Patent Ductus Arteriosus and Coarctation of the Aorta
Adam S. Goldberg
Richard A. Krasuski
I. PATENT DUCTUS ARTERIOSUS—INTRODUCTION
A. The ductus arteriosus is a fetal communication between the descending aorta just distal to the left subclavian artery and the main pulmonary artery near its bifurcation. A patent ductus arteriosus (PDA) occurs when the ductus arteriosus fails to close and regress after birth to form the ligamentum arteriosum. PDA occurs in approximately 1 of 2,000 live births, but it is relatively uncommon among the adult population. In infants, it accounts for 10% to 12% of all congenital heart disease.
B. Natural history. The natural history depends on the size of the PDA, the direction of the shunt, and the development of any associated complications. At birth, 95% of patients with isolated PDA have left-to-right shunts and normal, or near-normal, pulmonary pressures. Patients with normal pulmonary artery pressures and no evidence of chronic left ventricular volume overload have a better prognosis. If untreated, life expectancy of patients with PDA is shortened; one-third of patients with PDA die by the age of 40 and almost two-thirds die by the age of 60. With a PDA, congestive heart failure (CHF) can occur because of chronic left heart volume overload. In patients with death related to PDA, CHF is the most common cause. Development of right-to-left shunting is also an ominous sign because it reflects the development of advanced pulmonary vascular disease and associated elevation in right-sided cardiac pressures (see Chapter 32 for discussion on Eisenmenger’s syndrome).
C. Risk factors. Factors that increase risk for PDA include maternal rubella infection, birth at high altitude, premature birth, female sex, and genetic factors. In infants born at < 28 weeks of gestation, there is a 60% incidence of PDA. PDAs are twice as common in female infants as in male infants and in some instances have a genetic component. In a family in which one child has a PDA, there is approximately a 3% risk of having a PDA in subsequent offspring.
II. ANATOMY AND PATHOPHYSIOLOGY
A. Embryology.
The ductus arteriosus is a normal and essential component of cardiovascular development that originates from the distal sixth left aortic arch. A PDA is most commonly funnel shaped with the larger aortic end (ampulla) distal to the left subclavian artery, then narrowing toward the pulmonary end, with insertion at the junction of the main and left pulmonary arteries. The Krichenko classification system describes the angiographic appearance of PDA (Table 31.1). In right-sided aortic arch, the anatomy of PDA can vary significantly: the PDA can arise from the left innominate artery and insert into the proximal left pulmonary artery or arise distal to the right subclavian artery with insertion into the proximal right pulmonary artery. Bilateral PDAs can also occur.
B. Fetal circulation.
The presence of the ductus arteriosus in the fetal circulation is essential to allow right-to-left shunting of nutrient-rich, oxygenated blood
from the placenta to the fetal systemic circulation, thereby bypassing the fetal pulmonary circuit. In the normal fetal circulation, oxygenated blood travels from the mother through the placenta to the fetus. The oxygen-rich blood traverses the fetal inferior vena cava, right atrium, right ventricle, and main pulmonary artery. The fetal pulmonary arteries are constricted and have high pulmonary vascular resistance. Oxygenated blood bypasses the fetal pulmonary circulation and enters through the ductus arteriosus to the lower resistance systemic circulation. Oxygenated blood then enters the fetal aorta distal to the left subclavian artery, perfuses the fetal systemic circulation, becomes deoxygenated, and returns to the maternal circulation. In the fetus, the ductus arteriosus is kept open by low arterial oxygen content and placental prostaglandin E2 (PGE2).
from the placenta to the fetal systemic circulation, thereby bypassing the fetal pulmonary circuit. In the normal fetal circulation, oxygenated blood travels from the mother through the placenta to the fetus. The oxygen-rich blood traverses the fetal inferior vena cava, right atrium, right ventricle, and main pulmonary artery. The fetal pulmonary arteries are constricted and have high pulmonary vascular resistance. Oxygenated blood bypasses the fetal pulmonary circulation and enters through the ductus arteriosus to the lower resistance systemic circulation. Oxygenated blood then enters the fetal aorta distal to the left subclavian artery, perfuses the fetal systemic circulation, becomes deoxygenated, and returns to the maternal circulation. In the fetus, the ductus arteriosus is kept open by low arterial oxygen content and placental prostaglandin E2 (PGE2).
TABLE 31.1 Krichenko Classification of Patent Ductus Arteriosus Appearance on Angiography | ||||||||||||||||||
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C. Birth.
Several changes occur at birth to initiate normal functional closure of the ductus arteriosus within the first 15 to 18 hours of life. Spontaneous respirations result in increased blood oxygen content. Prostaglandin levels decrease because of placental ligation and increased metabolism of prostaglandins within the pulmonary circulation by prostaglandin dehydrogenase. The combination of increased oxygen content and lowered circulating prostaglandin levels usually results in closure of the ductus arteriosus. Generally, the ductus arteriosus is hemodynamically insignificant within 15 hours and completely closed by 2 to 3 weeks. The fibrotic remnant of this structure persists in the adult as the ligamentum arteriosum. Spontaneous closure of a PDA is unlikely in term infants after 3 months and in preterm infants after 12 months.
