Patent ductus arteriosus (PDA) occurs in 5-10% of all congenital heart defects, excluding premature infants. PDAs are very common in preterm babies and can have significant physiological effects. It is important to recognise that PDA in the preterm infant and PDA in term babies and older children are two very distinct conditions with different implications and management. This article primarily focuses on the PDA as a congenital heart defect, with a separate section dealing with PDA in preterm babies at the end.
The ductus arteriosus is, in developmental terms, a remnant of the sixth aortic arch and connects the pulmonary artery to the proximal descending aorta just after the left subclavian artery origin. It is a normal structure in fetal life.
In utero the lungs are not expanded. Gas exchange occurs at the placenta and only about 10% of the circulation passes through the lungs. The ductus arteriosus connects the pulmonary artery to the aorta to shunt most of the blood away from the lungs. After delivery it closes and the blood passes through the opened lungs. Failure of the ductus arteriosus to close can lead to overloading of the lungs. The shunt is left to right unless pulmonary hypertension occurs and pulmonary pressure exceeds systemic pressure.
After birth the ductus closes functionally in 12-18 hours and anatomically in 2-3 weeks. If it remains open beyond three months of life in preterm infants and beyond one year of life in full-term infants it is termed as persistent patency of ductus arteriosus because the incidence of spontaneous closure beyond these time limits is very low.
- The factors responsible for persistent patency of ductus arteriosus in term babies are not completely understood but genetic factors and intrauterine infection are likely to play a role.
- The reported incidence varies widely because of methodological variations in the population studied and definition of PDA.
- In babies born at term the incidence is reported as in 1 in 2,000 births which accounts for 5-10% of all congenital heart defects. If children with silent PDA (discovered incidentally by echocardiography done for another purpose) are included, the incidence increases to 1 in 500 births.
- It affects girls twice as often as boys but in congenital rubella syndrome the sex incidence is equal.
- Most cases are thought to be multifactorial due to combination of genetic predisposition and a critically timed environmental exposure such as aspyxia during delivery, rubella infection during pregnancy or unknown viral infections or chemicals.
- Genetic syndromes such as trisomy 21 and Holt-Oram syndrome.
- Exposure of a fetus to valproic acid in pregnancy.
- Birth at high altitude - because of exposure to low oxygen tension.
- Patients with a small PDA are usually asymptomatic.
- A large-shunt PDA may cause lower respiratory tract infection as well as feeding difficulties and poor growth during infancy, with failure to thrive because of heart failure.
- If the pulmonary circulation is markedly overloaded there will be tachycardia, tachypnoea and a wide pulse pressure.
- The precordium is hyperactive and a systolic thrill may be present at the upper left sternal border.
- The first heart sound is normal but the second is often obscured by the murmur.
- A grade 1 to 4/6 continuous ('machinery') murmur is best audible at the left infraclavicular area or upper left sternal border.
- In the case of a large PDA shunt, a diastolic mitral rumble may be heard because of the high flow rate across the mitral valve.
- Patients with a small PDA do not have the above-mentioned findings.
- Peripheral pulses are bounding as the run-off into the pulmonary circulation drops the diastolic pressure and causes a wide pulse pressure.
Click here to hear an example of the murmur:
A number of conditions present with a murmur similar to the continuous murmur of PDA or with bounding pulses and require differentiation from PDA. These include:
- Coronary arteriovenous fistula.
- Systemic arteriovenous fistula.
- Pulmonary arteriovenous fistula.
- Venous hum.
- Fallot's tetralogy (with absent pulmonary valve).
- Ruptured aneurysm of the sinus of Valsalva (seen in Marfan's syndrome).
- Aortopulmonary septal defect (aortopulmonary window).
The only investigation needed to confirm the diagnosis and significance of PDA is echocardiograpy. Occasionally, CXR and ECG are also performed.
- Echocardiography confirms the diagnosis and characterises the anatomy and physiology of the PDA. A complete echocardiogram includes measurement of cardiac chambers and function, two-dimensional imaging of PDA anatomy and Doppler assessment to define PDA shunt flow. The ratio of left atrial size to aortic root size can be used to estimate the degree of PDA shunt.
- If the shunt is significant, CXR will show enlargement of the pulmonary arteries, veins, left atrium and left ventricle. Such features usually require a ratio of pulmonary flow to systemic flow of at least 2:1. In older people a PDA may be calcified and visible on a plain film.
- ECG is often normal in small or moderate PDA but there may be signs of left ventricular hypertrophy (LVH). A large PDA may be associated with signs of biventricular hypertrophy (BVH) and in those with pulmonary hypertension, right ventricular hypertrophy (RVH) may be present.
- Indometacin is ineffective in term infants with PDA and should not be used. Medical management is limited to use of decongestive measures such as diuretics in those with features of heart failure.
- PDA closure is indicated for any symptomatic infant, child or adult (with exclusion of those with fixed high pulmonary vascular resistance). Closure is also indicated in asymptomatic patients with left heart volume load. This can be done either by surgery or interventional techniques at any age.
- Surgical closure is reserved for patients in whom a non-surgical closure technique is not considered applicable. In infants with heart failure or pulmonary hypertension, surgery is performed on an urgent basis. The standard surgical procedure is ligation and division of the ductus through left posterolateral thoracotomy without cardiopulmonary bypass.
