eMedicine Specialties > Pediatrics: Cardiac Disease and Critical Care Medicine > Cardiology
Patent Ductus Arteriosus
Updated: Jul 23, 2009
Introduction
Background
Patent ductus arteriosus (PDA) is one of the more common congenital heart defects. The presentation widely varies. Depending on the size of the patent ductus arteriosus, the gestational age of the neonate, and the pulmonary vascular resistance, a premature neonate may develop life-threatening pulmonary overcirculation in the first few days of life. Conversely, an adult with a small patent ductus arteriosus may present with a newly discovered murmur well after adolescence.
During fetal life, the ductus arteriosus is a normal structure that allows most of the blood leaving the right ventricle to bypass the pulmonary circulation and pass into the descending aorta. Typically, only about 10% of the right ventricular output passes through the pulmonary vascular bed.
The ductus arteriosus is a remnant of the distal sixth aortic arch and connects the pulmonary artery at the junction of the main pulmonary artery and the origin of the left pulmonary artery to the proximal descending aorta just after the origin of the left subclavian artery. Most typically, it is a left aortic remnant. A right-sided patent ductus arteriosus can occur, or the ductus arteriosus can be present on both the right and the left. Although a left ductus arteriosus is a normal structure during normal fetal development, the presence of a right ductus arteriosus is usually associated with other congenital abnormalities of the cardiovascular system, most typically involving the aortic arch or conotruncal development.
Pathophysiology
A patent ductus arteriosus produces a left-to-right shunt. In other words, it allows blood to go from the systemic circulation to the pulmonary circulation. Therefore, pulmonary blood flow is excessive.
Schematic diagram of left-to-right shunt of blood flow from descending aorta via patent ductus arteriosus (PDA) to main pulmonary artery
The magnitude of the excess pulmonary blood flow depends on relatively few factors. The larger the internal diameter of the narrowest portion of the ductus arteriosus, the larger the left-to-right shunt. If the ductus arteriosus is restrictive, then the length of the narrowed area also affects the magnitude of the shunt. A longer ductus is associated with a smaller shunt. Finally, the magnitude of the left-to-right shunt is partially controlled by the relationship of the pulmonary vascular resistance to the systemic vascular resistance.
If the systemic vascular resistance is high and/or the pulmonary vascular resistance is low, the flow through the ductus arteriosus is potentially large. Beginning at the ductus arteriosus, the course of blood flow in a typical patent ductus arteriosus with pulmonary overcirculation is as follows: patent ductus arteriosus, pulmonary arteries, pulmonary capillaries, pulmonary veins, left atrium, left ventricle, aorta, patent ductus arteriosus. Therefore, a large left-to-right shunt through a patent ductus arteriosus results in left atrial and left ventricular enlargement. Additionally, the pulmonary veins and the ascending aorta can be dilated with a sufficiently large patent ductus arteriosus. Also, if little or no restriction is present at the level of the patent ductus arteriosus, pulmonary hypertension results.
The ductus arteriosus is normally patent during fetal life. This patency is promoted by continual production of prostaglandin E2 (PGE2) by the ductus. Prostaglandin antagonism, such as maternal use of nonsteroidal anti-inflammatory medications, can cause fetal closure of the ductus arteriosus. This can be associated with severe fetal cardiovascular compromise.
Normally, functional closure of the ductus arteriosus occurs by about 15 hours of life in healthy infants born at term. This occurs by abrupt contraction of the muscular wall of the ductus arteriosus, which is associated with increases in the partial pressure of oxygen (PO2) coincident with the first breath. This was first demonstrated by multiple experiments in the 1940s and has been subsequently confirmed. Although the neonatal ductus appears to be highly sensitive to changes in arterial oxygen tension, the actual reasons for closure or persistent patency are complex and involve manipulation by the autonomic nervous system, chemical mediators, and the ductal musculature.
Although functional closure usually occurs in the first few hours of life, true anatomic closure, in which the ductus loses the ability to reopen, may take several weeks. Cassels et al defined true persistence of the ductus arteriosus as a patent ductus arteriosus present in infants older than 3 months.1
Frequency
United States
The estimated incidence in children born at term is between 0.02% and 0.006% of live births. This incidence is increased in children who are born prematurely, children with a history of perinatal asphyxia, and, possibly, children born at high altitude. Perinatal asphyxia usually only delays the closure of the ductus, and, over time, the ductus typically closes without specific therapy.
Mortality/Morbidity
Low birthweight premature infants
As many as 20% of neonates with respiratory distress syndrome have a patent ductus arteriosus. In babies who are less than 1500 g at birth, many studies show the incidence of a patent ductus arteriosus to exceed 30%. The increased patency in these groups is thought to be due to both hypoxia in babies with respiratory distress and immature ductal closure mechanisms in premature babies. Premature babies, particularly low birthweight neonates, are more likely to have problems related to patent ductus arteriosus. Spontaneous closure of the patent ductus arteriosus in premature neonates is common, but respiratory distress and impaired systemic oxygen delivery (congestive heart failure) often drive the need for therapy to effect ductal closure in this group. Low birthweight neonates with a patent ductus arteriosus are more likely to develop chronic lung disease.
