Patent Ductus Arteriosus
Dateline: 08/17/97
This week, I'm taking a diversion from coronary artery disease to discuss something one reader
requested me to write about - the birth defect called Patent Ductus Arteriosus (PDA).
What is a PATENT DUCTUS ARTERIOSUS ?
As the child develops inside mother's body before birth, it cannot "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, then, has no function. It is a waste of
blood flow.
In an attempt to make use of this blood 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 ?
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 higher pressure area
(aorta) to a lower pressure area (pulmonary artery).
The extra blood in the lungs causes frequent "chest colds". It also increases the lung blood pressure,
and causes the blood vessels to become hard and thick - Pulmonary Hypertension. When the PDA
is large, and particularly in small children, the enormous blood flow may cause Heart Failure. Early
repair may be needed in these cases.
What happens if PDA is left untreated ?
The changes I have mentioned earlier 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 be kept open, until repair
of the associated condition is performed. A medicine called Prostaglandin is used to keep the
ductus open.
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 such a
situation. 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 most common method to close PDA is by 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
then sew the edges closed. The advantage with the more difficult second method is the extremely
low risk of late opening up (or "re-canalization") of the duct again.
Using catheters, nowadays, interventional cardiologists can place metal "coils" across the PDA.
When blood contacts these coils, it clots (becomes hardened) and blocks the PDA. Over time a
scar forms and permanently seals off the duct.
The surgeon, then, not to be outdone, came up with the idea of minimal intervention surgery. Using specially designed instruments passed through small puncture holes in the chest, a metal clip is applied around the PDA after isolating it. If necessary, this procedure can be performed under anesthesia 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 the best ?
Each method 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 many more things. 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 anyway need operation.
What are the risks involved in closure ?
PDA closure is a safe procedure - whichever way it is done. 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. 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.
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