDA is by operation. The first surgical closure of PDA was done in 1938 by Dr.Gross.

PDA closure is NOT an open heart operation. It is performed through an opening on the left side of the chest. The surgeon identifies the PDA and passes a tape or thread around it and ties it off. Some surgeons prefer to divide the PDA into two after placing a clamp on both ends, and sew them closed.

The advantage with the more difficult second method is the absence of late re-opening (or “re-canalization”) of the duct.

There are some non-surgical methods to close PDA as well.

Minimally Invasive PDA closure

The interventional cardiologists – or “catheter-pushers” – entered the scene next. Using a fine tube threaded into an artery in the groin, they were able to place “coils” made of metal inside the PDA. When blood comes into contact with these coils, it “clots” – that is, it becomes hard. This clot blocks the PDA. Over time, a scar forms and the PDA is firmly closed shut. Isn’t that smart ?

The surgeon, then, not to be outdone, came up with the idea of minimal intervention surgery. Using specially designed long instruments passed through small puncture holes in the chest, a metal clip is placed around the PDA after isolating it.

When the clip is applied, the PDA is blocked. If necessary, this procedure can be performed under anaesthesia at the bedside of a sick infant in the intensive care unit.

Another method, that is sometimes useful and can be tried before surgery, is using a medicine called Indomethacin. It acts by blocking the effects of prostaglandin, which is a natural substance that keeps the ductus arteriosus open. When prostaglandin is blocked, the ductus closes.

Why are there so many methods ? Which one is best ?

The very fact that there ARE many methods indicates that there is no “best” one. Each has its own advantages and drawbacks.

The choice for a particular patient must however be made by the treating physician after analyzing many factors like age, patient’s condition, availability and safety of the different methods, chance of failure and much more.

Minimally invasive closure can be used in very sick new-born children, when surgery may have a high risk. Surgery is useful when other conditions are also present which need operation.

What are the risks involved in closure ?

PDA closure is a safe procedure – whichever way it is done. When surgical closure is elected, there is a small risk of injury to a nerve that controls the “vocal cords” – the sound box. If this happens, hoarseness of the voice may result.

The risk of death from surgery is almost zero. Again, a small chance of recurrence – or re-opening – of the closed ductus arteriosus is present with all types of treatment. This is least when the PDA is divided into two.

When a “minimally invasive” approach is used, sometimes, it is not possible to clearly see or isolate the PDA. Then it may be necessary to convert to a regular operation to complete the procedure.

What about life after repair ?

The answer in one word is – normal. Late problems are unusual after PDA closure, and patients return to a normal and productive life.

After surgery, hospital stay is usually around 2 to 7 days but differs from one geographic location to another. With catheter-based and minimal invasion methods, “next day” discharge is routine. Older patients can return to work in a short time.

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