Tetralogy of Fallot: Clinical Case and Viva QnA

Clinical Case: Tetralogy of Fallot

A 6-month-old male infant is brought to the emergency department by his parents due to episodes of cyanosis and difficulty breathing. The parents report that these episodes occur especially during feeding or when the baby cries. They've noticed a bluish tint to his lips and fingertips during these spells.

History:

• Full-term birth with no complications
• Poor weight gain since birth
• Easily fatigued during feeding
• No history of respiratory infections

Physical Examination:

• Weight: 5.8 kg (below 3rd percentile)
• Heart rate: 145 bpm
• Respiratory rate: 50 breaths/min
• Oxygen saturation: 85% on room air
• Visible cyanosis of lips and nail beds
• Clubbing of fingers
• Grade 3/6 systolic ejection murmur at the left sternal border
• Quiet second heart sound

Investigations:

• Chest X-ray: Boot-shaped heart, decreased pulmonary vascular markings
• ECG: Right axis deviation, right ventricular hypertrophy
• Echocardiogram: Large ventricular septal defect, overriding aorta, right ventricular outflow tract obstruction, right ventricular hypertrophy

Diagnosis:

Tetralogy of Fallot

Management:

1. Oxygen therapy
2. IV fluids for hydration
3. Propranolol to prevent hypercyanotic spells
4. Surgical repair scheduled for 3 months later

Outcome:

The patient underwent successful total surgical repair at 9 months of age. Post-operative course was uneventful, and he was discharged after 10 days. Follow-up at 1 year showed significant improvement in growth and development, with no residual cyanosis.

Varieties of Tetralogy of Fallot Presentation

1. Classic Tetralogy of Fallot:

   • Presents in infancy with cyanosis
   • Hypercyanotic spells (tet spells)
   • Poor feeding and failure to thrive
   • Systolic murmur at left sternal border

2. Pink Tetralogy of Fallot:

   • Minimal or no cyanosis at rest
   • Adequate pulmonary blood flow
   • May present later in childhood
   • Exercise intolerance and easy fatigability

3. Tetralogy of Fallot with Pulmonary Atresia:

   • Severe cyanosis from birth
   • Absence of murmur due to complete obstruction of right ventricular outflow
   • Dependent on patent ductus arteriosus for pulmonary blood flow
   • May have major aortopulmonary collateral arteries (MAPCAs)

4. Tetralogy of Fallot with Absent Pulmonary Valve:

   • Aneurysmal dilatation of pulmonary arteries
   • To-and-fro murmur due to pulmonary stenosis and regurgitation
   • Respiratory symptoms due to bronchial compression by dilated pulmonary arteries
   • May present with heart failure

5. Tetralogy of Fallot with Complete Atrioventricular Septal Defect:

   • Features of both TOF and AVSD
   • Severe cyanosis
   • Single AV valve with common atrium
   • More complex surgical repair required
   • Often associated with Down syndrome

What are the four classical components of Tetralogy of Fallot (TOF)?

The four components are: 1) Pulmonary stenosis (infundibular ± valvar), 2) Right ventricular hypertrophy, 3) Ventricular septal defect (subaortic and nonrestrictive), and 4) Overriding aorta (≤50% override). All result from anterior and cephalad deviation of the infundibular septum.

What is the embryological basis of TOF?

TOF results from anterior and superior displacement of the infundibular septum during cardiac development (weeks 6-8 of gestation). This leads to inadequate conus rotation and unequal division of the conotruncus, affecting both outflow tracts. The genetic basis often involves mutations in NKX2.5, JAG1, and other cardiac developmental genes.

What are the variations in pulmonary stenosis in TOF?

Pulmonary stenosis can occur at multiple levels: 1) Infundibular (always present), 2) Valvar (often bicuspid/dysplastic), 3) Supravalvar, 4) Branch pulmonary artery stenosis. Severity varies from mild to complete pulmonary atresia. The pattern and severity influence surgical approach and timing.

How does the pathophysiology of TOF affect oxygen saturation?

