Tetralogy of Fallot — branching viva

Examiner opening (Examiner)

You are the general paediatric registrar in the emergency department. A four-month-old girl is brought in cyanotic and agitated after a feed, with a systolic ejection murmur at the left upper sternal border and a single second heart sound. As you assess her she gets bluer and the murmur gets quieter. Talk me through your immediate assessment and management. [1]

Exemplar opening (Candidate)

This infant is having a hypercyanotic tet spell on the background of what is almost certainly tetralogy of Fallot, and I will treat it as an emergency now rather than observe. First, the airway, breathing and circulation: give 100 per cent oxygen and place her in the knee–chest position, which raises systemic vascular resistance and reduces the right-to-left shunt. I need intravenous access to give morphine 0.1 mg/kg to calm her and blunt the infundibular spasm, a 10 mL/kg isotonic saline bolus for preload, and phenylephrine 5 micrograms/kg intravenously to raise systemic vascular resistance if the spell continues. I will correct any acidosis with sodium bicarbonate. The softening murmur with deepening cyanosis is the paradox of a severe spell — the outflow is so narrowed that little blood reaches the lungs, so the murmur fades. [1]

Branch 1 — the underlying lesion (Examiner)

She stabilises. What is tetralogy of Fallot, and what is the single embryologic fault that produces all four features? [6]

Exemplar (Candidate)

Tetralogy of Fallot is the commonest cyanotic congenital heart defect presenting after infancy, and its four features — a malalignment ventricular septal defect, right ventricular outflow tract obstruction, an overriding aorta, and right ventricular hypertrophy — are the downstream consequences of a single fault: anterocephalad deviation of the infundibular, or outlet, septum. The septum shifts forward and upward, leaving the ventricular septal defect behind it, narrowing the right ventricular outflow tract in front of it, and pulling the aortic root over the defect so it overrides. Right ventricular hypertrophy develops over weeks as the right ventricle pumps against the obstruction. The key teaching point is that it is one lesion, not four. [6] [1]

Branch 2 — diagnosis (Examiner)

How will you confirm the diagnosis, and what might you be missing that would change her immediate management? [1]

Exemplar (Candidate)

Echocardiography is diagnostic and is the single most important investigation — it shows the ventricular septal defect, the overriding aorta, the site and severity of the outflow obstruction, and the size of the pulmonary arteries. The thing I must not miss is pulmonary atresia, in which there is no continuity between the right ventricle and the pulmonary arteries and the circulation is duct-dependent. If that is possible I start a prostaglandin infusion immediately, because the ductus is the only source of pulmonary blood flow — I do not wait for the echo to confirm it. A chest X-ray may show the boot-shaped heart, reduced pulmonary markings and a right aortic arch, and the ECG shows right-axis deviation and right ventricular hypertrophy, but these support rather than replace the echo. [1]

Branch 3 — definitive repair (Examiner)

Once stable, what is the surgical plan, and what is the controversy around the transannular patch? [5]

Exemplar (Candidate)

The modern standard is complete primary repair at around three to six months of age — closure of the ventricular septal defect with a patch and relief of the outflow obstruction by infundibular resection. Neonatal repair is reserved for duct-dependent or severe disease, and a staged approach (a modified Blalock–Taussig shunt or a transcatheter right ventricular outflow tract stent) is used for unfavourable anatomy such as very small pulmonary arteries. The transannular patch reliably relieves the obstruction but incises the pulmonary valve annulus, leaving the patient with free pulmonary regurgitation — the lifelong consequence is progressive right ventricular dilation, a substrate for arrhythmia, and the eventual need for pulmonary valve replacement. That is why modern practice favours a valve-sparing approach where the native valve will accommodate it, to defer or avoid the burden of pulmonary regurgitation. [5] [3]

Branch 4 — staged repair in low-resource settings (Examiner)

You are working where safe neonatal repair is not available. How does management change? [3]

Exemplar (Candidate)

Where neonatal or infant repair is not available, the goal is to secure pulmonary blood flow as a bridge to later repair. A transcatheter right ventricular outflow tract stent is an increasingly used option — it restores pulmonary blood flow and promotes pulmonary artery growth and can be a durable bridge for months. A surgical modified Blalock–Taussig shunt is the alternative. Late presentation with severe cyanosis, clubbing and secondary erythrocytosis is common in these settings, and the right-to-left shunt carries a high risk of brain abscess. Once the anatomy is favourable, complete repair is still offered, including into adulthood. [3] [1]

Branch 5 — late complications and sudden death (Examiner)

Fast-forward twenty years. She is repaired and well. What are you watching for, and what predicts sudden cardiac death? [4]

Exemplar (Candidate)

The central late problem is pulmonary regurgitation after a transannular patch, which dilates the right ventricle and drives arrhythmia. I surveil with serial cardiac MRI for right ventricular volumes and ejection fraction, and with ECG for QRS duration. A QRS duration over 180 milliseconds is a validated predictor of sustained ventricular tachycardia and sudden cardiac death — the highest arrhythmia burden of the repaired congenital lesions. I also watch for residual right ventricular outflow obstruction, branch pulmonary artery stenosis, aortic root dilation with aortic regurgitation, and infective endocarditis. Pulmonary valve replacement is timed by the MRI volume thresholds, and an implantable cardioverter defibrillator is considered for those at highest arrhythmia risk. [4] [5]

Branch 6 — transition and the family (Examiner)

She is now 16. What must happen before she leaves paediatric care? [2]

Exemplar (Candidate)

She needs a structured transition to an adult congenital heart disease service, not a discharge. The risks of lost follow-up, unplanned pregnancy, and non-adherence converge in early adulthood, when many sudden deaths and reoperations occur. Transition covers education about her lesion and her operations, self-management skills, counselling about contraception and pregnancy risk and the heritability of congenital heart disease, and a warm handover to the adult congenital cardiologist. She must understand that repaired is not cured, and that lifelong surveillance is mandatory. [2] [4]

Examiner wrap-up (Examiner)

Thank you. Summarise the three points you most want the examiner to remember. [1]

Exemplar (Candidate)

First, tetralogy of Fallot is one embryologic fault — anterocephalad deviation of the outlet septum — that produces all four features. Second, a hypercyanotic spell is a treated emergency: knee–chest, oxygen, morphine, fluid and phenylephrine, escalating to a shunt if refractory, and a softer murmur with deeper cyanosis means a worse spell. Third, repaired is not cured — pulmonary regurgitation drives right ventricular dilation and arrhythmia, a QRS over 180 milliseconds predicts sudden death, and every patient needs lifelong follow-up and structured transition to adult congenital care. [1] [4]