Peripheral Arterial Duplex Mapping - SD

Introduction

Hi, my name is George Bjo,
and I'm director of Vascular Ultrasound Services at
Montefiore Medical Center in New York City.
And today I'll be discussing with you the use
of duplex ultrasound for evaluation of the aorta,
iliacs,
femoral, popliteal, and tibial arteries.

Hi, my name is George Bjo,
and I'll be discussing the use of duplex ultrasound
for evaluation of patients prior to various endovascular
and open arterial procedures.

Objectives

Our objectives today will be to discuss the history
rationale and protocol for use of duplex scan assessment
of patients with suspected peripheral arterial occlusive
disease to describe techniques for imaging
of the lower extremity arteries to identify common pitfalls
of lower extremity arterial imaging to provide tips
and pearls for facilitating the examination
and overcoming those pitfalls.
And then we'll review a few representative cases.

Traditional Use of Contrast Arteriography

As you know, contrast arteriography has long been the gold
standard for evaluation
and imaging of the lower extremity arteries.
Interventionalists and vascular surgeons have a long
experience with this technique,
and they've reached a certain comfort level
with the images that are required.
These images are easily interpreted
and provide lots of detailed information,
and also serve as a great surgical guide,
for the performance of lower extremity bypass grafts.

Traditional Role of Arterial Duplex Scanning

Arterial duplex scanning, on the other hand,
has traditionally been used only to confirm the presence
of suspected peripheral arterial occlusive disease
or to confirm the presence
of a lesion seen on some other imaging study.
It was sometimes used to define the anatomic location
of stenotic
or occlusive lesion suspected,
by other indirect testing methods.
But traditionally arteriography was used prior
to all interventions,
and duplex was really rarely integrated into
the decision making process.

Rationale for Moving to Duplex Ultrasound

However,
there are various reasons why one might move away from the
more invasive contrast arteriogram,
and I've listed here a few of those issues, all
of which point to duplex ultrasound as a viable alternative
for imaging the lower extremity arteries.

The rationale for supposing that duplex ultrasound
could be used in this setting is based really on two genre
of studies in the literature.

Key Studies on Duplex Ultrasound Accuracy

The first that evaluated the ability
of duplex ultrasound to image the lower extremity arteries.

In this study from Dr.
Manetta published in the Journal of Vascular Surgery
of 1992, his team sought
to assess the accuracy of duplex ultrasound
to evaluate individual arteries
and to detect greater than 50% stenosis and or occlusion.
They looked at 150 patients in whom they compared the
duplex ultrasound to the contrast Arteriogram results.
Their results were very good.
They showed 99% visualization at and above the knee,
and the sensitivity
for documenting greater than 50% stenosis
that ranged from 89% at the iliac level
to 67% in the popliteal artery.
These results were equally
as good in the arteries below the knee.
Keep in mind that these results were obtained
with technology that dates back to 1992,
and with the exquisite imaging
and technology that we have today, imaging
of the lower extremity arteries has much more improved.

This study from the University of Washington
looked at 110 patients,
in whom they identified 50 lesions
that they thought were amenable
to percutaneous transluminal angioplasty based on the duplex
scan results in 47 or 50 of those lesions,
or 94%, the patients in fact went on
to get a percutaneous transluminal angioplasty.
There were three cases where a PTA was not performed
because the procedure was thought
to be technically difficult.
The take home message in this study,
however, is that there were no percutaneous transluminal
angioplasties done in patients found not to be suitable,
by the duplex scan.
In other words, the result
of the duplex scan did not exclude any patients
from receiving treatment.

Evolution of Duplex Scan Role

Based on those studies,
the landscape really was changed for us
in the vascular laboratory.
And the role of the duplex scan evolved really
to pre-intervention imaging and
or mapping to determine whether
or not a patient is a candidate
for an endovascular versus an open approach.
The goal was to identify the site of the lesion
to determine stenosis severity as well as the length
of the lesion, and also to assess the status
of the distal runoff in these patients,
a limited then intraoperative arteriogram can be performed
and then the intervention can be facilitated.
In general, the idea was to detect
and to localize severe disease
and eliminate the need for routine diagnostic arteriography.

With the evolution of the technology,
we further sought to answer the question, was duplex
good enough as a sole imaging modality prior
to lower extremity bypass grafting.

The group in Brooklyn, Dr.
Ashe's group, have been huge proponents
of this technique in this setting.
And they published a paper in 1998, title value
and Limitations of duplex ultrasonography
as the sole imaging method of preoperative evaluation
for popliteal and infra popliteal bypasses.

And our own group with Dr.
Wayne as the lead author, published a paper in the Journal
of Vascular Surgery in 1999, asking the same question.