The degree of right-to-left shunting through the VSD depends on: 1) Severity of RVOT obstruction, 2) Systemic vascular resistance, 3) Pulmonary vascular resistance. Right-to-left shunting leads to varying degrees of cyanosis. Dynamic infundibular obstruction can cause acute hypercyanotic spells.

What are the clinical features of TOF in infancy?

Features include: varying degrees of cyanosis (may be present at birth or develop later), poor feeding, failure to thrive, hypercyanotic spells, clubbing (in older infants), loud systolic murmur at left sternal border, single S2, and squatting position during spells in older infants who can walk.

Describe hypercyanotic spells in TOF. How are they managed?

Spells involve acute decrease in pulmonary blood flow due to infundibular spasm, causing severe cyanosis, hyperpnea, irritability, and syncope. Management includes: knee-chest position, oxygen, morphine, fluid bolus, sodium bicarbonate, phenylephrine/norepinephrine (increase SVR), and beta-blockers. May need urgent surgical intervention if refractory.

What are the ECG findings in TOF?

Classical findings include: right axis deviation, right ventricular hypertrophy (tall R waves in V1, deep S waves in V6), right atrial enlargement (tall P waves in II, III, aVF). QRS duration >180ms in adults suggests increased risk of arrhythmias and sudden death.

Describe the chest X-ray findings in TOF.

Classic 'boot-shaped' heart (coeur en sabot) due to RV hypertrophy and uplifted apex, concave pulmonary artery segment, right-sided aortic arch (25%), decreased pulmonary vascular markings. Size of cardiac silhouette varies with pulmonary blood flow.

What are the key echocardiographic findings in TOF?

Echo shows: anterior deviation of infundibular septum, large subaortic VSD, overriding aorta, RVOT obstruction (multiple levels possible), RV hypertrophy, pulmonary valve morphology, branch PA size/stenosis, coronary anatomy, and associated defects. Essential for surgical planning.

What associated cardiac anomalies can occur with TOF?

Common associations include: right aortic arch (25%), coronary artery anomalies (5-12%), additional VSDs (multiple in 3-5%), ASD (10%), aortopulmonary collaterals (more common in TOF-PA), persistent LSVC, and complete AV canal defect (especially in Down syndrome).

What genetic syndromes are associated with TOF?

Common associations include: 22q11.2 deletion syndrome (DiGeorge) in 15-20%, Down syndrome (trisomy 21), CHARGE syndrome, VACTERL association, Alagille syndrome, and cat eye syndrome. Genetic testing recommended, especially with dysmorphic features or other anomalies.

How do you evaluate coronary artery anatomy in TOF?

Evaluation includes: detailed echocardiography, cardiac CT/MRI, and often cardiac catheterization before surgery. Key abnormalities to identify: left anterior descending from right coronary (5-7%), large conal branch crossing RVOT, and single coronary artery. Affects surgical approach and timing.

What is the role of cardiac MRI in TOF?

MRI provides: detailed anatomy of PAs and collaterals, quantification of RV volume/function, pulmonary regurgitation, flow distribution between branch PAs, and coronary artery course. Essential for timing pulmonary valve replacement and long-term follow-up.

What are the indications for early primary repair of TOF?

Early repair (3-6 months) is preferred to prevent RV hypertrophy and fibrosis. Earlier repair indicated for: severe cyanosis, hypercyanotic spells, failure to thrive, or severe RVOT obstruction. Some centers perform repair in neonatal period if anatomy favorable.

When is initial palliation preferred over primary repair?

Palliation (usually modified BT shunt) considered for: very small PAs (

Describe the surgical approach to TOF repair.

Repair includes: VSD closure with patch, RVOT resection, pulmonary valvotomy/valvectomy ± transannular patch, and PA augmentation if needed. Transannular patch needed in 60-70% cases. Approach modified based on coronary anatomy and degree of RVOT obstruction.

What are the early postoperative complications after TOF repair?

