Patent Ductus Arteriosus
Embryology
The patent ductus arteriosus (PDA) is a remnant of the distal left sixth aortic arch, which connects the proximal descending aorta to the main pulmonary artery near the origin of the left pulmonary artery. During fetal life it is a vital structure essential for normal fetal development, diverting blood flow away from the high-resistance pulmonary circulation through the aorta to the placenta. The PDA normally closes spontaneously after birth. Persistent patency of the ductus arteriosus after the first few weeks of life represents a congenital malformation. Of note, some patients can survive only if the arterial duct remains patent. This includes neonates with pulmonary atresia (duct-dependent pulmonary circulation) or hypoplastic left heart syndrome variants (duct-dependent systemic circulation). Indeed, the use of prostaglandins to maintain neonatal duct patency in these circumstances is historically one of the major advances in pediatric cardiology.
In normal cardiovascular development, there is a left PDA with a left aortic arch. However, when the distal right embryonic arch persists, there may be a right PDA with a right aortic arch. Occasionally, however, a left PDA is found with a right aortic arch, which results in the duct coursing behind the trachea and esophagus, creating a vascular ring. Associated lesions are common, particularly in patients presenting in early life. The most common associated lesions are ventricular or atrial septal defects and coarctation of the aorta.
Incidence and Classification
The reported incidence of PDA is approximately 1 in 2000 full-term births. This accounts for 5% to 11% (median 7.1%) of all congenital heart malformations. However, if we include patients with a “silent PDA” (no audible heart murmur) whose defect is detected incidentally by echocardiography (usually) or angiocardiography performed for another reason, the incidence of patent ductus may be as high as 1 in 500 live births. The female-to-male ratio is approximately 2:1. Prematurity increases the incidence of PDA, but in term infants, genetic as well as environmental factors (eg, prenatal rubella infection during the first trimester) seem to play a key causal role.
PDA is usually an isolated lesion in the adult patient. The size and shape of the PDA varies greatly and impacts both the pathophysiology and the type of occluding device used when catheter intervention is considered. From a clinical perspective, PDA during adulthood can be graded as follows :
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Silent: Tiny PDA detected only by nonclinical means (usually echocardiography); no heart murmurs audible.
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Small: Audible ejection systolic or continuous murmur, sometimes radiating to the back. There is negligible hemodynamic change with normal peripheral pulses and normal left atrial and left ventricular size with no pulmonary hypertension.
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Moderate: Dynamic peripheral pulses (as with significant aortic regurgitation) and a continuous murmur is present. There is enlargement of the left atrium and left ventricle and usually some degree of pulmonary hypertension (usually reversible).
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Large: The adult presentation is with Eisenmenger syndrome physiology. Signs of pulmonary hypertension are evident. The continuous murmur, present in early life, has disappeared. There may be a high-pitched diastolic murmur of pulmonary regurgitation. Differential cyanosis (upper body oximetry higher than lower body oximetry) and toe clubbing are associated.
From an angiographic imaging perspective, Krichenko et al. described an anatomic classification that is mainly useful for guidance of transcatheter PDA closure ( Fig. 39.1 ). Ductal anatomy in the lateral projection is classified into five categories: type A is a conical ductus, with a well-defined aortic ampulla and constriction at the pulmonary end; type B is a large and very short ductus, mimicking an aortopulmonary window; type C is a tubular duct without any constriction at its pulmonary end; type D is a more complex ductus with multiple constrictions; and type E is an elongated ductus, frequently seen in premature babies.
Late Outcome
Patients with small silent PDAs have a normal life expectancy. Life expectancy is also normal in patients who survive surgical or catheter closure of a PDA in infancy or early childhood. Attention should be paid to patients who had some increase in pulmonary vascular resistance at the time of PDA closure. Such patients may present later in life with symptomatic pulmonary hypertension ( Box 39.1 ).
Patent Ductus Arteriosus
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Congestive heart failure (moderate PDA)
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Endarteritis
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Eisenmenger syndrome (large PDA)
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PDA aneurysm (common in young infants or secondary to endarteritis)
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PDA calcification (common in adults)
Aortopulmonary Window
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Congestive heart failure (a “small” window)
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Endocarditis (may be on associated lesions)
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Eisenmenger syndrome
All patients with a PDA are at risk of endarteritis (which may increase with advancing age); this risk is very low for patients with small silent PDAs. In the current era of transcatheter closure, adult patients with a small PDA are often considered for prophylactic closure to eliminate the endarteritis risk, although it is very small. Aneurysm formation of the duct is an important but uncommon complication.
Patients with moderately sized PDAs may also present during adulthood. Late presentation may be with a continuous murmur and dynamic pulses or with the development of left-sided heart dilation and left-to-right shunt–related pulmonary hypertension. The majority of adult patients with a moderate PDA will ultimately become symptomatic with dyspnea and/or palpitations (atrial fibrillation, secondary to longstanding left atrial dilation), although left ventricular systolic dysfunction and frank heart failure may also occur at the late stage of the disease.
