Tetralogy of Fallot: Surgical Perspective 

The original anatomic description of tetralogy of Fallot (TOF) included a tetrad of malformations, namely, ventricular septal defect (VSD), right ventricular (RV) outflow tract obstruction (RVOTO), aorta overriding the ventricular septum, and RV hypertrophy (RVH).

A uniform etiology may explain this anatomic tetrad. That is, the monology of anterior deviation of the infundibular septum causes hypoplasia of the subpulmonary infundibulum and thus accounts for all components of the tetrad.

Tetralogy of Fallot is the most common cyanotic heart defect seen in children beyond infancy. Furthermore, tetralogy of Fallot is the most common cyanotic congenital lesion that is likely to result in survival to adulthood. It is also currently the most common complex lesion to be encountered in the adult population after repair.

Nomenclature and classification of tetralogy of Fallot

The following 4 diagnostic subgroups of tetralogy of Fallot are described: (1) tetralogy of Fallot with absent pulmonary valve syndrome; (2) tetralogy of Fallot with common atrioventricular canal; (3) tetralogy of Fallot with pulmonary atresia; and (4) tetralogy of Fallot with pulmonary stenosis.

• Tetralogy of Fallot with absent pulmonary valve syndrome is a form of tetralogy of Fallot with a severely dysplastic pulmonary valve and markedly dilated pulmonary arteries. This relatively rare lesion represents only 3-5% of all cases of tetralogy of Fallot. Tetralogy of Fallot with an absent pulmonary valve is commonly associated with respiratory difficulties. Severe problems with oxygenation—and especially ventilation—are thought to be related to bronchial compression secondary to the marked pulmonary artery dilatation.
• Tetralogy of Fallot with common atrioventricular canal (atrioventricular septal defect [AVSD]) is the presence of both tetralogy of Fallot and complete AVSD. This rare lesion represents only 2% of all cases of TOF. Complete surgical repair of this lesion is riskier than repair of tetralogy of Fallot or AVSD alone. Nevertheless, combined complete repair is possible and usually successful.
• Tetralogy of Fallot with pulmonary atresia is a form of pulmonary atresia with VSD in which the intracardiac anatomy is tetralogy of Fallot. Tetralogy of Fallot with pulmonary atresia is commonly associated with hypoplastic branch pulmonary arteries and may be associated with major aortopulmonary collateral arteries (MAPCAs).
• Tetralogy of Fallot with pulmonary stenosis is the common form of tetralogy of Fallot. Tetralogy of Fallot with pulmonary stenosis is the focus of this article. In tetralogy of Fallot with pulmonary stenosis, pulmonary stenosis may be at the subvalvar, valvar, or supravalvar level or may involve any combination of these 3 levels.

The natural history of untreated tetralogy of Fallot includes the following:

• The degree of cyanosis is often related to the severity of RVOTO.
• Infants with acyanotic tetralogy of Fallot gradually become cyanotic.
• Patients who are already cyanotic become more cyanotic than before as a result of worsening infundibular stenosis and polycythemia.
• Polycythemia develops secondary to cyanosis.
• A relative state of iron deficiency (ie, hypochromia) may develop. Patients require monitoring for this condition.
• Hypoxic spells may develop in infants.
• Growth retardation may be present if cyanosis is severe.
• Brain abscess and stroke can occur but are rare.
• Subacute bacterial endocarditis is occasionally a complication.
• Aortic regurgitation may develop in some patients, particularly those with severe tetralogy of Fallot.
• Coagulopathy is a late complication of a long-standing cyanosis.

Tetralogy of Fallot is a conotruncal defect resulting from anterior malalignment of the infundibular septum. This single morphologic defect gives rise to the 4 main components of TOF: VSD, aortic valve overriding the ventricular septum, narrowing of the RV outflow tract (RVOT), and RVH.

Complex forms include tetralogy of Fallot with absent pulmonary valve and tetralogy of Fallot with pulmonary atresia with or without MAPCAs.

Frequency

Tetralogy of Fallot occurs in 10% of all congenital heart defects. It is the most common cyanotic heart defect seen in children beyond infancy.

Tetralogy of Fallot is a congenital defect without known environmental or genetic associations. Efforts to delineate the genetic etiology of tetralogy of Fallot are ongoing and represent an area of active research and investigation.

The prognosis of patients with unrepaired tetralogy of Fallot (TOF) is clearly inferior to the life expectancy of those undergoing repair. Therefore, whether or not to repair tetralogy of Fallot is not often debated.

