What is a PDA ?
PDA stands for a patent ductus arteriosus. This is a structure normally present in all fetuses. It connects the 2 great tubes/arteries coming out of the heart.
What is the role of a PDA in a fetus ?
The PDA allows blood to flow from the pulmonary artery into the main artery the aorta. The reason for this is the blood does not need to go into the lungs because the lungs are non-functional (baby is not breathing when inside the mother).
What happens to the PDA in normal newborn babies ?
Each one of us was born with a PDA. It closed some time after we were born. It usually closes in the first few days of life to first few weeks of life. The stimulus for closure is oxygen levels in blood. This level is higher after birth and stimulates the PDA to close.
What is the problem in PDA closure in premature babies ?
The premature babies are born with a PDA just like any other baby. But, their PDA has smaller amount of muscle only since it did not get enough time in utero. So, when exposed to higher amount of oxygen after birth, the PDA may still not close. This results in a patent ductus arteriosus. This affects the premature lungs of a baby more than that of a full term baby. While a full term baby may be able to tolerate a PDA for several months before requiring closure, a premature baby may need to have it closed much sooner.
How is a PDA stimulated to close in a newborn baby ?
PDA in a newborn baby, who is premature, is stimulated to close by giving certain medicines which block the effect of natural chemicals which keep it open. This is easily accomplished by giving Indomethacin. This is a medicine usually used for joint pains and other problems which acts by blocking the effect of normally existing Prostaglandins. The prostaglandins normally are responsible for keeping the duct open. Once blocked, the duct tends to close.
What if the duct does not close with indomethacin ?
If it does not close with Indomethacin, then surgery should be kept in mind. Sometimes a second dose of Indomethacin or a longer course may be required.
How easy or difficult is the PDA surgery ?
The surgery for PDA depends on the weight of the patient. Some of our patients have had surgery at weight as less as 800-900 grams. It also depends on how early the surgery is being done. If the team has waited too long the PDA would steal blood from the brain and from the lower half of body and result in brain issues, gut blood supply being low and the kidneys being hurt. In addition, the volume overload of the lungs would increase the lung pressure which would make the surgery (anesthesia) or the recovery from the surgery more prolonged.
Which PDAs can be closed in the cath lab ?
All PDAs in children weighing more than 3-4 Kg can be closed in the cath lab.
How are PDAs closed in the cath lab ?
PDAs are closed by entering the groin artery and vein. An angiogram is performed in the aorta and the PDA visualized. The PDA size is measured then. Using this information, the right device is selected.
How is the device implanted?
The PDA is crossed using a wire from the venous side (from pulmonary artery). Once the wire is secured, a sheath is taken over the wire. This sheath will carry the device.
The folded device is loaded into the back end of the sheath attached to a delivery cable. The cable is pushed in; the device gets pushed at the front end. Finally, the sheath is pulled back to uncover the device at the right place and device takes its shape. Part of the device is in the aortic ampulla (part of aorta which can accommodate the device) and part is in the pulmonary end.
How does the device stay in place ?
Device is designed for PDAs were the aortic pressure is higher than the pulmonary (usually difference in normal people between pulmonary artery and aorta is 70mmHg). The aortic disc in PDA device is bigger than the pulmonary; the aortic pressure pushes this disc against the wall and the pulmonary pressure being lower can’t push it away. So the device stays there itself.