Tetralogy of Fallot: Clinical Case and Viva QnA

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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.

5 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
25 Viva Questions and Answers on Tetralogy of Fallot

  1. Q: What are the four classic components of Tetralogy of Fallot?

    A: The four classic components are:

    1. Ventricular septal defect (VSD)
    2. Right ventricular outflow tract obstruction (RVOTO)
    3. Overriding aorta
    4. Right ventricular hypertrophy (RVH)

  2. Q: What is the embryological basis for Tetralogy of Fallot?

    A: Tetralogy of Fallot results from anterior and cephalad deviation of the infundibular septum during cardiac development. This leads to malalignment of the outlet septum, causing the four classic features of TOF.

  3. Q: What is the most common cyanotic congenital heart defect?

    A: Tetralogy of Fallot is the most common cyanotic congenital heart defect, accounting for approximately 5-10% of all congenital heart defects.

  4. Q: Describe the pathophysiology of cyanosis in Tetralogy of Fallot.

    A: Cyanosis occurs due to right-to-left shunting across the VSD. The degree of RVOTO determines the amount of shunting. As pulmonary blood flow decreases, more deoxygenated blood enters the systemic circulation, causing cyanosis.

  5. Q: What is a "tet spell" and what causes it?

    A: A "tet spell" or hypercyanotic spell is a sudden increase in cyanosis, often accompanied by irritability, hyperpnea, and sometimes loss of consciousness. It's caused by a sudden increase in right-to-left shunting, usually due to increased RVOTO from infundibular spasm or decreased systemic vascular resistance.

  6. Q: How do you manage an acute tet spell?

    A: Management of an acute tet spell includes:

    1. Knee-chest position or squatting (for older children)
    2. Oxygen administration
    3. IV fluids for volume expansion
    4. Morphine for sedation
    5. Phenylephrine to increase systemic vascular resistance
    6. Beta-blockers (e.g., propranolol) to relax infundibular spasm
    7. Sodium bicarbonate for metabolic acidosis if prolonged

  7. Q: What are the characteristic findings on chest X-ray in Tetralogy of Fallot?

    A: Characteristic findings include:

    1. "Boot-shaped" heart due to right ventricular hypertrophy and uplifted cardiac apex
    2. Decreased pulmonary vascular markings
    3. Right aortic arch in about 25% of cases

  8. Q: Describe the typical ECG findings in Tetralogy of Fallot.

    A: Typical ECG findings include:

    1. Right axis deviation
    2. Right ventricular hypertrophy
    3. Tall R waves in right precordial leads (V1, V2)
    4. Deep S waves in left precordial leads (V5, V6)

  9. Q: What are the key echocardiographic features in diagnosing Tetralogy of Fallot?

    A: Key echocardiographic features include:

    1. Large, subaortic VSD with aortic override
    2. Right ventricular outflow tract obstruction
    3. Right ventricular hypertrophy
    4. Dilated aortic root
    5. Assessment of pulmonary artery size and anatomy

  10. Q: What other cardiac anomalies are commonly associated with Tetralogy of Fallot?

    A: Common associated anomalies include:

    • Right aortic arch (25%)
    • Coronary artery anomalies (5-12%)
    • Atrioventricular septal defect
    • Multiple VSDs
    • Pulmonary atresia
    • Absent pulmonary valve syndrome

  11. Q: What genetic syndromes are associated with Tetralogy of Fallot?

    A: Genetic syndromes associated with Tetralogy of Fallot include:

    • 22q11.2 deletion syndrome (DiGeorge syndrome) - present in about 15% of TOF cases
    • Trisomy 21 (Down syndrome)
    • CHARGE syndrome
    • Alagille syndrome
    • VACTERL association

  12. Q: What is the optimal timing for surgical repair of Tetralogy of Fallot?

    A: The optimal timing for surgical repair has evolved over time. Currently, most centers perform elective repair between 3-6 months of age. Earlier repair (before 3 months) may be necessary for symptomatic infants with severe cyanosis or frequent tet spells. The trend is towards earlier complete repair rather than initial palliative procedures, unless anatomic or clinical factors necessitate a staged approach.

  13. Q: Describe the surgical technique for total correction of Tetralogy of Fallot.

    A: The surgical technique for total correction includes:

    1. Median sternotomy and cardiopulmonary bypass
    2. Right ventriculotomy or trans-atrial approach
    3. VSD closure with a patch
    4. Relief of RVOTO:
      • Infundibular muscle resection
      • Pulmonary valvotomy if needed
      • Patch augmentation of RVOT and/or main pulmonary artery
    5. Closure of atrial septal defect if present
    6. Reconstruction of pulmonary arteries if hypoplastic

  14. Q: What is a Blalock-Taussig shunt and when is it used in Tetralogy of Fallot?

    A: A Blalock-Taussig shunt is a palliative procedure that creates a connection between the subclavian artery and the pulmonary artery. It's used to increase pulmonary blood flow and improve oxygenation. In modern practice, it's primarily used in:

    • Very small infants (<3 kg) where complete repair carries high risk
    • Patients with pulmonary atresia or severely hypoplastic pulmonary arteries
    • As a bridge to complete repair in complex cases

  15. Q: What are the potential long-term complications after surgical repair of Tetralogy of Fallot?

    A: Potential long-term complications include:

    • Pulmonary regurgitation
    • Right ventricular dilatation and dysfunction
    • Residual or recurrent RVOTO
    • Arrhythmias (atrial and ventricular)
    • Sudden cardiac death
    • Endocarditis
    • Aortic root dilatation and aortic regurgitation
    • Exercise intolerance

  16. Q: How is pulmonary regurgitation managed in patients with repaired Tetralogy of Fallot?

    A: Management of pulmonary regurgitation includes:

