Wednesday, March 17, 2010


About patent ductus arteriosus (PDA)
A patent ductus arteriosus (PDA) is a heart defect that occurs when a blood vessel in the heart called the ductus arteriosus fails to close after birth, as it normally should. The ductus arteriosus is present in every normally developing fetus and is actually is required for the survival of the fetus.

Prior to birth the lungs are collapsed and the fetus receives all its oxygen from the mother. The blood returning to the heart must be detoured away from the lungs. There are two detours present in all fetuses. One connects the two receiving chambers – foramen ovale. The other is the ductus arteriosus.

Closure of either of these prior to birth puts such an increased workload on the fetal heart and circulatory system that survival of the fetus is unlikely. Both of these channels close shortly after birth when the newborn is breathing on his or her own and blood must be pumped directly out to the lungs.
Potential problems that PDA may cause

The size of the patent ductus arteriosus (PDA) determines the severity of the problem. If the PDA is no bigger than the point of a needle, only a small amount of blood can squeeze through the tiny opening. Symptoms for this tiny PDA may be very mild or not even noticeable.

If the PDA is larger than a needlepoint, the child may develop signs and symptoms of heart failure, including poor feeding habits, slow weight gain, constant sweating, labored breathing and a fast heart rate. The increased volume of blood in the lungs may also cause frequent chest colds and pneumonia.

The defect can also lead to endocarditis, an infection that inflames the valves and lining of the heart. If endocarditis develops, the consequences can be life-threatening and irreversible. Endocarditis can occur with a large or small PDA.

If unrepaired, a large PDA can cause damage to the lining of the lung vessels from high blood flow, which can lead to a permanent hardening of the arteries in the lungs. If this occurs, the pressure in the lungs rises, and oxygen-poor blood is forced into the PDA and out to the body. The result is a condition called cyanosis, in which the skin, lips, fingernails and other parts of the body turn a shade of blue from the circulation of oxygen-poor, “blue” blood. This condition is called Eisenmenger syndrome. This condition is very rare in the United States. The arteries and veins in the lungs in patients with Eisenmenger syndrome have permanent scarring that is usually irreversible. This is termed “end-stage” and closure of a PDA is no longer possible.

Heart failure is also associated with untreated PDAs, especially among the very young or in the elderly. Finally, PDA can cause pulmonary hypertension, or increased blood pressure in the lungs. This can eventually lead to vascular (blood vessel) disease. In some cases, a PDA can also cause kidney disease. In very small or very premature newborns a PDA may lead to abnormal blood flow to the intestine resulting in bleeding in the bowel and even loss of the bowel.
Diagnosis methods for PDA

Unlike many congenital heart defects, a PDA cannot be diagnosed in utero because it is a normal feature of a developing fetus. Instead, the condition is diagnosed by the presence of symptoms after birth.

A patent ductus arteriosus (PDA) causes rather forceful blood flow, which makes a sound known as a heart murmur. Listening for this murmur is the most widely used method to screen for heart disease in infants. By listening to the chest with a stethoscope (a procedure called auscultation), the physician may be able to detect a murmur, which begins softly as the heart begins its pumping cycle, and peaks just before and after the second heart “thump.” The murmur is the noise of blood being forced through the PDA.

The murmur of a PDA is often not noted for several weeks after birth because the pressure in the arteries leading to the lungs may be high enough that there may be very little flow through the PDA. As the pressure in the pulmonary arteries drops below that in the aorta the flow through the PDA will increase and the intensity of the murmur becomes more evident.

In addition to listening to the patient's heart, the physician will take the baby’s pulse at birth. The physician may notice a bounding pulse, in which the pulse reaches a higher intensity than normal, then quickly disappears.

When PDA is suspected, a patient may undergo a series of tests such as:

Echocardiogram. This test uses sound waves to visualize the structures and functions of the heart. A moving image of the patient’s beating heart is displayed on a video screen, where a physician can study the heart’s thickness, size and function. The image also shows the motion pattern and structure of the four heart valves, revealing any potential leakage (regurgitation) or narrowing (stenosis). During this test, a Doppler ultrasound may be done to evaluate blood flow through the PDA. This is the definitive test in diagnosing a PDA. It may also help in judging the significance of the defect and whether there are any other associated malformations.

