Tetralogy of Fallot
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.
Case 1: Tetralogy of Fallot (TOF) no pulmonary stenosis
Parasternal long axis view indicating overriding aorta and sub-aortic large ventricular septal defect shunting bidirectionally.
PSAX showing the VSD in 2D. The pulmonary valve can be seen and is opening nicely with no evident RVOT obstruction. Mild deviation of the conal septum with no obstruction.
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
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
Flow acceleration by colour in the pulmonary artery in the PLAX
Mild narrowing of the pulmonary valvular annulus
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)
Parasternal long axis (PLAX) indicating a ventricular septal defect with overriding aorta
In PLAX, the anterior sweep indicates a small pulmonary artery with a thick pulmonary valve likely atretic (confirmed with colour to be virtual atresia)
MAPCAs by colour flow
PSAX showing the VSD and the narrow RVOT
PLAX indicating pulmonary valvular atresia - virtual, trickle colour passing.
Apical views by 2D and 2D-Colour showing the VSD and the overriding aorta with flow from LV and RV going to the Aorta
Sweep in the apical view showing the relationship between the RV/LV and Aorta with VSD