Tetralogy of Fallot

Definition

Tetralogy of Fallot (ToF) is the most common cyanotic congenital heart defect. It comprises four features: a ventricular septal defect (a hole between the pumping chambers), pulmonary stenosis (narrowing of the outflow from the right ventricle to the lungs), an overriding aorta (positioned over both ventricles), and right ventricular hypertrophy (thickening of the right pumping chamber). All four arise from a single developmental error, and the severity of the outflow obstruction determines almost everything about how the child presents.

Pathophysiology

One embryological error, four features

The four components are not independent defects but consequences of a single event: anterior and superior deviation of the outflow septum during early cardiac development. This narrows the right ventricular outflow tract, leaves the ventricular septum incomplete, allows the aorta to sit over the defect, and — because the right ventricle must pump against the obstruction — produces hypertrophy over time.

Right-to-left shunting and cyanosis

Because the ventricular septal defect is large and unrestrictive, pressures equalise between the ventricles, and the direction of flow is determined by the balance between pulmonary outflow resistance and systemic vascular resistance. Where the outflow obstruction is significant, deoxygenated blood takes the easier path across the defect into the aorta, bypassing the lungs entirely and producing cyanosis.

Tet spells

This balance explains the classic hypercyanotic spell. Crying, feeding, distress or dehydration lowers systemic vascular resistance or provokes infundibular spasm, abruptly increasing right-to-left shunt. Cyanosis deepens, the murmur paradoxically quietens as flow to the lungs falls, and acidosis and hypoxia set up a vicious cycle. Squatting — which older unrepaired children adopt instinctively — raises systemic vascular resistance and reverses the shunt, which is why it works.

The long-term consequence of repair

Surgical repair relieves the obstruction, and in doing so frequently sacrifices the pulmonary valve. Decades of free pulmonary regurgitation then volume-load the right ventricle, causing progressive dilatation, falling right ventricular function, exercise limitation and arrhythmia. The dominant clinical problem in adult ToF is therefore not the original defect but the long-term cost of its repair — which is why lifelong specialist follow-up is not optional.

Co-morbidities

ToF is associated with genetic conditions, most importantly 22q11.2 deletion (DiGeorge) syndrome — which brings immune deficiency, hypocalcaemia, palatal abnormalities, learning difficulty and psychiatric risk — and with Down syndrome, Alagille syndrome and VACTERL association. Other cardiac anomalies frequently coexist, including right aortic arch, additional septal defects and anomalous coronary arteries, the last of which materially affects surgical planning. After repair, adults commonly develop pulmonary regurgitation, right ventricular dilatation, atrial and ventricular arrhythmia, branch pulmonary artery stenosis, aortic root dilatation and reduced exercise capacity.

Prevalence

ToF accounts for roughly 1 in 3,000 live births and about 10% of congenital heart disease. With modern surgery the great majority survive to adulthood — long-term survival after repair now exceeds 90% at 30 years — so there is a large and growing population of adults living with repaired ToF. In Australia this population now outnumbers the paediatric one, and many are lost to specialist follow-up in early adulthood, which is a recognised and preventable cause of late morbidity.

Causes and risk factors

• Abnormal development of the cardiac outflow tract in the first eight weeks of pregnancy. Most cases are sporadic with no identifiable cause.
• Genetic syndromes — 22q11.2 deletion in around 15% of cases, and Down, Alagille and CHARGE syndromes.
• Family history of congenital heart disease, which raises recurrence risk modestly.
• Maternal diabetes, particularly poorly controlled pre-gestational diabetes.
• Maternal phenylketonuria, rubella infection, and exposure to retinoic acid, anticonvulsants or excess alcohol in early pregnancy.
• Advanced maternal age.

Nothing the parents did or omitted causes the great majority of cases, and saying so directly matters — parental guilt after a congenital heart diagnosis is common and rarely volunteered.

Symptoms

In infancy

A loud systolic murmur, often detected before any cyanosis; poor feeding with sweating and breathlessness during feeds; poor weight gain; and cyanosis that varies with activity and crying. Severity depends on the degree of outflow obstruction, so presentation ranges from a well “pink” baby to profound neonatal cyanosis requiring urgent intervention.

