Park's Pediatric Cardiology for Practitioners, 6th Ed.

Obstructive Lesions

Lesions that produce obstruction to ventricular outflow such as pulmonary stenosis (PS), aortic stenosis (AS), and coarctation of the aorta (COA) are discussed in this chapter.

Pulmonary Stenosis

Prevalence

Isolated PS occurs in 8% to 12% of all congenital heart defects (CHDs). PS is often associated with other CHDs, such as tetralogy of Fallot (TOF), single ventricle, and others.

Pathology

1. PS may be valvular, subvalvular (infundibular), supravalvular, or within the RV cavity (i.e., “double-chambered RV”).

2. In valvular PS, the pulmonary valve is thickened, with fused or absent commissures and a small orifice (Fig. 13-1A). Although the RV is usually normal in size, it is hypoplastic in infants with critical PS (with a nearly atretic valve). Dysplastic valves (consisting of thickened, irregular, immobile tissue and a variably small pulmonary valve annulus) are frequently seen with Noonan’s syndrome.

3. Isolated infundibular PS is rare; it is usually associated with a large ventricular septal defect (VSD), as seen in TOF (see Fig. 13-1B).

4. Aberrant hypertrophied muscular bands (running between the ventricular septum and the anterior wall) divide the right ventricular (RV) cavity into a proximal high-pressure chamber and a distal low-pressure chamber (double-chambered RV). A “dimple” in the ordinarily smooth RV surface is found during surgery (see Chapter 15).

5. Supravalvular PS (or stenosis of the pulmonary arteries), isolated or in association with other CHDs, occurs in 2% to 3% of all patients with CHD. The stenosis may be single, involving the main pulmonary artery (PA) (see Fig. 13-1) or either of its branches, or multiple, involving both the main and several smaller peripheral PA branches (not shown). Commonly associated defects are pulmonary valve stenosis, VSD, and TOF. Peripheral PA stenosis is often seen in association with congenital syndromes; such as Williams syndrome, Noonan’s syndrome, Alagille syndrome, Ehlers-Danlos syndrome, and Silver-Russell syndrome or congenital rubella syndrome. PA stenosis is discussed further in Chapter 15.

Clinical Manifestations

History

1. Children with mild PS are completely asymptomatic. Exertional dyspnea and easy fatigability may be present in patients with moderately severe cases. Heart failure or exertional chest pain may develop in severe cases.

2. Newborns with critical PS may present with poor feeding, tachypnea, and cyanosis.

Physical Examination (Fig. 13-2)

1. Most patients are acyanotic and well developed. Newborns with critical PS are cyanotic and tachypneic.

2. A right ventricular tap and a systolic thrill may be present at the upper left sternal border (and occasionally in the suprasternal notch).

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FIGURE 13-1 Anatomic types of pulmonary stenoses (PSs). A, Valvular stenosis. B, Infundibular stenosis. C, Supravalvular PS (or stenosis of the main pulmonary artery [PA]). Abnormalities are indicated by arrows. AO, aorta; LV, left ventricle; RA, right atrium; RV, right ventricle.

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FIGURE 13-2 Cardiac findings of pulmonary valve stenosis. Abnormal sounds are shown in black. Dots represent areas with systolic thrill. EC, ejection click.

3. A systolic ejection click is present at the upper left sternal border only with valvular stenosis. The S2 may split widely, and the P2 may be diminished in intensity. An ejection-type systolic murmur (grade 2–5 of 6) is best audible at the upper left sternal border, and it transmits well to the back, too. The louder and longer the murmur, the more severe the stenosis is.

4. Hepatomegaly may be present if congestive heart failure (CHF) develops.

5. In newborns with critical PS, cyanosis may be present (caused by a right-to-left atrial shunt), and signs of CHF with hepatomegaly and peripheral vasoconstriction may be found.

6. In patients with peripheral PA stenosis, a midsystolic murmur in the pulmonary valve area is well transmitted to the axillae and back. Occasionally, a continuous murmur is audible over the involved lung field.

Electrocardiography

1. The electrocardiogram (ECG) findings are normal in mild cases.

2. Right-axis deviation (RAD) and right ventricular hypertrophy (RVH) are present in moderate PS.

3. Right atrial hypertrophy (RAH) and RVH with “strain” may be seen in severe PS.

4. Neonates with critical PS may show left ventricular hypertrophy (LVH) because of a hypoplastic RV and relatively large left ventricle (LV).

Radiography

1. Heart size is usually normal, but the main PA segment may be prominent with valvular stenosis (caused by poststenotic dilatation) (Fig. 13-3). Cardiomegaly is present only if CHF develops.

2. Pulmonary vascular markings are usually normal but may decrease with severe PS.

3. In neonates with critical PS, lung fields are oligemic with a varying degree of cardiomegaly.

Echocardiography

1. Two-dimensional echocardiography in the parasternal short-axis view (see Fig. 5-2) shows thick pulmonary valve cusps with restricted systolic motion (doming). The subcostal long-axis view (see Fig. 5-5) may show similar findings. The size of the pulmonary valve annulus can be estimated. The main PA is often dilated (poststenotic dilatation).

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FIGURE 13-3 Posteroanterior view of chest radiograph in pulmonary valve stenosis. Note a marked poststenotic dilatation (arrow) and normal pulmonary vascularity. (Courtesy Dr. Ewell Clarke, San Antonio, TX.)

2. The Doppler study can estimate the pressure gradient across the stenotic valve by the simplified Bernoulli equation. Multiple echocardiographic views, including parasternal short-axis and subcostal long-axis views, should be used to obtain the maximum flow velocity. The instantaneous pressure gradient estimated by Doppler echo is slightly greater than the peak-to-peak systolic pressure gradient obtained by cardiac catheterization. The severity of PS (by Doppler gradient) may be classified as follows.

a. Mild: A pressure gradient less than 35 to 40 mm Hg (or RV systolic pressure <50% of the LV pressure).

b. Moderate: A valve pressure gradient of 40 to 70 mm Hg (or RV pressure 50%–75% of the LV pressure).

c. Severe: A pressure gradient greater than 70 mm Hg (or RV pressure ≥75% LV pressure).

3. Dysplastic valves are characterized by a noticeably thickened and immobile leaflet and hypoplasia of the pulmonary valve annulus.

4. In neonates, Doppler pressure gradient may underestimate the severity of PS because the PA pressure may be higher than normal, especially in those with PDA with a left-to-right shunt.

Natural History

1. The severity of stenosis is usually not progressive in mild PS. For example, more than 95% of patients with an initial Doppler gradient less than 25 mm Hg did not need operation over a 25-year period. The majority of the patients with mild PS (<35 mm Hg) do well without intervention.

2. In moderate or severe PS, the severity tends to progress with age.

3. CHF may develop in patients with severe stenosis. Sudden death is possible in patients with severe stenosis during heavy physical activities.

