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