Peripheral Vascular Disease - HD

Introduction

I am Larry Edleman from Thomas Jefferson University
Hospitals and the Sydney Kimmel Medical College.
Today I'm gonna lecture about peripheral arterial doppler.
I have no financial relationships to describe.

Importance of Peripheral Arterial Disease

Peripheral arterial disease
is important for two reasons.
One, because it affects the limbs that are involved
and it's a general cardiovascular risk that's present.

Ankle-Brachial Index (ABI)

When we talk about peripheral arterial disease,
from the physiologic point of view, we use an ABI
and an ABI of less than 0.9 is considered abnormal.
And when we look at patients who have low ABIs
or peripheral arterial disease, their risk
for cardiovascular disease is from 10 to 20% at five years.
And this represents a high risk group.
Based on the descriptions by the Framingham heart project,
borderline patients have slightly lower risk.
And of course, normal patients whose ABI is above one are
at the lowest risk.

Relation to Survival

Not only is this an issue with cardiovascular disease,
but survival itself.
And when we look at the outcomes of patients over time
with peripheral arterial disease,
there is a clear relationship between those
with asymptomatic PAD, those with symptomatic PAD
and those with severe PAD, the population of 50
and older can present with PAD without symptoms.
They can present with some kind of chest pain,
in fact about 40 to 50% due.
And then patients can present
with more classic symptoms such as claudication
or critical limb ischemia.

Outcomes for Critical Limb Ischemia

When we present with critical limb ischemia, fortunately one
of the rarer presentations, the one year outcomes are quite
profound with amputation
and mortality being at 50%
and alive with two limbs being only 50%.

Outcomes for Claudication

When we deal with claudication, we can see
that the outcomes are a little better, of course.
And I wanna remind you that stable claudication is the most common and worsening claudication does
happen in the minority.
And rarely these patients do progress
to critical limb ischemia.
Cardiovascular morbidity
and mortality, as we've talked about, is also quite high
in this group of patients who present with claudication.

Understanding the Ankle-Brachial Index

I alluded to the a**l brachial index before
and it's a very simple way to
evaluate your patients in general
for peripheral arterial disease.
But in particular, it's a nice physiologic test when used
with duplex to get some sense of the physiology.
The idea is that significant lesions are pressure reducing
and that the ankle pressures then are lower when there's
disease in the arterial system going to it.
It's done quite easily with blood pressure cuffs
or it can be done with ultrasound machines.
And it's quite simple. There are two vessels in the leg,
the anterior tibial and the posterior tibial.
And the doppler can hear when the pressure is obliterated.
And there are two arms, the right
brachial and left brachial.
The ABI is taken by the higher of the two brachial
and the higher of the two anterior tibial or to stylos
and posterior tibial.
If your posterior tibial pressure is 60
and your brachial blood pressure is 120, your ABI is 0.5.
And that's true even if your other vessel in your leg has no
pressure at all, it is the higher of the two.
Similarly, if your brachial
blood pressures are 120 on one side
and a hundred on the other, the ankle brachial limb index is
derived with 120 the higher of the two.

Interpreting ABI Values

There are lots of different ways
to parse the ankle brachial index,
but for the most part it's clear that a pre,
that when you're at 0.9 or below, it's an abnormal waveform.
When it's above one, it's a normal waveform.
And between the two
or borderline, we often use waveform analysis
to see if it's normal or whether it's mildly abnormal
to help us decide that.
And we can use the waveform analysis in duplex continuous
wave doppler or pulse volume recordings.

Non-Compressible Vessels

One other thing needs to be stated.
When you have a vessel which is stiff from calcifications,
then the vessels cannot be closed
and you won't get an accurate reading.
And these are called non-compressible vessels.
Where that occurs is someplace between 1.3
and 1.4 with 1.4 being definitive.
Between 1.3
and 1.4, there are two groups of patients,
the very normal patients
who have really good pressures in their ankles
and the calcified pressure patients.
And those can be again, distinguished
by looking at things like waveform.
And when we look at mortality, again, the ABI is related to
that with this kind
of intermediate group being in the 1.3 to 1.4.

