AUTHOR AND EDITOR INFORMATION

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INTRODUCTION

Section 2 of 11  

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Background

Subvalvular aortic stenosis (SAS) is a fixed form of anatomic obstruction to egress of blood across the left ventricular outflow tract (LVOT). Although classified as a congenital heart defect, its rarity at birth and during infancy, its progressive course, and its high rate of postoperative recurrence suggest that it may be an acquired condition.

Subaortic stenosis has a spectrum of anatomic variants and usually has a variable, progressive course. Associated congenital heart defects are found in 25-50% of patients with SAS, the most common defects include ventricular septal defect (VSD), patent ductus arteriosus, coarctation of aorta, bicuspid aortic valve, abnormal left ventricular (LV) papillary muscle, atrioventricular septal defect, Shone complex, interrupted aortic arch, and persistent superior left vena cava.

Pathophysiology

Boundaries of the LVOT are formed posterolaterally by the anterior leaflet of the mitral valve and anteromedially by the interventricular septum.

Fixed lesions of the LVOT that cause SAS have a spectrum of morphologies. The 4 basic anatomic variants are (1) a thin discrete membrane consisting of endocardial fold and fibrous tissue, (2) a fibromuscular ridge consisting of a thickened membrane with a muscular base at the crest of the interventricular septum, (3) a fibromuscular ring or collar circumferentially attached to the LVOT and to the base of the anterior mitral leaflet, and (4) a diffuse fibromuscular tunnel-like narrowing of the LVOT.

Types 1 and 2 account for 70-80% of all cases of SAS. Located 0.5-1.5 cm beneath the aortic valve, types 1 and 2 involve a variable extent of LVOT. Distinctions between types 2 and 3 are not always clear. A steep (>130°) aortoventricular septal angle, increased mitral-aortic separation, and an exaggerated aortic override are present in children who later develop SAS.

LVOT obstructions secondary to accessory tissue, an anomalous basal attachment of the anterior mitral leaflet, and an anomalous chordal attachment of mitral valve occur but are uncommon. Abnormalities of the aortic and mitral valves frequently develop during the natural course of SAS because of tethering by encroaching fibroelastic tissue of the membrane and fibromuscular ridge. Thickening of the aortic valve and mild asymmetric poststenotic dilatation of the ascending aorta result from repetitive trauma and vibrations from a subaortic jet of blood. In this setting, aortic regurgitation often develops and may persist, even after the SAS is removed. Clinically significant obstruction to ejection due to SAS results in concentric LV hypertrophy, often with an excessive septal bulge. This effect leads to a cycle of further obstruction and localized fibromuscular growth.

Frequency

United States

The overall prevalence of isolated SAS is low. SAS is estimated to occur in up to 0.08% of the general population. No genetic inheritance is known for SAS, and few familial incidences are reported. SAS accounts for 15-20% of all fixed LVOTs and approximately 1% of all congenital heart defects.

Mortality/Morbidity

• Sudden cardiac death is possible, as SAS is a progressive disorder. Although natural history studies have not delineated the annual mortality rate, 2-10% of sudden deaths are reported in untreated individuals who have severe LVOT obstruction. Close follow-up care is important to detect the progressive course of the disease and to prevent sudden death.
• Aortic regurgitation develops in nearly 65% of patients in the clinical course of the disease, and its detection is a function of timely follow-up care. Although the aortic regurgitation is usually mild, its incidence and severity increases with an increasing LVOT pressure gradient. This finding reflects progressive damage to the aortic valve by the high-velocity jet of blood that SAS produces. Aortic regurgitation adds volume overload to an already pressure-overloaded LV and predisposes the patient to myocardial damage. In some patients with SAS, progressive aortic regurgitation requires aortic valve repair or replacement at the time of surgical intervention. SAS may recur even after surgical resection appears to be complete.
• Bacterial endocarditis is reported in 13-25% of patients with SAS, and it is most likely to occur in patients with a damaged aortic valve. Bacterial endocarditis can result in hemodynamically significant aortic regurgitation and congestive heart failure (CHF).

Sex

The male-to-female ratio of SAS is 2:1 to 3:1. Distinctions in the natural histories and postoperative courses of SAS between male and female patients have not been clearly defined. However, more male than female patients require repeat operation.

Age

Isolated SAS is rarely seen at birth or during infancy. SAS may develop in some patients after they undergo repair of associated congenital heart defects (eg, VSD), usually by age 2 years. Exceptions include patients with Shone complex and interrupted aortic arch who have SAS in the first year of life. SAS has variable and unpredictable rates of progression in children, whereas the rate of progression in adults is slow.