Chest x-ray. A radiation-based imaging test that offers the physician a picture of the general size, shape, and structure of the heart and lungs. This test may show congestion of the lungs because of increased fluid.

Electrocardiogram (EKG). A recording of the heart's electrical activity as a graph on a moving strip of paper or video monitor. The highly sensitive electrocardiograph machine helps detect heart irregularities, disease and damage by measuring the heart's rhythms and electrical impulses. This test is generally normal in the child with a PDA unless the defect is so large that there is considerable, chronic overwork to the pulmonary blood vessels and left ventricle.

Among premature infants, PDA can possibly be detected by such symptoms as troubled breathing, abnormal heart rhythm and other symptoms of heart failure.

Treatment and prevention of PDA

There are a number of methods to treat a patent ductus arteriosus (PDA). Each involves little risk to the life of the patient, and the overall survival rate is 99 percent. The patient’s age and the presence of other congenital heart defects are two of the most important factors that determine how and when the PDA will be repaired.

In a premature baby, a medication called indomethacin may be given to stimulate the ductus arteriosus muscles to contract, thus closing the ductus arteriosus. The medicine works by blocking the effects of prostaglandin. This medicine is usually given in several courses, usually 12 to 24 hours apart. It has a number of possible side effects, however, which include kidney dysfunction and internal bleeding.

Medication is not effective to close the PDA in a full-term infant or older child. In this case, the patient might be given diuretics to reduce blood pressure until their condition is stabilized and a treatment course can be chosen. Two methods are available to close a PDA in these patients: catheter-based procedures and surgery. Catheter-based procedures are not available for preterm infants. In these fragile patients, if indomethacin is unsuccessful or if the medication cannot be employed because of other medical conditions the newborn has, surgical closure is the only means of dealing with a symptomatic PDA.

Catheter-based procedures are techniques in which a catheter is inserted through a blood vessel in the body and guided all the way to the heart, where it can be used by a physician for a number of procedures, including coil embolization. Coil embolization is a relatively new technique that has been adopted by many institutions since it was first implemented for PDA in 1992. It is now one of the most common interventional procedures performed and has been successful in over 95 percent of the cases, although there is a small risk of embolism, or blood clots, during the procedure itself.

Coil embolization uses a coil made of surgical steel in which synthetic fibers are embedded. The coil is delivered via a catheter that is threaded through an artery or vein (e.g., in the groin) to the site of the PDA. Placed inside the PDA, the coil is held in place while the fibers encourage the formation of a blood clot, sealing the PDA closed. Researchers are working on coils that are retrievable so they can be repositioned several times during the procedure to ensure a good fit. These newer coils reduce the risk of embolism caused by the coil itself.

The decision to recommend surgery, in both term and preterm infants, relies on several factors, including the age of the infant and the degree of the opening. Surgery is an acceptable alternative, even among preterm infants, but it is usually not recommended for very small PDAs even if the infant did not respond to indomethacin therapy. Among older infants, a PDA of 1 or 2 mm is not likely to cause any abnormalities in blood flow, but there is a risk that the PDA could be a site for infection of the heart in the future.

During surgery, the infant is given general anesthesia and the surgeon enters the chest through a small incision under the left arm (thoracotomy). One in the chest, the surgeon ties off the ductus arteriosus between the aorta and the pulmonary artery. Less than 1 percent of these blood vessels reopen, making this technique among the most reliable procedures.

Surgery is usually reserved only for symptomatic newborns who require a ventilator to support their breathing. The extra work on the heart and lungs because of a PDA may interfere with the newborn’s ability to breath without the machine. Closure of a PDA in this setting may allow the newborn to breath without the ventilator. There are several possible complications from surgery that are not present with device closure.

Another type of surgery, called video-assisted thoracoscopic surgery (VATS), involves the use of specialized long instruments, which are inserted through small puncture holes in the chest to close PDAs. This does not require spreading of the ribs which shortens the recovery time. The instruments place a metal clip around the PDAs, which seals the defect.

