Disclosure 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. TOF is the most common cyanotic heart defect seen in children beyond infancy. Furthermore, TOF 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 TOF Four diagnostic subgroups of TOF are described: (1) TOF, absent pulmonary valve syndrome; (2) TOF, common atrioventricular canal (AVSD); (3) TOF, pulmonary atresia; and (4) TOF, pulmonary stenosis. TOF, absent pulmonary valve syndrome is a form of TOF with a severely dysplastic pulmonary valve and markedly dilated pulmonary arteries. This relatively rare lesion represents only 3-5% of all cases of TOF. TOF 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. TOF, common atrioventricular canal (AVSD) is the presence of both TOF 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 TOF or AVSD alone. Nevertheless, combined complete repair is possible and usually successful. TOF, pulmonary atresia is a form of pulmonary atresia with VSD in which the intracardiac anatomy is TOF. TOF with pulmonary atresia is commonly associated with hypoplastic branch pulmonary arteries and may be associated with major aortopulmonary collateral arteries (MAPCAs). TOF, pulmonary stenosis is the common form of TOF. TOF with pulmonary stenosis is the focus of this article. In TOF with pulmonary stenosis, pulmonary stenosis may be at the subvalvar, valvar, or supravalvar level, or it may involve any combination of these 3 levels. History of the Procedure: The natural history of untreated TOF includes the following:
Problem: TOF 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 TOF with absent pulmonary valve and TOF with pulmonary atresia with or without MAPCAs. Frequency: TOF occurs in 10% of all congenital heart defects. It is the most common cyanotic heart defect seen in children beyond infancy. Etiology: TOF is a congenital defect without known environmental or genetic associations. Efforts to delineate the genetic etiology of TOF are ongoing and represent an area of active research and investigation.
The prognosis of patients with unrepaired TOF is clearly inferior to the life expectancy of those undergoing repair. Therefore, little debate exists as to whether or not to repair TOF. The timing of surgery and the initial surgical procedure performed in the patient with symptomatic TOF remain controversial. The nature of the RVOTO often dictates the symptoms. In cyanotic TOF, hypercyanotic episodes (TOF 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 TOF 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 exists regarding the timing of surgery in children with asymptomatic TOF. 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 TOF between 4 and 6 months of age. History
Relevant Anatomy: Anatomy and associated defects The VSD in TOF is a perimembranous defect with extension into the subpulmonary region. Additional muscular VSDs may be present. The RVOTO is found most frequently 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 with time (TOF 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 TOF such as TOF with pulmonary atresia. Other associated anomalies include a right aortic arch (present in 25% of patients), ASD (typically secundum ASD or patent foramen ovale), and patent ductus arteriosus (PDA). Abnormal coronary arteries are present in about 5% of patients with TOF. 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. A RV tap along the left sternal border and a systolic thrill at the upper and mid- 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- 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 TOF, 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. |
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Lab Studies:
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Other Tests:
Diagnostic Procedures:
Medical therapy: In the cyanotic patient, conservative management includes the following:
In the acyanotic patient, medical management is similar to management of a patient with a VSD and may include diuretics (furosemide [Lasix]), digoxin, and afterload reduction (captopril). Transcatheter interventions The role of transcatheter interventions for TOF is controversial. Most centers do not use transcatheter interventions for TOF and instead perform surgical palliation and repair, as discussed below. Some centers advocate balloon dilation of RVOT infundibular and pulmonary valvar stenosis. The balloon dilation of pulmonary valvar stenosis is more likely to be successful than the dilation of infundibular stenosis. Cutting-balloon angioplasty of pulmonary artery stenosis in TOF has been investigated, but it is not commonly performed. Transcatheter interventions do play a major role in the rehabilitation of the distal pulmonary arteries in the setting of TOF with pulmonary atresia. Surgical therapy: History of the procedure TOF holds a central place in the history of surgery for congenital heart disease. TOF is the first cyanotic cardiac lesion to be