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Patent ductus arteriosus

pda_crop_sm.jpgThe ductus arteriosus is a tube-like connection between the aorta and pulmonary artery. It is open or “patent” in all babies before they are born. After birth, the ductus arteriosus is supposed to close, usually within hours to a few days. A ductus that doesn't close is common in premature infants but rare in full-term babies. It is abnormal to have a persistently open or a patent ductus arteriosus (PDA). See the illustration (by Rashid Idriss).

This defect allows blood to mix between the pulmonary artery and the aorta. It is similar to a septal defect because it allows blood to flow from the one side of the circulation to the other, so that a shunt occurs. The shunt is usually left to right because the pressures are higher in the aorta than in the pulmonary artery and blood flows to the path of least resistance. When this happens, some blood that should flow through the aorta to nourish the body returns to the lungs before doing so. If the ductus arteriosus is large, a lot of “extra” blood flows to the lungs instead of the body. This may result in breathing difficulty, tiring quickly and poor growth.

Diagnosis 

Most children with a PDA have no symptoms unless it is very large. A PDA diagnosis is usually suspected after the detection of an abnormal murmur during the physical examination. The murmur of a PDA has special qualities to distinguish it from normal murmurs. There are other features of a PDA, which can be detected on a physical examination. The diagnosis is confirmed with echocardiography. Sometimes a PDA may be present without abnormal murmurs or the other usual findings to suggest a PDA. This is called a “clinically silent” PDA and is diagnosed by echocardiography as an "incidental finding" — a test obtained for something else and the PDA found “by accident.”

Symptoms

In some children symptoms may not occur until after the first weeks or months of life. If the ductus arteriosus is small, no symptoms may occur.

Treatment

Once diagnosed, closure of the ductus is usually recommended. In larger ones, closure is recommended to improve symptoms. In a small ductus, closure is recommended to prevent an infection called endarteritis. In some infants, usually premature infants, the PDA can be closed with a drug called indomethacin. Several doses of indomethacin may be necessary to effectively close the PDA. Sometimes, PDAs cannot be closed by this method. In large infants, children and adults, closure of the ductus can usually be performed during cardiac catheterization. In some cases this is not possible and surgery may be recommended.

A cardiac surgeon can close the ductus arteriosus by tying it or clipping it, without opening the heart. This procedure is called ligation of the PDA or ductal ligation. This can usually be done one of two ways:

  1. An incision is made on the left chest near the armpit, through which the ductus (PDA) is exposed where it attaches to the aorta. The tie or clip is placed directly around it, and the flow across the PDA is immediately stopped.
  2. Alternatively, the same clipping or tying of the PDA can be done through four small incisions on the left chest, with the assistance of a videoscope and special instruments designed for use through tiny incisions.

Treatment Risks

The risks of almost any surgical operation or interventional catheterization include bleeding, infection and sedation. Special risks of PDA closure in the catheterization laboratory include dislodgement of the closure device (low risk), and narrowing of the left pulmonary artery or aorta (also low risk). Special risks of PDA surgical closure include injury to one of the nerves that control the vocal cords, and injury to the left pulmonary artery or aorta. Both procedures have a small risk of recurrence depending on exactly how the closure is performed.

Long-term Effects

Untreated, a large PDA can lead to symptoms of congestive heart failure or Eisenmenger syndrome. It may also increase the risk for an infection called endarteritis (similar to endocarditis). Medical, interventional catheter and surgical methods usually succeed, restoring normal circulation. The risk of endarteritis in a completely closed PDA is felt to be no higher than the general population and no special precautions such as prophylaxis against bacterial endocarditis are needed. In a completely closed PDA, a normal lifestyle and outlook can be expected.

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