The timing of surgery and the initial surgical procedure performed in the patient with symptomatic tetralogy of Fallot remain controversial. The nature of the right ventricular (RV) outflow tract obstruction (RVOTO) often dictates the symptoms. In cyanotic tetralogy of Fallot, hypercyanotic episodes (tetralogy of Fallot spells) may occur with agitation or irritability. If the episode is profound, the child develops severe cyanosis, often with hypotension, hemodynamic instability, and altered consciousness.

Medical management of tetralogy of Fallot spells often includes use of mechanical ventilation, inotropes, and an alpha-agonist such as phenylephrine hydrochloride (Neo-Synephrine) to increase pulmonary blood flow. In neonates with spells, prostaglandins may be used to reestablish ductal patency; however, this approach is not always successful.

Patients whose condition is refractory to medical management and stabilization require urgent surgical intervention. In some centers, these patients are treated with initial surgical palliation with a systemic-to-pulmonary artery shunt and subsequent complete repair, whereas, in other centers, these children are treated with urgent primary complete repair.

Controversy also surrounds the timing of surgery in children with asymptomatic tetralogy of Fallot. In asymptomatic patients, some centers advocate that elective repair be performed from the neonatal period, whereas other centers wait until 1 year of age. Most surgeons repair the infant with asymptomatic tetralogy of Fallot between age 4 and 6 months.

History

• The diagnosis may be established with fetal ultrasonography.
• A heart murmur is usually audible at birth.
• Most patients are symptomatic with cyanosis at birth or shortly thereafter.
• Dyspnea upon exertion, squatting, or hypoxic spells develop later, even in mildly cyanotic infants.
• Infants with acyanotic tetralogy of Fallot (pink tetralogy of Fallot) may be asymptomatic or may show signs of congestive heart failure (CHF) from a large left-to-RV shunt.
• Immediately after birth, severe cyanosis is seen in patients with tetralogy of Fallot and pulmonary atresia or severe pulmonary stenosis. These neonates may be ductal dependent and require urgent prostaglandin infusion to maintain ductal patency.

Anatomy and associated defects

The ventricular septal defect (VSD) in tetralogy of Fallot (TOF) is a perimembranous defect with extension into the subpulmonary region. Additional muscular VSDs may be present.

The right ventricular (RV) outflow tract obstruction (RVOTO) is most frequently found in the form of infundibular stenosis (45%) and rarely only at the level of the pulmonary valve (10%). A combination of the 2 may also occur (30%). The pulmonary valve is atretic in the most severe form of the anomaly (15%). In some children, pulmonary atresia develops over time (tetralogy of Fallot with acquired pulmonary atresia).

The pulmonary annulus and main pulmonary artery are hypoplastic in most patients. The pulmonary artery branches are usually small, with variable peripheral stenosis. Narrowing at the origin of the left pulmonary artery is particularly common.

Systemic collateral arteries feeding into the lungs are occasionally present, especially in severe cases of tetralogy of Fallot such as tetralogy of Fallot with pulmonary atresia.

Other associated anomalies include a right aortic arch (present in 25% of patients); atrial septal defect (ASD), typically secundum ASD or patent foramen ovale; and patent ductus arteriosus (PDA).

Abnormal coronary arteries are present in about 5% of patients with tetralogy of Fallot. The most common abnormality is the left anterior descending (LAD) coronary artery arising from the right coronary artery (RCA) and passing over the RVOT. This coronary anomaly can necessitate modification of the surgical approach because a transannular ventriculotomy may jeopardize the LAD that arises from the RCA.

Physical examination

Varying degrees of cyanosis, tachypnea, and clubbing are present.

An RV tap along the left sternal border and a systolic thrill at the mid-left and upper-left sternal borders are commonly present.

An ejection click that originates in the aorta may be audible.

The S2 is usually single because only the aortic component can be heard.

A long, loud (grade 3-5/6), ejection-type systolic murmur is heard at the mid-left and upper-left sternal borders. This murmur originates from the pulmonary stenosis but may be easily confused with the holosystolic murmur of a VSD. The more severe the RVOTO, the shorter and softer the systolic murmur. In a neonate with tetralogy of Fallot, pulmonary atresia, and profound cyanosis, the heart murmur is either absent or soft, though a continuous murmur representing PDA may occasionally be audible.

In the acyanotic form, cyanosis is absent, and a long systolic murmur resulting from VSD and infundibular stenosis is audible along the entire left sternal border.