A large PDA is rare in adults living in the developed world, with most having been repaired in infancy and childhood. Pulmonary hypertension is usual in these patients and may not reverse entirely with early childhood closure of the defect. Many patients with a large PDA are symptomatic, with dyspnea, fatigue, or palpitations. Eisenmenger PDA has a similar prognosis to Eisenmenger ventricular septal defect, although symptoms may be less marked and exercise tolerance better because carotid chemoreceptors are exposed to higher oxygen saturations. The Eisenmenger PDA is further discussed in Chapter 52 .
Outpatient Assessment
Patients with Repaired Patent Ductus Arteriosus
Patients with a PDA repaired during childhood have normal unrestricted lives with anticipated normal survival. The occasional patient with a large unrestricted PDA who had closure beyond the first 1 to 2 years of life has the potential for progressive pulmonary vascular disease. If evidence of pulmonary hypertension exists, such a patient should have lifelong follow-up. Residual patency of the duct is another complication seen after surgical or device closure. It may be associated with a minor left-to-right shunt, which is insignificant in hemodynamic terms, but these patients remain at risk of infective endocarditis/endarteritis (see the discussion on assessing the native or residual PDA later in this chapter). Occasionally, patients who underwent catheter closure of a PDA during childhood may have a left pulmonary artery stenosis. This is, however, usually mild and unlikely to require further intervention or have any long-term prognostic implications.
Patient with Unrepaired or Residual Patent Ductus Arteriosus
The initial diagnostic workup should include the following:
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Confirm the presence of PDA or residual PDA and identify any associated lesions.
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Assess the magnitude of left-to-right shunting.
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Assess the degree of pulmonary hypertension, if present.
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Identify the presence and size of a ductal aneurysm, if present.
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Determine whether the duct is calcified, if surgical repair is planned.
The diagnostic workup should include, at a minimum:
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thorough clinical assessment,
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oximetry (obtained in room air on both fingers and toes),
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chest radiography,
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electrocardiography, and
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transthoracic echocardiography.
The diagnostic workup may also require:
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cardiac catheterization to estimate the degree and direction of shunting when not available by other means,
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coronary angiography in patients with risk factors or patients older than 40 years if surgical repair is contemplated, and/or
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computed tomography (CT) and/or cardiac magnetic resonance (CMR) imaging.
Clinical Examination
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Full, dynamic pulses (with a wide pulse pressure and low diastolic pressure) suggest a hemodynamically significant PDA.
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A continuous murmur in the upper left sternal edge, sometimes radiating to the back, is consistent with a significant PDA; occasionally, a long ejection murmur and not a continuous murmur may be audible.
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Patients with a large PDA and Eisenmenger complex do not have a continuous murmur but have signs of pulmonary hypertension and lower body (differential) cyanosis and toe clubbing. A right ventricular lift and prominent second heart sound also suggest advanced pulmonary hypertension.
Electrocardiography
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Broad P waves and tall/deep QRS complexes are suggestive of left atrial and left ventricular overload, respectively.
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Right ventricular hypertrophy, evidenced by tall RV1 usually with right axis deviation, suggests significant pulmonary hypertension.
Chest Radiography
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Dilated central pulmonary arteries with increased pulmonary vascular markings, with left atrial and left ventricular dilation, all suggest a significant left-to-right shunt.
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Calcification may be seen in the posteroanterior and lateral views in the older patient with a PDA; this has clinical implications (see later).
Echocardiography
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Size and maximum diameter of the PDA can be estimated with two-dimensional (2D) echocardiography, but this is usually difficult to ascertain in the adult.
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Determine if left atrial and left ventricular dilation are present, which in turn suggests a significant left-to-right shunt in the setting of a hemodynamically important PDA.
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Continuous-wave Doppler interrogation across the PDA provides indirect information on pulmonary arterial pressures and pulmonary vascular disease. The presence of a systolic pressure gradient greater than 64 mm Hg across the PDA suggests there is no significant pulmonary hypertension. When the systolic pressure gradient between the aorta and the pulmonary artery is less than 64 mm Hg, a significant diastolic pressure gradient may suggest possible reversible pulmonary vascular disease. However, such patients need to be studied formally with cardiac catheterization, including reversibility studies and perhaps test balloon occlusion of the PDA before proceeding to closure.
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Additional assessment of right ventricular and pulmonary arterial systolic pressure should be attempted with continuous wave Doppler imaging when echocardiographic tricuspid regurgitation is present.
Cardiac Catheterization
Diagnostic catheterization is mostly reserved for patients with elevated pulmonary pressures to evaluate the pulmonary vascular resistance and magnitude of shunting before a potential intervention. Oxygen saturations in the ascending and descending aorta usually differ through the ductus. It is therefore not possible to calculate with accuracy the systemic blood flow, because the proportions of flow to the ascending and descending aorta are not known. Some centers use acute reversibility studies with vasodilators to assess pulmonary arterial pressure and resistance, when pulmonary arterial pressure is greater than two-thirds of systemic arterial pressure.
Computed Topography and Cardiac Magnetic Resonance
Cardiac CT can assess the degree of calcification, which may be important if surgical therapy is contemplated. CMR and CT may also be useful in defining the anatomy in patients with unusual PDA geometry (eg, ductal aneurysm) and in patients with associated abnormalities of the aortic arch ( Fig. 39.2 ). Finally, CMR may be useful in the assessment of hemodynamic consequences of left ventricular volume overload (measurement of left ventricular volumes and function as well as degree of left-to-right shunt).