CLINICAL

Section 3 of 11  

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History

Symptoms of subvalvular aortic stenosis (SAS), even with severe stenosis, are rare in infancy and uncommon in early childhood. Symptoms of associated congenital heart defects frequently mask those of SAS. Isolated SAS may be diagnosed relatively late in life because of the progressive nature of the lesion and because patients lack symptoms that prompt evaluation. In most patients, SAS is detected in the course of follow-up care for associated congenital heart defects or during evaluation of a heart murmur. When present, symptoms include dyspnea on exertion, effort syncope and presyncope, angina, orthopnea, CHF, and sudden cardiac death. Most of these symptoms occur in children, adolescents, and young adults aged 10-21 years with moderate or severe LVOT obstruction and peak-to-peak pressure gradients of more than 50 mm Hg.

• Exertional dyspnea is the most common symptom, occurring in as many as 40% of symptomatic patients. Exertional dyspnea with orthopnea reflects various degrees of pulmonary venous hypertension due to elevated LV filling pressure resulting from impaired diastolic compliance of the hypertrophied LV.
• Effort syncope and presyncope occur more frequently in SAS than they do in stenosis of the aortic valve. Syncope during exertion occurs because cerebral perfusion decreases when arterial pressure declines consequent to systemic vasodilation in the presence of a fixed cardiac output. Presyncope may manifest as a graying-out spell or as dizziness on effort because of exertional hypotension. In pediatric patients, syncope and presyncope at rest rarely occur, and their presence may indicate a cardiac arrhythmia, notably transient ventricular arrhythmia.
• Angina may occur in as many as 25% of symptomatic patients with more-than-mild LVOT obstruction. Exertion commonly precipitates the condition, and rest relieves it. Angina occurs in the absence of coronary artery disease. It results from the combination of increased oxygen demand by hypertrophied myocardium and reduced oxygen delivery secondary to excessive compression of coronary vessels.
• CHF only occasionally occurs in pediatric patients. When present early in life, CHF usually results from associated congenital heart defects. Cardiac output usually is well maintained, and systolic function is well preserved in children with isolated SAS until severe obstruction develops.
• Sudden cardiac death, unlike hypertrophic cardiomyopathy, is reported in a small percentage of patients with SAS. Sudden cardiac death is usually not the first clinical manifestation of the disease. It almost always occurs in previously symptomatic patients who had an LVOT pressure gradient of more than 50 mm Hg.

Physical

• The physical growth of the child with SAS is usually normal.
• Peripheral pulses are symmetric and rarely of small volume unless severe LVOT obstruction is present.
• A prominent a wave in the jugular venous pulse occasionally occurs in children with SAS. This a wave reflects reduced right ventricular compliance consequent to hypertrophied ventricular septum.
• A palpable carotid thrill and a left parasternal thrill are present in one third of patients with mild SAS (pressure gradient <50 mm Hg) and in approximately one half of patients with more-than-mild SAS.
• A forceful LV apical impulse is present in most patients with moderate or severe SAS.
• The first heart sound is normal.
• The second heart sound can be narrowly split or single because of prolonged LV systole. Paradoxic splitting of the second heart sound, which suggests associated LV dysfunction, may occur in severe SAS.
• An ejection click opening the ejection murmur is absent in isolated SAS. This is an important clue for differentiating this murmur from that of aortic valve stenosis.
• A low-pitched ejection systolic murmur of 2-4/6 intensity is best appreciated in second and third left parasternal spaces, with radiation to suprasternal notch. This murmur is typically present in all cases of isolated SAS. The length of the murmur is proportional to the degree of obstruction.
• A high-pitched early diastolic murmur of aortic regurgitation in the same area is present in 30-50% of patients.
• A pansystolic murmur of mitral regurgitation due to dysfunction of the papillary muscle is sometimes heard.

Causes

The etiology of SAS still is not fully understood. Fixed SAS may be the postnatal expression of a latent congenital lesion brought out by many mechanisms, such as genetic predisposition, certain anatomic characteristics of LVOT, hemodynamic abnormalities associated with other cardiac lesions, or surgical interventions that result in chronic flow disturbance in the outflow tract.