4. Without appropriate management, most neonates with critical PS die (see Management).

Management

Medical

1. Newborns with critical PS and cyanosis require emergency treatment to reduce mortality.

a. These babies may temporarily improve with prostaglandin E1 infusion, which reopens the ductus arteriosus, and other supportive measures.

b. Balloon valvuloplasty is the procedure of choice in critically ill neonates. Immediate reduction in pressure gradient can be achieved in more than 90% of these neonates.

c. Some of these infants are not able to maintain effective forward flow through the pulmonary valve because of noncompliant or hypoplastic RV. Some of them may need one of the following: (1) a prolonged prostaglandin (PG) infusion (for 3 weeks), (2) ductal stenting, or (3) systemic-to-pulmonary shunt surgery.

d. In neonates, complications of the balloon procedure are more common than in older patients, with a mortality rate of up to 3%, a major complication rate of 3.5%, and a minor complication rate of 15%.

e. About 15% of the patients require reintervention (either repeat valvuloplasty or surgery for infundibular stenosis or dysplastic valve) at a later time.

f. Even dysplastic valves appear to mature after the balloon procedure.

2. Balloon valvuloplasty is the procedure of choice for the valvular stenosis at all ages.

a. Indications for the balloon procedure may include the following.

1) A resting pressure gradient of greater than 40 mm Hg with the patient sedated in the catheterization laboratory.

2) If the catheterization gradient is 30 to 39 mm Hg, the balloon procedure may be reasonable.

3) Symptoms attributable to PS with a catheterization gradient greater than 30 mm Hg. The symptoms may include angina, syncope or presyncope, and exertional dyspnea.

4) The procedure is useful and reasonable in patients with dysplastic pulmonary valve, as commonly seen in Noonan’s syndrome. It has a lower success rate with the valvuloplasty (65%). If balloon valvuloplasty is unsuccessful, surgery is indicated.

b. Results: The balloon procedure carries an extremely low risk, is painless, is less costly than surgery, and shortens hospital stay.

1) A good outcome is achieved in 85% of patients with valvular stenosis. Restenosis after balloon dilatation is extremely rare.

2) Pulmonary regurgitation (PR) after balloon dilatation is common, occurring in 10% to 40% of patients. PR is usually well tolerated, although rarely some of these patients may become candidates for pulmonary valve implantation. Therefore, a balloon smaller than previously recommended (i.e., 120%–140% of the annulus) may be preferable.

3) After relief of severe PS (either by balloon or surgery), a hypertrophied dynamic infundibulum may cause a persistent pressure gradient, with rare occurrences of fatal outcome (“suicidal right ventricle”). Propranolol may be given to reduce hyperdynamic infundibular obstruction. The reduction of this gradient occurs gradually over weeks.

3. Restriction of activity is not necessary in children with this condition except in cases of severe PS (Doppler gradient >70 mm Hg).

Surgical

Indications and Timing

1. Surgical valvotomy should be limited to patients with more complex lesions or those in whom balloon procedure is contraindicated or failed.

2. Other types of obstructions (e.g., infundibular stenosis, anomalous RV muscle bundle) with significant pressure gradients require surgery on an elective basis.

3. If balloon valvuloplasty is unsuccessful or unavailable, infants with critical PS and CHF require surgery on an urgent basis.

Procedure

1. Through a midsternal incision, pulmonary valvotomy is performed for pulmonary valve stenosis under cardiopulmonary bypass. The approach is through the PA. Neonates with critical PS may require a transventricular valvotomy or the insertion of a transannular patch (or both) while receiving prostaglandin E1 infusion. If severe infundibular hypoplasia is present, a systemic-to-PA shunt is also performed.

2. Dysplastic valves often require complete excision of the valves. Simple valvotomy may be ineffective.

3. Infundibular stenosis requires resection of the infundibular muscle and patch widening of the right ventricular outflow tract.

4. Stenosis at the main PA level requires patch widening of the narrow portion.

5. Anomalous muscle bundles require surgical resection.

Mortality

Surgical mortality occurs in fewer than 1% of older children. The rate is about 10% in critically ill infants.

Aortic Stenosis

Prevalence

Left ventricular outflow tract obstruction (LVOTO), which includes stenosis at, below, or above the aortic valve, represents up to 10% of all CHDs. Valvular AS is the most frequent (71%) followed by subvalvular stenosis (23%) and supravalvular stenosis (6%). Aortic valve stenosis occurs more often in males (male-to-female ratio of 4:1).

Pathology

1. Stenosis may be at the valvular, subvalvular, or supravalvular level (Fig. 13-4).

2. Valvular AS may be caused by a bicuspid aortic valve, a unicuspid aortic valve, or stenosis of the tricuspid (or tricommissural) aortic valve (see Fig. 13-4B). A bicuspid aortic valve with a fused commissure and an eccentric orifice accounts for the most common form of aortic valve stenosis (75%) (Fig. 13-5B). Less common is the unicuspid valve with one lateral attachment (see Fig. 13-5A). A valve that has three unseparated cusps with a stenotic central orifice is the least common form (see Fig. 13-5C). Many bicuspid aortic valves are nonobstructive during childhood and become stenotic in adult life because of calcification of the valve.

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FIGURE 13-4 Anatomic types of aortic stenoses. A, Normal. B, Valvular stenosis. C, Supravalvular stenosis. D, Discrete subaortic stenosis. E, Idiopathic hypertrophic subaortic stenosis (this condition is discussed in Chapter 18).

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FIGURE 13-5 Anatomic types of aortic valve stenoses. Top row is the side view, and bottom row is the view as seen in surgery during aortotomy. A, Unicuspid aortic valve. B, Bicuspid aortic valve. C, Stenosis of a tricuspid aortic valve. (From Goor DA, Lillehei CW: Congenital Malformations of the Heart. New York, Grune & Stratton, 1975.)

3. Symptomatic neonates with so-called critical neonatal aortic valve stenosis have primitive, myxomatous valve tissue, with a pinhole opening. The aortic valve ring and ascending aorta are almost always hypoplastic. Hypoplasia of the mitral valve, LV cavity, or LVOT and a VSD are also frequently found, often requiring one-ventricular repair (Norwood operation followed by Fontan operation).

4. Supravalvular AS is an annular constriction at the upper margin of the sinus of Valsalva (see Fig. 13-4C). Occasionally, the ascending aorta is diffusely hypoplastic. This is often associated with Williams syndrome (which includes mental retardation, characteristic facies, and multiple PA stenosis).

5. Subvalvular (subaortic) stenosis may be in the form of a discrete narrowing or a long tunnel-like fibromuscular narrowing of the LVOT.

a. Discrete stenosis occurs more often than tunnel stenosis and accounts for about 10% of all AS cases. It may be simple membranous ridge or collar (more common) or fibromuscular ridge with or without membrane. Some subaortic stenosis is believed to develop as the result of turbulence in an abnormally shaped LVOT, which causes endocardial injury and subsequent proliferation and fibrosis.

1) Two thirds of the patients have associated cardiac lesions, such as VSD, patent ductus arteriosus (PDA), or COA.

2) In one third of the patients, the stenosis is isolated; familial isolated subaortic membrane has been reported.

3) In some patients, there is history of surgical intervention, such as membranous VSD closure or PA banding (9 months to 8 years before the development of the membrane).

b. Tunnel-like subaortic stenosis is often associated with hypoplasia of the ascending aorta and aortic valve ring, as well as thickened aortic valve leaflets. It is usually associated with other LV anomalies, including Shone complex (comprising supramitral ring, parachute mitral valve, subaortic stenosis, and COA).

c. Another type of subvalvular stenosis is idiopathic hypertrophic subaortic stenosis (see Fig. 13-4E), a primary disorder of the heart muscle (discussed in Chapter 18).