Available Tests in Ultrasound and Vascular Lab

There are a bunch of different tests that are available
to us in ultrasound and in the vascular lab.
We can use Doppler CW Doppler simply
and use it with pressure measurements.
And there are also ways to measure the volume of the limb
that's called pulse volume recording or photo tomography.
And they give you slightly different pieces of information
and they can be helpful in evaluating people quickly.

Role of Doppler Ultrasound and Other Tests

Where does doppler ultrasound
and these other tests fit in?
If the test is to screen disease
or to simply follow whether a disease is improving
or not, the ABI
and the pulse volume recordings
of the physiologic tests are very good for that.
But we also sometimes wanna know the anatomical location
and the difference between stenotic
disease, an occlusive disease.
And for those we need maps
to test the disease that's present.
That could be something as aggressive as angiography
or something semi invasive such as MRA or CTA, which may
or may not require contrast and of course, duplex.
And this requires some specialized skill
'cause it is a slightly difficult study,
but it can be mastered in people who are interested in
duplex arch ultrasound.

Understanding the Disease

Let's talk about the disease for a minute.
You can see here that there is a patient here
with an occluded vessel,
but the vessel rec canalizes
through collaterals.
And this makes it very different than say,
the internal credit artery
where the vessel includes throughout its entire course up
until it reaches the area of the siphon
where the ophthalmic artery is.
In addition, there's no standard
blood flow velocity in vessels.
And these velocities will change if you're
moving or if you're at rest.
Velocities can vary along a vessel.
They vary between vessels
and we have not only occlusions which can recanalize,
but we also have multiple vessels which can be involved.
You can have a situation
where there are tandem lesions that are present.
All these issues make duplex a pretty sophisticated doppler ultrasound examination.

Blood Flow Velocities

Let's talk about velocities.
Velocities vary in the vessels, as you can see here.
In general, they go down as you go more distal in the leg.
And I don't really memorize these
because I don't use absolute velocities with the exception
of the tibial vessels where I wanna remember
that the tibial vessel is about 55,
and so two standard deviations is about 35
centimeters per second.
When I start seeing velocities below that, I am knowing
that that is too low.

Detecting Stenosis in Duplex Ultrasound

The hallmark of duplex ultrasound is
to look for a stenosis.
And the things that we look for in the stenosis are
the velocity increase in the stenosis,
which has been explained to us by rnli.
And what happens in the stenosis itself is
as the blood is compressed, it's going much faster
and the energy of the blood flow is converted
to kinetic high velocity energy.
Because of that high velocity,
the pressure in the stenosis is lower, and
because the stenosis is pressure reducing, it is also lower
pressure at the other end of the stenosis.
The pressure gradient is very important to us
because it tells us
how well we're getting blood down the leg.
And it's also a way for us
to determine if a stenosis is going to be significant
because in the peripheral artery, one
of the ways we define significance is by pressure reducing
or flow reducing or flow limiting stenosis.
All those terms are similar for the most part we tend
to think about in the peripheral arterial system,
pressure reducing lesions.
And we talk about pressure reducing lesions when the,
when we have the findings of elevated velocity
in the stenosis and turbulence downstream from the stenosis.
Because of that high velocity in the stenosis,
we can see this in our doppler
where the velocities go up in systole
and also go up in diastole.
And if we're really in a small vessel,
we can actually see all the blood is flowing in
one direction here.
And there's very little spectral broadening
because all the blood is moving as one.
And you can see here the turbulence in the tissue itself here represented
by a brewery beyond the stenosis,
we have the velocity no longer maintaining
itself and going down.
And because blood does not like
to be going from a small space
to a large space at high velocity, the blood breaks down
and becomes turbulent and random.
And this is seen by a variety of different things.
Here you can see a Leonardo describing what's happening here in this water.
And here you can see this computer generated representation of the crazy looking flow
that occurs beyond the stenosis.
The jet is firing out
and then the area of turbulence
and then eventually the waveforms will become back
to laminar flow if you get further down.
And what we do when we see this blood
that's twirling in multiple directions,
we're gonna get waveforms that have forward
and reverse flow that are simultaneous
and we're gonna see lots of different velocities
'cause each of these areas are gonna give you different
directions and different velocities of flow.
We see the spectral broadening.
In addition, we can see these
little vortices that are forming.
You can see these lines
that are forming on our spectral doppler, which are related
to these little vortices
that are appearing instantaneously and going away.

