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Tetralogy Of Fallot

Tetralogy of Fallot

1. Definition

A. Anatomic Features
1) RVOT obstruction (infundibular stenosis)
2) VSD
3) Aorta dextroposition, overrides VSD
4) RV hypertrophy
B. The VSD and infundibular stenosis determine the pathophysiologic features
C. The morphology, clinical course, and management of tetralogy of Fallot with pulmonary stenosis (TOFPS) is distinctly different from that of tetralogy of Fallot with pulmonary atresia (TOFPA)

2. Morphology

A. Underdevelopment of the right ventricular infundibulum results in:
1) Anterior-leftward malalignment of the infundibular septum
2) This malalignment determines the degree of right ventricular outflow tract obstruction
3) A large subaortic ventricular septal defect (malalignment VSD) results
4) The aorta overrides the VSD into the right ventricle
B. Tetralogy of Fallot with pulmonary stenosis (TOFPS)
1) The hypoplastic RVOT is associated with pulmonary valve stenosis, which may extend into the pulmonary trunk
2) The branch pulmonary arteries usually have normal arborization and are rarely significantly hypoplastic.
C. Tetralogy of Fallot with pulmonary atresia (TOFPA)
1) Variable pulmonary blood supply
a) ductus arteriosus
b) aortopulmonary collaterals: prenatal remnant and abnormal histologic characteristics
(1) Intracardiac morphology is similar to TOFPS.
D. Morphologic categories of Right Ventricular Outflow Obstruction
1) Infundibular to valvar stenosis -- most common
2) Infundibular + valvar + small annulus -- common
3) Isolated infundibular stenosis -- minority
4) Dominant valvar stenosis -- rare
5) Diffuse right ventricular outflow hypoplasia -- often in infants presenting with cyanosis

3. Pathophysiology

A. The VSD is usually large (nonrestrictive)
B. The relative resistance of the RVOT and systemic vascular bed determines the pathophysiology
C. In TOFPA, the source of pulmonary blood flow heavily influences the clinical presentation

4. Clinical Presentation

A. Cyanosis
1) Usually constant
2) May be intermittent with hypoxic spells
3) Infants with severe infundibular stenosis + valvar stenosis are deeply cyanotic from birth
4) Cyanosis occurs later in infants with classic dominant infundibular stenosis
B. Moderate systolic ejection murmur
1) The murmur disappears during a spell
2) Continuous murmurs may be found in patients with aortopulmonary collaterals
C. Polycythemia
D. Clubbing
1) Develops in older children, usually after 6 months of age

5. Diagnostics

A. Chest X-ray
1) "Boot-shaped" heart is most common in older infants and children
B. EKG
1) Demonstrates right ventricular hypertrophy and right axis deviation
C. Echocardiography
1) VSD and RVOTO easily visualized
2) Can also delineate coronary artery anatomy, AV valve morphology, and central pulmonary arteries
D. Catheterization
1) Is not required in all patients
2) Indicated if echo cannot completely define anatomy
3) Indicated for concern about increased pulmonary vascular resistance
4) Cranial tilt views necessary for delineating branch pulmonary stenoses
5) In TOFPA, catheterization will identify aortopulmonary collaterals

6. Natural History

A. Determined by the severity of the RVOT obstruction
B. 25% of untreated infants die in 1st year of life
C. Risk of death is greatest in 1st year, then constant until about age 25

7. Treatment

A. The majority of patients have adequate saturation and can undergo elective repair
1) Progressive hypoxemia (saturation 75-80%) is an indication for operation
2) Occurrence of spells is a second indication for operation
B. TOFPS
1) Asymptomatic children with uncomplicated morphology should have elective repair between 3 and 24 months of age
2) Very young infants with complicated morphology can be managed with a staged shunt (usually modified Blalock-Taussig)
3) Many centers now perform single-stage complete repair regardless of age, avoiding:
a) prolonged RVOTO and subsequent RVH
b) prolonged cyanosis
c) postnatal angio- and alveologenesis
C. TOFPA
1) Treatment strategy depends on the pulmonary artery anatomy
2) The goal is to repair the defect and provide blood flow from the RV to as many pulmonary segments as possible
3) There are many surgical options, including:
a) shunting and second-stage repair
b) relieve RVOTO and leave VSD open, adding a shunt as necessary to maintain saturation
c) the residual VSD can be closed after further development of the pulmonary vasculature
d) unifocalization or ligation of aortopulmonary collaterals may be necessary

8. Operative Strategy

A. Dissect and resect infundibular stenosis through the right atrium
B. Close ASD/PFO; neonatal PFO should be left open to assist systemic output in early postop period
C. Open and enlarge the pulmonary valve and/or annulus
D. Close VSD, which corrects overriding aorta

9. Results

A. Current hospital mortality is 2-5%
B. Risk factors for early death:
1) very young age
2) older age
3) severity of annular hypoplasia
4) small size of pulmonary arteries
5) need for transannular patch (debatable)
6) high peak RV to LV pressure ratio
7) previous palliative operations
8) multiple VSDs
9) co-existing cardiac anomalies
a) Survival at 5 years is about 90%