Background
Tetralogy of Fallot (TOF) with pulmonary stenosis is the common form of tetralogy of Fallot, and it is the focus of this article.
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 Tetralogy of Fallot: (1) ventricular septal defect (VSD), (2) aortic valve overriding the ventricular septum, (3) narrowing of the right ventricular (RV) outflow tract (RVOT), and (4) 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 and occurs in 10% of all congenital defects. Furthermore, tetralogy of Fallot is the most common cyanotic congenital lesion that is likely to result in survival to adulthood. It is also the most common complex lesion to be encountered in the adult population after repair. Environmental associations with tetralogy of Fallot include maternal diabetes mellitus, retinoic acid exposure, and maternal phenylketonuria (PKU). This defect has a frequent association with the 22q11 chromosomal deletion and can also be seen associated with trisomy 21, 18, or 13. Other possible genetic associations are currently an ongoing area of active research.
Complex forms include tetralogy of Fallot with absent pulmonary valve and tetralogy of Fallot with pulmonary atresia with or without major aortopulmonary collateral arteries (MAPCAs).
See also Tetralogy of Fallot, Tetralogy of Fallot With Pulmonary Atresia, and Tetralogy of Fallot With Absent Pulmonary Valve.
Historical information
Tetralogy of Fallot holds a central place in the history of surgery for congenital heart disease; it was the first cyanotic cardiac lesion to be successfully managed with surgical palliation and was one of the first cardiac lesions to undergo successful intracardiac repair.
The classic Blalock-Taussig (BT) shunt procedure developed in 1945 involved direct end-to-end anastomosis between the subclavian artery and the pulmonary artery. This technique required transection of the subclavian artery. Professor Marc deLeval modified this procedure using an interposition conduit between subclavian artery and pulmonary artery. This modified BT shunt (also, deLeval shunt, Great Ormond Street [GOS] shunt), is currently the most commonly used systemic–to–pulmonary artery shunt.
Since the introduction of cardiopulmonary bypass, the trend has been for early and complete repair. The cardiopulmonary bypass machine is used to perform complete intracardiac repair of tetralogy of Fallot (see Corrective Surgery).
Nomenclature and Classification
The following 4 diagnostic subgroups of tetralogy of Fallot (TOF) are described [1, 2] : (1) tetralogy of Fallot with absent pulmonary valve syndrome; (2) tetralogy of Fallot with common atrioventricular (AV) canal; (3) tetralogy of Fallot with pulmonary atresia; and (4) tetralogy of Fallot with pulmonary stenosis.
Tetralogy of Fallot with absent pulmonary valve syndrome
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 AV canal
Tetralogy of Fallot with common AV canal (AV septal defect [AVSD]) is the presence of both tetralogy of Fallot and complete AVSD. This rare lesion represents only 2% of all cases of Tetralogy of Fallot. 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
Tetralogy of Fallot with pulmonary atresia is a form of pulmonary atresia with ventricular septal defect (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
As noted in the introductory section, tetralogy of Fallot with pulmonary stenosis is the common form of tetralogy of Fallot. In this condition, pulmonary stenosis may be at the subvalvar, valvar, or supravalvar level, or it may involve any combination of these 3 levels.
Anatomy
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.
Right ventricular (RV) outflow tract obstruction (RVOTO) is present in the majority of cases of TOF, but it may be variable in severity. In addition to the subpulmonic obstruction, stenosis often coexists at the valvar and supravalvar levels. 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.
Prognosis
The overall outcome after surgical repair of tetralogy of Fallot (TOF) has steadily improved since the technique was initially developed. [3] The continued improvement in outcome can be attributed to improved intraoperative technique, including the avoidance of excessive right ventricular (RV) outflow tract obstruction (RVOTO) muscle resection, improved cardiopulmonary bypass techniques (especially for infants), and improved postoperative care.
In the current era, survival to discharge after repair in most reported series is 95-99%, whereas in the early 1980s, the survival rate after TOF repair was approximately 90%. Thus, the current mortality risk for uncomplicated tetralogy of Fallot repair should approach 0%.
In a historical series, late survival was documented in 814 patients undergoing complete repair at the University of Alabama at Birmingham as 93% at 1 month and at 1 year, 92% at 5 years, and 87% at 20 years. [4] These survival rates were only slightly less than those of an age-matched, race-matched, and sex-matched control population. In the current era, late survival should even be better than it was in this series.
In the earliest days of surgical repair, postoperative complete heart block was a major problem. The rate of postoperative complete heart block decreased to 5% in earlier series and less than 1% in most recent series.
When the Society of Thoracic Surgeons Congenital Heart Surgery Database was used to analyze data from 941 patients undergoing TOF repair in 1998-2003, tetralogy of Fallot with pulmonary stenosis was present in 888 patients; tetralogy of Fallot with absent pulmonary valve syndrome was present in 34 patients; and tetralogy of Fallot with common atrioventricular canal (AVSD) was present in 19 patients. [5] The overall survival after discharge was 98.7%, with the highest risk among patients with TOF with absent pulmonary valve syndrome, who had a survival rate to discharge of only 91.2%. The incidence of insertion of a permanent pacemaker due to heart block was only 0.5%. [5]
Finally, in general, the prognosis for patients with TOF is excellent. In a study from the Society for Thoracic Surgery, patients undergoing repair of TOF between 2005-2009 at 74 centers had and an overall operative mortality rate of 1.1%, with many centers reporting no operative mortality. [6] A long-term follow-up study reported that among 1-year survivors after repair of TOF, actuarial 10-, 20-, 30-, and 36-year survival rates were 97%, 94%, 89%, and 85%, respectively. [7] In this group, patients without preoperative polycythemia and without an RV outflow patch had a 36-year actuarial survival rate of 96% and normal life expectancy.
Complications
Complications of the surgery for repair of TOF with pulmonary stenosis include the following:
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Hemorrhage
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Infection
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Heart block
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Residual or recurrent ventricular septal defect (VSD)
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Residual or recurrent RVOTO
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Pulmonary insufficiency
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RV dysfunction
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Heart failure
Patients requiring a pulmonary transannular patch develop progressive RV dilatation and are at higher risk of developing ventricular dysfunction and signs and symptoms of congestive heart failure.
Postoperative patients carry a lifelong risk of developing ventricular arrhythmias and sudden cardiac death. RV hypertrophy, ventricular dysfunction, residual RVOTO, prolonged QRS duration on ECG (>180 ms), and advancing age have all been reported to be predictors of ventricular arrhythmia and sudden death. [8, 9] Patients who do not receive a right ventriculotomy incision may be at lower risk of arrhythmia. [10]