Complications include: low cardiac output syndrome, residual RVOT obstruction, arrhythmias (JET common), heart block, residual VSD, pulmonary regurgitation, bleeding, and pleural effusions. RV diastolic dysfunction common early post-op due to hypertrophy and cardioplegia.

What are the long-term complications after TOF repair?

Common issues include: pulmonary regurgitation, RV dilation/dysfunction, exercise intolerance, arrhythmias (atrial/ventricular), sudden cardiac death risk, branch PA stenosis, residual RVOT obstruction, and aortic root dilation. Regular follow-up needed lifelong.

What are the indications for pulmonary valve replacement after TOF repair?

Indications include: severe PR with RV dilation (EDVi >160mL/m2), decreased RV function, exercise intolerance, sustained arrhythmias, QRS duration >180ms, or significant TR. Earlier intervention may be considered to preserve RV function.

How do you assess RV function in repaired TOF?

Assessment includes: MRI (gold standard) for volumes and EF, 3D echo, tissue Doppler, strain imaging, exercise testing, and biomarkers (BNP). Consider both systolic and diastolic function. Serial measurements more valuable than single measurements.

What factors increase risk of sudden cardiac death in TOF?

Risk factors include: QRS duration >180ms, severe RV dilation, LV dysfunction, previous ventriculotomy, sustained VT, severe PR, residual RVOT obstruction, and older age at repair. Risk stratification guides ICD placement decisions.

How do you manage pregnancy in repaired TOF?

Management requires pre-pregnancy assessment of: RV/LV function, arrhythmias, residual lesions, and exercise capacity. Higher risk with significant PR, RV dysfunction, or residual RVOT obstruction. Monthly follow-up during pregnancy recommended. Consider PVR before pregnancy if indicated.

What exercise recommendations apply to TOF patients?

Recommendations based on: hemodynamics, arrhythmia risk, and exercise testing results. Most patients with good repair can participate in moderate activities. Competitive sports need individual assessment. Regular exercise encouraged within appropriate limits.

How do you manage arrhythmias in repaired TOF?

Management includes: treating hemodynamic lesions (PR, RVOT obstruction), antiarrhythmic medications, catheter ablation for sustained SVT/VT, and ICD placement if high risk. Prevention involves timely PVR and avoiding severe RV dilation.

What is TOF with pulmonary atresia? How does management differ?

TOF-PA involves complete obstruction of pulmonary outflow with variable PA anatomy and collateral supply. Management more complex, often requiring staged approach with initial palliation. MAPCAs need evaluation and possible unifocalization. Complete repair may not be possible in all cases.

What is the role of catheter interventions in TOF?

Interventions include: branch PA stenting, collateral embolization, transcatheter PVR (Melody/Sapien in suitable candidates), and treatment of residual RVOT obstruction. Timing and appropriateness depend on anatomy and clinical status.

Describe the natural history of unoperated TOF.

Without surgery, mortality ~50% by age 3, 80% by age 20. Survivors develop progressive cyanosis, clubbing, polycythemia, exercise intolerance, and right heart failure. Early repair dramatically improves survival (>90% 20-year survival with modern surgery).

What is the significance of aortopulmonary collaterals in TOF?

Collaterals develop to supplement pulmonary blood flow, more common in TOF-PA. Can cause pulmonary overcirculation post-repair, heart failure, and hemoptysis. Management strategy includes selective embolization vs incorporation into repair depending on anatomy and PA size.

How do you evaluate RV diastolic function in TOF?

Evaluation includes: tissue Doppler E/E' ratio, tricuspid inflow patterns, hepatic vein flow reversal, right atrial size, and MRI-derived metrics. Important for timing interventions and assessing early post-repair function. Often abnormal due to RV hypertrophy and fibrosis.

What are the effects of chronic cyanosis in unoperated/palliated TOF?

Effects include: polycythemia, increased blood viscosity, bleeding tendency, iron deficiency, cerebral abscess, stroke, endocarditis risk, and growth delay. Regular monitoring of hematocrit, iron studies, and appropriate prophylaxis needed.

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