Evaluating Stenosis Significance with Ratios

Because we don't have a standard velocity, we have
to have a way of evaluating how a stenosis is significant.
And the typical way that we do this is with a ratio.
And the peak systolic velocity ratio is the standard
for peripheral arteries.
And it's the highest velocity in that jet divided
by a velocity in a relatively normal segment
before the area of narrowing.
And this will give you a number that's higher than
one when there's narrowing.
And typically we talk about stenosis
that are greater than two as being diagnostic
of a greater than 50% stenosis.
There are some grading systems that use more
categories, but I tend to just use this simple category
of 50 to 99%
because this represents both a pressure reducing lesion.
And it gets to be
a little bit more complicated when you have tandem lesions
to describe them with too much sophistication
or too much differentiation.
Of course, occlusions have no flow at all,
and milder stenosis are identified
by having plaque narrowing by color doppler,
but less than a two to one velocity ratio.
Some groups do like a slightly different number than
here, but in the United States, most groups use a ratio
of two to one colored ular narrowing
and plaque being present.

Waveform Distal to Stenosis

We also want to identify
what the waveform looks like distal to this.
And we always talk about the three parts of the waveform.
Here in this representation, we move the doppler
through the area of narrowing and the axillary artery.
And again, any peripheral artery,
whether it's lower extremity
or upper extremity, you can use this criteria.
And here we have a stenosis ratio of 4.8 indicating a greater than 50% stenosis.
As we alluded to, there are some groups that like
to use other ratios such as four to one for 75% stenosis,
and some groups do use relative numbers
for the peak systolic velocity
or the end diastolic velocity.
But I haven't used it.
If you think that this is advantageous to you,
you can think about using some of these scales.
To remind you once again that a single number
is not the way to diagnose the stenosis.
You have to profile the stenosis
and looking at the vessel in front of the stenosis
and beyond the stenosis to see the three parts of it.
And I call these the three musketeers to remind people
of it again, the normal velocity in front of the stenosis,
the jet inside the stenosis,
and the post stenotic stenosis here.
And you can see here the jet quite nicely
with the disturbed flow forward and reverse ill-defined edge
and spectral board that's notorious.
As you go further down from a stenosis, as you get relain,
you will start
to see a different kind of waveform shape.
Here we can see the waveform shape further distally is no
longer has that forward and reverse flow
and the edge of the envelope is beginning
to identify itself.
There is still some spectral broadening,
but the shape has clearly changed a little bit.
And this is the beginning of the relain flow.
And depending on the shape of this, you may have a tartus parvis waveform.

Tardus Parvus Waveform

What do we mean by that?
What we mean by that is the fact
that when you have pressure reducing lesions
or flow limiting lesions,
that the waveform shape will change, that the
velocities will typically go down
and it will take longer to reach peak systolic velocity.
That's the tartus part.
And that the difference between systole
and diastole pressure
and doppler waveforms will be closer to one another.
You'll have less pulsatility less difference between the two.
And this is the parvis tous waveform.
It can also be described
as the monophasic peripheral waveform.
And it's related to the fact that when you have a stenosis,
you've filtered out all your complicated signal,
which is here with your multiple different directions
and turned it into something simpler.

