Doppler Evaluation of Peripheral Arterial Disease - HD

Introduction

Hi, I'm John Pedo.

I am vice chair of radiology at the North Shore LIJ health system, and I'm affiliated with the Hofstra North Shore LIJ School of Medicine.

I will be discussing the Doppler evaluation of peripheral arterial disease.

In this presentation, I will review the techniques and protocols for the duplex examination of the peripheral arteries.

We will review the diagnostic criteria for arterial stenosis and review color and pulse dola signs of significant peripheral arterial disease.

Diagnostic Tests for Peripheral Arterial Disease

Now, there are multiple diagnostic tests that can be employed in the evaluation of the peripheral arteries.

We usually start out with the indirect tests, which include the ankle brachial index.

We then may proceed to ultrasound.

Other diagnostic tests include magnetic resonance angiography, multi detector CT angiography, and of course conventional arteriography.

Now, a non-invasive diagnosis of peripheral arterial disease is obviously a desirable alternative to arteriography.

Regardless of the test you use, it should not only detect the presence of disease but also be able to distinguish severe from non-surgical lesions.

We can also use these tests to evaluate the res results of treatment such as angioplasty, stents and bypass grafts.

Limitations of Noninvasive Tests Like CT and MRA

Now, the noninvasive tests including CT and MRA have limitations in that they require contrast material may be contraindicated in patients with renal failure and there were also risks for possible allergic response to contrast material.

The use of radiation for CT angiography and concern about metallic implants with MRI ultrasound has proven to be safe and diagnostic in the evaluation of the peripheral arteries.

Identifying Significant Stenosis

In vivo and in vitro tests have shown that one can identify a significant stenosis by determining a greater than 50% diameter reduction.

We identify this as a drop in blood pressure and blood flow across the lesion and we can detect these stenosis with systolic pressure measurements such as the ankle brachial index.

These are easily obtained, very sensitive and are very valuable as a screening examination for peripheral arterial disease.

Ankle Brachial Index

The ankle brachial index is the ratio of systolic blood pressures between the arm and the ankle.

Normally, the ankle brachial index is greater than one.

When the ankle brachial index drops below one but is greater than 0.5, we usually consider single segment disease.

When it drops below 0.5, then we become concerned that the patient has multis, segmental disease and as it drops even lower, we get concerned for tissue loss and gangrene.

Other Indirect Tests

As I mentioned, there are a number of indirect tests that can be used for the evaluation of the peripheral arteries.

The ankle brachial index is very sensitive and easily performed.

We also employ segmental pressure measurements, pulse volume recordings, and dola wave forms in our evaluation treadmill.

Exercise testing can be helpful for the evaluation of patients with claudication as these stress tests can help bring out disease that may not be identified at resting pressures.

Indirect tests have proven to be useful for screening and demonstrate the level of disease for further evaluation with ultrasound.

Example of Indirect Tests

Here's an example of one of our indirect tests here on this examination.

You can see the ankle brachial indices are identified on the chart here.

We also can see that there are segmental pressure measurements listed adjacent to the blood pressure cuffs along both lower extremities and these measurements are then flanked by the pulse volume recordings that we see on both sides.

In this patient, we see that the ankle brachial index on the right is 0.98, which is close to normal, but there is a significant reduction in the ankle brachial index on the left, which is seen here to be 0.61.

When we review the segmental pressure measurements, we can see that there's a significant reduction in pressure across the left thigh level and pressures remain decreased as we move down the lower extremity.

We also will observe that there's a decrease in amplitude in the pulse VI recordings as we move from the thigh to the calf level, indicating to us that there is likely a significant lesion at the femoral popliteal level.

Limitations of Non-Invasive Tests

One must recognize that there are limitations of the non-invasive tests.

Underlying arterial calcification can preclude adequate pressure measurements as these vessels can be non-compressible.

These tests are also limited in that they cannot, cannot precisely localize the disease, nor can they determine the number of underlying lesions.

The indirect tests also are unable to discriminate from a significant stenosis from occlusion.

Doppler Imaging Protocols

There are different doppler imaging protocols.

Depending on the situation, one can perform ultrasound as a screening evaluation of the abdominal aorta to the lower extremity, or we can do a detailed study of the level or segment of interest that is identified from the indirect tests.

