0:01

Okay, so chronic total occlusion is probably not a

0:05

familiar topic to many.

0:06

Um, it's been called the final frontier

0:08

in interventional cardiology.

0:10

Uh, and it's much more familiar to invasive angiographers,

0:13

but it's becoming a use case for coronary ct, uh, not

0:17

for diagnosis, but for treatment planning.

0:20

Um, so when you look at a chronic total occlusion, you have

0:23

to think about definitions.

0:25

It's gotta be a complete occlusion on ICA, which stands

0:28

for invasive coronary angiography

0:30

or cath, uh, meaning Timmy zero.

0:32

So that's the Timmy score from, uh, the, uh, uh,

0:34

acute coronary syndrome trials,

0:36

but meaning there's no flow, there's not late flow,

0:38

there's not delayed flow, there's nothing.

0:40

Um, there has to be an age of greater than three months, um,

0:44

either by an invasive angiography three months ago

0:46

or by a obvious history like there was in myocardial

0:49

infarction outside the hospital.

0:52

And it's actually seen in 15 to 30%

0:55

of invasive coronary angiograms.

0:56

And as you know, if you're using CT the way

0:59

that it's usually most appropriately used,

1:02

CT generally selects for low to intermediate risk.

1:05

So we don't see it nearly as much.

1:07

We see it maybe a few percent, um, not even 5% of, uh,

1:11

coronary CT cases.

1:13

Uh, I want to show you this case example

1:15

because I think it's a nice illustration.

1:17

This happened to be a patient

1:18

that I scanned almost a decade ago,

1:21

and, uh, this was in a patient in our emergency

1:23

department with dyspnea.

1:25

It turned out they also had COPD, uh,

1:27

but what we didn't know before we did the image is

1:29

that they had had a total occlusion

1:31

of the right coronary artery.

1:32

If you look at this case, it's got a very long segment, uh,

1:36

occlusion, but I also do see flow in the distal RCA.

1:39

That's common because you get collaterals.

1:41

And so, um, this patient did not know they had

1:43

a myocardial infarction.

1:44

They did not know their right coronary area was occluded.

1:47

Uh, and I don't even think it was a cause

1:48

of their acute chest pain.

1:50

It made, it contributed,

1:51

but there was actually a lung disease.

1:52

And what you see here is in this long segment occlusion is

1:55

it, it passes the heuristic

1:57

that we know we don't see great tiny lumens with, with ct.

2:01

That's something that's the, the territory

2:03

of an angiography.

2:04

But when we see what looks like an occlusion,

2:06

so no contrast at all in the CT

2:08

for longer than 1.5 centimeters, you can bet

2:12

that being a chronic occlusion rather

2:14

than a severe stenosis.

2:15

So if you see something shorter than that, you may favor

2:18

a severe stenosis or a subtotal occlusion,

2:21

but in this case, it's a very long segment.

2:23

Uh, you can even see that the contrast in the proximal RCA

2:27

is a little brighter than the distal RCA

2:29

because that contrast probably got

2:31

there through collaterals.

2:32

The collaterals sometimes are visible by ct,

2:34

and sometimes they're microscopic collaterals,

2:36

or we call microvascular collaterals

2:38

even through the myocardium.

2:40

So know that just because contrast got there doesn't mean it

2:42

got there antegrade, it might go retrograde.

2:46

Now, the prognosis of a chronic total occlusion is fairly

2:49

poor if untreated.

2:50

Um, it temps at PCI or percutaneous coronary intervention.

2:54

So cath with stenting is low,

2:56

and there's only moderate success rates.

2:58

Sometimes you have to move on

3:00

to a coronary artery bypass graft, cabbage, um,

3:03

and a lot of patients just get medical managed

3:05

and they actually, um, suffer from anginal symptoms.

3:09

Um, the chronic total occlusion is associated with age,

3:12

the standard cardiovascular risk factors, smoking,

3:15

hypertension, hyperlipidemia,

3:17

and, um, the right coronary artery tends

3:19

to meet more common than the LAD like I've just shown you.

3:22

We can debate a lot about the benefits

3:24

of whether someone should be revascularized.

