Anatomy of Tetralogy of Fallot by Dr. Peter Lang.
Now the first thing I want to do is say that conceptually there really aren't four parts
of Tetralogy of Fallot, but there is one part.
Let me draw you a very simple heart.
And
this is oversimplified.
We've got a right ventricle.
Coming into the right ventricle is a tricuspid valve.
Leaving it is a pulmonary artery which branches into a right and left side.
The muscular part of the ventricular septum, the outflow portion of the ventricular septum.
A left ventricle.
Mitral valve coming into the left ventricle, and the aorta.
So let me tell you that this portion up here of the ventricular septum we're going to call
the conal septum.
And the first concept I want to make is that there's really one thing that makes Tetralogy
of Fallot.
And that is when there is a malalignment between the conal septum, and the rest of the ventricular
septum, everything else follows.
So the conal septum, instead of coming in here we're going to get rid of it, and I'm
just going to remove the pulmonary artery for a moment.
And remove the lower part of the aorta for a moment, and I'm going to take the conal
septum, and I'm going to bring it over here.
And so it is malaligned with the rest of the ventricular septum.
And this is going to be rightward, and it's going to be anterior, and it's going to be
superior.
And when this happens there is a ventricular septal defect.
It's big, and it's not going to close spontaneously.
What happens then is the pulmonary artery, and the pulmonary outflow tract, is squeezed
between this conal septum and what's going to be the right ventricular free wall.
And so we're going to have the VSD, which is our first part of Tetralogy of Fallot.
And we're going to have the subpulmonary narrowing, which is the second part of Tetralogy of Fallot.
And the aorta is going to override the septum because it's going to be coming over this
way, and instead of being closed by a ventricular septum in the normal position, it's going
to appear to override the ventricular septum.
And sometimes it actually will move quite rightward.
And then finally-- so that's the third part of Tetralogy of Fallot-- and the last part
has to do with the right ventricular muscle, which is going to hypertrophy because there
is systemic pressure in the right ventricle, because there's a huge VSD and the pressure
equalizes on both sides.
And so Tetralogy of Fallot has the four components which Fallot talked about.
But there really is one primary, ideologic anatomic problem, and that is, once again,
the malalignment of the conal septum with the rest of the ventricular septum, because
it's anterior, superior, and to the right.
You get your VSD.
You get your subpulmonary stenosis.
You get your overriding aorta, and the right ventricular hypertrophy follows suit.
So that's Tetralogy of Fallot.