Clinical Manifestations

History

1. Neonates with critical or severe stenosis of the aortic valve may develop signs of hypoperfusion or respiratory distress caused by pulmonary edema within days to weeks after birth.

2. Most children with mild to moderate AS are asymptomatic. Occasionally, exercise intolerance may be present.

3. Exertional chest pain, easy fatigability, or syncope may occur in a child with severe degree of obstruction.

Physical Examination (Fig. 13-6)

1. Infants and children with AS are acyanotic and are normally developed.

2. Except for neonates with critical AS, blood pressure is normal in most patients, but a narrow pulse pressure is present in severe AS. Patients with supravalvular AS may have a higher systolic pressure in the right arm than in the left (caused by the jet of stenosis directed into the innominate artery, the so-called Coanda effect).

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FIGURE 13-6 Cardiac findings of aortic valve stenosis. Abnormal sounds are indicated in black. Systolic thrill may be present in areas with dots. EC, ejection click.

3. A systolic thrill may be palpable at the upper right sternal border, in the suprasternal notch, or over the carotid arteries.

4. An ejection click may be heard with valvular AS. The S2 splits either normally or a bit narrowly. The S2 may split paradoxically in severe AS (see Fig. 13-6). A harsh, grade 2 to 4 of 6, midsystolic murmur is best heard at the second right or left intercostal space, with good transmission to the neck and apex. A high-pitched, early diastolic decrescendo murmur, which results from aortic regurgitation (AR), may be audible in patients with bicuspid aortic valve and in those with discrete subvalvular stenosis.

5. Peculiar “elfin facies,” mental retardation, and friendly “cocktail party” personalities may be associated with supravalvular AS (e.g., Williams syndrome).

6. Newborns with critical AS may develop signs of reduced peripheral perfusion (with weak and thready pulses, pale cool skin, and slow capillary refill) triggered by ductal constriction. The clinical picture may mimic overwhelming sepsis with low cardiac output. The heart murmur may be absent or faint but becomes louder when CHF improves.

Electrocardiography

In mild cases, the ECG is normal. LVH with or without strain pattern may be present in severe cases (Fig. 13-7). Correlation of the severity of AS and the ECG abnormalities is relatively poor.

Radiography

1. The heart size is usually normal in children, but a dilated ascending aorta or a prominent aortic knob may be seen occasionally in valvular AS, resulting from poststenotic dilatation.

2. Significant cardiomegaly does not develop unless CHF occurs later in life or if AR becomes substantial.

3. Newborns with critical AS show generalized cardiomegaly with pulmonary venous congestion.

Echocardiography

1. Valvular AS

a. In the parasternal short-axis view of the two-dimensional (2D) echocardiogram, normal aortic valves are tricuspid, with three cusps of approximately equal size. In diastole, the normal aortic cusp margins form a Y pattern (Fig. 13-8). In systole, a bicuspid aortic valve appears as a noncircular (i.e., football-shaped) orifice (see Fig. 13-8). Stenosis of the tricuspid aortic valve appears as a heavy Y pattern in diastole and as a small, centrally located orifice in systole, with three thickened commissures distinctly visible. A unicommissural aortic valve, which is seen often in infants with critical AS, is seen as a circular orifice positioned eccentrically within the aortic root and without visible distinct cusps.

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FIGURE 13-7 Tracing from a 7-year-old boy with severe aortic stenosis. It shows left ventricular hypertrophy, with a probable “strain” pattern.

b. In the parasternal long-axis view of the 2D echocardiogram, doming of the thick aortic valve with restriction to the opening is seen in systole. Reverse doming during diastole commonly occurs in the unicuspid valve, occurs less frequently in the bicuspid valve, and does not occur in the tricuspid aortic valve.

c. Doppler pressure gradient is best obtained from the apical five-chamber view with the cursor placed distal to the stenotic aortic valve in the sinus of Valsalva.

d. Doppler studies can estimate the severity of the stenosis by using the simplified Bernoulli equation (see Chapter 5). However, the Doppler-derived gradient (i.e., instantaneous gradient) may be approximately 20% higher than the peak-to-peak systolic pressure gradient obtained under sedation during cardiac catheterization. The severity of AS by Doppler peak (and mean) gradient and by peak-to peak gradient may be classified as follows (Graham et al, 2005).

1) Mild: A peak Doppler of less than 40 mm Hg (mean Doppler <25 mm Hg) or peak-to-peak gradient of less than 30 mm Hg

2) Moderate: A peak Doppler of 40 to 70 mm Hg (mean Doppler of 25–40 mm Hg) or peak-to-peak gradient of 30 to 50 mm Hg

3) Severe: A peak Doppler of greater than 70 mm Hg (mean Doppler of >40 mm Hg) or peak-to-peak gradient of greater than 50 mm Hg

2. Subvalvular AS

a. The type of subaortic stenosis is best imaged in the parasternal long-axis view, apical long-axis view, and apical five-chamber view just beneath the aortic valve.

b. One should note whether the stenosis is membrane, fibromuscular ridge, or diffuse tunnel-like fibromuscular narrowing (tunnel stenosis).

c. For the membranous type, one should note (1) the length of the membrane, (2) the pressure gradient across the obstruction, (3) the distance of the membrane from the hinge point of the aortic valve, (4) extension of the membrane onto the aortic or mitral valve, (5) the presence of aortic regurgitation, and (6) associated cardiac lesion. Some of these have been linked to the risk of recurrence requiring surgery.

d. The pressure gradient across the subaortic stenosis is best obtained in the apical five-chamber view with the cursor placed immediately distal to the obstruction but proximal to the aortic valve.

3. Supravalvular AS is seen as a narrowing of the ascending aorta in the parasternal long-axis view and apical long-axis view. The suprasternal view best shows diffuse hypoplasia of the ascending aorta. Doppler pressure gradient is obtained with the cursor distal to the stenosis in the ascending aorta.

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FIGURE 13-8 Diagram of parasternal short-axis scan showing normal tricuspid (left column) and bicuspid aortic valves (three right columns) during diastole and systole. Three nearly equal-sized aortic cusps are imaged in a normal aortic valve, which opens widely during systole. The systolic opening pattern distinguishes a raphe from a commissure. With a bicuspid aortic valve, various commissural orientations are imaged. The most common pattern demonstrates commissures at the 4 or 5 o’clock and the 9 or 10 o’clock positions, with raphe at the 1 or 2 o’clock position (46%). (Modified from Brandenburg RO Jr, Tajik AJ, Edwards WD, et al: Accuracy of 2-dimensional echocardiographic diagnosis of congenitally bicuspid aortic valve: Echocardiographic-anatomic correlation in 115 patients. Am J Cardiol 51:1469-1473, 1983.)