The protocol for the lower extremity evaluation with Doppler ultrasound can be either a mapping or a focused exam.

In either case, we'll use gray scale to evaluate for the presence of plaque color.

Doppler is valuable to identify areas of abnormal flow by sweeping the vessels for narrowing and aliasing, and we use pulse doppler to sample each arterial segment and also at sites of flow abnormality that are identified on our C Doppler exam.

Lower Extremity Arterial Mapping

When we perform lower extremity arterial mapping, we can start at any level.

Many times we'll begin at the abdominal aorta near the iliac bifurcation and sweep down to the level of the ankles.

This examination will include both sagal and transverse views using both gray scale and color doppler to identify sites of calcification and abnormal flow.

And then we'll also use pulse staler to evaluate waveforms and peak systolic velocities at multiple locations.

So lower extremity arterial mapping again can be performed from the abdominal aorta moving our way down the common and external iliac arteries through the femoral bifurcation to include the superficial ND femoral arteries and of course through the lower extremity to evaluate the popliteal artery and trifurcation vessels to the level of the ankle.

Focused Duplex Exam

Many times we prefer to do a focused duplex end cauli flow Doppler examination to examine the abnormal segments defined by our indirect tests.

This allows us to determine the location, length, and degree of stenosis that is suggested by those indirect studies.

We can also use the examination to help determine the need for intervention with angioplasty and or stent placement, and we can also follow patients that have been treated either with angioplasty or stent placement and follow the progression of known disease.

Example of Superficial Femoral Artery Stenosis

Here's an example of a superficial femoral artery stenosis.

Here on the color Doppler image, we can see that there's marked wall calcification narrowing of the lumen and aliasing at the site of the stenosis.

This is helpful because we can place the sample volume across this lesion to determine the peak systolic velocity within the stenosis.

In this case, we see that the highest velocity within the stenosis in the superficial femoral artery is approximately 450 centimeters per second.

Important Areas of Disease

Now, it is important to recognize that we can identify atherosclerotic disease at the bifurcation points, so of course we'll be able to see significant lesions at the aortic bifurcation, iliac bifurcation, femoral bifurcation, and of course the tibial trifurcation.

Another important area is the superficial femoral artery at the level of the adductor canal as this is an important site of disease in diabetic patients.

Transducer Selection and Settings

For our studies, we typically will use a linear transducer with an average frequency range of five megahertz, but the transducer selection will depend on the patient body habitus.

For a very large patient, we may choose to go down in our frequency to get better depth penetration and may use a curved rate transducer with a lower frequency range of two to three megahertz.

Obviously, in a small patient or a pediatric patient, we may choose to use a higher frequency to get appropriate resolution.

We'll optimize the gray scale and the color doppler parameters for each individual patient and adjust the pulse repetition frequency so that we will detect hemodynamic disturbances in areas of flow abnormality.

It is important to adjust the PRF for each patient so that we do not see aliasing in areas of normal flow.

Then we will perform pulse staler examination in regions of abnormal flow or color aliasing to determine the peak systolic velocity and accurately characterize lesions identified on our examination.

Normal Peripheral Arterial Flow

Probably the most important concept in this presentation is to recognize normal peripheral arterial flow.

Normal wave forms in the upper and lower extremities have a phasic configuration.

We will see an initial high velocity fluid flow component in systole, and this represents ventricular contraction with propulsion of red blood cells down into the lower extremity.

After that, we will see an early diastolic reverse flow component, which we believe is related to peripheral resistance as the vessels will branch into smaller and smaller arteries, arterials and capillary beds.

The third component occurs later in diastole.

We see a low velocity forward flow component, which is likely related to elastic recoil, and the evaluation of the peripheral arterial waveforms will not only look at the phasic shape, but we will look at the systolic window as the red blood cells should be moving at approximately the same velocity at any given point in time, and we'll also look at the velocity range.

It's important to recognize that no matter where we sample from the upper or lower extremities, we should see a normal phasic waveform.

Here we see a sample obtained from the distal aorta and approximately iliac artery maintaining that normal phasic appearance.

And here's a sample taken from the right subclavian artery.

The normal peak systolic velocity range for the peripheral arteries is typically about 80 to a hundred centimeters per second in the femoral arteries, and there's a slight reduction in velocity as we move down the extremity.