successfully managed with surgical palliation and TOF is one of the first cardiac lesions to undergo successful intracardiac repair. On November 29, 1945, Alfred Blalock performed the first systemic-to-pulmonary artery shunt procedure to palliate TOF in a child by increasing pulmonary blood flow. Blalock's use of a subclavian artery–to–pulmonary artery anastomosis, the Blalock-Taussig shunt (BT shunt), which was named after the cardiac surgeon who initially performed the operation on human children, Alfred Blalock and cardiologist working with Blalock, Helen B. Taussig, was developed in the animal research laboratory at Johns Hopkins University by the surgical technician Vivien T. Thomas working with Blalock. This was the first truly successful palliation of congenital heart disease and created an international sensation. "Blue babies" from all over the world came to the Johns Hopkins Hospital in Baltimore to be treated. In 1946, Potts descried a descending aorta–to–pulmonary artery systemic-to-pulmonary artery shunt (Potts-Smith shunt). In 1962, Waterston described an ascending aorta–to–pulmonary artery systemic-to-pulmonary artery shunt. The Potts-Smith and Waterston type shunt procedures were technically easier to perform than classic BT shunting in small infants. However, both the Potts-Smith and Waterston shunts often resulted in excessive pulmonary blood flow, distortion of the pulmonary artery, and problems during subsequent complete TOF repair. As a consequence, these 2 shunts are essentially no longer utilized. The classic 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. At The Great Ormond Street Hospital for Children in London, England, Professor Marc deLeval modified this procedure using an interposition conduit between subclavian artery and pulmonary artery. Known as the modified BT shunt, this is currently the most commonly used systemic-to–pulmonary artery shunt. Synonyms for the modified BT shunt include the deLeval shunt and the GOS shunt. Since the introduction of cardiopulmonary bypass, the trend has been for early and complete repair. C. Walt Lillehei performed the first successful intracardiac repairs by using cross-circulation, an innovative technique involving parental bypass in which the patient's circulation is attached to and supported by the parent's circulation. In 1954, Lillehei and Varco performed the first intracardiac repair of TOF by using parental cross-circulation at the University of Minnesota. They closed a VSD and relieved an RVOTO under direct vision. Although this innovative technique was the first surgical procedure with the potential for a 200% mortality rate (patient and parent), it also acted as a stimulus for the subsequent development of a functional mechanical cardiopulmonary bypass machine. In 1955, Kirklin performed the first successful repair of TOF with a pump oxygenator was performed 90 miles away from the University of Minnesota at the Mayo Clinic. Today, the cardiopulmonary bypass machine is used to perform complete intracardiac repair of TOF, as described below. Surgical decision making A systemic-to-pulmonary artery shunt is indicated in patients in whom the risk in complete repair is considered to be higher than the cumulative risk in 2-stage repair. The timing and type of surgical intervention in TOF is controversial. In asymptomatic patients, elective repair has been advocated from the neonatal period up until 1 year of age. Most surgeons perform repair in infants with asymptomatic TOF between 4 and 6 months of age. In symptomatic or cyanotic patients, depending on institutional preferences, complete repair can be performed as a primary single-stage procedure or as a 2-stage approach, with initial systemic-to–pulmonary artery shunting. Preoperative details: The preoperative evaluation includes an assessment of functional status and pulmonary evaluation. Chest radiographic findings may depict the classic boot-shaped heart. Echocardiography is diagnostic, and associated anomalies can be excluded. Cardiac catheterization is indicated before repair of TOF in patients with previous palliation and when aortopulmonary collaterals and pulmonary artery branching abnormalities are suspected. Intraoperative details: Palliative surgery The role of palliative surgery for TOF is controversial. Patients whose conditions are 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. In other centers, these children are treated with urgent primary complete repair. Creation of a systemic-to–pulmonary artery shunt can be performed from the midline by means of a sternotomy or thoracotomy. Advantages of the sternotomy approach include the simple use of cardiopulmonary bypass if necessary. Advantages of the thoracotomy approach include the preservation of a virgin sternotomy approach with a simplified sternotomy for the eventual complete repair with minimal adhesions. A modified BT shunt procedure is most commonly performed by using a polytetrafluoroethylene (Gore-Tex; W.L. Gore & Associates, Newark, DE) tube graft anastomosed end-to-side to the right subclavian artery and end-to-side to the right pulmonary artery. The modified BT shunt is most commonly created on the side opposite the aortic arch. Therefore, with a left aortic arch, a right modified BT shunt is typically created. With a right aortic arch, a left modified BT shunt typically is created. Corrective surgery Complete repair can be performed as a single-stage procedure or as a 2-stage approach, with initial systemic-to–pulmonary artery shunting. Complete surgical repair involves closure of the VSD and relief of the RVOTO. A median sternotomy approach is used with cardiopulmonary bypass. Two potential surgical approaches are the transventricular approach and the transatrial approach. Transventricular repair with a right ventriculotomy in the infundibulum allows for exposure of the VSD and patch closure of the infundibular incision. With the transatrial approach, the VSD and subpulmonary obstruction can be approached from a transatrial direction. Muscle resection is performed to relieve the RVOTO. The goals of complete repair are relief of all obstruction to blood flow from the RV to the pulmonary artery and closure of the VSD. The relief of RVOTO may involve resection of obstructing RVOT muscle bundles, creation of an RVOT patch, creation of a transannular RVOT patch, pulmonary valvotomy or valvectomy, and pulmonary arterioplasty of the main and branch pulmonary arteries. The VSD is usually closed with a patch taking great care to avoid damage to the conduction system. Assessment of the pulmonary annulus using predicted mean-normal diameters of the pulmonary valve annulus corrected for body surface area provides some guidance for enlarging the pulmonary annulus (transannular patching). A conduit connection from the RV to the pulmonary arteries may be necessary in patients with pulmonary atresia, anomalies of the coronary arteries, or severe multilevel obstruction and hypoplasia. Distal pulmonary arteries and branch pulmonary artery stenosis can be managed at the time of surgery by using autologous pericardial patch enlargement. Additional work on the branch pulmonary arteries can be accomplished preoperatively and postoperatively by means of the transcatheter approach. In neonates and young infants, use of a transannular patch is most likely, and extensive RVOT muscle resection is not usually necessary. In older children, use of a transannular patch is relatively unlikely, and extensive RVOT muscle resection is common. Postoperative details: After surgery, various residual abnormalities may be encountered, ranging from a nearly normal-appearing heart to one in which substantial RV dysfunction and residual RVOTO. Two-dimensional echocardiography and Doppler techniques can be the definitive means for monitoring patients with respect to the recovery of RV function and the development of complications, such as recurrent RVOTO and residual or recurrent VSD. Postoperative pulmonary insufficiency can be associated with late RV dysfunction and may necessitate intervention. Follow-up care: Clinical, ECG, and echocardiographic follow-up monitoring is indicated. Echocardiography is the diagnostic modality of choice for follow-up.
Today, the mortality risk for uncomplicated TOF repair should approach 0%. Complications of the surgery include the following:
The overall outcome after surgical repair has steadily improved since the technique was initially developed. The continued improvement in outcome can be attributed to improved intraoperative technique, including the avoidance of excessive RVOT muscle resection, improved cardiopulmonary bypass techniques (especially for infants), and improved postoperative care. In the early 1980s, the survival rate after TOF repair was approximately 90%. In the current era, survival to discharge after TOF repair in most reported series is 95-99%. Late survival was documented in 814 patients undergoing complete repair reported in 1989 at the University of Alabama at Birmingham. After complete repair, survival rates at 1 month and at 1, 5, and 20 years, were 93%, 93%, 92%, and 87%, respectively. These survival rates were only slightly less than those of an age-, race-, and sex-matched control population. In the current era, late survival should even be better than it was in this historical 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. The Society of Thoracic Surgeons Congenital Heart Surgery Database was used to analyze data from 941 patients undergoing TOF repair in 1998-2003. TOF, pulmonary stenosis was present in 888 patients. TOF, absent pulmonary valve syndrome was present in 34 patients. TOF, common atrioventricular canal (AVSD) was present in 19 patients. The overall survival after discharge was 98.7%. The risk was highest among patients with TOF, absent pulmonary valve syndrome patients, 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%.
