Is Tetralogy of Fallot (TOF) duct dependent?

Tetralogy of Fallot and Duct Dependency

Tetralogy of Fallot (TOF) can be duct-dependent, particularly in severe forms with pulmonary atresia or critical pulmonary stenosis, where pulmonary blood flow is maintained through a patent ductus arteriosus (PDA). 1

Spectrum of Duct Dependency in TOF

TOF exists on a spectrum of severity that determines whether pulmonary blood flow is duct-dependent:

Duct-Dependent Forms

• TOF with Pulmonary Atresia (TOF-PA):

  • Characterized by complete atresia of the pulmonary valve with no direct communication between right ventricle and pulmonary arteries 1
  • When pulmonary arteries are confluent and supplied by a PDA (unifocal pattern), the circulation is duct-dependent 1
  • Profound cyanosis and cardiovascular collapse occur when the duct closes 1

• TOF with Critical Pulmonary Stenosis:

  • Severe cases with minimal antegrade pulmonary blood flow may be duct-dependent 2
  • Neonates with severe pulmonary stenosis often require immediate intervention 3

Non-Duct-Dependent Forms

• Classic TOF with moderate pulmonary stenosis:

  • Adequate pulmonary blood flow through the stenotic pulmonary valve
  • Oxygen saturations typically between 75-90% 4

• "Pink" TOF:

  • Mild pulmonary stenosis with minimal cyanosis
  • Oxygen saturations >90% 4
  • Adequate pulmonary blood flow without duct dependency 3

Clinical Presentation of Duct-Dependent TOF

• Rapid clinical deterioration when the ductus begins to close
• Profound cyanosis that worsens with ductal closure 1
• Cardiovascular collapse requiring immediate intervention 1
• Hypoxemia unresponsive to supplemental oxygen

Management Approach for Duct-Dependent TOF

Immediate Management

• Prostaglandin E1 infusion to maintain ductal patency until definitive intervention 5
• Continuous monitoring of oxygen saturation and hemodynamic status

Surgical Options

1. Primary complete repair:

   • Increasingly performed even in neonates with duct-dependent TOF 3
   • Involves VSD closure and establishing RV-PA continuity
   • May be preferred to avoid mortality associated with staged approach 2

2. Staged repair:

   • Initial palliative shunt (modified Blalock-Taussig shunt) followed by complete repair
   • High inter-stage mortality (up to 22.7%) reported in some series 2
   • Consider for very small pulmonary arteries that may benefit from growth before complete repair 1

3. Ductal stenting:

   • Alternative to surgical shunt in selected cases 6
   • Technically challenging due to ductal tortuosity in TOF-PA 6
   • Risk of acute stent thrombosis requires careful monitoring 6

Anatomical Considerations

• Pulmonary artery morphology is crucial in determining approach:
  • Confluent, good-sized PAs with pulmonary trunk → Fallot-like repair with trans-annular patch 1
  • Confluent, good-sized PAs without pulmonary trunk → RV-PA conduit repair 1
  • Confluent but hypoplastic PAs → Initial shunt or RVOT reconstruction to promote PA growth 1

Long-term Outcomes and Follow-up

• CMR imaging recommended every 2-3 years for routine follow-up 1
• Monitor for complications:
  • Pulmonary regurgitation
  • RV volume overload and dysfunction
  • Residual RVOT obstruction
  • Arrhythmias 4

Special Considerations

• 22q11.2 deletion is common in TOF-PA and associated with:

  • Higher prevalence of pulmonary artery anomalies
  • Possible need for more complex surgical approaches 1
  • Increased risk of adverse outcomes 1

• Mortality risk is higher in duct-dependent forms of TOF, particularly with:

  • Non-confluent pulmonary arteries
  • Multiple MAPCAs instead of a single PDA 7

The management of duct-dependent TOF requires prompt recognition and intervention to establish reliable pulmonary blood flow, with the specific approach determined by the pulmonary artery anatomy and institutional expertise.