Peripheral Arterial Waveform Analysis

Let's talk about this peripheral
arterial waveform for a minute.
Here you can see what a normal waveform looks like.
We've talked about stenosis,
but the hallmark
for a normal peripheral artery waveform is this reverse
component, which is right here.
And what we see is that there's a fast upstroke,
and then in part of Sicily there's actually a reverse
component and that's related to reflected waves
that are created by the arterials
that are present in the peripheral arterial circulation.
And as the forward component
and the backward component go back
and forth, you may have a series
of waveforms that go back and forth.
In this case, there's another forward component.
You may actually see forward
and backward components in this as well.
But it's the first reverse component
that's the most important.
And the one we typically look for
to identify a normal vessel which is present
and we lose them in a variety of different abnormalities.
Here we have the normal waveform
of this reverse component.
Again, a slightly smaller velocity that's present,
but that's okay, it's a more peripheral vessel.
As we go below, we see what we've seen
before, the high velocity systolic
component where you're in the jet.
You can see that it's all moving at one velocity.
No spectral broadening, but high systolic
and forward diastolic flow.
And going now to this waveform that we've seen
before, it's the parvis tar waveform.
There's one new waveform here in the upper right,
which is a staccato type of waveform.
And this is the typical waveform
that you may see when you're in front of a stenosis.
And the waveform has a very abrupt forward component.
And then you may either have no flow at all
or a little backward component from the reflection,
but this is again, a different waveform where
you're in front of the stenosis.
Just wanted to point out the staccato waveform
that you see when you're in front of significant stenosis
and the tardis pars waveform that you get when you're
beyond significant stenosis.

Extent of Tardus Parvus Waveforms

How far can we go with tardis pars waveforms?
Here's a normal input
and you can see again there's multiple phases
that are present here, many more than three.
But the most important thing is it's got the fast forward
component first and a reverse component right afterwards.
Beyond this, we have an occlusion
and the waveform has changed shape now
into something which resembles the tartus parvis waveform,
although the upstroke is not terribly bad at this point.
And this may be related to things such as collateralization
or something called pressure recovery.
As we go further down, however, the waveform does change
and you can see that it's getting more blunted
and we have almost no difference between slyly.
This would be a more classic tardis parus waveform.
And then this patient was cooperative,
had another occlusion which was present.
And you can see that the waveform has gone even further
blunted to where there's virtually no difference
between systole and diastole.
And this almost looks like a vein,
but in fact this is the most profound, most filtered
tardis parus wave that you can have.

Duplex Mapping

In duplex mapping. We want to think about three parts.
The inflow part, which is the iliac
and common femoral vessel.
You wanna look directly at the vessel,
but you can also quickly look at this by looking at
how fast the common femoral artery accelerates,
how quickly it reaches peak.
Then we want the kind of the meat of the leg itself,
the fem poplar heel segment, which we can do quite nicely
by scanning through in color and mapping that area out.
And then getting spectral doppler at a variety of sites,
including suspicious sites and some standard sites.
And then we wanna look at the runoff
and runoff varies quite a bit between lab to lab.
If you're interested just in defining
where the blood vessels are running,
you might just do color mapping to determine
where an entry point for a bypass graft might be.
Or you can look at general waveform shapes and velocity
and get a sense of how much disease is present.
Or you can do the full blown duplex map
where you really scan up
and down the vessels that are there.
Recognizing that the calf is very long.
There are three vessels to study the posterior tibial,
the perineal, and the anterior tibial artery.
And here's a duplex map where you can kind
of see the normal waveform shape of the common femoral.
As we go down, we see a little bit
of delayed upstroke here in the popple teal,
but there was no real significant waveform.
Nothing we called at this point,
but then when we get to the runoff vessels, you can see
that there's marked abnormality.
We don't have a good continuous color line.
And the velocities here are more the staccato
low velocity waveforms.
Again, remembering that this is only
14 centimeters per second.
Here the anterior tibula is the least affected.
You can see it's got a slightly more normal waveform.
And again, a very staccato,
almost non-existent waveform in the perineal artery.
Again, we can identify quickly where the level
of disease is, which will help identify which kind
of surgery or intervention may be most appropriate.

Protocol for Duplex Examination

The protocol is really to look for normals
and if it's normal to really just sample a selected site in
the vessel and to interrogate any suspicious areas
with color doppler
and record both the highest velocity in the mirror area
of narrowing something proximal to the area of narrowing
and distal to the area of narrowing.
Again, I want you
to keep on remembering these three components
that we expect with everybody.

