Obstructive Lesions

A. Prevalence

Isolated PS occurs in 4% to 8% of all CHDs.

B. Pathology and Pathophysiology

• 1.

  PS may be valvular (90%), subvalvular (infundibular), or supravalvular (i.e., stenosis of the main PA). Stenosis of the PA branches is presented in Chapter 10 .

  • a.

    In valvular PS, the pulmonary valve is thickened, with fused or absent commissures and a small orifice. A poststenotic dilatation of the MPA usually develops with valvular PS.

  • b.

    In neonates with critical PS, the RV, tricuspid valve, right ventricular outflow tract (RVOT), and pulmonary artery are commonly underdeveloped.

  • c.

    Dysplastic pulmonary valve (with thickened, irregular, immobile tissue) is frequently seen with Noonan syndrome.

  • d.

    Infundibular PS is usually associated with a large VSD as seen in TOF. The poststenotic dilatation is not seen with subvalvular stenosis.

• 2.

  In so-called double-chambered RV, abnormal muscular bands (running between the ventricular septum and the anterior wall) divide the RV cavity into a proximal high-pressure chamber and a distal low-pressure chamber.

• 3.

  Pulmonary artery stenosis may occur in the main pulmonary artery, its main branches, or in the small distal pulmonary arteries. This topic is discussed in a separate heading in this chapter.

• 4.

  Depending on the severity of PS, a varying degree of RVH develops. The RV is usually normal in size, but in newborns with critical PS, the RV is hypoplastic.

C. Clinical Manifestations

• 1.

  Usually asymptomatic with mild PS. Exertional dyspnea and easy fatigability may be seen in moderately severe cases, and CHF occurs in severe cases. Neonates with critical PS are cyanotic and tachypneic.

• 2.

  An ejection click is present at the ULSB with valvular PS ( Fig. 8.1 ). The S2 may split widely, and the P2 may be diminished in intensity. A systolic ejection murmur (grade 2 to 5/6) with or without systolic thrill is best audible at the ULSB and transmits fairly well to the back and axillae. The louder and longer the murmur, the more severe is the stenosis. Neonates with critical PS may have only a faint heart murmur, if any.

  

• 3.

  The electrocardiogram (ECG) is normal in mild PS. RAD and RVH are present in moderate PS. RAH and RVH with “strain” pattern are present in severe PS. Neonates with critical PS may show LVH (due to hypoplastic RV and relatively large LV).

• 4.

  Chest radiographs show normal heart size and a prominent MPA segment (i.e., poststenotic dilatation). PVMs are normal but may be decreased in severe PS.

• 5.

  Two-dimensional echo and Doppler echo studies:

  • a.

    Thickened pulmonary valve with restricted systolic motion (doming) and a poststenotic dilatation of the MPA are commonly seen.

  • b.

    The severity of PS (by peak Doppler pressure gradient) may be classified as follows:

    • (1)

      Mild: <35 to 40▒mm Hg (or RV pressure <50% of LV pressure).

    • (2)

      Moderate: gradient 40 to 70▒mm Hg (or RV pressure 50% to 75% of LV pressure).

    • (3)

      Severe: >70▒mm Hg (or RV pressure ≥75% of LV pressure).

• 6.

  Natural history: The severity of the obstruction is usually not progressive in mild PS, but it tends to progress with age in moderate or severe PS. CHF may develop in patients with severe stenosis. Sudden death is possible in patients with severe stenosis during heavy physical activities.

D. Management

A. Prevalence

A group of lesions that produce LV outflow tract obstruction account for 10% of all CHD. Aortic valve stenosis occurs more often in males (male-to-female ratio of 4:1).

B. Pathology and Pathophysiology

• 1.

  LVOT obstruction may occur at the valvular, subvalvular, or supravalvular levels ( Fig. 8.2 ).

  

• 2.

  Valvular stenosis may be caused by a bicuspid aortic valve, a unicuspid aortic valve, or stenosis of the tricuspid (or tricommissural) aortic valve ( Fig. 8.3 ).

  • a.

    By far the most common type of aortic valve stenosis is bicuspid aortic valve (BAV), accounting for 75% of AS ( Fig. 8.3B ). In addition, it is the most common cardiac malformation with prevalence of 0.5% to 2% of the general population, diagnosed by echo studies. Many cases of BAV are nonobstructive during childhood. More than 50% of the patients with BAV have aortic dilatation that is now considered primary aortopathy (rather than the result of hemodynamic abnormality). BAV is believed to be an inheritable disorder (i.e., autosomal dominant disease with incomplete penetrance) with a male-to-female ratio of 3:1.

