Tetralogy of Fallot

Description

Tetralogy of Fallot was originally described as a combination of four abnormalities: ventricular septal defect (VSD), right ventricular outflow tract obstruction, overriding aorta and right ventricular hypertrophy. There is typically an anterior malalignement of the conal septum. The right ventricular hypertrophy is a consequence of the overriding aorta exposing the RV to systemic pressures, the large VSD equalizing pressure +/- RVOT obstruction. The VSD is a perimembranous defect. In some cases, TOF can be associated with complete atresia of the pulmonary valve (TOF-Pulmonary Atresia) or with coronary anomalies. The rare form of TOF with absent pulmonary valve is associated with an absent / rudimentary pulmonary annulus which is stenotic. Because of the free pulmonary insufficiency, there is progressive dilation (aneurysmal) of the pulmonary arteries, which may lead to severe obstruction of the airways. Some are associated with an absent ductus. 

More of Fetal TOF with absent pulmonary valve syndrome.

Case 1: Tetralogy of Fallot (TOF) no pulmonary stenosis

Apical views indicating the Tetralofy of Fallot, the large perimembranous central ventricular septal defect with aortic override. The mild deviation of the conal septum with no significant obstruction and the pulmonary valve and main pulmonary artery of normal size without obstruction.

Subcostal views showing the aorta override and the mild deviation of the conal septum

Small patent arterial duct (PDA) measuring 0.21 cm, shunting briefly right to left in early systole and left to right most of the cardiac cycle.

Case 2: Tetralogy of Fallot (TOF) mild pulmonary stenosis

PLAX with sweep in 2D and in Colour indicating the overriding Aorta and the malalignement ventricular septal defect

Apical view with sweep in 2D and 2D colour showing the overriding aorta, malalignement VSD and some mild aortic insufficiency. 

Case 3: Tetralogy of Fallot (TOF) with major aortopulmonary collateral arteries (MAPCAs)

MAPCAs by colour flow

Apical views by 2D and 2D-Colour showing the VSD and the overriding aorta with flow from LV and RV going to the Aorta

Subcostal view for visualization of the VSD, Pulmonary valvular atresia (virtual) and some MAPCAs observed by Colour

Catheterism indicating the MAPCAs

Presentation on TOF - Absent Valve by Louise Gervais and Jean-Francois Trudel

Presentation on Tetralogy of Fallot by Laila Wazneh NNP &  Kathryn Jones NNP - NNPs at Montreal Children's Hospital

TET spell

Main principle is to use non-pharmacological intervention to revert the TET spell crisis:

1. Calm the infant to decrease oxygen demands and relieve anxiety (attempt to calm the crying irritable infant by non pharmacologic methods)

   1. Calm, quiet room or gentle music, soothing measures, avoid any painful or distressful interventions, limit the personnel to key members in the room, decrease amount of ambient light to provide a calmer environment.

2. Place patient knee chest position – this position will increase peripheral resistance in the lower extremities and increases SVR; and this will decrease right to left shunt through VSD and improve pulmonary blood follow

3. Provide 100% oxygen (pulmonary vasodilator) by blow-by or hood. Avoid containment measures or elements that may agitate the child. 

4. Contact cardiology team to be aware of situation

If these non-pharmacological elements fail - will need pharmacological opiates to reduce distress:

5. Subcutaneous morphine 0.05 mg/kg or 0.1 mg/kg. 

6. May also attempt intranasal fentanyl 3-5 mcg/kg. 

7. If IV already in place – use IV route. Avoid putting IV at beginning of TET spell as this may worsen the situation in terms of agitation of the child.

If this fails (refractory Tet spell):

8. Make sure cardiovascular surgery team aware of situation

9. Obtain IV or intra-osseus and administer: Bolus 10-20 mL/kg of Normal Saline and then pass to next steps of the algorithm:

10. IV beta blocker (esmolol), which leads to relaxation of RVOT with improved pulmonary blood flow. Unless baby is hypotensive. If baby hypotensive go to Phenylephrine first. 

    1. Emolol 100-500 mcg/kg/dose loading over 1 min and then 100-300 mcg/kg/min infusion.

11. Phenylephrine 5 mcg/kg/dose over 1 minute and then 0.1 to 0.4 mcg/kg/min infusion (peripheral vasoconstriction)

12. Bicarbonate if very acidotic. (1-2 mmol/kg/dose)

13. Keep operating room on standby

There is a nice algorithm available also on the web here from Perth Children's Hospital.

Another algorithm available here.

Echocardiography in TOF with pulmonary stenosis and a small PDA

Short axis outlining the RCA and the pulmonary valve. The thymus is well vizualized on top (although this is not sufficient to rule out Di George syndrome)

Right sided aortic arch in this particular scan by evaluation of the branching pattern of the first aortic vessel. 

Pathological example from the Maude Abbott Medical Museum

Echocardiographic Assessment of Tetralogy of Fallot (TOF) and Variants (theoretical concepts):

1. Types of TOF

Typical TOF

• Defined by anterior malalignment of the conal septum, leading to:

  • Right ventricular outflow tract obstruction (RVOTO).

  • Large, unrestrictive ventricular septal defect (VSD).

  • Overriding aorta.

  • Right ventricular hypertrophy (RVH) (develops postnatally).

TOF with Pulmonary Atresia (TOF/PA)

• Spectrum of hypoplasia or atresia of the central pulmonary arteries.

• Aortopulmonary collaterals (APCs) are common:

  • Abnormal, tortuous vessels that connect the systemic and pulmonary circulations.