• Polygenic inheritance
• • Studies of hearts of Newfoundland puppies, which are predisposed to develop SAS in early life, showed striking similarities with the clinical progression observed in humans.¹ The puppies had persistent embryonic tissue in LVOT that was capable of proliferation. However, no such tissue is found in human lesions.
  • Because instances of SAS among several members of human families are few, the role of genetic inheritance in humans is unclear.
• Morphogenetic basis of SAS
• • Certain anatomic characteristics of LVOT promote a chronic flow disturbance in the outflow tract. LVOT is longest and narrowest in patients who have SAS. A steep (>130°) aortoventricular septal angle, increased mitral-aortic separation, and exaggerated aortic override are present in children who later develop SAS.
  • Focal abnormal myocardium similar to that found in hypertrophic cardiomyopathy may be present in patients with some congenital heart defects, including SAS.
  • Some have hypothesized that such LVOT morphology inherently increases fluid shear stress on the interventricular septum and induces an abnormal endothelial and muscle-proliferative response in the outflow tract with eventual formation of a fibromuscular ridge.
• Hemodynamic basis of SAS: Alternation in left-sided flow before and after repair of associated congenital heart defects likely causes turbulence in LVOT and adds to fluid shear stress on the interventricular septum, as discussed above. Therefore, both morphologic abnormalities and flow disturbance may be synergistically instrumental in the formation of SAS.

DIFFERENTIALS

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Other Problems to be Considered

Other coexistent defects (eg, VSD, interrupted aortic arch, Shone complex, atrioventricular septal defects)

WORKUP

Section 5 of 11  

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Lab Studies

• No specific laboratory blood tests are required in the workup of subvalvular aortic stenosis (SAS).

Imaging Studies

• Echocardiography
• • Echocardiography helps in defining and localizing SAS. It reveals the extent of LVOT involvement, the degree of LV hypertrophy, the indices of LV performance, and the parameters of diastolic function of the LV. Secondary effects, such as the degree of aortic insufficiency, mitral regurgitation, or poststenotic dilatation of the aorta, may be assessed. Finally, associated congenital heart defects and their influence on the hemodynamic effects of SAS may be evaluated.
  • Two-dimensional (2D) echocardiography with color Doppler imaging is the current modality of choice to establish the diagnosis of SAS. This noninvasive method allows for serial evaluation of the progression of the lesion and of the results of intervention.
  • M-mode echocardiography provides indirect evidence of SAS by revealing early closure (from the Venturi effect of the jet formed by the SAS) and the coarse flutter of the aortic valve leaflets.
  • 2D echocardiography reveals and defines the position of lesions, the extent of involvement of the LVOT (in tunnel-like SAS), and the associated defects. Apical views reveal the relationship of the SAS to surrounding structures (eg, mitral valve), and parasternal and subcostal long-axis views reveal the proximity of SAS to the aortic valve (see Media file 1).
  • Three-dimensional echocardiography can produce images of SAS with depictions of the morphology and extent remarkably similar to those observed during surgical visualization.
  • Multiplanar transesophageal echocardiography (TEE) provides superior definitions of the lesion, making it an ideal tool for intraoperative evaluation of the lesion to guide surgical resection and to evaluate the immediate results at the time of surgery. TEE is also useful for diagnostic purposes in patients with a poor acoustic window in whom transthoracic imaging results are not definitive.
• Doppler imaging
• • A peak instantaneous and a mean pressure gradient across the LVOT estimated during continuous wave Doppler interrogation provides measures of the severity of LVOT obstruction.
  • When used as a guide to cardiac intervention, Doppler interrogation does not permit the clinician to accurately estimate the pressure gradient in the presence of multiple obstructive LVOT lesions in series, a large VSD, or a tunnel-like obstruction.
  • Color Doppler evaluation reveals the presence and severity of aortic and mitral regurgitation.

Other Tests

• ECG reveals a variable degree of LV hypertrophy in 50-80% of patients, even in those with mild stenosis.
• ECG findings are occasionally normal in patients with severe stenosis.
• A prominent Q wave in the left precordial leads may be present from septal hypertrophy.
• Strain pattern is visible on the ECG in approximately 25% of patients and indicates severe obstruction.