Natural History

1. Chest pain, syncope, and even sudden death (1%–2% of cases) may occur in children with severe AS.

2. Heart failure occurs with severe AS during the newborn period or later in adult life.

3. Bicuspid aortic valve, the most common type of AS, becomes frequently more severe with time in a significant number of patients. Isolated AR tends to occur in younger patients. Early signs of calcification occur in the second to third decades of life with worsening of AS and eventual worsening of AR. Valve replacement may be required in many adult patients.

4. Progressive worsening of AR is possible in discrete subaortic stenosis. The jet of the subaortic stenosis damages the aortic valve with resulting AR.

Management

Medical

1. For critically ill newborns with CHF, the patients are stabilized before surgery or balloon valvuloplasty by the use of rapidly acting inotropic agents (usually dopamine) and diuretics to treat CHF and intravenous infusion of prostaglandin E1 to reopen the ductus. Mechanical ventilation may be useful. Neonates and young infants with CHF from critical AS require the balloon valvuloplasty (or surgery) on an urgent basis.

2. For asymptomatic patients with mild to moderate stenosis a serial echo-Doppler ultrasound evaluation is needed at approximately 1- to 2-year intervals. It is needed more often in children with severe stenosis because AS, of all severities, tends to worsen with time.

3. Exercise stress test (EST) may be indicated in asymptomatic children with peak gradients above 50 mm Hg or mean Doppler gradient above 30 mm Hg who are interested in athletic participation or in becoming pregnant.

4. Balloon valvuloplasty

a. Indications: Percutaneous balloon valvuloplasty has replaced open surgical valvotomy as the treatment of choice for children with moderate to severe congenital aortic valve stenosis in the majority of centers. For subaortic stenosis, the balloon procedure is not effective. The following may be indications for the procedure according to the American Heart Association (Feltes et al, 2011).

• In newborns with isolated critical valvular AS who are ductal dependent

• In children with isolated valvar AS who have depressed LV systolic function

• In children with isolated valvar AS who have a resting peak-to-peak systolic gradient of 50 mm Hg or greater by cardiac catheterization

• In children with isolated valvar AS who have a resting peak systolic gradient 40 mm Hg or greater, if there are symptoms of angina or syncope or ischemic ST-T wave changes on ECG at rest or with exercise

b. Results of the valvuloplasty: Although the results of aortic balloon valvuloplasty are promising, they are not as good as those for PS. A technically adequate balloon dilatation will typically reduce the catheter peak-to-peak systolic gradient to 20 to 35 mm Hg. The optimal ratio of balloon-annulus diameter is 0.9 to 1.0. Larger balloon diameter is associated with a greater risk of developing AR after the procedure.

The long-term outcome after a successful valve dilatation is good, but late restenosis and aortic valve regurgitation eventually necessitate reintervention in the majority of patients. The freedom from reintervention was 67% after 5 years in children; it was lower (48%) in newborns (Feltes et al, 2011). Serious complications (e.g., major hemorrhage, loss of the femoral artery pulse, avulsion of part of the aortic valve leaflet, perforation of the mitral valve or left ventricle) can occur.

5. Activity restrictions (Graham et al, 2005)

a. No limitation in activity is required for mild AS.

b. For patients with moderate AS, varying levels of activity restriction are required as suggested below.

1) Those with mild or no LVH by echo, no LV strain on ECG, and normal EST findings may participate in competitive sports in class IA, IB, and IIA.

2) Those with supraventricular tachycardia (SVT) or multiple or complex ventricular tachycardia (VT) at rest or with exercise may participate only in low-intensity competitive sports in class IA and IB (see Fig. 34-1).

c. Patients with severe AS should not participate in any competitive sports.

Surgical

Indications and Timing

1. Valvular AS: If the balloon valvuloplasty has failed to relieve the pressure gradient or if severe AR results after the balloon procedure.

2. Subaortic membrane: Most commonly accepted indications for surgical intervention are a peak gradient greater than 35 mm Hg and at least mild AR. Occasionally, the presence of one of them may be an indication for intervention. Most centers accept the onset of AR as an indication for surgical removal of the membrane.

Patients with the following are considered low risk and are recommended for medical follow-up rather than surgical intervention: those with (1) no or trace AR, (2) Doppler gradient of 30 mm Hg or less, (3) the membrane not in proximity to the aortic valve (>6 mm), and (4) thin and mobile aortic valve. The risk of recurrence after surgical removal of the membrane has been a concern (see later for further discussion).

3. Tunnel-type subaortic stenosis: A gradient of 50 mm Hg or greater is considered an indication for surgery.

4. Supravalvular AS: Surgery is advisable for patients with supravalvular AS when there is a peak pressure gradient across the stenosis greater than 50 to 60 mm Hg, severe LVH, or appearance of new AR.

Procedures (and Mortality)

1. Closed aortic valvotomy, using calibrated dilators or balloon catheters without cardiopulmonary bypass, may be performed in sick infants. This procedure has a low surgical mortality rate.

2. Newborns with “critical AS” (with hypoplasia of the aortic annulus, ascending aorta, and mitral annulus, small LV cavity, and MR from papillary muscle infarction) have a poor prognosis. The Norwood procedure (see Chapter 14) may be preferable (for future Fontan operation) to aortic valvotomy. A mortality rate for sick neonates with critical AS has decreased to around 10%, although it was much higher in the past, up to 40% to 50%.

3. Valvular AS: The following procedures are performed for aortic valve stenosis: aortic valve commissurotomy, aortic valve replacement, or the Ross procedure.

a. Aortic valve commissurotomy is usually tried if stenosis is the predominant lesion. Fused commissures are divided with a knife to within 1 mm of the aortic wall. Only commissures with adequate leaflet attachments to the aortic wall are opened because division of rudimentary commissures produces severe AR.

b. Aortic valve replacement may be necessary if AR is the predominant lesion. Valve replacement is done by using a mechanical prosthetic valve or homografts. The advantage of the mechanical valve is durability, but it has the tendency of thrombus formation on the valve with a potential embolization. Because of this tendency, patients require warfarin, with its attendant risks of bleeding, in addition to aspirin. Homografts have the advantage of a lower incidence of thromboembolism, but deterioration of the homograft (caused by generation and calcification) is likely to occur within a decade or two.

c. Because of accelerated degeneration of homograft or bioprosthesis valves, a mechanical valve is usually used in adolescents. For adolescent girls or women in whom pregnancy is desired, homografts may be a good alternative until the childbearing years are completed because of the known teratogenic effects of warfarin. A recent study in adults suggests that increased serum cholesterol level (>200 mg/dL) may be a risk factor for bioprosthetic valve calcification, so lowering cholesterol levels is recommended.

d. In the Ross procedure (pulmonary root autografts), the autologous pulmonary valve replaces the aortic valve, and an aortic or a pulmonary allograft replaces the pulmonary valve. The Ross procedure is more complex than simple aortic valve replacement because it requires coronary artery implantation (Fig. 13-9). The pulmonary valve autograft has the advantage of documented long-term durability; it does not require anticoagulation and remains uncompromised by host reactions. There is evidence of the autograft’s growth, making it an attractive option for aortic valve replacement in infants and children. Mild regurgitation of the neoaortic valve occurs frequently, which may result from a preexisting pulmonary valve regurgitation. The patient’s own aortic valve may be used for pulmonary position after aortic valvotomy (“double” Ross procedure). An early mortality rate for the Ross procedure (and the Ross/Konno procedure) is less than 5%.

