Patent ductus arteriosus
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Patent ductus arteriosus (PDA) is a congenital heart defect wherein a child's ductus arteriosus fails to close after birth. Symptoms include shortness of breath and cardiac arrhythmia, and may progress to congestive heart failure if left uncorrected.
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Overview
Normal ductus arteriosus closure
In the developing fetus, the ductus arteriosus (DA) is a shunt connecting the pulmonary artery to the aortic arch that allows much of the blood from the right ventricle to bypass the fetus' fluid-filled lungs. During fetal development, this shunt protects the lungs from being overworked and allows the right ventricle to strengthen.
When the newborn takes its first breath, the lungs open and pulmonary pressure decreases below that of the left heart. At the same time, the lungs release bradykinin to constrict the smooth muscle wall of the DA and reduce bloodflow. Additionally, because of reduced pulmonary resistance, more blood flows from the pulmonary arteries to the lungs and thus the lungs deliver more oxygenated blood to the left heart. This further increases aortic pressure so that blood no longer flows from the pulmonary artery to the aorta via the DA.
In normal newborns, the DA is closed within 15 hours after birth, and is completely sealed after three weeks. A nonfunctional vestige of the DA, called the ligamentum arteriosum, remains in the adult heart.
Patent ductus arteriosus
In PDA, the newborn's ductus arteriosus does not close, but remains patent. Patent DA is common in infants with persistent respiratory problems such as hypoxia, and has a high occurrence in premature children. In hypoxic newborns, too little oxygen reaches the lungs to produce sufficient levels of bradykinin and subsequent closing of the DA. Premature children are more likely to be hypoxic and thus have PDA because of their underdeveloped heart and lungs.
A patent ductus arteriosus allows oxygenated blood to flow down its pressure gradient from the aorta to the pulmonary arteries. Thus, some of the infant's oxygenated blood does not reach the body, and the infant becomes short of breath and cyanotic. The heart rate hastens, thereby increasing the speed with which blood is oxygenated and delivered to the body. Left untreated, the infant will likely suffer from congestive heart failure, as his heart is unable to meet the metabolic demands of his body.
Signs and symptoms
While some cases of PDA are asymptomatic, common symptoms include:
- tachycardia or other arrhythmia
- respiratory problems
- shortness of breath
- heart murmur
- enlarged heart
- cyanosis
Diagnosis
PDA is usually diagnosed using non-invasive techniques. Electrocardiography (ECG), in which electrodes are used to record the electrical activity of the heart, can be used to detect cardiac arrhythmias associated with PDA.
A chest X-ray may be taken, which reveals the structure of the infant's heart and the size and configuration of its chambers. In some instances, the X-ray itself may reveal a patent ductus arteriosus.
Echocardiography, in which sound waves are used to capture the motion of the heart, is also useful in detecting PDA.
Treatment
Both surgical and non-surgical methods of treatment are available. Surgically, the DA may be closed by ligation, wherein the DA is manually tied shut, or with intravascular coils that physically constrict the DA.
Fluid restriction and prostaglandin inhibitors such as indomethacin have also been used in successful non-surgical closure of the DA. This is an especially viable alternative for premature infants.
External links
- MedlinePlus Medical Encyclopedia: Patent ductus arteriosus (http://www.nlm.nih.gov/medlineplus/ency/article/001560.htm) (including diagram)
- High-Risk Newborn - Patent Ductus Arteriosus (PDA) (http://www.schneiderchildrenshospital.org/peds_html_fixed/peds/hrnewborn/pda.htm)
- Fetal Circulation (http://mcb.berkeley.edu/courses/mcb135e/fetal.html)
- Fetal blood flow (http://www.meritcare.com/hwdb/showtopic.asp?module_abbrev=HWKB4&pd_hwid=hw255772&topic_name=Fetal%20blood%20flow&sequence=1)de:Ductus arteriosus