Accuracy of Duplex Mapping

This has been done for more than 20 years,
and you can see that in an early study using color mapping,
we have extremely high specificity except for the perineal,
which is a very difficult vessel for us to see.
And it varies. Interestingly enough,
in this case the popliteal wasn't that good,
but I think with more modern equipment, this area is not
as blind a spot as possible.
We can look at this a different way in a
different patient group.
This was from 2010 where they mapped out two things.
Here is the correlation between the two,
and you can see that the correlation is actually rather good
through most of the femoral popliteal segment.
And the tibial perineal trunk is a little problematic, as is the peroneal.
But for the posterior tibial
and anterior tibial, we can actually do very well except
for very distally and for even just having success.
That is to say being able to get, detect things again
as you're in the distal vessels,
the velocities may be quite low,
calcifications can be quite extensive,
and it may be hard to get even a signal.
You can see the runoff vessels here
can be much more difficult.
But we can do very well in the inflow in the
femoral popliteal segment.
And this is reiterated in by other groups.
This is a group out of New York
where they looked at many, many studies
and they had some trouble.
But this is a thousand scans.
All of these numbers are 73, we're talking about 73
and a thousand patients.
But the infra popliteal clearly were the
hardest vessels to see.
And the biggest problem were twofold
as we've discussed the calcifications in the vessel
and the low velocities that are present.

Challenges in Imaging

Things that can cause problems
as you'd expect is the patient condition such
as critical limb ischemia, diabetes,
which does cause calcified vessels
and calcifications for other reasons such as renal disease.
And one more time, poor runoff in calcification are the most
common reasons why we have trouble.

Tandem Lesions

We mentioned tib disease, we mentioned that the fact
that there may be other lesions that are present.
And when you have a pressure reducing lesion,
your pressure down, the rest resting is lower
and you have now encountered another stenosis.
What happens? The question is, does do these vessels
respond the same way?
Do you still get normal ratios
or are the ratios distal to the first stenosis?
Impossible to analyze.
And it turns out that somebody has looked at this
cures an article from the 1990s, which have shown that
using ratios in multiple levels of stenosis is just as good
as when you have a single level of stenosis.
And we can use the peak systolic velocity ratio
as our marker for the disease, which is present
at both the first lesion and subsequent tandem lesions.

Postoperative Evaluation

Let's talk a little bit about postoperative evaluation.
You need to know what the status of the patient is,
what kind of treatment they have.
There are many, many treatments that could be possible,
including combination treatments such as bypass grafts,
but then they may be revised in some way.
They may use vein grafts, they may use prosthetic grafts,
they may have gone back
and forth, use some in some how many levels were fixed,
were there problems that were
left at the end of the surgery?
All these things need to be known.
And obviously speaking to the surgeon who does this
or having a copy
of the operating report is always very helpful for this.
In addition, with endovascular treatment,
we may even be adding postoperative appearances
with things like angioplasty and stents into this.

Evaluating Grafts and Stents

What we're looking for when we do our stent evaluation is
to look for stenosis in the graft.
And if the graft has been there for a while to look
for atherosclerosis developing around the graft.
In the native vessels, there are vein cuffs
that may be causing obstruction.
Rarely there are fistulas that may actually be intentional.
Some surgeons leave small AV fistulas
to keep flow going and some don't.
You need to know what the surgeon was planning.
And we look for collections around the graft
that sometimes are present after surgery,
but obviously in the proper setting,
infection may be possible.

Velocity Ratios in Grafts

We've talked about the peak systolic velocity of two
to one and does that value work for graft?
And it turns out it really doesn't.
In looking at a bunch of graphs, the group out
of Florida with Dr.
Bandi, this is one of those papers
has looked at various lesions
and a velocity of two to one is just as likely to kind
of stay stable as it is to kind of regress or progress.
The lesions which are more problem are the ones when the
ratio is greater than 3.5
or the velocities are greater than three.
When we see these numbers, those are the ones
that we want to concentrate on.
When we see velocities ratios that are above two,
it's not normal, but we're gonna continue
to monitor those patients whereas we're gonna think about
intervention when we have these
higher ratios that are present.