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FIGURE 13-9 Ross procedure (pulmonary root autograft). A, The two horizontal lines on the aorta (AO) and pulmonary artery (PA) and two broken circles around the coronary artery ostia are lines of proposed incision. The pulmonary valve, with a small rim of right ventricle (RV) muscle, and the adjacent PA are removed. B, The aortic valve and the adjacent aorta have been removed, leaving buttons of aortic tissue around the coronary arteries. C, The pulmonary autograft is sutured to the aortic annulus and to the distal aorta, and the coronary arteries are sutured to openings made in the PA. The pulmonary valve is replaced with either an aortic or a pulmonary allograft. LV, left ventricle; RA, right atrium.

4. Subvalvular AS

a. Excision of the membrane is done for discrete subvalvular AS. There is a tendency for recurrence after surgical excision. The recurrence rate is as high as 25% to 30%. Risk factors for recurrence include (a) younger age (<4 year), (b) high-pressure gradient (>50 mm Hg), (c) proximity of the membrane to the aortic valve (<6 mm), and (d) extension of the membrane to the aortic or mitral valves. Some centers delay surgery until after 10 years of age because recurrence is very rare at this age. More aggressive resection of the membrane and extensive myectomy reduced the recurrence but resulted in higher complication of atrioventricular block (14%). The surgical mortality rate for subaortic membrane is near 0%.

b. For complex LVOT obstruction (e.g., aortic stenosis combined with a diffuse subaortic stenosis or hypoplastic annulus), the Ross procedure can be combined with Konno operation (the Ross-Konno procedure) (Fig. 13-10). The mortality for tunnel subaortic stenosis is less than 5%.

4. Supravalvular AS: With the most common hourglass type of supravalvular AS, a reconstructive surgery is done using a Y-shaped patch. For the diffuse form of obstruction, the patch is extended superiorly into the transverse arch to relieve all obstruction. Death occurs for supravalvular stenosis in fewer than 1% of cases, although diffuse narrowing of the ascending aorta is a risk factor.

Postballoon and Postoperative Follow-up

1. Annual follow-up examination is necessary for all patients who had the aortic valve balloon procedure or surgery to detect development of stenosis or regurgitation. In 10% to 30% of patients, significant AR develops after valvotomy or the balloon procedure.

2. Recurrence of discrete subaortic stenosis occurs in 25% to 30% after surgical resection of the membrane and as long as 17 years after the initial procedure, requiring a long, periodic follow-up. Some of these patients require reoperation at a later age.

3. Anticoagulation is needed after a prosthetic mechanical valve replacement. The international normalized ratio (INR) should be maintained between 2.5 and 3.5 for the first 3 months and 2.0 to 3.0 beyond that time. Low-dose aspirin (75–100 mg/ day for adolescents) is also indicated in addition to warfarin (American College of Cardiology/American Heart Association [ACC/AHA] 2006 Guidelines).

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FIGURE 13-10 The Ross-Konno procedure. A, Intended incision in the ascending aorta and around the aortic annulus and excision boundaries for the pulmonary artery and right ventricle (RV) are shown. Intended incisions to harvest buttons of aortic wall around the coronary artery ostia are also shown. B, The pulmonary artery autograft has been harvested (with an extra portion of the RV, not shown) for the Ross procedure. The aortic root and aortic valve are completely excised. C, The small obstructed left ventricular outflow tract (LVOT) is shown. The intended incision in the LVOT and the interventricular septum is noted by the dotted line, which will result in a V-shaped widening of the LVOT. D, The posterior portion of the pulmonary autograft is sutured to the original LVOT. E, The LVOT is reconstructed by suturing the extra portion of the RV to the widened V-shaped LVOT. The coronary arteries have been reimplanted. F, The RVOT is reconstructed by inserting a pulmonary homograft between the RV body and the distal end of the pulmonary artery. LCA, left coronary artery; LVOT, left ventricular outflow tract; RCA, right coronary artery; SVC, superior vena cava. Other abbreviations used are the same as in Figure 13-9.

4. After aortic valve replacement with bioprosthesis and no risk factors, aspirin (75–100 mg), but not warfarin, is indicated. When there are risk factors (which include atrial fibrillation, previous thromboembolism, LV dysfunction, and hypercoagulable state), warfarin is indicated to achieve an INR of 2.0 to 3.0 (ACC/AHA 2006 Guidelines).

Coarctation of the Aorta

Prevalence

Coarctation of the aorta occurs in 8% to 10% of all cases of CHD. It is more common in males than in females (male-to-female ratio of 2 to 1). Among patients with Turner’s syndrome, 30% have COA.

Pathology

1. The usual location of COA is juxtaductal, just distal to the left subclavian artery; less often it is proximal to the origin of the left subclavian artery.

2. The most common associated anomaly is bicuspid aortic valve, which occurs in more than 50% and up to 85% of all patients with COA.

3. COA also occurs as part of other CHDs, such as transposition of the great arteries and double-outlet right ventricle (e.g., Taussig-Bing abnormality).

4. Intracerebral aneurysm (berry aneurysm) is present in approximately 10% of patients with COA (Connolly et al, 2003).

5. In symptomatic infants with COA, other associated cardiac defects such as aortic hypoplasia, abnormal aortic valve, VSD, and mitral valve anomalies are often present. In these infants, during fetal life, the descending aorta is supplied mostly via right-to-left ductal flow because the amount of antegrade flow through the relatively small aortic arch and isthmus is reduced (see Fig. 10-3). With ductal closure, a reduced antegrade aortic flow to the descending aorta produces symptoms early in life. Good collateral circulation has not developed in these infants (see Chapter 10). Occasionally, infants without associated defects may become symptomatic because of LV failure, which results from a sudden increase in pressure work in early postnatal life.

6. In asymptomatic infants and children with COA, during fetal life, the descending aorta is supplied by both normal amount of antegrade aortic flow through the aortic isthmus and normal ductal flow because associated cardiac defects are rare in these children except for bicuspid aortic valve. Good collateral circulation gradually develops between the proximal aorta and the distal aorta during fetal life.

7. Major collateral circulation between the aortic segments proximal and distal to the coarctation comprises (1) the internal mammary artery anteriorly, (2) arteries arising from the subclavian artery by way of the intercostal arteries, and (3) the anterior spinal artery (Fig. 13-11).

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FIGURE 13-11 Collateral circulation in coarctation of the aorta. Anteriorly, the internal mammary artery leads to the epigastric arteries for the supply to the lower extremity. The arteries arising from the subclavian artery and supplying the scapula communicate, by way of intercostal arteries, with the descending aorta, thereby supplying blood to the abdominal organs. The anterior spinal artery is also enlarged. a., artery; Coarc, coarctation; Inf., inferior; Lat., lateral; Sup, superior. (From Moller JH, Amplatz K, Edwards JE: Congenital Heart Disease. Kalamazoo, MI, Upjohn, 1971.)

The presentation of patients with COA occurs in a bimodal distribution: newborn infants with circulatory symptoms in the first weeks of life and asymptomatic infants and children. Clinical manifestation and management are quite different in these two groups; therefore, they are presented under separate headings.