  • b.

    Much less common is the unicuspid valve with one lateral attachment ( Fig. 8.3A ).

  • c.

    A valve that has three unseparated cusps with a stenotic central orifice is the least common form ( Fig. 8.3C ).

  

• 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, the mitral valve, and the LV cavity are almost always hypoplastic (often requiring Norwood operation followed by Fontan operation).

• 4.

  Supravalvular AS occurs at the upper margin of the sinus of Valsalva. This is often associated with Williams syndrome. Patients with supravalvular AS may also have coronary artery ostial stenosis with increased risk of sudden cardiac death.

• 5.

  Subvalvular (subaortic) stenosis may be either discrete (simple membrane or fibromuscular ridge) or diffuse tunnel-like fibromuscular narrowing (tunnel stenosis). Discrete subaortic stenosis is more common than the tunnel stenosis and is often associated with other lesions such as VSD, PDA, or COA. Tunnel-like subaortic stenosis is often associated with hypoplasia of the valve ring and the ascending aorta.

• 6.

  Natural history: Hypertrophy of the LV may develop if the stenosis is severe. Dilatation of the ascending aorta seen in BAV may progress. AR usually develops with subaortic AS.

C. Clinical Manifestations

• 1.

  Patients with mild to moderate AS and those with BAV are asymptomatic. Exertional chest pain or syncope may occur with severe AS. CHF develops within the first few months of life with critical AS.

• 2.

  Blood pressure (BP) 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 (due to the jet of stenosis directed into the innominate artery, the so-called Coanda effect).

• 3.

  A systolic thrill may be present at the URSB, in the suprasternal notch, or over the carotid arteries. An ejection click may be audible with valvular AS. A harsh systolic ejection murmur (grade 2 to 4/6) is best audible at the second right intercostal space or third left intercostal space ( Fig. 8.4 ), with good transmission to the neck and frequently to the apex. A high-pitched, early diastolic decrescendo murmur of AR may be audible in patients with bicuspid aortic valve and those with discrete subvalvular stenosis. In symptomatic infants with critical AS, the heart murmur may be absent or faint, and the peripheral pulses are weak and thready.

  

• 4.

  The ECG is normal in mild cases. LVH with or without a strain pattern is seen in more severe cases.

• 5.

  Chest radiographs are usually normal in children, but a dilated ascending aorta may be seen occasionally in valvular AS. A significant cardiomegaly develops with CHF or substantial AR.

• 6.

  Echo and Doppler studies are diagnostic.

  • a.

    The parasternal short-axis view of the two-dimensional echocardiography shows the anatomy of the aortic valve: bicuspid, tricuspid, or unicuspid. Normal aortic valves are tricuspid, with three cusps of approximately equal size. In diastole the normal aortic cusp margins form a Y pattern, which opens widely during systole ( Fig. 8.5 ). In systole, a bicuspid aortic valve appears as a noncircular (i.e., football-shaped) orifice ( Fig. 8.5 ). 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.

    

  • b.

    The Doppler pressure gradient is best obtained in the apical “five-chamber” view. The Doppler pressure gradient (instantaneous gradient) is approximately 20% higher than the peak-to-peak systolic pressure gradient obtained during cardiac catheterization.

  • c.

    The severity of the stenosis is defined by a peak velocity across the aortic valve and a mean Doppler gradient across the valve as follows.

    • (1)

      Mild: Peak velocity 2.0–2.9▒m/sec (or mean Doppler gradient ≤20▒mm Hg)

    • (2)

      Moderate: Peak velocity 3.0–3.9▒m/sec (or mean Doppler gradient between 20 and 39▒mm Hg).

    • (3)

      Severe: Peak velocity of ≥4.0▒m/sec (or mean Doppler gradient of ≥40▒mm Hg) (or aortic valve area of ≤1.0 cm ² or indexed valve area ≤0.6 cm ² /m2).

  • d.

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

  • e.

    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.

• 7.

  Magnetic resonance imaging (MRI).

  If unclear from echo study, MRI can clarify the level and mechanism of anatomic obstruction. It may be a reliable tool for serial evaluation of aortic dilatation in patients with BAV.

• 8.

  Natural history.

  • a.

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

  • b.

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

  • c.

    With BAV, progressive aortic dilatation may occur. Rarely, aortic dilataton may lead to aortic aneurysm.

  • d.

    BAVs are nonobstructive during childhood and become stenotic or significantly regurgitant in adult life due to calcification of the valve. Valve replacement may be required in many adult patients.

  • e.

    Progressive worsening of AR is possible in discrete subaortic stenosis.

D. Management