Tet spells

Episodes of deep, sudden cyanosis with irritability progressing to lethargy, rapid deep breathing, and in severe cases syncope or seizure. They occur most often on waking, during feeding or with prolonged crying, and their appearance is an indication for prompt surgical repair.

In unrepaired older children

Now rare in Australia but seen in migrant populations: cyanosis, clubbing, polycythaemia, exercise intolerance and instinctive squatting.

In repaired adults

Often none for decades, then insidious exercise limitation, breathlessness, palpitations or, occasionally, syncope. Because decline is gradual and patients adjust their lives around it, symptoms are consistently under-reported — which is why objective exercise testing is part of routine surveillance rather than a response to complaint.

Warning signs

Diagnosis

Why diagnosis matters

Diagnosis — increasingly antenatally — allows planned delivery at a cardiac centre, timely surgical repair in infancy, and entry into the lifelong specialist follow-up that detects and treats later complications before they cause irreversible harm. Both major international guidelines emphasise that follow-up must be lifelong and in a dedicated adult congenital heart disease service.^1,2

How is it diagnosed?

Echocardiography is the diagnostic test, frequently at the 20-week anomaly scan or in the newborn period, defining the four components and the degree of outflow obstruction. ECG shows right axis deviation and right ventricular hypertrophy, and chest X-ray classically shows a boot-shaped heart with reduced pulmonary vascular markings.

Cardiac MRI in adults

The key surveillance investigation in adulthood. Cardiac MRI quantifies the pulmonary regurgitant fraction, right ventricular end-diastolic and end-systolic volumes and ejection fraction, and detects myocardial fibrosis — measurements that directly determine the timing of pulmonary valve replacement in an otherwise asymptomatic patient.

Exercise testing

Cardiopulmonary exercise testing gives an objective measure of functional capacity that patients cannot self-report accurately, and carries independent prognostic weight in adult congenital heart disease. Serial testing detects the decline that precedes symptoms.

Rhythm monitoring

Holter and extended ambulatory monitoring screen for atrial and ventricular arrhythmia, which increase in prevalence from the third decade after repair and are a leading cause of late morbidity and sudden death.

Investigations for related conditions

Genetic testing, particularly for 22q11.2 deletion, with genetic counselling for the family and for the patient contemplating pregnancy. Assessment also covers aortic root dimensions, branch pulmonary artery stenosis, residual septal defects, and dental health given endocarditis risk.

Management

Management and goals

In infancy, the goal is safe, timely repair. Thereafter it is lifelong surveillance and well-timed intervention — replacing the pulmonary valve before right ventricular dilatation becomes irreversible, treating arrhythmia, and supporting a full and active life. The central management question in adult ToF is one of timing, not of whether.

Surgical repair in infancy

Complete repair — closing the ventricular septal defect and relieving the right ventricular outflow obstruction — is typically performed between three and six months of age, with excellent results. A palliative shunt is used first in neonates too small or unstable for full repair. Where the outflow must be opened widely, a transannular patch is used, which relieves obstruction at the cost of pulmonary regurgitation.

Managing tet spells

Acute management is knee-to-chest positioning, calm handling, oxygen, fluids, morphine and, if needed, phenylephrine or beta-blockade. Recurrent spells are an indication to bring repair forward.

Pulmonary valve replacement

The major intervention of adult life, performed surgically or by catheter. Timing is the crux: too early exposes the patient to repeated valve replacements over a lifetime, too late leaves irreversible right ventricular dysfunction. Right ventricular volume thresholds guide the decision, based on evidence that normalisation of right ventricular volumes is achievable only below certain preoperative volumes.³ Contemporary analysis suggests earlier intervention in selected patients is associated with better outcomes, and criteria continue to evolve.⁴

Arrhythmia management

Atrial arrhythmias are common and often amenable to catheter ablation. Ventricular arrhythmia risk is stratified using right ventricular function, QRS duration, prior surgery and MRI findings, with implantable defibrillators used in selected patients.