Otherwise healthy infants, children, adolescents, and adults
In the preantibiotic era, Campbell et al estimated the natural history mortality rates for untreated patent ductus arteriosus to be 0.42% per year from age 2-19 years, 1-1.5% per year in the third decade, 2-2.5% per year in the fourth decade, and 4% per year in persons older than 40 years.2 Currently, with the availability of antibiotics to treat endocarditis and low-risk surgery and catheter techniques to obliterate the patent ductus arteriosus, the mortality rate appears to be quite low except in the extremely premature infant.
Sex
The female-to-male ratio is 2:1 if not associated with other risk factors. In patients in whom the patent ductus arteriosus is associated with a specific teratogenic exposure, such as congenital rubella, the incidence is equal between the sexes.
Age
The ductus arteriosus is always patent in the fetus if the cardiovascular system is otherwise normal. Normally, the ductus arteriosus closes functionally in the first 10-18 hours of life. Prematurity, perinatal distress, and hypoxia delay closure of the ductus arteriosus; however, most children who are found to have a ductus arteriosus have no history of precedent risk factors.
Clinical
History
The typical child with a patent ductus arteriosus (PDA) is asymptomatic.
- A history of premature birth, perinatal distress, or perinatal hypoxia may be present.
- Some series have suggested that children born at extreme altitude have an increased incidence of a persistent patent ductus arteriosus.
- Occasionally, a history of feeding difficulties and poor growth during infancy, described as failure to thrive, is found. However, frank symptoms of congestive heart failure are rare.
- In the low birthweight premature infant, diagnosing a patent ductus arteriosus on auscultation may be difficult. Babies that have a more severe clinical course of hyaline membrane disease may have a higher prevalence of patent ductus arteriosus. The exact reason for this is unclear.
Physical
As many as one third of children with patent ductus arteriosus are small for their age. In the presence of significant pulmonary overcirculation, tachypnea, tachycardia, and a widened pulse pressure may be found.
- 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. The second heart sound (S2) is often obscured by the murmur. Phonocardiographic data from the past suggested the occurrence of paradoxical splitting of S2 related to premature closure of the pulmonary valve and a prolonged ejection period across the aortic valve.
- In 1898, Gibson described the classic murmur. Subsequently, the classic patent ductus arteriosus murmur has been referred to as a machinery murmur, which is continuous. The murmur may be accentuated in systole. Typically, the murmur is loudest at the left upper chest. If the pulmonary-to-systemic blood ratio approaches or exceeds 2:1, an apical flow rumble, caused by high flow into the left ventricle, is frequently present. Also, because flow through the left ventricle into the aorta is increased, an aortic ejection murmur may be present. If the patent ductus arteriosus is small, the amplitude of the murmur may increase with inspiration as pulmonary impedance drops.
- The peripheral pulses are often referred to as bounding. This is related to the high left ventricular stroke volume, which may cause systolic hypertension. The phenomenon of bounding pulses also is caused by the low diastolic pressure in the systemic circulation as blood runs off from the aorta into the pulmonary circulation.
- In the low birthweight premature infant, the classic signs of a patent ductus arteriosus are usually absent. The classic continuous murmur is rarely heard. A rough systolic murmur may be present along the left sternal border, but a small baby with a large patent ductus arteriosus and significant pulmonary overcirculation may have no murmur. In that case, typically, precordial activity is increased and peripheral pulses are bounding. The increased precordial activity is caused by the large left ventricular stroke volume. Bounding pulses are caused by the relatively low systemic arterial blood pressure due to the continuous runoff of blood from the aorta into the pulmonary artery.
Causes
- Familial cases of patent ductus arteriosus have been recorded, but a genetic cause has not been determined. In infants born at term who have a persistent patent ductus arteriosus, the recurrence rate among siblings is 5%. Some early evidence suggests that as many as one third of cases are caused by a recessive trait labeled PDA1, located on chromosome 12, at least in some populations.
- Several chromosomal abnormalities are associated with persistent patency of the ductus arteriosus. Implicated teratogens include congenital rubella (associated with patent ductus arteriosus and pulmonary artery branch stenosis), fetal alcohol syndrome, maternal amphetamine use, and maternal phenytoin use.
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References
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Further Reading
Keywords
patent ductus arteriosus, patent arterial duct, PDA, congenital heart defect, aorticopulmonary shunt, aorticopulmonary communication, ductus arteriosus, pulmonary hypertension, respiratory distress syndrome, congestive heart failure, rubella, fetal alcohol syndrome