Symptomatic Infants

Clinical Manifestations

History

Poor feeding, dyspnea, or signs of acute circulatory shock may develop in the first 6 weeks of life. Figure 13-12 provides an explanation for hemodynamic deterioration in the newborn period. The newborn discharge examination may have been normal as a result of incomplete obliteration of the aortic end of the ductus, which would permit blood flow to the descending aorta. After ductal obliteration, the aortic lumen narrows with loss of the space provided by the aortic end of the ductus.

Physical Examination

1. Infants with COA are pale and experience varying degrees of respiratory distress. Oliguria or anuria, general circulatory shock, and severe acidemia are common. Differential cyanosis may be present; for example, only the lower half of the body is cyanotic because of a right-to-left ductal shunt (particularly after prostaglandin E1 [PGE1] infusion).

2. Peripheral pulses may be weak and thready as a result of CHF. A blood pressure differential may become apparent only after improvement of cardiac function with administration of rapidly acting inotropic agents.

3. The S2 is single and loud; a loud S3 gallop is usually present. No heart murmur is present in 50% of sick infants. A nonspecific ejection systolic murmur is audible over the precordium. The heart murmur may become louder after treatment.

Electrocardiography

A normal or rightward QRS axis and RVH or right bundle branch block (RBBB) are present in most infants with COA rather than LVH; LVH is seen in older children (see Chapter 10) (Fig. 13-13).

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FIGURE 13-12 Explanation for hemodynamic deterioration seen in some infants with coarctation of the aorta (COA) in the first days of life. A, Coarctation is at the juxtaductal position, so that space is added to the narrowed aorta (AO) by the ductus. B, After ductal obliteration, the added lumen is lost, and the aorta becomes severely obstructed, although the severity of the coarctation is unchanged. PA, pulmonary artery.

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FIGURE 13-13 Tracing from a 3-week-old infant with coarctation of the aorta. Note a marked right ventricular hypertrophy.

Radiography

Marked cardiomegaly and pulmonary edema or pulmonary venous congestion are usually present.

Echocardiography

Two-dimensional echocardiography and color-flow Doppler studies usually show the site and extent of the coarctation (Fig. 13-14).

1. In the suprasternal notch view, a thin wedge-shaped “posterior shelf” is imaged in the posterolateral aspect of the upper descending aorta, which is distal to the left subclavian artery.

2. Varying degrees of isthmic hypoplasia are present. The third percentile value of normal internal dimension of the aortic isthmus at 40-week gestation is 5.4 mm.

3. The transverse aortic arch may be hypoplastic also. Poststenotic dilatation of the descending aorta is usually imaged. Bicuspid aortic valve is frequently present. Other associated defects such as VSD can be imaged.

4. Echocardiographic diagnosis of neonatal COA in the presence of patent ductus arteriosus is difficult. Ramaciotti et al (1993) suggested the following diagnostic criteria for neonatal COA: an aortic isthmus 3 mm or smaller without PDA or 4 mm or smaller in the presence of PDA. The ratio of the aortic isthmus to the descending aorta at the diaphragm smaller than 0.64 is also a reliable sign of COA in the presence of PDA.

5. Doppler studies above and below the coarctation site should be obtained, as shown in Figure 13-14, in assessing the severity of the coarctation (see Chapter 5 for further discussion).

6. Delayed rate of systolic upstroke and diastolic flow in the abdominal aorta may hint the presence of coarctation.

Other Imaging

Magnetic resonance imaging (MRI) has become the imaging modality of choice after echocardiographic diagnosis of the condition. Cardiac catheterization is no longer needed for anatomic assessment. It is performed primarily for interventional treatment.

Natural History

About 20% to 30% of all patients with COA develop CHF by 3 month of age. If COA is undetected and untreated in a symptomatic infant, early death may result from CHF and renal shutdown.

Management

Medical

1. In symptomatic neonates, PGE1 infusion should be started to promote ductal patency and establish flow to the descending aorta and the kidneys.

2. Intensive anticongestive measures with short-acting inotropic agents (e.g., dopamine, dobutamine), diuretics, and oxygen should be started.

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FIGURE 13-14 Echocardiogram (A) and diagram (B) of a suprasternal long-axis view of coarctation of the aorta. A narrowing is present in the upper descending aorta distal to the left subclavian artery. The transverse aortic arch and aortic isthmus are mild to moderately hypoplastic. Doppler estimation of pressure gradients should be obtained at two X marks, proximal and distal to the coarctation for accurate estimation of the pressure gradient.

3. Metabolic disturbances (e.g., acidosis and hypoglycemia) should be recognized and treated promptly.

4. When the patient is stabilized, either surgical repair or balloon procedure should be performed because the improvement from anticongestive measures is usually temporary.

5. Although surgical repair has been the primary treatment for COA at most centers, balloon angioplasty with or without stent implantation has emerged as a less invasive alternative to surgery for sick infants. This is controversial, however. Balloon angioplasty appears to be associated with a higher rate of recoarctation than surgical repair, and the rate of complications (including femoral artery injury) is high during infancy. Some centers use cutting balloons or low-profile stents in very sick infants, which do not require overexpansion of the coarctation segment and thus are less likely to produce aneurysms. When stents are used in small infants, they are usually not expandable to adult size, requiring surgical removal at a later date.

Surgical

Indications and Timing

1. If CHF or circulatory shock develops early in life, surgical repair (extended resection with an end-to-end anastomosis) should be performed on an urgent basis. A short period of medical treatment, as described earlier, improves the patient’s condition before surgery.

2. If there is a large associated VSD, which occurs in 17% to 33% of patients with COA, one of the following procedures may be performed:

a. COA and VSD can be repaired in the same operative setting if the VSD is nonrestrictive. Both are performed through a median sternotomy.

b. Only coarctation repair is performed if the VSD appears restrictive. Approximately 40% of restrictive VSDs close spontaneously. If CHF cannot be managed medically, VSD is surgically closed within days or weeks after the initial coarctation surgery.

c. PA banding is performed if the PA pressure remains high after completing COA surgery. Later the VSD is closed, and the PA band is removed between 6 and 24 months of age.

Procedures

The choice of surgical procedures varies greatly from institution to institution, but the following procedures are popular (Fig. 13-15).

1. Extended resection and end-to-end anastomosis is preferred to other surgical options. It consists of resecting the coarctation segment and anastomosing the proximal and distal aortas (Fig. 13-15top). Because most of symptomatic neonatal COA is associated with hypoplasia of the isthmus and occasionally of the aortic arch, extended resection with end-to-end anastomosis has been performed with a lower recurrence rate (<10%).

2. Subclavian flap aortoplasty consists of dividing the distal subclavian artery and inserting a flap of the proximal portion of this vessel between the two sides of the longitudinally split aorta throughout the coarctation segment (see Fig. 13-15middle). The vertebral artery is ligated to avoid subclavian steal. The recurrence rate is lower (10%–40%) than that with the patch aortoplasty.

3. With patch aortoplasty, the aorta is opened longitudinally through the coarctation segment and extending to the left subclavian artery, and the fibrous shelf and any existing membrane are excised. An elliptic woven Dacron patch is inserted to expand the diameter of the lumen (see Fig. 13-15bottom). Patch aortoplasty has the highest recurrence rate (≤50%).

