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Aortic Stenosis

Aortic Stenosis/ Left Ventricular Outflow Tract Obstruction

1. Definitions

A. obstruction of the left ventricular outflow tract secondary to aortic valve pathology
B. aortic valve abnormalities are the most common form of congenital heart disease
1) the majority of these patients are asymptomatic until midlife
2) less commonly, aortic valve stenosis becomes symptomatic in childhood
3) When the patient is symptomatic in the neonatal period, this is referred to as neonatal critical aortic stenosis and represents less than 10% of all patients with congenital aortic stenosis

2. Morphology

A. The malformation involves the aortic valve cusps, which are dysplastic and thickened
1) There is an abnormal number of cusps
2) Unicuspid valves are the most common cause of neonatal critical AS
3) Bicuspid valves are seen more commonly in children that present at a later age
4) All valves have a rudimentary raphe and 3 interleaflet triangles
B. There are associated left ventricular effects from these dysplastic valves
1) Left ventricular hypertrophy develops
2) The left ventricular cavity is usually small, although occasionally dilated
3) Subendocardial fibroelastosis is often present, especially in neonates
C. Other associated congenital heart defects
1) Concurrent left sided lesions (e.g. SAM, coarctation)
2) Patent ductus arteriosus
3) Ventricular septal defect

3. Pathophysiology

A. LVOTO => LVH => LV hypertension => LV systolic and diastolic dysfunction => increased LA pressure => left-to-right shunting across PFO => increased RV volume => increased flow across PDA
B. This series of events is well-tolerated in the fetus, although the left ventricle may become severely impaired by the process of fibroelastosis
C. After birth, the development of symptoms depends upon these factors:
1) the degree of LVOTO
2) the degree of prenatal injury to the left ventricle
3) completeness of the transition from fetal circulation to neonatal (in-series) circulation

4. Diagnosis

A. History
1) Neonates - may have circulatory collapse or cyanosis (if PDA)
2) Infants - have poor feeding and other indicators of failure to thrive
B. Systolic ejection murmur
C. Electrocardiogram demonstrates LVH
D. Echocardiography
1) evaluate the valve
2) estimate the gradient
3) assess the status of the left ventricle
E. Catheterization
1) assess the gradient and LV function
2) percutaneous balloon valvuloplasty for neonatal criticial AS

5. Clinical Presentation

A. Neonate/Infant: Critical AS, worst valve pathology
B. Child: Less severe valve deformity, bicuspid valves present later
C. Adult: Bicuspid valve, calcareous
D. Elderly: Tricuspid valve, degenerated

6. Management

A. Resuscitate the neonate and maintain the patent ductus with PGE
B. Percutaneous balloon valvuloplasty is usually successful in these patients and should be considered first-line therapy
C. Operative strategy
1) Valvotomy is preferred in the neonate, infant, and child
2) Valvotomy is a salvage operation in neonates and infants and has high operative risk
3) In older children, valvotomy is the palliative operation of choice
4) Replacement of the aortic valve is performed in adults and the elderly

7. Results

A. Neonates and infants
1) Results seem to be dependent upon associated left-sided pathology (e.g. LV size, MV and AV cross-sectional area)
2) If left-sided structures are severely hypoplastic, consider management as a single ventricle
B. Valvotomy operative risk
1) Neonate/Infant: 12.5% (range 25-79%)
2) Less than 1 year: less than 4%
C. Reoperation after valvotomy
1) 10 years: 2-5%
2) 20 years: 35-50%
3) Neonate: 5.5x higher rate of reoperation than if valvotomy performed after age one

8. Summary (Aortic Valve Stenosis)

A. Anomaly of aortic valve cusps
B. Associated left-sided pathology
C. Interventions include percutaneous balloon valvuloplasty and operative valvotomy
D. Obstructive gradients are reduced with appropriate intervention
E. Interventions in children are palliative
F. Many patients will require reoperation

SUBVALVULAR AORTIC STENOSIS

1. Definitions

A. obstruction of the left ventricular outflow tract below the aortic valve
B. it is associated with a variety of other cardiac anomalies in 2/3 of patients

2. Morphology

A. Localized form, also known as fibromuscular
1) Seldom presents before 6 months
2) Obstruction occurs at a point between the aortic valve and the anterior leaflet of the mitral valve
3) It may be acquired and is associated with many other lesions
B. Diffuse form, also known as tunnel, muscular, or hypertrophic obstructive cardiomyopathy
1) Spectrum of defects and a variety of etiologic factors
2) The idiopathic type appears to be genetic

3. Pathophysiology

A. The fibromuscular form is present in infants and peaks in adolescence
B. Hypertrophic cardiomyopathy presents later in life

4. Diagnosis and Management

A. Echocardiography is the test of choice
B. If surgery is contemplated, perform catheterization to assess gradient
C. Indications for surgery include the presence of symptoms and a gradient greater than 50mm Hg

5. Operative Strategy

A. Localized form
1) Resect the fibrotic membrane
2) Consider septal myectomy
3) Enlarge the aortic root if complex
B. Diffuse form
1) Aortoseptal approach between the right and left coronary cusps
2) Preserve the aortic valve if normal
3) Septal resection or patch; if the septum is patched, the aortic valve must be replaced
4) Repair or replace aortic valve

6. Results

A. Reoperation for recurrent stenosis or aortic valve incompetence is frequent
B. Reoperation increases after 5 years
C. Complete initial relief of obstruction may reduce re-operation and aortic insufficiency
D. Early operation may improve results

SUPRAVALVULAR AORTIC STENOSIS

1. Definitions

A. obstruction of the left ventricular outflow tract above the aortic valve
B. there are three forms: sporadic, familial, and Williams' syndrome

2. Morphology

A. The lesion can take various forms ranging from localized to diffuse and symmetric to asymmetric
B. It is often associated with degenerative coronary artery disease
C. Characteristics
1) Complete anomaly of aortic root
2) Narrowing of sinus rim
3) Thickening of media and intimal hyperplasia
4) Coronary ostia may be obstructed
5) Aortic valve cusps involved (thickened)
6) Aortic valve cusps normal length (buckled)
7) Associated subvalvular LVOTO

3. Classification

A. Localized: 33%
1) with associated LVOTO: 45%
B. Diffuse: 15%
C. Severe associated anomaly: 7%
(Texas Heart Institute 1991)

4. Diagnosis and Management

A. As with subvalvular AS, echocardiography is the test of choice
B. Perform catheterization to assess gradient if surgery is indicated
C. Indications for surgery include the presence of symptoms and a gradient greater than 50mm Hg

5. Operative Strategy

A. Asymmetric localized form - Use the classical non-coronary sinus patch
B. Symmetric localized form - 2 patch technique (more frequent), 3 patch technique, or resection may be employed
C. Pericardial patches may be used for sinus enlargement in the 3-patch technique
D. Diffuse form - Extended patch with "endarterectomy" of the thickened media - All operations are palliative and many patients (25-30%), if not all, require reoperation in 10-20 years