I'll very quickly go over the results of our study.
We looked at 41 patients,
who were undergoing arterial reconstruction, all
of whom had both duplex ultrasound and arteriography.
The observers were blinded to the results of the angiogram
and were asked to predict the operation
and the anastomosis based on the duplex results.
Those predictions were then compared
to the actual surgery that was performed.
The results are as follows.
We were able to
predict femoral popliteal versus infra popliteal bypass in
90% of the patients.
And in those patients, we were able
to predict the anastomotic sites in 90% of the patients.
We were able to predict infra popliteal bypass
anastomosis in only 24% of the patients.
And the primary issue in this case was the inability
of the duplex to predict the preferred
outflow tibial vessel.
We felt that by duplex alone, we couldn't really
determine which vessel was best
for anastomosis based on the ultrasound image,
using techniques that I'm about to describe, we've been able
to create arterial maps such as the one that you see here,
and use these maps then to predict the type
of intervention that will be most appropriate
for the patient in question.
This has allowed us to decide again, what type
of intervention is appropriate or even possible.
These interventions can range from endarterectomy
to bypass, angioplasty, thrombectomy, lysis,
and in some cases, conservative therapy,
when the results of the duplex scan show
that really no viable interventional procedure
was appropriate.
And this has allowed us to avoid arteriography altogether.

Techniques for Arterial Mapping

Let's quickly talk about some of the techniques
for arterial mapping and just go over very quickly some
helpful hints.

One of the things that I like to say is
that the technologist should get comfortable
before the start of the examination.
These exams can be quite labor intensive, can take up
to 60 to 90 minutes to perform,
and you really wanna be comfortable
before you get into the room, get all the information that you need, all the equipment
that is necessary in order to complete the examination.

In general, we tend to do one leg at a time,
and we inform the patient of such.
If the patient requires a bilateral study, we tend to
schedule the patient for another day, use all
of the information that's available,
the wave form information, the velocity information, as well
as the color flow image in order
to create your arterial map.
And then we use two other techniques,
and that is a quick scan technique in the thigh.
And a bottom up technique in the calf,
which I'll elaborate on shortly, very important, is
to create the arterial map as you go along.
This is not the kind of study
that can be easily reproduced at the end of the day
after you scan 10 or 12 patients or so.
There's just too many details
to recreate at the end of the day.
And so what we do is we create the map segmentally.
As we evaluate the aorta to the aortic bifurcation,
we would then go and create that map, evaluate the iliacs,
and create the map of the iliacs,
then go onto the femoral popliteal segment,
and then onto the tibial artery,
scanning one tibial artery at a time,
and creating the map as we go along.

Evaluation of the Aorta and Iliac Arteries

Most examinations start at the level
of the femoral artery.
In fact, however, there is a set of patients, a subset
of patients in whom evaluation of the aorta
and the iliac arteries is necessary.
And we have algorithms in place to identify those patients.
Any patients with a decreased femoral artery pulse
with an abnormal femoral artery acceleration time,
any patient with symptoms that are referable
to the aorta and the iliac arteries, will go on
to get an evaluation of direct imaging, evaluation
of the aorta and the iliac arteries.
And we have a low threshold for evaluating
these patients.

NPO is a plus minus.
We don't typically find that we need
to have our patients be NPO.
However, if that segment
of the arterial system is gas out,
we will reschedule the patient
after having the patient be NPO overnight.

Typically we use low frequency transducers
as these vessels tend to be deep
for evaluating the proximal vessels.
However, we find that this is not always necessary.
And my recommendation would be
to use the highest frequency transducer available
that allows you to see all the vessels of interest.

The aortic bifurcation is best seen
with the patient turned to his or her left,
and with the transducer position just in front
of the right iliac crest.
And if you do that, you can produce images such as the one
that I show here with the aorta and the right
and left iliac arteries, very nicely seen.

In order to evaluate the iliac, the common
and the external iliac arteries, you may have
to turn the patient into a lateral decubitus position
with the side being evaluated, turned upwards.

My preferred method of evaluating the iliac arteries,
however, is to start at the groin level using a linear array
transducer, and then to follow the arteries proximally
to the level
of the aortic bifurcation.
Either one of these techniques will work,
and occasionally we'll use
combinations of both techniques.

Femoral-Popliteal Segment

The examination is then carried on
through the femoral popliteal segment
where the common femoral, the origin
of the deep femoral artery, the
femoral artery in the thigh,
and the popliteal arteries are evaluated.