  • Can arise directly from the aorta or from primary/secondary branches above or below the diaphragm.

TOF with Absent Pulmonary Valve

• Unguarded right ventricular outflow causes:

  • Free pulmonary regurgitation (PR), leading to RV dilation.

  • Aneurysmal dilation of the main, right, and left pulmonary arteries (PAs).

  • Absent PDA in most cases.

• VSD characteristics:

  • Large, unrestrictive, subaortic, involving the membranous septum.

• Additional Features:

  • Anterior malalignment of the conal septum with infundibular hypoplasia, causing subpulmonary obstruction.

  • Variable degrees of right-sided obstruction, including pulmonary annular hypoplasia and valvular dysplasia.

  • Main and branch PA hypoplasia or discrete stenoses.

  • Right aortic arch (25%).

  • Coronary anomalies (5%): A large branch of the **right coronary artery (RCA) may supply the LAD territory and cross over the RVOT.

2. Pathophysiology of TOF and Variants

• Cyanosis due to right-to-left shunting at the VSD.

• If a PFO or ASD is present, an additional right-to-left shunt at the atrial level may occur if RV and RA pressures exceed LA pressure.

• Severity of cyanosis depends on the degree of RVOTO.

  • "Pink TOF": Minimal RVOTO → left-to-right VSD shunt → possible congestive symptoms.

  • TOF/PA: Pulmonary flow is entirely dependent on systemic-to-pulmonary connections (e.g., PDA, bronchial arteries, APCs).

  • TOF with absent pulmonary valve: Severe pulmonary regurgitation results in RV volume overload.

3. Echocardiographic Goals

Preoperative Assessment

1. Right Ventricular Outflow Tract (RVOT) Obstruction

   • Image the infundibulum and pulmonary valve using:

     • Subxiphoid views.

     • Parasternal short-axis (PSSA) and long-axis (PSLA) views.

   • Define the level(s) of obstruction using color and spectral Doppler:

     • Pulsed-wave Doppler (PW) across RVOT and pulmonary valve.

     • Continuous-wave Doppler (CW) to measure gradients.

2. Pulmonary Atresia

   • Measure distance between RVOT and main pulmonary artery (MPA).

3. Pulmonary Arteries

   • Assess pulmonary annulus, MPA, and branch PAs for size, confluence, and presence of stenosis.

   • Use low and high parasternal and infraclavicular windows to visualize branch PAs as distally as possible.

4. VSD Assessment

   • Determine location, size, and relationship to the tricuspid and aortic valves.

   • Rule out additional VSDs.

   • Note: Equal LV and RV pressures result in low-velocity transseptal flow, so decrease the Nyquist limit to improve flow visualization.

5. Coronary Arteries

   • Identify origin and course, particularly in relation to the RVOT.

   • Rule out a coronary artery crossing the RVOT.

6. Aortic Arch Anatomy

   • Determine sidedness and branching pattern.

   • Note: ~25% of TOF patients have a right aortic arch.

7. Ductus Arteriosus and Systemic-Pulmonary Collaterals

   • Assess for a PDA (left or right-sided).

   • Evaluate descending aorta and subclavian arteries with color Doppler for aortopulmonary collaterals (APCs).

   • Risk of APCs increases if the branch PAs and PDA are small.

8. Associated Anomalies

   • ASD vs. PFO.

   • Mitral stenosis or subaortic stenosis (rare but should be ruled out).

   • Left superior vena cava (LSVC).

   • Partial anomalous pulmonary venous connection (PAPVC).

9. Aortic Dimensions

   • Measure aortic annulus, root, sinotubular junction (STJ), and ascending aorta at the level of the right pulmonary artery (RPA).

Postoperative Assessment

1. RVOT and MPA Obstruction

   • Assess for residual obstruction using 2D, color, and spectral Doppler.

   • Measure peak and mean gradients.

2. Aneurysm Formation

   • Rule out aneurysms of the RVOT or MPA (look for large echo-free spaces anterior/lateral to the RVOT and MPA).

3. RV-to-PA Conduit Evaluation

   • Assess for stenosis and measure peak and mean gradients from multiple views.

4. Pulmonary Regurgitation (PR)

   • Evaluate PR severity using:

     • Color Doppler jet width.

     • CW Doppler across the pulmonary valve (slope of retrograde flow).

     • Flow reversal in the branch PAs.

5. Branch PA Stenosis

   • Use low and high parasternal and infraclavicular views to assess distal PAs.

   • Measure diameters of normal and stenotic segments.

6. Residual Shunts

   • VSDs: Determine size, location, direction of flow, and peak transseptal gradient.

   • ASDs: Evaluate residual atrial-level shunts and direction of flow.

7. Tricuspid Valve and RV Function

   • Assess tricuspid regurgitation (TR) severity.

   • Estimate RV pressure using:

     • TR jet velocity.

     • Trans-VSD gradient.

     • Septal configuration (systolic septal flattening suggests RV volume load, but may be misleading if RBBB or septal dyskinesia is present).

8. RV Size and Function

   • Assess RV volume overload (diastolic septal flattening, qualitative RV size, and 3D RV volume).

   • Evaluate RV function using:

     • 2D imaging from multiple views.

     • 3D echo (if feasible).

     • TAPSE (tricuspid annular plane systolic excursion).

9. Systemic-Pulmonary Collaterals

   • Evaluate for aortopulmonary collaterals and runoff in the descending aorta using spectral Doppler.

10. Aortic Dimensions and LV Function

• Reassess aortic annulus, root, and ascending aorta.

• Evaluate LV size and function.