Example of Vein Bypass Graft

Here's an example of a vein bypass graft
where we're going through the bcast graft.
We can see here in the area of color aliasing,
we can see that there's high velocity here of 315.
And in terms of looking at it compared to the,
to the weight form in front of a ratio of 5.2.
This is a graph that we were worried about.
Some people also look at the average peak velocity.
They take several waveform through the graft
and kind of get an average.
And as you know, the velocity is related to the size of the graft.
Big grafts will have lower velocities with the same amount
of flow, but in a relatively normal size graft,
if you have low velocity, you have low flow
and that puts the graft at risk.
As a rule, low velocity can be worrisome.
What that number exactly is, is difficult.
Some people have talked about 45, 40 or even lower.
But when we start to talk about that range in the forties,
we start to be worried about it.
And of course, if you have serial studies, you can compare
what the average velocity is doing over time.
Remembering that velocity is not very helpful
when you have a big graft
or when you're putting the graft into a very small vessel
where you don't expect that high volume of flow
because it's really just feeding a limited portion
of the leg or foot.

Risk Stratification for Grafts

Dr. Bandi and his group have done a number
of very important papers about this,
and I like the way he thinks about patients.
He puts them at low risk, intermediate risk,
and those patients who are at high risk for repair
and the highest risk to repair as soon as he can.
Just present this information here
where the low risk, as you can imagine,
have no change in the ABI have plic velocities below two
and good average systolic velocities.
The intermediate group is now having a ratio above two,
but no pressure drop.
And these patients are followed a little bit more closely
and the two highest groups have an ABI
that may or may not be dropping.
If it's dropping, that puts it in the highest level.
And these groups have ratios that are above 3.5. Okay?
For the highest risk group, the ones
that he's gonna be most concerned about,
there's either a low average velocity or a drop in ABI
and this elevated ratio of 3.5.

Aortoiliac Grafts

Aorta iliac grafts can also be done with this.
They do have their own problems
and one of the things that people have looked at is the
ability to look at iliacs, which can be quite difficult.
One of the ways people have done this is
with an appropriate abdominal probe where instead
of scanning from the aorta down,
they scan from the common femoral or inguinal crease up,
and that pushes bowel out of the way.
And this has allowed this particular group
to have visualization in 95% to reduce the
effect of the bowel gas.
A oral iliac stents have a slightly different ratio.
As a rule iliacs are always a little bit different than
the leg itself.
And the numbers that we're particularly interested in
as a ratio of 2.5 for identifying problems with iliac stents.

Waveform Shapes in Aortoiliac Stents

How about looking at waveform shapes?
Would a biphasic waveform
or aphasic waveform be helpful to you?
Yes, but in this case it really, many patients with
stent problems will in fact maintain aphasic
or biphasic waveform, possibly through collateralization
via other the iliac
or vessels around the hip.
But a monophasic waveform is what we expect,
and we do see it in about 40% of patients
with stent dysfunction.
This group has done very well in this group in
evaluating aortoiliac stents.

Angioplasty and Stents

The last group I wanna talk about are those with angioplasty
or stents, which have pretty good accuracy
and it's always changing.
These stents are really undergoing revision.
But the general protocol is similar.
You take the velocity through the stent,
you look at a disease-free segment proximal to the stent
and look distal to the stent for the three
findings of stenosis.
For identifying stent significance, you can see that 50% may not be the best
and 60% or 80% are actually frequently numbers
that are people using to determine when
to intervene on stents.
And again, when we look at this,
we're interested in looking at ratios which are
above 3.5 when we're dealing with the highest grades of
stent stenosis being present.
And we can do a pretty good job of looking at this
with very good specificity
and reasonable sensitivity when we're looking
at stents that are present.

Conclusion

I hope this has been helpful to you to understand some
of the findings of peripheral arterial studies,
recognizing that protocols are very important,
but understanding the basic tenets of pressure,
ABIs and profiling stenosis can help us.
Thank you very much.