Although its cause is unknown and it cannot be prevented, PDA occurs much more commonly in premature and very low birth-weight (VLBW) infants. Infants are also at much greater risk if the mother contracts rubella (German measles) near the time of birth. Fortunately rubella is rarely seen in this country because of routine vaccination. Pregnant women are also routinely checked for immunity to rubella, usually on their first obstetrical visit along with several other blood tests.

The ductus arteriosus is considered patent (open) if it does not seal itself within three days after the baby is born.

A large patent ductus arteriosus results in a left-to-right shunt, causing blood to move across the open blood vessel from the left side of the heart (aorta) to the right (pulmonary artery). This raises blood pressure in the pulmonary circulation and increases work on the right ventricle. At the same time, there is increased pulmonary return to the left side of the heart (because of the increased blood volume in the right side of the heart), which adds additional stress on the left side of the heart. This can result in an expanded left atrium and ventricle. If the degree of patency (openness) is large enough, it can eventually cause pulmonary vascular disease, as well as symptoms associated with heart failure because the heart is unable to pump enough oxygen-rich blood to satisfy the body.

Although a PDA is often harmful to the baby, there are times when a PDA can be helpful (e.g., tetralogy of Fallot) because it establishes some semblance of normal blood flow. When other heart defects are present, a PDA may serve a crucial and life-sustaining function. In patients with blockage of blood flow to the lungs, for example, a PDA allows blood to flow to the baby’s lungs. Similarly, among babies born with complex congenital heart defects with abnormal circulation, a PDA may enable the baby to live by mixing oxygen-rich and oxygen-poor blood.

One such abnormality is transposition of the great arteries, in which the positions of the aorta and pulmonary artery are reversed, resulting in two sets of parallel circulation. Without a PDA or some way for blood to cross the septal barrier, the baby would rapidly die. In some cases, physicians may administer a special drug called prostaglandin E1 that will keep the ductus arteriosus open long enough to allow such a baby to get into surgery.

About 35,000 babies are born every year with heart defects, according to the American Heart Association. A PDA is one of the 10 most common heart defects in the United States. Premature babies are most at risk for the condition. Other risk factors include maternal rubella (German measles) during pregnancy, birth in a city or town at high altitude, and a family history of PDA.
Role of the ductus arteriosus

During fetal development, the lungs are not yet functioning, and the fetus relies on the mother to supply it with fresh, oxygen-rich blood through the umbilical cord. Although the pulmonary artery will carry oxygen-poor blood to the lungs after birth, there is no reason for blood to go to the lungs before birth for two reasons. First, the fetal blood already contains oxygen from the placenta and second, the fetal lungs will not contain any oxygen from the air. Therefore, the pulmonary artery carries blood that is rich in oxygen from the placenta through the ductus arteriosus and to the aorta, which funnels the blood to the rest of the fetus’ body.

After birth, there are several factors that must occur to close the ductus. First, during pregnancy, the vessel is held open by circulating prostaglandin, a hormone-like fatty acid that helps control smooth muscle contraction. After birth, the level of prostaglandin in the blood declines and there is an increased level of vasoconstrictive substances. At the same time, there is an increased pressure with the ductus arteriosus itself due to the presence of oxygen in the blood after the baby takes its first breath. As a result, the ductus arteriosus typically closes within the first 24 hours after birth.

Within two to three days, a scar forms over the site of the ductus, sealing it permanently. The pulmonary artery now works to bring oxygen-poor blood from the right ventricle to the lungs, where the blood can receive a fresh supply of oxygen from the inhaled air.

If it remains open, then it is known as a patent ductus arteriosus (PDA) and is considered a congenital heart defect. This is a problem because of the way the normal, mature heart operates. In a normal heart, the pressure is greater in the left side of the heart. Thus, in a heart with a PDA, blood is pushed from the left side of the heart back into the right side of the heart. This raises the blood volume in the pulmonary artery and lungs, while also decreasing the amount of oxygen-rich blood flowing to the body. Over time, this can result in pulmonary disease (e.g., pulmonary hypertension), kidney disease, and left-sided heart failure.


Ayuz said...


Post a Comment