Procedures

• Cardiac catheterization is not routinely indicated.
• • Cardiac catheterization is helpful in patients with LVOT obstruction in series and tunnel-like obstruction to delineate the site and severity of LVOT obstruction, and it is used for preoperative hemodynamic evaluation in SAS associated with other congenital heart defects.
  • Careful pullback pressure measurements performed with an end-hole or high-fidelity manometer-tipped catheter from the LV to the aorta allow delineation of the pressure gradient and exact site of obstruction in the LVOT.
  • A left ventriculogram obtained in a cranially angulated left anterior oblique orientation delineates SAS and reveals aortic valve stenosis, if present (see Media file 2).
• Echocardiography enables evaluation of the following:
• • Definition and location of SAS
  • Extent of involvement of LVOT
  • Early aortic valve closure from its involvement and its associated lesion
  • Aortic regurgitation
  • Mitral regurgitation
  • LV hypertrophy
  • Poststenotic aortic dilatation
  • Diagnostic features of associated congenital heart defects
  • LV systolic performance
  • Filling characteristics

Histologic Findings

Histologic findings are the same for lesions of the fibromuscular ridge or collar and for tunnel-like lesions. A composite of different tissue cells, which varies from patient to patient, is present. Abundant amounts of irregularly oriented and dense collagen fibers and thin, short elastic fibers are visible. Also visible are sparsely scattered fibroblasts with elongated nuclei and smooth muscle cells. Vascularity is generally absent.

TREATMENT

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Medical Care

Subvalvular aortic stenosis (SAS) is progressive. Intervention is often required at some point in the clinical course of the disease to relieve LVOT obstruction. Diagnostic evaluation can be performed on an outpatient basis.

• Indications for intervention
• • The criteria for and timing of intervention have been controversial because of a high rate of postoperative recurrence of the lesion and because of an increasing incidence (up to 65%) of aortic regurgitation after surgery.
  • In most centers, a peak pressure gradient of more than 40 mm Hg across LVOT and a mild or higher degree of aortic regurgitation are indications for intervention.
  • Some advocate early intervention to prevent recurrence and damage to the aortic valve. Early surgical intervention is also indicated in patients with tunnel-type and rapidly progressive lesions of the fibromuscular ridge.
• Intervention: Percutaneous balloon dilation of discrete SAS is reported and can substantially reduce the LVOT pressure gradient. However, relief of LVOT obstruction is relatively brief. Therefore, balloon dilation is not typically thought to be useful in SAS.

Surgical Care

Surgery of choice for discrete fibromuscular SAS is complete resection with myotomy, with or without myomectomy through an aortotomy. Children, adolescents, and young adults with clinically significant aortic regurgitation may require aortic valvoplasty or replacement.

• For tunnel-type SAS with small LV-aortic junction, an aortoventriculoplasty (Konno procedure) may be required. This involves excision and replacement of the aortic valve with a prosthesis, patch augmentation of ventricular septum to enlarge LVOT, and pericardial patch closure of the right ventriculotomy, which is used to gain access to the LVOT.
• For recurrent SAS and for tunnel-type SAS with normal LV-aortic junction and aortic valve, perform a modified Konno procedure (ie, without aortic valve excision and replacement).
• For complex subaortic stenosis or tunnel stenosis, current surgical practices are individualized but may employ an aortoventriculoplasty in combination with aortic root replacement by using a prosthetic aortic valve, an aortic valve allograft, or a pulmonary valve autograft (Ross-Konno procedure).

Consultations

Consult a pediatric cardiologist and a pediatric cardiac surgeon, as needed.

Diet

No special diet is required. If present, manage obesity and high body mass index with weight reduction.

Activity

Competitive sports and games, weight training, and strenuous exercises should not be permitted if patients have any of the following: clinically significant LVOT obstruction (peak pressure gradient >40-50 mm Hg), more-than-mild aortic regurgitation, marked LV hypertrophy, or clinically significant ventricular or supraventricular arrhythmia.

MEDICATION

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Subvalvular aortic stenosis (SAS) is a fixed mechanical obstruction in the LVOT. Most pediatric patients are asymptomatic. Therefore, medical therapy has no role for such patients. Old reviews reported that CHF occurs in small percentages of patients. However surgical intervention is currently undertaken before CHF develops. If SAS progresses to the point that CHF or clinically significant LV dysfunction develops, standard medical therapy for those conditions is indicated until surgery can be performed.

FOLLOW-UP

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Further Inpatient Care

• Further inpatient care may be required for evaluation and surgery as well as for postoperative recovery.

Further Outpatient Care

• Routine follow-up care is required for both patients undergoing surgery and those who are not.
• • Because of the possibility of rapid progression, follow-up care for infants and young children should be more frequent (eg, every 4-6 mo) until the rate of progression is understood.
  • Other children may be followed up at intervals of 3-12 months, depending on the severity of their obstruction and associated lesions.
• Long-term postoperative follow-up care is indicated for all patients with Subvalvular aortic stenosis (SAS).
• • About 10-25% of patients may have a residual gradient in excess of 50 mm Hg.
  • The known high incidence of recurrence (mean rate, one episode every 2 years among older children and adults) and the possible progressive worsening of aortic regurgitation after surgery underscore the need for long-term surveillance in patients who are at risk for repeat operation and other late morbidity.

