Saturday, September 23, 2017

Introduction to Patent Ductus Arteriosus



Patent ductus arteriosus (PDA)
is a condition in which the ductus arteriosus does not close. (The word “patent” means open.)

The ductus arteriosus is a blood vessel that allows blood to go around the baby’s lungs before birth. Soon after the infant is born and the lungs fill with air, the ductus arteriosus is no longer needed. It usually closes in a couple of days after birth.

PDA leads to abnormal blood flow between the aorta and pulmonary artery, two major blood vessels that carry blood from the heart.

A small patent ductus arteriosus often doesn’t cause symptoms or problems and may never need treatment. Untreated, a large patent ductus arteriosus can cause too much poorly oxygenated blood to flow through the heart, weakening the heart muscle and causing heart failure and other complications.

In some cases, such as in transposition of great vessels (the pulmonary artery and the aorta), a PDA may need to remain open. In this cardiovascular condition, the PDA is the only way that oxygenated blood can mix with deoxygenated blood. In these cases, prostaglandins are used to keep the patent ductus arteriosus open.

Pathophysiology
Failure of ductus arteriosus contraction in preterm neonates has been suggested to be due to poor prostaglandin metabolism because of immature lungs. Furthermore, high reactivity to prostaglandin and reduced calcium sensitivity to oxygen in vascular smooth muscle cells contribute to contraction of the ductus. The absence of ductus arteriosus contraction in full-term neonates might be due to failed prostaglandin metabolism most likely caused by hypoxemia, asphyxia, or increased pulmonary blood flow, renal failure, and respiratory disorders.

Causes
  • Familial cases of patent ductus arteriosus (PDA) have been recorded, but a genetic cause has not been determined.
  • Several chromosomal abnormalities are associated with persistent patency of the ductus arteriosus.
  • Implicated teratogens include congenital rubella infection in the first trimester of pregnancy, particularly through 4 weeks’ gestation (associated with patent ductus arteriosus [PDA] and pulmonary artery branch stenosis), fetal alcohol syndrome, maternal amphetamine use, and maternal phenytoin use.
  • Prematurity or immaturity of the infant at the time of delivery contributes to the patency of the ductus.
  • Other causes include low birth weight (LBW), prostaglandins, high altitude and low atmospheric oxygen tension, and hypoxia.
Incidence
As an isolated lesion, patent ductus arteriosus (PDA) represents 5-10% of all congenital heart lesions. It occurs in approximately 0.008% of live premature births.

Clinical Signs and Symptoms
A small PDA may not cause any symptoms. However, some infants may have symptoms such as:
  • Fast breathing
  • Poor feeding habits
  • Rapid pulse
  • Shortness of breath
  • Sweating while feeding
  • Tiring very easily
  • Poor growth
Babies with PDA often have a heart murmur that can be heard with a stethoscope. However, in premature infants, a heart murmur may not be heard.

Findings upon cardiac examination include the following:
  • If the left-to-right shunt is large, precordial activity is increased, with the magnitude of increased activity related to the magnitude of left-to-right shunt
  • The apical impulse is laterally displaced; a thrill may be present in the suprasternal notch or in the left infraclavicular region
  • The first heart sound (S1) is typically normal, and the second heart sound (S2) is often obscured by the murmur
  • The murmur may be only a systolic ejection murmur, or it may be a crescendo/decrescendo systolic murmur that extends into diastole
  • Occasionally, auscultation of the patent ductus arteriosus (PDA) reveals numerous clicks or noises.
Diagnosis and Workup
PDA is usually diagnosed using non-invasive techniques.

Echocardiography

Echocardiography, in which sound waves are used to capture the motion of the heart, and associated Doppler studies are the primary methods of detecting PDA.

ECG
Electrocardiography (ECG), in which electrodes are used to record the elecrical activity of the heart, is not particularly helpful as there are no specific rhythms or ECG patterns which can be used to detect PDA.

Chest X-ray
A chest X-ray may be taken, which reveals the overall size of neonate’s heart (as a reflection of the combined mass of the cardiac chambers) and the appearance of the blood flow to the lungs. A small PDA most often shows a normal sized heart and normal blood flow to the lungs. A large PDA generally shows an enlarged cardiac silhouette and increased blood flow to the lungs.

Management

Conservative Approach
If the rest of the baby’s heart and blood flow is normal or close to normal, the goal is to close the PDA. If the baby has certain other heart problems or defects, keeping the ductus arteriosus open may be lifesaving. Medicine may be used to stop it from closing.

Sometimes, a PDA may close on its own. In premature babies it often closes within the first 2 years of life. In full-term infants, a PDA rarely closes on its own after the first few weeks.

Pharmacological measure
When treatment is needed, medications such as indomethacin or a special form of ibuprofen are often the first choice. Medicines can work very well for some newborns, with few side effects. The earlier treatment is given, the more likely it is to succeed.

Medical Procedure

If these measures do not work or can’t be used, the baby may need to have a medical procedure.

A transcatheter device closure is a procedure that uses a thin, hollow tube placed into a blood vessel. The doctor passes a small metal coil or other blocking device through the catheter to the site of the PDA. This blocks blood flow through the vessel. These coils can help the baby avoid surgery.

Surgery
Surgery may be needed if the catheter procedure does not work or it cannot be used. Surgery involves making a small cut between the ribs to repair the PDA. Surgery has risks, however. Weigh the possible benefits and risks with your health care provider before choosing surgery.

Prognosis

The prognosis is generally considered excellent in patients in whom the patent ductus arteriosus (PDA) is the only problem.

Spontaneous closure in those older than 3 months is rare. In those younger than 3 months, spontaneous closure in premature infants is 72-75%

Survival rates are decreased in patients with large shunts.

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