III. CLINICAL PRESENTATION
A. Symptoms.
Severity of symptoms depends on the degree of left-to-right shunting; and it is determined by the size of the PDA, ductal resistance, cardiac output, as well as the systemic and pulmonary vascular resistances. PDA size is categorized by the degree of left-to-right shunting determined by the pulmonary-to-systemic flow ratio: Qp:Qs (Table 31.2). Between 25% and 40% of patients with PDA are asymptomatic, especially those with a small PDA. They are often diagnosed by auscultation
of a continuous murmur on examination or incidentally during diagnostic testing. With larger PDAs, symptoms may develop. The most common symptom is exercise intolerance followed by dyspnea, peripheral edema, and palpitations. As is often the case in adult congenital heart disease, a previously well-tolerated PDA may become manifest in the setting of acquired heart disease such as ischemia, essential hypertension, and valvular disease.
of a continuous murmur on examination or incidentally during diagnostic testing. With larger PDAs, symptoms may develop. The most common symptom is exercise intolerance followed by dyspnea, peripheral edema, and palpitations. As is often the case in adult congenital heart disease, a previously well-tolerated PDA may become manifest in the setting of acquired heart disease such as ischemia, essential hypertension, and valvular disease.
TABLE 31.2 Patent Ductus Arteriosus Size by Qp:Qs | ||||||||
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B. Physical examination.
Patients with PDAs may present with a wide range of physical findings. Pulse pressure may be wide because of diastolic runoff into the PDA, and peripheral pulses may be bounding. The jugular venous pressure is often normal with a small PDA, whereas with a large PDA, prominent a and v waves may be present. Precordial palpation often reveals a normal precordial impulse with a small PDA and a prominent left ventricular impulse with a large PDA. A harsh, continuous murmur may be heard at the left first or second intercostal space. The murmur envelops the second heart sound (S2) and decreases in intensity during diastole. A small PDA has a soft, high-frequency, continuous murmur, whereas a large PDA classically has a machinerylike, loud murmur. With a large PDA, a middiastolic apical murmur may occur because of increased diastolic flow across the mitral valve. If pulmonary hypertension is present, a right ventricular lift may be present and the pulmonic component of S2 will have increased intensity. The duration of the diastolic murmur reflects pulmonary artery pressures; elevated pulmonary artery pressures lead to a decreased gradient for left-to-right flow through the PDA during diastole, which results in a shorter diastolic murmur. As pulmonary pressure increases, the systolic component of the murmur shortens. Right-to-left flow may not generate a systolic murmur. For patients with a right-to-left shunt, a pathognomonic physical finding is differential cyanosis of the lower extremities and left hand.
C. Complications.
The most common complications of PDA include CHF, infective endocarditis, and pulmonary hypertension. CHF occurs through volume overload of the left side of the heart and may be accompanied by atrial fibrillation. Vegetations generally develop on the pulmonary side of the PDA, and septic lung emboli may occur. Untreated PDAs with audible murmurs have a risk of infective endocarditis of 0.45%/y after the second decade. Spontaneously occurring aneurysms of the ductus arteriosus have been reported, although they are typically seen in association with endarteritis or among very young or very old patients. Pulmonary hypertension develops as a result of increased pulmonary vascular flow from a large PDA with significant left-to-right flow. Elevation in right-sided pressures may eventually result in Eisenmenger’s physiology, right-to-left flow, and isolated cyanosis and clubbing of lower extremities (occurring in 5% of unrepaired PDA patients) with signs of pulmonary hypertension.
D. Differential diagnosis.
The differential diagnosis of PDA includes ventricular septal defect associated with aortic insufficiency, aortopulmonary window, pulmonary atresia with systemic collateral vessels, innocent venous hum, and arteriovenous communications such as pulmonary arteriovenous fistula, coronary artery fistula, systemic arteriovenous fistula, and ruptured sinus of Valsalva aneurysm.
IV. LABORATORY TESTING
A. Hematology.
Blood laboratory results are generally unremarkable, although compensatory erythrocytosis may be present in the setting of long-standing cyanosis resulting from a right-to-left shunt.
B. Electrocardiogram (ECG).
ECG is neither sensitive nor specific for PDA. The ECG for a patient with a small PDA is often normal. Depending on the duration and hemodynamic significance of the PDA, electrocardiographic criteria for left atrial enlargement or left ventricular hypertrophy may be present. If pulmonary hypertension exists, the ECG may demonstrate right ventricular hypertrophy or right atrial enlargement.
C. Chest radiography (CXR).
CXR is neither sensitive nor specific for PDA. A normal chest radiograph implies a small, hemodynamically insignificant PDA. With a large PDA, left atrial and left ventricular enlargement may be present, as well as increased pulmonary vascularity. With right-to-left shunting from pulmonary hypertension, the main pulmonary artery is frequently enlarged. The PDA occasionally appears as a separate convexity between the aortic knob and the pulmonary trunk. Calcification of the PDA may be visualized in older individuals.
V. DIAGNOSTIC TESTING.
Standard transthoracic echocardiography (TTE) is the preferred initial diagnostic modality because of its low cost and noninvasive nature. Transesophageal echocardiography (TEE) may be required in subjects with suboptimal echocardiographic windows. Cardiac catheterization is typically reserved for therapeutic intervention.
A. TTE has a 42% sensitivity and 100% specificity for the diagnosis of PDA. The suprasternal notch view is usually best for demonstrating the PDA, particularly its aortic origin. The complete course of a PDA may be difficult to follow in some patients because of its tortuosity. Color Doppler imaging can often reveal flow between the descending aorta distal to the left subclavian artery and the pulmonary trunk. It is imperative to demonstrate color Doppler flow within the pulmonary artery, typically on a high parasternal short-axis view. Color Doppler and continuous wave Doppler help determine the direction of flow in the PDA. The timing of flow (systolic or diastolic) depends on pressure gradients between the systemic and pulmonary circulation. Quantitative assessment of shunt velocity is valuable to estimate the degree of restriction across the PDA. This measurement becomes important when planning transcatheter intervention. Diastolic aortic flow reversal is seen in the descending aorta if the shunt is significant. Associated left atrial and left ventricular enlargement also suggest a hemodynamically significant lesion.