Keep in mind that in most cases,
this will be the most common area for disease.
And this is that area where we use the quick scan
technique first.
And what we'd like to do is turn on the color flow image
and using the color flow image alone,
evaluate the common femoral artery down to the level of the
popliteal behind the knee to get a quick scan
and scout the area before we go in
and start to acquire all the doppler
and to the images that are necessary to create the map.
I think this saves quite a bit of time,
because it very quickly allows us to image
stenosis and occlusions where they may be present.

We use the color flow map as a guide.
We also mark stenosis and occlusions as we see them,
and we measure the lengths of those stenosis.

A good tip here is to use the veins as landmarks.
As you can see in this patient,
the knee has been bent
and the leg has been externally rotated to give us access
to all of the vessels of interest from the level
of the inguinal ligament down to the knee.

The patient is in reverse Trendelenburg in order
to allow blood to pull in the veins
and allow us to use those veins as landmarks to identify
the arteries of interest.

If you're gonna have any issue in terms of imaging
the lower extremity arteries, it'll probably be in the area
of the distal thigh where the superficial femoral artery
becomes the above knee popliteal tends
to dive deep into the musculature.
And then again, at the level of the proximal calf,
where the tibioperoneal trunk
and the peroneal artery can be quite deep,
in these areas, you can turn the patient on his or her side,
or perhaps turn the patient prone
and evaluate the above knee popliteal
and peroneal arteries from the back.
You can also opt to use a lower frequency transducer
to image these deeper structures.

Tibial Arteries

Our next stop would be the tibial arteries,
which we evaluate again, from the level
of the popliteal artery down to the ankle.
This would probably be the most difficult
and time consuming part of the examination,
especially in patients with multi-level
occlusive disease
that will result in low flow velocities.
It'd also be difficult in patients
with diabetes in whom there may be
a lot of calcification.

The vessels of interest are the tibioperoneal trunk,
the anterior and posterior tibial arteries, as well
as the peroneal arteries.

You want to use a low PRF
and a narrow color box in order
to facilitate the color flow image.

In this area, we use a bottom up technique,
and that is we start evaluation by
identifying the tibial arteries at or near the ankle.
They tend to be very superficial,
relatively superficial here, and easy to image
and visualize and then follow those vessels up.

Keep in mind that if the patient is a candidate
for a distal bypass graft, you would not want to bypass
above the level of an occlusion.
And so imaging from the top down only
to run into an occlusion might
result in a lot of wasted time.
So, again, we start from the bottom
and work our way up in these vessels.

Although we do image the entirety of those vessels,
we assess those vessels for patency
and as well as for quality.
In terms of a target for a distal anastomosis site,
it may be difficult to quantify stenosis in these vessels.
Again, as in patients with multi-level occlusive disease.
The drop in pressure from those multiple lesions above
that level may make it difficult to elicit a focal area
of increased velocity at
what may be a hemodynamically significant stenosis.

Pedal Vessels

The examination is then carried out to the level
of the pedal vessels,
where we evaluate the distal anterior tibial artery,
the dorsalis pedis artery
and the posterior tibial artery as they enter the foot.

These vessels, again, will be very superficial.
You'll want to use high frequency transducers.
Be careful not to apply too much
pressure over these vessels.
As again, in these low flow situations, any pressure at all
may compress the vessel
and make it appear as if the artery is occluded.

Pay close attention
to flow direction at these levels.
As you may be fooled into believing
that an artery with flow
that's moving in the wrong direction, in fact is patent.
And you may have missed a stenosis or a significant stenosis
or an occlusion above that level, bypassing to
that artery above that level could result in graft failure.
So, flow direction is important.

And again, in terms of the distal leg
and in the foot, you wanna mark any areas that appear
to be best for an anastomosis.

Common Pitfalls and Tips

You may run into some problem areas.
Of course, the pelvic vessels,
because of their depth, may be difficult to visualize.
We find that using multiple approaches
and the appropriate transducers allows us
to better image these vessels.

The adductor hiatus
where the superficial femoral artery dives deep into the
musculature, because the above knee popliteal
can also be difficult to image and evaluate.
Again, multiple approaches, using a medial approach
to image the distal SFA
and then imaging from the back, the above knee
popliteal, working from the ankle level
and working approximately to overlap those areas will help
to make sure that you evaluate the entirety of that vessel.

The popliteal trifurcation, of course, can be deep
and often difficult to visualize.
We find, again, using low frequency transducers can help,
that can also be of assistance.

In terms of imaging the peroneal artery in the calf,
there is a segment of the anterior tibial artery, just
beyond the origin that will not be visualized as it crosses
through the interosseous membrane.
In this case, you'll wanna use combinations
of doppler both above at the origin
and then beyond the interosseous membrane.
On the lateral aspect of the leg to
evaluate the anterior tibial artery, significant changes
in the wave form should clue you into the possibility
that there is something going on in that segment
that's not visualized.