Transition and lifelong follow-up

The transfer from paediatric to adult congenital services in late adolescence is the point at which patients are most often lost to follow-up — frequently because they feel well. Structured transition programmes, and explaining plainly that feeling well does not mean the right ventricle is well, are worth the effort they take.

Medications

Medications in tetralogy of Fallot

There is no drug therapy for the defect itself. Beta-blockers are used to reduce infundibular spasm in infants with spells and for arrhythmia in adults; antiarrhythmics and anticoagulation are used as indicated; and where right or left ventricular dysfunction develops, standard heart failure therapy applies. Iron deficiency is looked for and corrected, since it worsens exercise capacity disproportionately in this group.

Endocarditis prevention

Patients with repaired congenital heart disease involving prosthetic material, and those with residual defects adjacent to prosthetic material, remain at elevated risk of infective endocarditis and fall within the group for whom antibiotic prophylaxis before certain dental procedures is recommended.⁵ Meticulous dental hygiene, regular dental review and prompt investigation of unexplained fever matter more than the prophylaxis itself, and patients should be told never to accept a course of antibiotics for an undiagnosed fever before blood cultures are taken.

Correct use of medications

Beta-blockade blunts the exercise heart-rate response, which is relevant to exercise prescription. Anticoagulation requires the usual counselling around bleeding, interactions and pregnancy. Any new medication is checked against the patient’s cardiac history by the congenital service rather than assumed safe.

Multi-system manifestations

Right heart and exercise capacity

Progressive right ventricular dilatation and dysfunction from chronic pulmonary regurgitation is the central long-term problem, producing exercise intolerance that is objectively measurable long before it is reported. Reduced peak oxygen uptake in adult congenital heart disease is comparable in severity to that seen in chronic heart failure and independently predicts hospitalisation and death.⁶

Arrhythmia and sudden death

Atrial flutter and fibrillation, and ventricular tachycardia arising from surgical scar and the ventricular septal defect patch, increase steadily with time from repair and represent the principal cause of late sudden death.

22q11.2 deletion syndrome

Where present, the syndrome brings its own multi-system burden: thymic hypoplasia with immune deficiency, hypoparathyroidism and hypocalcaemia, palatal abnormalities affecting speech and feeding, learning difficulty, and a substantially raised risk of psychiatric illness in adolescence and adulthood.

Neurodevelopment

Children with cyanotic congenital heart disease who undergo infant cardiac surgery have measurably higher rates of learning difficulty, attention problems and executive dysfunction, related to both the underlying condition and the perioperative course. Developmental surveillance is part of long-term care.

Pregnancy

Most women with repaired ToF tolerate pregnancy well, but risk rises with right ventricular dysfunction, severe pulmonary regurgitation, arrhythmia or residual lesions. Pre-pregnancy counselling in a specialist service, including genetic counselling given the 22q11.2 association, is essential rather than advisable.

Aorta, kidneys and liver

Progressive aortic root dilatation occurs in a minority and requires surveillance. Chronic low cardiac output and venous congestion in advanced right heart failure affect renal and hepatic function, contributing to the systemic decline seen in late disease.

Living with tetralogy of Fallot

Attending lifelong follow-up

The single most important step a patient can take. Complications develop silently and are treatable when detected early and considerably less so when they present as symptoms. Feeling well is not evidence that the right ventricle is coping.

Staying physically active

Most people with repaired ToF should be active, and exercise is safe and beneficial when prescribed individually. European guidance sets out individualised exercise prescription for adults with congenital heart defects based on the underlying lesion, ventricular function, rhythm and exercise-test findings, rather than blanket restriction.⁷ Historic over-restriction has caused real harm in this population, producing deconditioning and obesity that compound the cardiac limitation.

Understanding warning symptoms

Palpitations, syncope or near-syncope, worsening breathlessness, ankle swelling and unexplained persistent fever all warrant contact with the congenital service rather than waiting for the next appointment.

Dental and infection care

Regular dental review, excellent oral hygiene, avoiding piercings and non-sterile tattooing, and carrying a card recording the cardiac history and endocarditis risk.

Work, insurance and driving

Most occupations are open, with individualised advice where the work is physically demanding or safety-critical. Practical issues around insurance, superannuation and, for some, driving after arrhythmia or device implantation are best addressed early with the specialist team.

