Obstructive Lesions





I. Pulmonary Stenosis


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.




    Fig. 8.1


    Cardiac findings of pulmonary valve stenosis. Abnormal sounds are shown in black. Dots represent areas with systolic thrill. EC , Ejection click.


  • 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


Medical and Nonsurgical




  • 1.

    For neonates with critical PS and cyanosis, prostaglandin E 1 (PGE 1 ) infusion should be started to reopen the ductus. 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. Complications of the balloon procedure are more common than in older patients, with a mortality rate of up to 3%. Even dysplastic valves appear to mature after the balloon procedure. About 15% of the patients require reintervention (either repeat valvuloplasty or surgery) at a later time.


  • 2.

    Balloon valvuloplasty is the procedure of choice for significant pulmonary valve stenosis. Cardiac catheterization is recommended for the balloon procedure in patients with a Doppler pressure gradient near 50▒mm Hg. Indications for the balloon procedure may include the following.



    • a.

      Pressure gradient >40▒mm Hg with the patient sedated in the catheterization laboratory.


    • b.

      If the catheterization pressure gradient is 30 to 39▒mm Hg, the balloon procedure is reasonable.


    • c.

      Symptoms (angina, syncope, or presyncope) attributable to PS with catheter gradient >30▒mm Hg.


    • d.

      It is reasonable to try on dysplastic pulmonary valve (with lower success rate of 65%).



  • 3.

    Complications of the balloon procedure.



    • a.

      PR is common after balloon dilatation (occurring in 10% to 40%). Therefore use of a balloon 120% to 130% of the pulmonary annulus is recommended to reduce the incidence of PR.


    • b.

      Following relief of severe PS (either by balloon or surgery), hypertrophied dynamic infundibulum may cause a persistent pressure gradient, with rare occurrences of fatal outcome (“suicidal right ventricle”); in this case intravenous propranolol could be given during cardiac catheterization. After balloon valvuloplasty oral propranolol may be given to reduce hyperdynamic infundibular obstruction. The reduction of this gradient occurs gradually over weeks



  • 4.

    Restriction of activity is usually not indicated except for severe PS.



Surgical




  • 1.

    Surgical valvotomy is occasionally indicated in patients with valvular PS in whom balloon valvuloplasty is unsuccessful.


  • 2.

    Surgery is indicated in patients with dysplastic pulmonary valves that are resistant to dilatation. Dysplastic valve may need to be completely excised because simple valvotomy may be ineffective.


  • 3.

    Surgery is also indicated for infundibular stenosis and anomalous RV muscle bundle with significant pressure gradients.


  • 4.

    If balloon valvuloplasty is unsuccessful, infants with critical PS require surgery on an urgent basis.


  • 5.

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



Follow-Up


Periodic echo studies are indicated to detect recurrences or worsening of the stenosis.


II. Aortic Stenosis


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 ).




    Fig. 8.2


    Anatomic types of left ventricular outflow tract obstruction. (A) Normal. (B) Valvular stenosis. (C) Supravalvular stenosis. (D) Discrete subaortic stenosis.


  • 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 ).




    Fig. 8.3


    Anatomic types of aortic valve stenosis. The top row shows 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, D. A., & Lillehei, C. W. (1975). Congenital malformations of the heart . New York: Grune & Stratton.


  • 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.




    Fig. 8.4


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


  • 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.




      Fig. 8.5


      Diagram of parasternal short-axis scan of normal tricuspid ( left column ) and bicuspid aortic valves ( three right columns ) during diastole and systole. The most common pattern of the bicuspid aortic valve demonstrates commissures at the 4- or 5-o’clock and the 9-or 10-o’clock positions, with raphe at the 10 or 2-o’clock position (45%).

      Modified from Brandenburg, R. O., Jr., Tajik, A. J., Edwards, W. D., Reeder, G. S. Shub, C., & Seward, J. B. (1983). Accuracy of 2-dimensional echocardiographic diagnosis of congenitally bicuspid aortic valve: echocardiographic-anatomic correlation in 115 patients. American Journal of Cardiology, 51 (9), 1469–1473.


    • 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


Medical and Nonsurgical




  • 1.

    In critically ill neonates and infants with CHF, anticongestive measures with fast-acting inotropic agents and diuretics, with or without PGE 1 infusion, are indicated, in preparation for either balloon valvuloplasty or surgery.


  • 2.

    A serial echo Doppler ultrasound evaluation is needed at 1- to 2-year intervals for patients with mild to moderate stenosis, and more often for severe stenosis.


  • 3.

    Because of the progressive nature of aortic dilatation in children with BAV, annual echocardiographic measurement of the aortic root and ascending aorta is recommended.


  • 4.

    Recent American Heart Association recommendations include echocardiographic screening of first-degree relatives of patients with BAV (because approximately 9% of them may have the BAV).


  • 5.

    Exercise stress testing may be indicated in children with AS who are interested in athletic participation.


  • 6.

    Activity restrictions. No limitation in activity is required for mild AS. For patients with moderate AS, varying levels of activity restriction are required (see Chapter 25 ). Patients with severe AS should not participate in any competitive sports.


  • 7.

    Balloon valvuloplasty.



For moderate to severe valvular AS, percutaneous balloon aortic valvuloplasty has replaced open surgical valvotomy as the treatment of choice.


Indications: The following may be indications for the procedure according to the AHA.



  • a.

    Asymptomatic children and young adults, with a (catheter-derived) peak systolic ejection gradient ≥50▒mm Hg.


  • b.

    Symptomatic patients (with angina, syncope), patients with resting or exercise-induced ECG changes, patients planning to become pregnant, or patients who plan to participate in competitive sports, if they have a gradient ≥40▒mm Hg.


  • c.

    Infants with valvular AS with depressed LV systolic function, regardless of pressure gradient.


  • d.

    Neonates who require maintenance of a patency of ductus arteriosus for adequate systemic perfusion, regardless of pressure gradient.


  • e.

    Results of the valvuloplasty: The procedure typically reduces the catheter peak-to-peak systolic gradient to 20 to 35▒mm Hg. The optimal ratio of balloon-annulus diameter is 0.8 to 0.9. 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 for 5 years is 67% for children; it is lower (48%) in newborns.



Surgical




  • 1.

    For neonates with “critical AS”:


    A sick newborn with critical AS who had failed balloon valvuloplasty may have one of the following two.



    • a.

      Closed aortic valvotomy, using calibrated dilators or balloon catheters without cardiopulmonary bypass, may be tried.


    • b.

      In some neonates, Norwood procedure (see Chapter 9 ) may be necessary due to other associated lesions (i.e., MS, borderline LV size, LVOT obstruction).



  • 2.

    For valvular AS:


Apr 11, 2021 | Posted by in CARDIOLOGY | Comments Off on Obstructive Lesions
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