0:01

The next topic we're going to discuss is transmurality.

0:05

Transmurality is the way we grade the

0:06

extent of late gadolinium enhancement

0:08

within the wall of the myocardium.

0:11

Um, this is an important concept because

0:13

it helps give the practice, the referring

0:15

physicians an idea of how severe the abnormality

0:18

is that we're describing on cardiac MRI.

0:21

Um, oftentimes if you don't include transmurality,

0:23

then you're going to get a phone call or an email

0:25

asking you to give some more information and tell

0:28

the referring about the degree of transmurality.

0:31

Um, transmurality as a concept is easiest

0:34

to think about in the world of ischemia.

0:37

Um, particularly in the world of, uh,

0:39

patients with prior myocardial infarction.

0:42

And I have here a couple of slides that are taken from

0:45

what is really considered to be the seminal paper in

0:48

the world of, uh, ischemic imaging with cardiac MRI,

0:51

uh, or viability imaging.

0:53

Um, this was a study done by, uh, Ray Kim.

0:55

Um, he's up in Boston.

0:57

Um, published in New England Journal way back in 2000.

1:01

They really established cardiac MRI as a

1:03

useful tool for the assessment of viability.

1:05

Um, and so what they did, uh, in this study, and why

1:08

it's important to us, uh, as we review, uh, cardiac

1:12

imaging, um, is that they really established that

1:15

transmurality has an important link to function and

1:18

an important link to the treatment of patients and, and,

1:21

and informs, uh, what would be the best treatment

1:24

for patients who have, uh, ischemic heart disease.

1:27

So, if you look at this set of images, you can see

1:30

that on the left side, we have multiple figures that

1:33

depict patients with increasing degrees of transmurality.

1:36

So, on the far-right image, this patient had a

1:39

small right coronary artery myocardial infarction.

1:42

You can see that the amount of wall

1:45

involved by enhancement is relatively thin.

1:48

So the degree of transmurality is defined as the

1:50

percentage of the wall that is involved by scar.

1:54

So generally, we divide it up into

1:56

quarters or 25% increments.

1:59

So, for instance, if you have a 25% transmural

2:01

myocardial infarction, it's only going to involve

2:04

25% of the wall, just like this example here.

2:08

As you get increasing severity of transmurality, you're

2:11

going to get further and further increases

2:13

in the amount of wall that's involved.

2:15

So, for instance, in the middle image now, we have

2:18

roughly 50% transmural myocardial infarction.

2:21

So the amount of the wall that's involved extends

2:24

over to about 50% of the entire myocardium.

2:27

Then, finally, the most severe category would

2:29

be in the 75% to a 100% category.

2:33

You're going to see basically nearly the entire

2:35

myocardium involved by enhancement or just a

2:39

little thin rim or even no non-enhancing tissue.

2:44

So, for instance, in this case, you can

2:45

see there's all this bright signal here.

2:49

And then there's maybe just a little thin, thin

2:51

rim of non-enhancing tissue out in the periphery.

2:55

So this is very extensive, nearly completely

2:58

transmural, 75% to a 100% transmural

3:02

myocardial infarction. On the anterior wall here,

3:03

you can see that this is wall, and the

3:05

entire wall is involved by enhancement.

3:09

So therefore, this segment right here, you could

3:11

say, is 100% transmural myocardial infarction.

3:14

So why is the extent of

3:16

transmural enhancement important?

3:18

Well, in this paper, what they were able to show

3:20

was that the more enhancement that you have in each

3:23

myocardial segment, the less likely it was that that

3:26

particular segment could recover function after they

3:30

improved blood flow doing a coronary artery bypass.

3:34

So they looked at all the patients with cardiac MRI

3:37

before they did coronary artery bypass surgery, and they

3:40

categorized whether you had a segment of the myocardium

3:43

that was dysfunctional, meaning it wasn't thickening

3:47

as much as normal, and whether or not that same segment

3:51

had any enhancement. And they categorized all the

3:54

dysfunctional segments into ones with 0 enhancement,

3:59

1 to 25 enhancement, and so on, on an increasing basis.

4:03

And so they saw, for all the dysfunctional segments,

4:06

that the ones with greater degrees of enhancement,

4:09

so the ones with either 50% to 75% enhancement,

4:13

or the ones with 75% to 100% enhancement,

4:17

the likelihood of improved contractility after the

4:21

surgery was super duper low for these patients.

4:26

So what that means is that if you have

4:29

50% or greater transmural enhancement in the

4:32

myocardium, in the segment with dysfunction,

4:36

if you go and fix the blood flow to that segment,

4:38

that segment is unlikely to get any better.

4:41

So the likelihood is less than 20% that if

4:45

you do in fact restore blood flow to a segment that

4:48

has greater than 50% transmural enhancement,

4:52

it's less than 20% likely that they're going

4:54

to actually have any meaningful recovery of function.

4:57

So this led to the whole concept of

4:59

cardiac MRI for viability imaging.

5:01

Basically, the idea is that if you do a cardiac

5:04

MRI and you find that there's really, really

5:06

extensive enhancement, say for instance,

5:09

in this case over here on the left, you've

5:11

got 75% to a 100% enhancement

5:14

all throughout the anterior wall,

5:15

and the patient has a lot of dysfunction.

5:17

Should I send this patient to surgery?

5:20

The answer is no, you shouldn't have them sent

5:22

to surgery because the likelihood that they're

5:24

going to get any benefit from surgery is very low.

5:27

So they would be undergoing a cardiopulmonary bypass,

5:31

CABG, all the complications associated with that

5:33

very extensive surgery with a very, very low likelihood

5:37

of recovering any functioning in a meaningful way.

5:41

The extent of enhancement is also important

5:43

in the setting of non-ischemic cardiomyopathy.

5:45

People look at the extent of enhancement, and that

5:47

helps them determine the severity of disease.

5:50

It's not quite the one-to-one ratio or the nice sort

5:53

of, uh, differentiation between 50% or greater

5:56

having a very significant importance compared to less

6:01

than 50% that we see for ischemic disease.

6:03

But nonetheless, it's helpful to get an

6:05

idea of the quantity of myocardial scar,

6:08

um, when you describe the transmurality.

6:10

This is an example on the left of a

6:12

patient with hypertrophic cardiomyopathy.

6:15

You can see that this patient has a whole

6:17

lot of enhancement here in the mid septum.

6:20

And I would say that that enhancement is

6:22

probably on the range of 50% to 75%

6:25

This patient on the right hand side has sarcoidosis.

6:28

And you can see that this patient

6:30

has a range of different enhancement

6:32

severity throughout the myocardium.

6:34

You've got this area here, which is

6:35

probably roughly 50% severity.

6:37

You've got this area here, which is nearly

6:40

completely transmural as is this here.

6:42

And then some other spots here

6:44

and there may be less than 50%

6:46

So it kind of goes on. Certainly, when we're

6:48

describing the cardiac MRI for this patient,

6:51

we don't describe every single individual spot,

6:54

but we give kind of a gist of, you know, how severe is

6:57

the extent of disease overall in the myocardium.

7:00

And that helps practitioners understand how extensive

7:03

the fibrosis is, how much damage is there to the heart.

7:06

Um, and they get an idea of, um, how, how, uh,

7:10

aggressively, they need to treat this patient.