Introduction
Background
Tetralogy of Fallot (TOF) is a complex of anatomic abnormalities arising from the maldevelopment of the right ventricular infundibulum.
In 1888, Fallot described the anatomy as consisting of pulmonary artery stenosis, ventricular septal defect (VSD), deviation of the aortic origin to the right, and right ventricular hypertrophy. Today, it is apparent that it is the degree of right ventricular outflow tract (RVOT) obstruction (infundibular stenosis) that accounts for the deleterious hemodynamics of TOF. See Media file 1 for a schematic illustration of these abnormalities.
Anatomic findings in tetralogy of Fallot.
Pathophysiology
Wide variation exists in the basic anatomic morphology, pathophysiology, clinical signs and symptoms, and surgical methods of therapy for TOF. Pathophysiology is dependent primarily upon severity of the right ventricular outflow tract (RVOT) obstruction. RVOT obstruction determines the severity of right-to-left shunting, which is typical.
Frequency
United States
TOF represents approximately 10% of cases of congenital heart disease and is the most common cause of cyanotic congenital heart disease.
Mortality/Morbidity
Natural history is variable.
- Natural history is determined mainly by the degree of RVOT obstruction.
- Approximately 25% of untreated patients with TOF and RVOT obstruction die within the first year of life, 40% by 4 years, 70% by 10 years, and 95% by 40 years. However, cases of survival of patients into their 80s have been reported.
Sex
Incidence of tetralogy of Fallot (TOF) is slightly higher in males than in females.
Age
TOF occurs in newborns.
Clinical
History
- Cyanosis may be present at or shortly after birth but usually develops within the first few years of life.
- First presentation may include poor feeding, cyanosis during feeding, fussiness, tachypnea, and agitation.
- Symptoms generally progress secondary to hypertrophy of the infundibular septum. Worsening of the RVOT obstruction leads to right ventricular hypertrophy, increased right-to-left shunting, and systemic hypoxemia.
- Cyanosis generally progresses with age and outgrowth of pulmonary vasculature and demands surgical repair.
- Dyspnea on exertion is common.
- Squatting (a compensatory mechanism) is uniquely characteristic of a right-to-left shunt that presents in the exercising child. Squatting increases the peripheral vascular resistance, which diminishes the right-to-left shunt and increases pulmonary blood flow.
- Hypoxic "tet" spells are potentially lethal, unpredictable episodes that occur even in noncyanotic patients with TOF. The mechanism is thought to include spasm of the infundibular septum, which acutely worsens the RVOT obstruction. These spells can be aborted with relatively simple procedures.
- The rare patient may remain marginally and imperceptibly cyanotic, or acyanotic and asymptomatic, into adult life.
- Severe cyanosis may present at birth in a patient with TOF and associated pulmonary atresia.
- Birth weight is low.
- Growth is retarded.
- Development and puberty may be delayed.
Physical
- Right ventricular predominance on palpation
- May have a bulging left hemithorax
- Systolic thrill at the lower left sternal border
- Aortic ejection click
- Single S 2 - Pulmonic valve closure not heard
- Systolic ejection murmur - Varies in intensity inversely with the degree of RVOT obstruction
- More cyanotic patients have greater obstruction and a softer murmur.
- An acyanotic patient with TOF (pink tet) has a long, loud, systolic murmur with a thrill along the RVOT.
- Cyanosis and clubbing - Variable
- Squatting position
- Scoliosis - Common
- Retinal engorgement
- Hemoptysis
Causes
- As one of the conotruncal malformations, tetralogy of Fallot (TOF) can be associated with a spectrum of lesions known as CATCH 22 (cardiac defects, abnormal facies, thymic hypoplasia, cleft palate, hypocalcemia). Cytogenetic analysis may demonstrate deletions of a segment of chromosome band 22q11 (DiGeorge critical region).
- Ablation of cells of the neural crest has been shown to reproduce conotruncal malformations.
- These abnormalities are associated with the DiGeorge syndrome and branchial arch abnormalities.
- TOF may be associated with maternal stressful life events during pregnancy.
- TOF frequently is associated with the following:
- Fetal hydantoin syndrome
- Fetal carbamazepine syndrome
- Fetal alcohol syndrome
- Maternal phenylketonuria (PKU) birth defects
More on Tetralogy of Fallot |
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| Multimedia: Tetralogy of Fallot |
| References |
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References
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Further Reading
Keywords
tetralogy of Fallot, TOF, Fallot tetrad, Fallot's tetrad, right ventricular outflow tract obstruction, congenital heart disease, maldevelopment of right ventricular infundibulum, subaortic ventricular septal defect, right ventricular infundibular stenosis, aortic valve positioned to override the right ventricle, right ventricular hypertrophy, right-to-leftshunting, cyanosis, hypertrophy of the infundibular septum, dyspnea, retarded growth, aortic ejection click, systolic thrill, systolic ejection murmur, clubbing, scoliosis, squatting position, retinal engorgement, hemoptysis, conotruncal abnormalities, DiGeorge syndrome, branchial arch abnormalities, fetal hydantoin syndrome, fetal carbamazepine syndrome, fetal alcohol syndrome, maternal phenylketonuria birth defects