Mental health and transition to adult care

Growing up with a heart condition, repeated procedures, and uncertainty about the future carry a real psychological burden, and anxiety and depression are more common than in the general population. Adolescence and the transition to adult services is a vulnerable period for both mental health and disengagement from follow-up.

Prognosis

Long-term survival after repair is very good and continues to improve, with most patients reaching middle age and beyond. The determinants of outcome in adulthood are pulmonary regurgitation and right ventricular size and function, arrhythmia, and objectively measured exercise capacity — all of which are detectable on surveillance and modifiable by timely intervention. Late mortality is driven principally by sudden arrhythmic death and progressive heart failure. The most consequential modifiable factor is not medical at all: whether the patient remains engaged with a specialist adult congenital heart disease service across their whole life.

Role of the physiotherapist

Most people with repaired ToF can and should be physically active, and physiotherapy is central to making that both safe and effective. The starting point is an individualised plan agreed with the cardiologist, informed by residual lesions, right ventricular function, rhythm and exercise-test findings — not a generic cardiac protocol and not blanket caution.

Exercise training works in this population. A systematic review of exercise training programmes in children and young adults with congenital heart disease found improvements in exercise capacity with no significant adverse events, supporting training as safe and beneficial across a range of lesions.⁸ Australian recommendations for exercise in adolescents and adults with congenital heart disease set out how to prescribe it by lesion and functional status, and are the practical reference for programme design.⁹ Both aerobic and resistance components are included, with resistance training addressing the peripheral muscle weakness that contributes independently to exercise limitation.

Ongoing physiotherapy contributions include objective functional assessment that complements formal exercise testing and often detects decline earlier; education on pacing, warning symptoms and when to escalate; support through the transition from paediatric to adult services, where physiotherapists frequently maintain contact when others lose it; and rehabilitation after any cardiac surgery, covering respiratory care, sternal precautions, thoracic and shoulder mobility and graded reconditioning. Perhaps the most valuable long-term role is countering a lifetime of over-restriction — many of these patients were told as children to avoid sport, and rebuilding the confidence to exert themselves safely improves both fitness and quality of life more than any single intervention.

Part 1 · References

1. Baumgartner H, De Backer J, Babu-Narayan SV, et al. 2020 ESC guidelines for the management of adult congenital heart disease. Eur Heart J 2021;42(6):563–645.
2. Stout KK, Daniels CJ, Aboulhosn JA, et al. 2018 AHA/ACC guideline for the management of adults with congenital heart disease. Circulation 2019;139(14):e698–e800.
3. Therrien J, Provost Y, Merchant N, Williams W, Colman J, Webb G. Optimal timing for pulmonary valve replacement in adults after tetralogy of Fallot repair. Am J Cardiol 2005;95(6):779–782.
4. Bokma JP, Geva T, Sleeper LA, et al. A propensity score-adjusted analysis of clinical outcomes after pulmonary valve replacement in tetralogy of Fallot. Heart 2018;104(9):738–744.
5. Delgado V, Ajmone Marsan N, de Waha S, et al. 2023 ESC guidelines for the management of endocarditis. Eur Heart J 2023;44(39):3948–4042.
6. Diller GP, Dimopoulos K, Okonko D, et al. Exercise intolerance in adult congenital heart disease: comparative severity, correlates, and prognostic implication. Circulation 2005;112(6):828–835.
7. Budts W, Börjesson M, Chessa M, et al. Physical activity in adolescents and adults with congenital heart defects: individualized exercise prescription. Eur Heart J 2013;34(47):3669–3674.
8. Duppen N, Takken T, Hopman MTE, et al. Systematic review of the effects of physical exercise training programmes in children and young adults with congenital heart disease. Int J Cardiol 2013;168(3):1779–1787.
9. Tran D, Maiorana A, Ayer J, et al. Recommendations for exercise in adolescents and adults with congenital heart disease. Prog Cardiovasc Dis 2020;63(3):350–366.

References are numbered in citation order (Vancouver/BMJ style) and were current at the time of writing. Guidelines are living documents — verify against the latest version before clinical use.