    1. Regular follow-up with echocardiography and cardiac MRI
    2. Pulmonary valve replacement when indicated, based on:
      • Symptoms (exercise intolerance, arrhythmias)
      • RV dilatation (RV end-diastolic volume >150 mL/m² or RV/LV ratio >2)
      • RV dysfunction
      • QRS duration >180 ms
    3. Transcatheter pulmonary valve replacement in suitable candidates
    4. Medical management of right heart failure if present

  17. Q: What is the role of cardiac MRI in the follow-up of repaired Tetralogy of Fallot?

    A: Cardiac MRI plays a crucial role in the follow-up of repaired TOF:

    • Quantification of pulmonary regurgitation
    • Accurate assessment of RV volumes and function
    • Evaluation of RVOT anatomy and pulmonary arteries
    • Detection of residual VSDs or other intracardiac shunts
    • Assessment of aortic root dimensions
    • Myocardial fibrosis detection with late gadolinium enhancement
    • Guiding timing of pulmonary valve replacement

  18. Q: Describe the pathophysiology and management of right ventricular failure in adults with repaired Tetralogy of Fallot.

    A: Pathophysiology and management include:

    • Pathophysiology:
      1. Chronic pulmonary regurgitation leading to RV volume overload
      2. Residual RVOTO causing RV pressure overload
      3. RV myocardial fibrosis and dysfunction
      4. Tricuspid regurgitation due to annular dilatation
    • Management:
      1. Timely pulmonary valve replacement
      2. Medical therapy: diuretics, ACE inhibitors, beta-blockers
      3. Cardiac resynchronization therapy in selected cases
      4. Treatment of arrhythmias
      5. Exercise training and cardiac rehabilitation
      6. Heart transplantation in end-stage cases

  19. Q: What are the indications for pulmonary valve replacement in repaired Tetralogy of Fallot?

    A: Indications for pulmonary valve replacement include:

    1. Severe pulmonary regurgitation with:
      • RV end-diastolic volume >150 mL/m² or RV/LV ratio >2
      • RV end-systolic volume >80 mL/m²
      • RV ejection fraction <47%
    2. Symptomatic pulmonary regurgitation (exercise intolerance, heart failure)
    3. Sustained atrial or ventricular arrhythmias
    4. QRS duration >180 ms or progressive QRS prolongation
    5. Moderate to severe tricuspid regurgitation
    6. RVOT obstruction with RV systolic pressure >2/3 systemic pressure

  20. Q: What are the potential complications of pregnancy in women with repaired Tetralogy of Fallot?

    A: Potential complications include:

    • Right heart failure
    • Arrhythmias
    • Progression of pulmonary regurgitation
    • Systemic embolism in the presence of a right-to-left shunt
    • Increased risk of miscarriage
    • Higher incidence of small for gestational age infants
    • Increased risk of congenital heart disease in offspring (3-5%)

  21. Q: How do you counsel patients with repaired Tetralogy of Fallot regarding exercise and sports participation?

    A: Counseling should be individualized based on the patient's clinical status, but general guidelines include:

    • Encourage regular aerobic exercise for most patients
    • Avoid isometric exercises and competitive sports in patients with:
      • Severe pulmonary regurgitation
      • RV dysfunction
      • Significant residual RVOTO
      • Sustained arrhythmias
    • Recommend cardiopulmonary exercise testing to guide exercise prescription
    • Advise patients to self-monitor for symptoms during exercise
    • Regular follow-up and reassessment of exercise capacity

  22. Q: What is the role of catheter interventions in the management of patients with repaired Tetralogy of Fallot?

    A: Catheter interventions play an important role in:

    1. Transcatheter pulmonary valve replacement (e.g., Melody valve, Edwards SAPIEN valve)
    2. Balloon dilatation of residual pulmonary stenosis
    3. Stenting of branch pulmonary artery stenosis
    4. Closure of residual VSDs
    5. Occlusion of aortopulmonary collaterals
    6. Electrophysiology studies and catheter ablation for arrhythmias

  23. Q: Describe the approach to managing atrial and ventricular arrhythmias in adults with repaired Tetralogy of Fallot.

    A: The approach includes:

    1. Regular ECG monitoring and 24-hour Holter studies
    2. Electrophysiology study for risk stratification
    3. Management of hemodynamic abnormalities (e.g., pulmonary valve replacement)
    4. Antiarrhythmic medications
    5. Catheter ablation for recurrent atrial arrhythmias or monomorphic VT
    6. ICD implantation for primary or secondary prevention of sudden cardiac death
    7. Cardiac resynchronization therapy in selected cases

  24. Q: What are the indications for ICD implantation in adults with repaired Tetralogy of Fallot?

    A: Indications for ICD implantation include:

    • Secondary prevention:
      • Survived cardiac arrest
      • Sustained ventricular tachycardia
    • Primary prevention (consider if multiple risk factors present):
      • LV dysfunction (LVEF <35%)
      • RV dysfunction
      • QRS duration >180 ms
      • Extensive RV scarring on cardiac MRI
      • Inducible sustained VT on electrophysiology study
      • Frequent nonsustained VT

  25. Q: How does the presence of a right aortic arch affect the surgical approach in Tetralogy of Fallot?

    A: The presence of a right aortic arch affects the surgical approach in the following ways:

    • Modifies the approach to the branch pulmonary arteries
    • May require adjustment of cardiopulmonary bypass cannulation strategy
    • Affects the choice of shunt in palliative procedures (left-sided BT shunt may be preferred)
    • Increases the likelihood of vascular ring, requiring assessment and potential division of ligamentum arteriosum
    • May be associated with other conotruncal anomalies, necessitating careful preoperative assessment
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