4. A conduit insertion between the ascending and descending aorta may be performed for severe, long-segment COA (not shown).

Mortality

The mortality rate for COA surgery is less than 5%. The mortality rate for repair of COA and VSD at the same time is less than 10%.

Complications

1. Postoperative renal failure is the most common cause of death.

2. Residual obstruction or recoarctation occurs in 6% to 33% of all patients, but the recurrence rate is lower after surgery than that after balloon angioplasty.

Postoperative Follow-up

1. An examination every 6 to 12 months to check for recurrence of COA is necessary, especially when surgery is performed in the first year of life.

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FIGURE 13-15 Surgical techniques for repair of coarctation of the aorta (COA). Top, End-to-end anastomosis. A segment of coarctation is resected, and the proximal and distal aortas are anastomosed end to end. Middle, Subclavian flap procedure. The distal subclavian artery is divided, and the flap of the proximal portion of this vessel is used to widen the coarcted segment. Bottom, Patch aortoplasty. An elliptic woven Dacron patch is inserted to expand the diameter of the lumen. Regardless of the type of operative procedure, the ductus arteriosus is always ligated and divided.

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FIGURE 13-16 Cardiac findings of coarctation of the aorta. A systolic thrill may be present in the suprasternal notch (area shown by dots). EC, ejection click.

2. Balloon angioplasty (with or without stent) may be performed if a significant recoarctation develops.

3. Physicians should watch for and treat systemic hypertension.

Asymptomatic Infants and Children

Clinical Manifestations

History

Most children are asymptomatic. Occasionally, a child complains of weakness or pain (or both) in the legs after exercise.

Physical Examination (Fig. 13-16)

1. Patients grow and develop normally.

2. Arterial pulses in the leg are either absent or weak and delayed. There is hypertension in the arm or the leg systolic pressure is equal to or lower than the arm systolic pressure. In normal children, the oscillometric systolic pressure in the thigh or calf is 5 to 10 mm Hg higher than that in the arm. With use of the auscultatory method, the leg systolic pressure may be as much as 20 mm Hg higher than in the arm in normal children (see Chapter 2).

3. A systolic thrill may be present in the suprasternal notch. The S2 splits normally, and the A2 is accentuated. An ejection click is frequently audible at the apex or at the base (or both), which may originate in the associated bicuspid aortic valve or from systemic hypertension. An ejection systolic murmur grade 2 to 4 of 6 is heard at the upper right sternal border and mid-or lower left sternal border. A well-localized systolic murmur is also audible in the left interscapular area in the back. Occasionally, an early diastolic decrescendo murmur of AR from the bicuspid aortic valve may be audible in the third left intercostal space (see Fig. 13-16).

Electrocardiography

Leftward QRS axis and LVH are commonly found. The ECG is normal in approximately 20% of patients.

Radiography

1. The heart size may be normal or slightly enlarged.

2. Dilatation of the ascending aorta may be seen.

3. An E-shaped indentation on the barium-filled esophagus or a “3 sign” on overpenetrated films suggests COA (see Fig. 4-10).

4. Rib notching between the fourth and eighth ribs may be seen in older children but rarely in children younger than 5 years of age (see Fig. 4-9).

Echocardiography

1. The suprasternal notch 2D echo demonstrates a discrete shelf-like membrane in the posterolateral aspect of the descending aorta. Associated findings such as isthmus hypoplasia, poststenotic dilatation, and diminished pulsation in the descending aorta may be present. Bicuspid aortic valve is frequently present.

2. Doppler examination often demonstrates a pattern of diastolic runoff, especially in patients with robust collaterals or tight stenosis. Continuous-wave Doppler flow profile distal to the coarctation is composed of two superimposed signals representing low-velocity flow in the proximal descending aorta and high-velocity flow across the coarctation. As discussed earlier, a more accurate estimation of the gradient is obtained by the expanded Bernoulli equation, in which the peak velocities obtained from the segments proximal and distal to the coarctation site are used. This is because the flow velocity proximal to the coarctation is often higher than 1.5 m/sec and it cannot be ignored in the Bernoulli equation. In severe COA with extensive collaterals, the Doppler-estimated gradient may underestimate the severity of the coarctation because the blood flow through the coarctation site is decreased.

Other Imaging

Magnetic resonance imaging with three-dimensional reconstruction supplemented by gadolinium contrast has become the imaging modality of choice. Cardiac catheterization is no longer needed for anatomic assessment.

Natural History

1. LV failure, rupture of the aorta, intracranial hemorrhage (i.e., rupture of a berry aneurysm of the arterial circle of Willis), hypertensive encephalopathy, and hypertensive cardiovascular disease are rare complications seen in adulthood.

2. A bicuspid aortic valve may cause stenosis or regurgitation with age.

Management

Medical

1. Children with mild COA should be watched regularly for hypertension in the arm and for increasing pressure differences between the arm and leg. Reduced BP readings in the lower extremities may be caused by femoral artery injuries resulting from previous surgeries or interventional procedures.

2. Balloon angioplasty for native unoperated coarctation is controversial, although most centers perform balloon dilatation for recurrent coarctation. Some centers continue to use the balloon procedure for the native COA, but other centers prefer a surgical approach.

Indications for balloon intervention include the following according to a recent recommendation by the AHA (Feltes et al, 2011):

• Transcatheter systolic gradient across COA of greater than 20 mm Hg and suitable anatomy, irrespective of patients’ age.

• Transcatheter systolic gradient of les than 20 mm Hg with suitable angiographic anatomy:

a. In the presence of significant collateral vessels

b. In patients with univentricular heart

c. In patients with significant LV dysfunction

• It may be reasonable to consider the procedure for native coarctation as a palliative procedure at any age when the patient has severe LV dysfunction, severe mitral regurgitation, or systemic disease affected by the cardiac condition.

The most common acute complication of the balloon angioplasty has been femoral artery injury and thrombosis, especially in small children. There is a possibility of aortic aneurysm formation with serious late complications. A recent single center analysis of balloon angioplasty versus surgical repair of native coarctation in children ages 3 to 20 years suggests the superiority of surgical repair over balloon procedure in terms of aortic aneurysm formation (0% vs. 35%), with some aneurysms developing 5 years after the procedure (Cowley et al, 2005).

3. A balloon-expandable stainless-steel stent implanted concurrently with balloon angioplasty is gaining popularity. Currently, the aortic stent is used for older children (at least 8 to 10 years old), and the stent used should be expandable to an adult size (minimum of 20 mm in diameter).

Advantages of the use of the expandable stent may include the following: (1) it does not require overexpansion of the coarcted segment, thereby reducing the chance of the development of aortic aneurysm; (2) it produces better results with greater reduction of pressure gradient than the balloon procedure alone; and (3) it can be reexpanded to the adult size, avoiding repeat surgical procedures.

Current recommendations for stent placement in native COA and recoarctation of the aorta are as follows according to the recent recommendations by the AHA (Feltes et al, 2011).

• For recoarctation, stent placement is indicated in patients who have a transcatheter systolic coarctation gradient greater than 20 mm Hg and are of sufficient size for safe stent placement which can be expanded to an adult size.

