Approach
The definitive treatment for tetralogy of Fallot (TOF) is complete surgical repair. All pre-operative patients with TOF need careful follow-up with their primary physician and a paediatric cardiologist. Attention to their weight gain is mandatory. Progression of cyanosis should be noted. Parents should be counselled 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 ischaemia and death.[17]
Management of a hypercyanotic spell consists of calming the child and manoeuvres 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][25][26]
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.[27]
Surgical management
Over the last 10-15 years, there has been a trend towards neonatal repair of both cyanotic and acyanotic infants with TOF, but this is often determined by their pulmonary anatomy.[27]
In acyanotic patients without spells, repair is usually undertaken in the first year of life and has a very low morbidity and mortality.[26][28]
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.[25][26]
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.[27][29]
Patients who undergo repair in childhood should be counselled 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 long-standing pulmonary regurgitation, and the need for pulmonary valve replacement in this setting.
The American Heart Association suggests using the following criteria for consideration of pulmonary valve replacement (surgical or transcatheter) in patients with repaired TOF and right ventricular outflow tract (RVOT) dysfunction:[30]
RVOT dysfunction is classified as any of the following:
Predominant regurgitation: pulmonary regurgitation fraction ≥25% and RVOT gradient ≤25 mmHg or predicted right ventricular systolic pressure (RVSP) ≤one third of systemic pressure
Predominant stenosis: pulmonary regurgitation fraction <25% and RVOT gradient ≥60 mmHg or predicted RVSP ≥two-thirds of systemic pressure
Mixed RVOT dysfunction: all other patients with intermediate measurements of pulmonary regurgitation and pulmonary stenosis
Patients with cardiac symptoms (exercise intolerance, signs/symptoms of heart failure, syncope, chest pain, or other cardiac-related symptoms) should be considered for pulmonary valve replacement if they meet one or more of the following risk criteria:
Right ventricular ejection fraction ≤46%
Left ventricular ejection fraction ≤50%
Peak VO₂ ≤70% predicted for age and sex
Right ventricular systolic pressure ≥two-thirds of systemic pressure
INDICATOR risk score ≥3[31]
Patients with no cardiac symptoms should be considered for pulmonary valve replacement if they meet two or more of the risk criteria outlined above
Patients with haemodynamically significant residual lesions should be considered for pulmonary valve replacement. Examples include:
Residual shunt with Qp/Qs ≥1.3
Tricuspid regurgitation fraction ≥20%
Branch pulmonary artery stenosis/hypoplasia with ≤30% flow
Aortic regurgitation fraction ≥20%
Infective endocarditis prophylaxis
This is recommended pre-operatively 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).[32] 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 post-intervention.[33]
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