RISK FACTORS : Documented increased incidence with increased maternal age,
Occasional familial occurrence
Medical therapy: Surgery is the definitive treatment for the cyanotic patient with TOF. The primary role of medical therapy is in preparation for surgery. Most infants have adequate saturations and usually undergo elective repair. In infants with acute cyanotic episodes, placing them in a knee-chest position may prove helpful in addition to administering oxygen and intravenous morphine. In severe episodes, intravenous propranolol (Inderal) may be administered, which relaxes the infundibular muscle spasm causing RVOTO. Progressive hypoxemia and the occurrence of cyanotic spells are indications for early surgery. Asymptomatic infants need no special medical treatment.
Surgical therapy: Factors that increase the risk for early repair of TOF include the following:
" Low birth weight
" Pulmonary artery atresia
" Major associated anomalies
" Multiple previous surgeries
" Absent pulmonary valve syndrome
" Young age
" Old age
" Severe annular hypoplasia
" Small pulmonary arteries
" High peak right ventricular-to-left ventricular pressure ratio
" Multiple VSDs
" Coexisting cardiac anomalies
Palliative procedures
The goals of palliation are to increase pulmonary blood flow independent of ductal patency and to allow pulmonary artery growth and even total correction. Occasionally, an infant with pulmonary atresia or an anomalous LAD coronary artery that crosses the right ventricular outflow tract may not be a surgical candidate for establishing transannular right ventricle-to-pulmonary artery continuity and may require placement of a conduit.
Although artificial conduits can be used, infants with extremely small pulmonary arteries may not tolerate total correction in infancy. These infants may require palliation instead of corrective surgery. Various types of palliative procedures have been developed, but the current procedure of choice is the Blalock-Taussig shunt.
The Potts shunts has been abandoned because of a tendency toward increased pulmonary blood flow and increasing difficulty with takedown at the time of corrective surgery. The Waterston shunt is sometimes used, but it also increases pulmonary artery blood flow. This shunt is more related to pulmonary artery stenosis, which generally requires reconstruction. The Glenn shunt is no longer used because of difficulty in performing a subsequent definitive repair.
Given the problems associated with the aforementioned shunts, placement of the modified Blalock-Taussig shunt (using a Gore-Tex graft between the subclavian artery and pulmonary artery) is the procedure of choice. Advantages of the modified Blalock-Taussig shunt include (1) preservation of the subclavian artery, (2) suitability for use on either side, (3) good relief of cyanosis, (4) easier control and closure at time of primary repair, (5) excellent patency rate, and (6) decreased incidence of iatrogenic pulmonary/systemic artery trauma.
The mortality rate is reportedly less than 1% when placing this shunt. However, the Blalock-Taussig shunt elicits a few complications, including hypoplasia of the arm, digital gangrene, phrenic nerve injury, and pulmonary artery stenosis.
The longevity of palliation after shunt placement varies according to the patient's age at the time of surgery and the type of shunt.
Other forms of palliation that are rarely used today include patching of the right ventricular outflow tract without cardiopulmonary bypass (CPB). This procedure can cause destruction of the pulmonary valve and significant intrapericardial adhesions, and the increased pulmonary artery blood flow can result in congestive heart failure; therefore, its role is limited to treatment of infants with TOF complicated by pulmonary atresia and/or hypoplasia of the pulmonary artery.
In very ill neonates with multiple medical problems, balloon pulmonary valvulotomy has been shown to increase oxygen saturation, thus obviating the need for emergency palliative surgery. However, perforation of the pulmonary artery is a risk with this procedure in neonates.
Corrective surgery
Primary correction is the ideal operation for treatment of TOF and is usually performed under CPB. The aims of the surgery are to close the VSD, to resect the area of infundibular stenosis, and to relieve the RVOTO. Before CPB is initiated, previously placed systemic-to-pulmonary artery shunts are isolated and taken down. Patients then undergo CPB. Associated anomalies, such as ASD or patent foramen ovale, are closed.
Postoperative details: All infants undergoing open-heart procedures are sent to the pediatric intensive care unit. Hemodynamic parameters must be followed postoperatively. All infants initially remain intubated on a ventilator until cardiac and respiratory status stabilize. To maintain systemic peripheral perfusion, adequate cardiac output and atrial pacing may be required. Patients should be weighed daily to follow volume status. Patients with heart block should have temporary atrioventricular pacing. If intrinsic conduction has not returned in 5-6 days, the patient probably needs a permanent pacemaker.
Results
The outcome of surgical repair is excellent with minimal morbidity and mortality. To date, no difference in operative mortality rates has been noted between transventricular and transatrial approaches.
The occasional patient has an elevated right ventricle-to-left ventricle pressure ratio. This may be due to a number of causes including a residual VSD, pulmonary artery stenosis, and pulmonary artery and valve atresia. These patients tend to do poor and echocardiography (ECHO) is warranted to find the cause. Surgical revision may be required to correct the etiology of the high RV pressures.
With improved techniques, excellent results with early 1-stage repair in infants have been reported. Overall, the mortality rate in most series is 1-5% when the repair is performed primarily or after a systemic-to-pulmonary artery shunt. Similarly, the mortality rate of infants undergoing palliative shunt placement is low (0.5-3%). The survival rate at 20 years is approximately 90-95%.
Improved techniques of myocardial protection with hypothermia, cardioplegia, and even total circulatory arrest are providing excellent results by enabling more precise anatomic repairs in younger infants. Nevertheless, infants receiving complete correction before age 1 year have an increased risk compared with patients older than 1 year.
Revision/reoperation
The literature suggests that approximately 5% of individuals will need a revision/reoperation at some point. Indications for early reoperation include a residual VSD or a residual RVOTO.
Residual VSDs are poorly tolerated in patients with TOF because these individuals cannot tolerate an acutely imposed volume overload. Small, residual VSDs are common after TOF repair and are usually clinically insignificant. A residual VSD with a 2:1 shunt or an RVOTO of greater than 60 mm Hg is an urgent indication for reoperation. Surgery can be performed with low risk and can result in dramatic improvements. Occasionally, pulmonary valve insufficiency may increase and may be associated with right ventricular failure. Recurrent RVOTO may be due to muscular fibrosis or hypertrophy. This problem is generally treated with a pulmonary valve replacement. Porcine valves are preferred over mechanical valves because they have less tendency to thrombose.
COMPLICATIONS :
Early postoperative complications include the creation of heart block and residual ventricular septal defects (VSDs). Ventricular arrhythmias are more common and are reportedly the most frequent cause of late postoperative death. Sudden death from ventricular arrhythmias has been reported in 0.5% of individuals within 10 years of repair. The arrhythmias are thought to occur in fewer than 1% of patients having an early operation. As with most heart surgery, the risk of endocarditis is lifelong, but the risk is much less than in a patient with an uncorrected tetralogy of Fallot.
OUTCOME & PROGNOSIS :
In the present era of cardiac surgery, children with simple forms of tetralogy of Fallot (TOF) enjoy good long-term survival with an excellent quality of life. Late outcome data suggest that most survivors are in New York Heart Association classification I, although maximal exercise capability is reduced in some. Sudden death from ventricular arrhythmias has been reported in 1-5% of patients at a later stage in life, and the cause remains unknown. The surgical procedures are still palliative, and continued cardiac monitoring into adult life is necessary.