Approach
The definitive treatment for TOF is complete surgical repair. All preoperative patients with TOF need careful follow-up with their primary physician and a pediatric cardiologist. Attention to their weight gain is mandatory. Progression of cyanosis should be noted. Parents should be counseled to alert their physicians should they notice the onset of hypercyanotic spells, as these would be an indication for urgent surgical intervention.
Management of hypercyanotic (tet) spells
An infant with TOF and hypercyanotic spells is a medical emergency because a prolonged hypercyanotic spell can result in brain ischemia and death.[17]
Management of a hypercyanotic spell consists of calming the child and maneuvers to increase the amount of blood exiting the right ventricle to the pulmonary vasculature instead of to the aorta. Often the best place for the infant is in the parent's arms. Initially, the infant should be positioned with the knees to the chest, as this will increase venous return to the heart (preload) and systemic afterload.
Oxygen should be given, but care should be taken not to increase the infant's stimulation. If the infant is still profoundly cyanotic, acidosis will result.
If these measures are not successful, medical therapy includes:
Adjunctive supportive measures such as volume repletion, reversal of acidosis, or morphine
Beta-blockers to relax the contracted infundibulum and to allow more time for right ventricular filling, improving pulmonary blood flow
Phenylephrine as a final medical option to increase systemic venous resistance and force more blood to the lungs.
Neonates with severely limited pulmonary blood flow causing profound cyanosis may benefit from prostaglandins (e.g., alprostadil) to maintain the patency of the ductus arteriosus. This provides an alternative source of pulmonary blood flow while the infant awaits urgent intervention.
If all medical therapies fail to resolve a spell and the neonate or infant remains severely cyanotic, urgent intervention will be needed. Options include catheter-based right ventricular outflow tract ballooning or stenting, Blalock-Taussig shunt placement (a small GORE-TEX tube placed from a systemic artery to the pulmonary arteries to increase pulmonary blood flow), stenting of a patent ductus arteriosus, immediate complete repair, or extracorporeal membrane oxygenation.[22][27][28]
Propranolol has been used in the past in the outpatient setting of an infant with spells to delay surgery. An infant with a single spell is considered an indication for urgent surgical repair, but propranolol may be used until surgery can be arranged.[29]
Surgical management
Over the last 10 to 15 years, there has been a trend toward neonatal repair of both cyanotic and acyanotic infants with TOF, but this is often determined by their pulmonary anatomy.[29]
In acyanotic patients without spells, repair is usually undertaken in the first year of life and has a very low morbidity and mortality.[28][30]
Patients with TOF with severe pulmonary stenosis may undergo complete neonatal repair at some institutions or alternatively may undergo a Blalock-Taussig shunt or stenting of a patent ductus arteriosus in the newborn period before complete repair.[27][28]
Excellent results with complete repair in the neonatal period have been reported, with one cohort reporting a 5-year survival rate of 93% in patients with TOF who underwent complete repair as a neonate.[29][31]
Patients who undergo repair in childhood should be counseled about the possible need for future surgical or transcatheter interventions. In particular, if relief of pulmonary obstruction requires a transannular patch, there is likely to be a significant amount of postoperative pulmonary regurgitation. There is an increasing awareness of the need to monitor patients for progressive dilation of the right ventricle secondary to longstanding pulmonary regurgitation, and the need for pulmonary valve replacement in this setting. Typically, magnetic resonance imaging measurements are used to quantify the pulmonary regurgitation and right ventricular size. One group has suggested that valve replacement before the right ventricular diastolic volume reaches 160 mL/m² allows for normalization of right ventricular volumes.[32] Another group found that no patient with a right ventricular volume >170 mL/m² had normalization of their right ventricular volumes after valve replacement.[33] While there is no consensus on the exact criteria for the timing of replacement of the pulmonary valve, one review suggests using the following criteria:[34]
Repaired TOF or similar physiology with moderate or severe pulmonary regurgitation (regurgitation fraction ≥25% measured by cardiovascular magnetic resonance imaging) and 2 or more of the following criteria:
Right ventricular end-diastolic volume index ≥160 mL/m² (Z score >5)
Right ventricular end-systolic volume index ≥70 mL/m²
Left ventricular end-diastolic volume index ≤65 mL/m²
Right ventricular ejection fraction ≤45%
Right ventricular outflow tract aneurysm
Clinical criteria: exercise intolerance, symptoms and signs of heart failure, cardiac medications, syncope, or sustained ventricular tachycardia.
Other hemodynamically significant lesions such as moderate or severe tricuspid regurgitation, residual atrial or ventricular septal defects, and severe aortic regurgitation may trigger referral for surgery in patients with moderate or severe pulmonary regurgitation. In the absence of the 6 criteria above, pulmonary valve replacement should be considered on a case-by-case basis.
Due to a higher risk of adverse clinical outcomes in patients who underwent TOF repair at age ≥3 years, pulmonary valve replacement may be indicated sooner and in the presence of less severe right ventricular dilation and dysfunction.
Infective endocarditis prophylaxis
This is recommended preoperatively and should be used for 6 months after repair. Those patients who have residual defects at the site or adjacent to the site of a prosthetic patch or prosthetic device should continue to receive lifelong infective endocarditis prophylaxis whenever undergoing an invasive procedure (e.g., dental procedures, or procedures on the respiratory tract or infected skin, skin structures, or musculoskeletal tissue).[35] European guidelines recommend advanced imaging modalities including echocardiography, computed tomography (CT), magnetic resonance imaging (MRI), and particularly, PET/CT imaging for diagnosing infective endocarditis in patients with Tetralogy of Fallot, due to their increased susceptibility to endocarditis postintervention.[36]
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