Transfer

• Transfer to a center experienced in the surgical treatment of SAS and its associated lesions may be required.

Deterrence/Prevention

• Advise patients to avoid participation in strenuous activities and in competitive sports.
• Administer prophylaxis against endocarditis when needed.

Complications

• Preoperative complications include progressive aortic valve damage, ventricular dysfunction, infective endocarditis, and sudden death.
• Postoperative complications include damage to aortic and/or mitral valve (<2% of patients), variable degree of heart block (<2-5% of patients), iatrogenic VSD (<2% of patients), and infective endocarditis.
• Rates of early and late surgical death are 10-20% in infants and 5-15% in older children undergoing surgery for tunnel-like SAS, especially in those with associated defects. This surgical mortality rate is higher than the rate for isolated SAS, which is estimated to be 0-6%.

Prognosis

• Postoperative survival rates are 85-95% at 15 years.
• Late mortality is mostly related to residual LVOT obstruction and repeat operation.
• The high postoperative recurrence rate (10-50% on >10-y follow-up) has been associated with a high preoperative LVOT pressure gradient (>50 mm Hg), tunnel-like lesions, incomplete removal of discrete SAS, and age younger than 10 years at surgery.
• The Ross-Konno procedure seems to reduce the postoperative recurrence rate for tunnel-like SAS.

Patient Education

• Counsel patient regarding the need for long-term regular follow-up care.
• Impose activity restrictions, as indicated, on the basis of the degree of residual hemodynamic abnormality.

MISCELLANEOUS

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Medical/Legal Pitfalls

• Failure to inform the patient and the family of exercise restrictions in severe cases of subvalvular aortic stenosis (SAS)
• Failure to inform the patient and the family of the need for antibiotic prophylaxis against endocarditis
• Failure to diagnose SAS and its associated lesions or to inform the patient of the risk of recurrence

Special Concerns

• Most children are asymptomatic. Therefore, diagnosis may be delayed.
• The patient and his or her family might not comply with follow-up care.
• More-than-mild subaortic stenosis poses a high risk during pregnancy. Therefore, close monitoring for CHF, follow-up by a multidisciplinary team, and delivery at a center experienced in dealing with such problems are warranted.

MULTIMEDIA

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Media file 1:  Echocardiogram of membranous subaortic stenosis. AO = aortic; LA = left atrium; LVOT = left ventricular outflow tract.
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Media type:  Echo

Media file 2:  Tunnel-type of subaortic stenosis (subvalvular aortic stenosis [SAS]). MV = mitral valve.
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Media type:

REFERENCES

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17. Singh GK, Shiota T, Cobanoglu A, et al. Diagnostic accuracy and role of intraoperative biplane transesophageal echocardiography in pediatric patients with left ventricle outflow tract lesions. J Am Soc Echocardiogr. Jan 1998;11(1):47-56. [Medline].
18. Somerville J, Stone S, Ross D. Fate of patients with fixed subaortic stenosis after surgical removal. Br Heart J. Jun 1980;43(6):629-47. [Medline].
19. Suri RM, Dearani JA, Schaff HV, Danielson GK, Puga FJ. Long-term results of the Konno procedure for complex left ventricular outflow tract obstruction. J Thorac Cardiovasc Surg. Nov 2006;132(5):1064-71. [Medline].
20. Vogt J, Dische R, Rupprath G, et al. Fixed subaortic stenosis: an acquired secondary obstruction? A twenty-seven year experience with 168 patients. Thorac Cardiovasc Surg. Aug 1989;37(4):199-206. [Medline].
21. Wilson W, Taubert KA, Gewtiz M, et al. Prevention of infective endocarditis. Guidelines from the American Heart Association. A guidelines from the American Heart Association Rheumatic Fever, Endocarditis, and Kawasaki Disease Committee, Council on Cardiovascular Disease in the Young, and the Council on Clinical Cardiology, Council on Cardiovascular Surgery and Anesthesia, and the Quality of Care and Outcomes Research Interdisciplinary Working Group. Circulation [serial online]. Accessed April 19, 2007. Available at http://circ.ahajournals.org/cgi/reprint/CIRCULATIONAHA.106.183095v1.pdf.
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Article Last Updated: Oct 3, 2007