- In asymptomatic well infants current practice is to wait until 1 year of age, with regular echocardiographic evaluation to check for spontaneous closure of the PDA. If the duct is still patent at 1 year of age it can be closed usually by occlusion at cardiac catheterisation (endovascular occlusion). National Institute for Health and Care Excellence (NICE) guidance has been produced and considers that current evidence on the safety and efficacy of endovascular occlusion of PDA appears to support the use of this procedure.The procedure should be performed in units where there are arrangements for cardiac surgical support in the event of complications. The choice of device depends largely on the size of PDA. Coils are suitable for closing of small- to medium-sized PDAs while larger PDAs require other devices such as the Amplatzer® patent ductus arteriosus device.
- Serious complications of transcatheter closure of PDA are rare and include device embolisation, femoral artery or vein thrombosis related to vascular access and infection.
- Whilst the ductus arteriosus is patent then the risk of endocarditis should be considered (there is no increased risk of endocarditis once repair is complete). Routine antibiotic prophylaxs is not indicated but during invasive procedures (eg, urinary or gastrointestinal procedures) involving areas of sepsis, suitable antibiotics should be given promptly (to cover all the likely organisms, including any known to cause endocarditis).
Many patients with small PDAs do not have any haemodynamic overload and apart from the risk of endarteritis have a normal prognosis. Those with significant left heart volume load can develop congestive heart failure or irreversible pulmonary vascular disease.
- In most older patients successful closure of the PDA can be achieved without complications, and long-term follow-up is not required.
- Children who have had a PDA closed need no further restrictions on their lives.
Patent ductus arteriosus in preterm neonates
PDA is a common diagnosis in extremely preterm infants, especially in those with lung disease. Approximately 65% of infants born at less than 28 weeks of gestation will have persistent patency of the ductus arteriosus and will be assigned the diagnosis of PDA at some time during the early neonatal period.
- In a preterm infant, PDA should be suspected if the respiratory distress because of hyaline membrane disease does not improve or worsens after initial improvement and the baby cannot be weaned off the ventilator.
- In the premature infant of low birth weight, the classical signs are usually absent. The continuous murmur is rarely heard. There may be a rough systolic murmur along the left sternal border but a small baby with a large PDA and significant pulmonary over-circulation may have no murmur. Physical examination commonly reveals bounding peripheral pulses, a hyperactive precordium, and tachycardia with or without gallop rhythm.
- In a premature baby, the ECG is not diagnostic. It is usually normal but may show LVH.
- The diagnosis is confirmed by echocardiography which not only allows the PDA to be visualised but also assesses the haemodynamic significance of the PDA.
- Management of PDA in the preterm infant remains controversial, with diverse approaches ranging from very conservative management to aggressive early closure of the duct pharmacologically or surgically.
- A recent meta-analysis of published randomised controlled trials has shown that while indometacin prophylaxis reduces incidence of intraventricular haemorrhage (IVH), symptomatic PDA and the need for surgical ligation, there was no reduction in other morbidities, including chronic lung disease (CLD), necrotising enterocolitis (NEC) and, most importantly, neurodevelopmental impairment.The authors of the meta-analysis conclude that depending on clinical circumstance and personal preference there may be a role for prophylactic indometacin in some infants on some neonatal units.
- Ibuprofen may possibly be a safer alternative that is less likely to cause oliguria.[10, 11]
- Surgical ligation of the duct is associated with significant morbidity (hypotension, pneumothorax, vocal cord paralysis) and mortality. A recent Scottish study has reported a one-year mortality of 12.8% and a 32% incidence of neurodisability in survivors undergoing duct ligation.
- Echocardiography-guided catheter closure of the ductus in small preterm babies in the neonatal intensive care unit has been reported from Oxford.
- Diuretics and restriction of fluid used to be recommended whilst awaiting spontaneous closure. However, the evidence base is poor and a systematic review of furosemide in preterm neonates with respiratory distress symptoms showed no long-term benefits and increased the risk of symptomatic PDA.
- PDA is commonly diagnosed in extremely preterm infants and is associated with numerous pathologies, including CLD, NEC and IVH. The evidence for some of these associations is conflicting and as association does not imply causation these should not be labelled as complications of PDA.
- It used to be believed that premature babies with significant PDA are more likely to develop bronchopulmonary dysplasia (BPD). However, although early pharmacological closure of PDA decreases the incidence of pulmonary and intraventricular haemorrhage, there is little evidence from controlled clinical trials to support or refute a causal role for PDA in the development of BPD.
- In infants weighing less than 1000 g, prophylactic non-steroidal anti-inflammatory drug (NSAID) use may aid closure and reduce the risk of subsequent morbidity.However, there is no evidence of long-term benefit.[16, 17]
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- Schneider DJ, Moore JW; Patent ductus arteriosus. Circulation. 2006 Oct 24 114(17):1873-82.
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- Endovascular closure of patent ductus arteriosus, NICE (2004)
- Prophylaxis against infective endocarditis: Antimicrobial prophylaxis against infective endocarditis in adults and children undergoing interventional procedures; NICE Clinical Guideline (March 2008)
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- Heuchan AM, Hunter L, Young D; Outcomes following the surgical ligation of the patent ductus arteriosus in premature infants in Scotland. Arch Dis Child Fetal Neonatal Ed. 2012 Jan 97(1):F39-44. doi: 10.1136/adc.2010.206052. Epub 2011 Aug 17.
- Bentham J, Meur S, Hudsmith L, et al; Echocardiographically guided catheter closure of arterial ducts in small preterm infants on the neonatal intensive care unit. Catheter Cardiovasc Interv. 2011 Feb 15 77(3):409-15. doi: 10.1002/ccd.22637. Epub 2010 Oct 6.
- Brion LP, Campbell DE; Furosemide for symptomatic patent ductus arteriosus in indomethacin-treated infants. Cochrane Database Syst Rev. 2001 (3):CD001148.
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