3:26

There's a lot of guidelines and there's difficulty.

3:28

The success rates are lower, but it might be helpful.

3:30

But rather than get into that know,

3:32

that's the decision making

3:33

that the interventional cardiologist

3:35

and the treating physicians have to decide.

3:37

However, um, there is a little bit

3:39

of data suggesting improved survival.

3:42

Now if you've decided to do it, um, there's a whole world

3:45

that opens up of interesting terminology and devices, um,

3:49

and it's actually a subspecialty skill

3:51

within interventional cardiology.

3:53

But where you come in as a CT imager is helping

3:56

to predict the, uh, success rates.

3:58

So that last bullet is the important one here.

4:01

They're very unpredictable and long procedural times.

4:03

When they do a chronic total occlusion procedure,

4:06

it ties up the cath lab,

4:07

and you as a CT imager have the best view as to whether

4:09

that will be successful.

4:11

Um, so what we know is

4:13

that you're not gonna worry about pretest risk.

4:15

You probably already have an invasive angiogram if you're

4:17

asked to do a CTA for this.

4:19

Um, the diagnosis can be very challenging.

4:21

Um, we know that CTA performs best when we have negative

4:24

cases or low to intermediate risk.

4:26

So, um, one of the things, uh,

4:28

we can use is the lesion length.

4:31

Some paper say nine,

4:32

the most conservative paper say 15 millimeters,

4:34

but, um, shorter length makes it likely

4:37

that it's a high grade stenosis.

4:38

And longer length means it's likely

4:40

to be a chronic occlusion technique.

4:42

Uh, means don't try to squeeze the last, uh,

4:45

bit of contrast out.

4:47

Use a healthy amount of contrast,

4:48

don't skimp on radiation dose.

4:50

You want motion free images,

4:52

and there are a lot of helpful CTA findings that you can use

4:55

to assist the, uh, report for planning.

4:57

So this is a tight stenosis, not an occlusion,

4:59

it's a subtotal occlusion.

5:01

It was very easily crossed

5:02

because there's a tiny channel the wire

5:04

was able to get right through the vessel.

5:05

Here's a different case.

5:06

This is somebody with a stent in the right coronary

5:09

artery and an occlusion.

5:10

And I can see here that the, the occlusion is not calcified.

5:13

So there is some calcified plaque in the proximal right

5:16

coronary artery on the sea view.

5:18

Um, whereas in the proximal to mid segment,

5:20

it's a noncalcified stenosis

5:22

and that's a lot easier to cross

5:24

with a wire than say if it was a calcified occlusion.

5:27

But that's a, not just a stenosis,

5:28

but actually a total occlusion.

5:30

It's a couple centimeters long.

5:32

And then we can also carefully look within the stent

5:34

and I can see that there's, uh, noncalcified, uh, stenosis

5:38

and then there is contrast filling the distal stent.

5:41

And then there's disease in the native distal artery.

5:44

So when you talk about stents, whether it's an occlusion

5:46

or not, it's important to outline in your report

5:49

and if you can make nice images

5:50

to show the interventionalist

5:52

that this disease is in the native RCA.

5:55

And then this is the stented segment.

5:56

There's actually probably two or three overlapping stents.

6:00

Nice to have history if you can get it.

6:01

Um, you're gonna look at the stent patency if you can,

6:05

and you're looking, gonna look at the contours of the stent

6:08

and see if there's any stent

6:09

fracture or any other abnormalities.

6:11

And then you want to comment specifically

6:13

that the disease you see here is back in the native vessel.

6:18

So it's a different treatment algorithm.

6:20

And there's a caveat when you're looking at stents.

6:23

We're better at two to three millimeter stents.

6:25

We're not as good at the small millimeter stents.

6:27

And the bigger stents, the newer stents

6:30

that are drug eluding tend to be thinner.

6:32

So older bare metal stents, which are kind

6:34

of more historical these days, they're harder

6:36

to see on a CT because they're thicker.

6:38

So, um, all important things for any stented patient.

6:41

And then if you're dealing with chronic total occlusions,

6:43

think about that length, think about the degree

6:45

of calcification and also how much calcification.