TOF versus double-outlet RV One area of controversy centers on the differentiation between TOF and double-outlet RV (DORV). The TOF manuscript of The International Congenital Heart Surgery Nomenclature and Database Project clearly stated that the distinction between DORV and TOF is controversial. Some authors use the term DORV when the pulmonary artery arises from the RV and when >50% of the aorta arises from the RV. Other authors use this term only when the pulmonary artery arises from the RV and when 90% or more of the aorta arises from the RV. Still others use the term only when fibrous continuity is absent between the aortic and mitral valves. In the DORV manuscript of The International Congenital Heart Surgery Nomenclature and Database Project, DORV is defined as a type of ventriculoarterial connection in which both great vessels arise predominantly from the RV. In the TOF manuscript of The International Congenital Heart Surgery Nomenclature and Database Project, Marshall Jacobs states, "It is inescapable that some hearts will be called TOF at some centers and DORV at other centers." Management of late pulmonary insufficiency After repair of TOF, many patients present in need of reoperative surgical reconstruction of the RVOT. The predominant physiologic lesion is often pulmonary insufficiency but varying degrees of RVOT may also be present. In the past, patients were thought to tolerate pulmonary insufficiency reasonably well. However, in some, the long-term effects of pulmonary insufficiency and subsequent RV dilatation and dysfunction are associated with poor exercise tolerance and increased incidences of arrhythmias and sudden death. Pulmonary valve insertion or replacement can be performed as treatment for pulmonary insufficiency to improve performance status, optimize hemodynamics, and improve control of arrhythmias. Indications for RVOT reconstruction in this setting and the surgical strategy continue to evolve. Several surgical options for pulmonary valve replacement are available, including the use of aortic and pulmonary homografts, stented and stentless porcine valves, porcine valve conduits, bovine jugular vein conduits, man-made polytetrafluoroethylene pulmonary valves, and even mechanical valves and mechanical valve conduits. Over the last several years, concerns regarding postoperative pulmonary insufficiency or combined insufficiency and stenosis have increasingly emerged. The brief about patients' tolerance of pulmonary insufficiency after valvectomy and/or transannular patching during repair of TOF is no longer simply accepted. The sequence of pulmonary insufficiency that causes volume overload leading to RV dilatation and dysfunction has been demonstrated with echocardiography and MRI. Exertional symptoms often follow these objective changes in ventricular function and size and can be documented with and exercise testing. Finally, life-threatening ventricular arrhythmias seem to be associated with relatively severe cases of pulmonary insufficiency and ventricular changes. RV dilatation and dysfunction are reversible after pulmonary valve replacement. Therefore, as the population of children with repaired congenital heart disease ages, an increasing number of patients will benefit from pulmonary valve insertion. However, recent data suggest a lack of notable recovery of RV indices after pulmonary valve replacement in adults with long-standing pulmonary insufficiency. Therefore, the timing of pulmonary valve replacement is of major importance in the overall maintenance of ventricular function and optimal long-term outcomes. In addition, a program of aggressive pulmonary valve replacement in conjunction with intraoperative cryoablation is effective in decreasing QRS duration and in controlling ventricular arrhythmias in patients with TOF and severe pulmonary insufficiency. In general, indications for pulmonary valve replacement are evolving but currently include patients with moderate-to-severe pulmonary insufficiency and/or stenosis and any of the following problems: exertional symptoms of New York Heart Association (NYHA) class II or worse, RV dysfunction and/or dilatation, decreased performance capacity on exercise testing, and/or ventricular arrhythmias and/or QRS duration >160 ms.
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