• For initial treatment of native COA or recurrent coarctation, it is reasonable to consider stent placement if there is:

a. A transcatheter systolic coarctation gradient of >20 mm Hg

b. A transcatheter systolic gradient of <20 mm Hg with systolic hypertension caused by the narrowing of the aorta

c. A long segment coarctation with a transcatheter systolic gradient >20 mm Hg

• For patients in whom balloon angioplasty has failed in the treatment of native or recurrent COA, it is reasonable to use stent placement.

4. Absorbable metal stent is in the experimental stage. The Magnesium Biocorrodible Stent (Biotroniks, Nulach, Switzerland) is an innovative stent made of a magnesium alloy (that also contains zirconium, yttrium, and rare earths), that can be deliverable through a 5-French sheath (Peuster et al, 2001). This could be used in infants and small children in whom repeat dilatation of the stent may be necessary.

Surgical

Indications and Timing

1. Significant narrowing of the aorta with pressure gradient greater than 20 to 30 mm Hg is considered an indication for surgery in asymptomatic children.

a. Blood pressure measurement showing hypertension in the arm with a large systolic pressure gradient of 20 to 30 mm Hg or greater by Doppler echocardiography or blood pressure measurement may be a relatively weak indication.

b. Reduction of aortic diameter by 50% at the level of COA in the presence of pressure gradient of more than 20 to 30 mm Hg is considered an absolute indication for surgery. The dimension of the coarctation segment can be determined by an echocardiographic study, but MRI may be a better choice for older children and adolescents.

c. Children with mild COA (<20 mm Hg gradient) may be considered for surgery if a prominent gradient develops with exercise.

2. The preferred age for surgery varies from center to center; some centers prefer ages of 2 and 3 years, and others prefer delaying it until 4 to 5 years of age. A lower incidence of hypertension is found in patients who had COA repair before 1 year of age. However, early surgery (i.e., before 1 year of age) appears to increase the chance of recoarctation. The risk of late recurrence of coarctation is low if the surgery is performed after 2 years of age. Older children are operated on soon after the diagnosis is made.

Procedures

1. Through a left thoracotomy incision, extended resection of the coarctation segment and end-to-end anastomosis is the procedure of choice for discrete COA in children (see Fig. 13-15).

2. Occasionally, subclavian artery aortoplasty or circular or patch grafts may be performed.

Mortality

The mortality rate is less than 1% in older children.

Complications

1. Spinal cord ischemia producing paraplegia may develop after cross-clamping of the aorta during surgery, which is probably related to limited collateral circulation. This develops in 0.4% of cases.

2. Rebound hypertension may occur in the immediate postoperative period as a result of an increased sympathetic activity (with elevated norepinephrine level).

3. Other rare complications may include recurrent laryngeal nerve injury, chylothorax, bleeding, and infection.

Postoperative Follow-up

1. During childhood, annual examinations should pay attention to the following.

a. Blood pressure differences in the arm and leg, which suggest recoarctation. Again, consider the possibility of femoral artery damage from previous procedures as the cause of the blood pressure differential.

b. Persistence or resurgence of hypertension in the arm and legs in some of the patients. The cause of the hypertension is not completely understood. Its occurrence appears to be proportional to the age of the child at the time of the operative repair.

c. Associated abnormalities such as bicuspid aortic valve or mitral valve disease.

d. Persistent myocardial dysfunction that was present before surgery.

e. Subaortic stenosis evolving years after the initial surgery in some patients.

2. Lifelong follow-up is indicated because of COA-related complications and frequent association of bicuspid aortic valve.

a. Systemic hypertension is common in adults and may predispose cerebral aneurysms in these patients to rupture with resulting stroke. Hypertension should be treated with beta-blockers.

b. Aneurysm formation and likelihood of dissection and rupture. Magnetic resonance angiography or computed tomography (CT) imaging is better than echocardiographic studies, performed perhaps every 2 to 5 years.

c. All patients with bicuspid aortic valve require a regular follow-up because some of these patients may require aortic valve surgery.

d. For a recurrence of the COA after either a surgical repair or a balloon angioplasty for native COA, a balloon angioplasty may be performed.

e. Coarctation stenting decreases recoil after the angioplasty and may reduce the late incidence of aneurysm formation, but this can be done only in older children and adolescents because it requires a large arterial (8 or 9 French) sheath.

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FIGURE 13-17 Three types of aortic arch interruptions. A, Type A. B, Type B. C, Type C (see text). AO, aorta; LCC, left common carotid; LS, left subclavian; MPA, main pulmonary artery; PDA, patent ductus arteriosus; RCC, right common carotid; RS, right subclavian.

Interrupted Aortic Arch

Prevalence

Interrupted aortic arch accounts for about 1% of all critically ill infants who have CHDs.

Pathology

1. This is an extreme form of COA in which the aortic arch is atretic or a segment of the arch is absent.

2. Depending on the location of the interruption, the defect is divided into the following three types (Fig. 13-17):

a. Type A: The interruption is distal to the left subclavian artery (occurring in 30% of cases).

b. Type B: The interruption is between the left carotid and left subclavian arteries (occurs in 43% of cases). An aberrant right subclavian artery is common. DiGeorge syndrome is reported in about 50% of patients with type B.

c. Type C: The interruption is between the innominate and left carotid arteries (occurs in 17% of cases).

3. Interrupted aortic arch is usually associated with PDA and VSD (occurring in >90% of cases). A bicuspid aortic valve occurs in 60% of all cases. Often there is mitral valve deformity (10% of cases), persistent truncus arteriosus (10% of cases), or subaortic stenosis (20% of cases).

4. DiGeorge syndrome occurs in at least 15% of these patients.

Clinical Manifestations

1. Respiratory distress, variable degrees of cyanosis, poor peripheral pulses, and signs of CHF or circulatory shock develop during the first days of life. Differential cyanosis is uncommon because of the frequent association of VSD.

2. Chest radiographs show cardiomegaly, increased pulmonary vascular markings, and pulmonary venous congestion or pulmonary edema. The upper mediastinum may be narrow because of the absence of the thymus, as is commonly found with DiGeorge syndrome. The ECG may show RVH in uncomplicated cases.

3. Echocardiography is useful in the diagnosis of the interruption and associated defects. Cardiac CT and MRI are used more frequently than angiography to clarify the anatomy before surgery.

Management

1. Medical treatment consists of PGE1 infusion (preferably before 4 days of age) with intubation and oxygen administration. Workup for DiGeorge syndrome (i.e., serum calcium) should be done. Hyperventilation that causes respiratory alkalosis and tetany should be avoided, and citrated blood (which causes hypocalcemia by chelation) should not be transfused in patients with DiGeorge syndrome. Blood should be irradiated before the transfusion.

2. Primary complete repair of the interruption and the VSD is recommended if the interruption is associated with a simple VSD. If it is associated with complex anomalies, the initial procedures should be banding the PA and repairing the interruption. Debanding and repair of the VSD and other cardiac anomalies should be done at a later date. A primary anastomosis, Dacron vascular graft, or venous homograft may be used to repair the interruption. The surgical mortality rate can be as low as 10% for initial surgery.