Be careful with the
dorsalis pedis artery at the extensor crease,
especially if the patient is in plantar flexion again,
in these low flow states, compression of
that vessel may fool you into thinking
that the artery is occluded.
Just quickly have the patient dorsiflex
and reevaluate that area to confirm patency
or occlusion if occlusion is suspected.

Representative Cases

Let's just go through a couple of cases
where we've used these techniques.

In this case, a patient came down
for evaluation in whom we identified a very large
popliteal artery occlusion in this case of the origin
of the anterior tibial artery with reconstitution distally.
And as you can see here, the distal peroneal
and posterior tibial artery are occluded,
and this is the corresponding arteriogram in that patient.
As you can see here, the popliteal artery is a
ragged looking artery.
Of course, you only see the lumen here in this patient
with a lot of clot within the popliteal artery aneurysm,
distally, we can see that there is a patent
anterior tibial artery, which correlates very nicely with the duplex scan.
It's occluded at its origin.
The peroneal artery is not visualized, it's occluded,
and the posterior tibial artery is not seen.
This patient went on to get two vein grafts
and interposition vein graft for repair
of the popliteal artery
and a distal vein graft down
to the distal anterior tibial artery
for repair of those issues.
And with a very nice result.

And again, this shows the power of the duplex scan
in this setting in patients who are contraindicated
for large contrast loads.

Here's a patient who presented with multiple occluded
prosthetic grafts,
in whom we performed a duplex mapping,
which showed a patent common femoral artery occlusion
of the distal superficial femoral
and above knee popliteal, with really only one vessel runoff
through the peroneal artery
and reconstitution of the posterior tibial artery distally.
And this patient went on to get a vein graft to
that peroneal artery, which reconstituted the
distal posterior tibial artery as predicted
by the duplex scan.

Philosophical Thoughts on Duplex Scanning and Physiologic Testing

Just wanna close with a little bit of
some philosophical thoughts.

There is a little bit of controversy out there about the
appropriate use of duplex scanning
and physiologic testing for the evaluation of patients
with suspected peripheral arterial occlusive disease.
And these are just some excerpts from the University of Vermont flow net.
And one person asked,
how does everyone out in the flow net land evaluate your
patients with arterial disease?
She followed up with a second question
after multiple responses, some
of which were contradictory,
asking if arterial duplex is more precise than an ankle
brachial index, and an ankle brachial index is included.
Why do labs use lower extremity PVs?
This seems like an extra step in another extra cost
to the patient, and really, they aren't.

And my response to these questions were
that the tests are not competitive, there
are many scenarios for which a duplex
and a physiologic test would be complimentary and
therefore appropriate at the same setting.

And the bottom line really in these patients is
that every good examination starts with a conversation
with the referring physician
to elucidate the rationale for the examination.

In addition, your best bet is to assess every patient
as an individual and perform the tests
or tests that are most appropriate given the patient's
history, the physical examination,
the clinical presentation, and the question at hand.

At Montefiore,
after a physiologic test confirms the presence
of peripheral vascular disease, we then use the duplex scan
to map the lower extremity arteries in patients in whom
an intervention is being considered.
This is the first step in the treatment plan.

We feel that the combination of physiologic testing
and duplex scanning where it's appropriate, helps us
to utilize our resources more appropriately
and not allocate the resources for imaging studies
where a physiologic test is enough.

We believe that this approach also allows us
to minimize the use of diagnostic arteriography,
but more importantly, in some cases, it avoids the need
for an unnecessary arteriogram in patients
who would not be candidates
for interventions based on the duplex scan.

Algorithm for Evaluation

And this currently is our algorithm for evaluation
of patients for suspected
peripheral arterial occlusive disease.

The patient is referred for testing
and a physiologic test is performed.
If that physiologic test is normal
and the patient does not have exercise related leg symptoms,
the patient is discharged to home.

If the physiologic test is abnormal, the patient goes on
to have a duplex ultrasound.
If an intervention is being considered,
if there's no intervention being considered, the patient
can be discharged home with or without the duplex.

In a normal study in a patient
who has exercise related leg symptoms,
a stress test is performed.
If the stress test is normal,
the patient is discharged home.

If the stress test is abnormal,
a duplex ultrasound again is performed.
If the intervention is being considered,
if no intervention is being considered,
the duplex is a plus minus,
and the patient is discharged home.

Conclusion

I hope that this has been helpful for you in terms
of your evaluation of patients with
suspected peripheral arterial occlusive disease.
And I'd like to thank you for your time and attention.