Tetralogy of Fallot (TOF)

00:01 Let's move on to tetralogy of Fallot.

00:06 Tetralogy of Fallot is the most common cyanotic heart disease and it frequently shows up on multiple choice tests.

00:14 So I think it's important to go through tetralogy and really understand what it is.

00:19 It's important to memorize the four findings in the tetralogy and I'm going to go through them now for you.

00:25 There are four major findings and it can look pretty complicated.

00:31 But if I go through it one step at a time, I think you'll understand it.

00:36 Here we go.

00:39 On the left side, you can see a normal heart.

00:43 On the right side of your slide, you can see tetralogy of Fallot.

00:48 I'm going to walk through the tetralogy, the four findings in tetralogy, and I'm going to make it so you're convinced that it's not as complicated as it sounds.

00:56 Let's start with an overriding aorta.

00:59 In these patients, there is that connection between the two ventricles called the VSD.

01:07 The aorta rides over that VSD and allows the mixed blood to go into the aorta.

01:15 That's why these infants are cyanotic.

01:17 Some of that right-sided blood is shunting to the left through that VSD and up into that overriding aorta.

01:24 Two of the findings in tetralogy are overriding aorta and VSD.

01:29 When you hear "tetralogy," it's not really true.

01:33 Maybe you could call it triology of Fallot because you couldn't really have an overriding aorta without a VSD.

01:40 if you imagine how could the aorta ride over both ventricles unless there's a hole between them? Additionally, these patients have some pulmonary stenosis.

01:51 Basically, as that area shifts over and you're allowing for that overriding aorta, there's a squeezing of the pulmonary artery allowing for stenosis.

02:04 That narrowed pulmonary stenosis results in a right ventricular hypertrophy.

02:11 Really, it's the biology of Fallot in that you're both having the VSD and the overriding aorta, and the pulmonary stenosis resulting at right ventricular hypertrophy.

02:26 However, realistically, this is just one thing.

02:31 You could call it "The Fallot" if you want.

02:33 The abnormal rotation of the conotruncal septum at the top part of the heart is it's abnormally rotated as opposed to the intraventricular septum - the bottom part of the heart - and this whole shifting results in all of these findings.

02:52 It's really just a shifting of the upper part against the lower part of the heart that results in the full tetralogy.

02:59 That might make it a little bit more clearer.

03:03 It's important to understand that children who have a high-degree of pulmonary stenosis are going to be sicker than children who have less pulmonary stenosis.

03:13 The key thing about how blue a baby is at birth is how much pulmonary stenosis there is.

03:20 In a baby with a lot of pulmonary stenosis, more of that blood is going to get shunted over to the left side.

03:26 In a baby with less pulmonary stenosis, it's going to go right up into the lungs, and that's going to be the distinguishing feature between a baby who's what we call a "pink tet" - someone with less stenosis and less cyanosis - versus a "blue tet" - a baby who has a lot of pulmonary stenosis and a lot of blood shunting.

03:47 Additional points that are high-yield are the boot-shaped appearance of the heart on CXR.

03:52 And the role of squatting in increasing peripheral vascular resistance and thus decreasing the magnitude of the right-to-left shunt.