The velocity range in the popliteal arteries is approximately 60 to 80 centimeters per second, And in the tibial arteries we'd expect velocity approximating 40 to 60 centimeters per second.

In our evaluation for peripheral arterial disease, we will look at three specific areas on our waveform.

We will look at the shape and again, notice here we have a normal phasic appearance.

We will look at the velocity range and we will look at the spectral window or envelope the area under the systolic peak.

Classification of Arterial Disease

Mild or Minimal Disease (1-19% Diameter Reduction)

The first classification of arterial disease is one to 19% diameter reduction, which we classify as mild or minimal disease, and the waveforms obtained from these segments.

We'd exec expect to see mild spectral broadening or minimal filling of the spectral envelope up to a 29% increase in the peak systolic velocity compared to the normal proximal segment.

And the normal proximal segment is usually about one to two centimeters above the level of the stenosis, so we will be comparing velocity measurements across that segment.

Notice also that we maintain our normal phasic appearance and that we have forward flow in systole, early diastolic reversal and a smaller velocity component.

Later in diastole,

Moderate Stenosis (20-49% Diameter Reduction)

a moderate stenosis is classified as up to a 20 to 49% diameter reduction.

Again, in this example, we see a increase in spectral broadening up to a 99% increase in the peak systolic velocity compared to the proximal segment, And it's important to recognize that we maintain a normal phasic appearance with a consistent reverse flow component

Significant Lesion (50-99% Diameter Reduction)

With a significant lesion, which is defined as a 50 to 99% diameter reduction.

We have a change in the waveform shape and it is important to recognize that the waveform will change when there is a significant stenosis and there'll be loss of the reverse flow component, so blood flow is only in one direction through the stenosis.

Notice. In this example, we have calcification in the wall aliasing on the color doppler display.

We placed the sample volume within the lesion and we angle corrected the direction of flow at 60 degrees or less.

The peak solic velocity in the lesion, again, approximately 450 centimeters per second notice.

There's mark spectral broadening as an almost complete fill in of the spectral window.

There's a greater than doubling of the peak systolic velocity compared to the proximal segment.

We describe this waveform shape as monophasic as we no longer have reversal of flow and flow is only in one direction across the stenosis, and as we continue to move the sample volume through the stenosis into the post stenotic area, we should identify post stenotic turbulence and this is an important sign of a hemodynamically significant lesion

Occlusion

in cases of occlusion.

Obviously, there'll be an absence of flow in the occluded segment.

One of the important clues for occlusion is that we'll have abnormal proximal waveforms and that they'll have very high resistance in d diastole.

Notice in this example of occlusion of the common femoral artery, we have a rapid systolic upstroke, a low peak systolic velocity of 21 centimeters per second, and absence of flow throughout diastole due to the high resistance caused by the obstruction.

If there is reconstitution of the distal arterial bed, we will see low resistance waveforms with a TARDIS pattern and we will similarly see low resistance flow in collaterals that supply the lower extremity due to vasodilatation from lower extremity is ischemia.

Collateral Flow

Here's an example of a collateral obtained in a patient with underlying occlusion.

Notice again the classic TARDIS parvis appearance with a slow rise to peak systole and damped velocity, so the hallmark of collateral flow are low velocity monophasic waveforms with a TARDIS parvis appearance.

These arterial waveforms lose their phasic character and again are related to decreased resistance from distal ischemia.

Patient Case Study

Let's take a look at this example.

Here's a patient that presented with right leg pain.

We noticed that the ankle brachial index is 0.71 on the right, which is significantly low.

As we look at the an at the segmental pressure measurements, we know that there's a significant reduction at the low thigh level and this persists as we move down the extremity Pulses.

Volume recordings demonstrate that there is decreased amplitude at the low thigh and calf levels compared to the contralateral side.

This indicates that there's likely a lesion across the femoral popal segment.

Ultrasound is very valuable to further explore and characterize this lesion here in the same patient.

Our we have a sample from the right common femoral artery, which has a normal waveform shape and a slightly elevated velocity of 145 centimeters per second.

We'll use color doppler here to sweep down the femoral artery looking for areas of stenosis or occlusion.

As we move into the proximal superficial femoral artery, we'll see calcification in the wall marked narrowing and aliasing indicated elevated velocities.

When we sample across this abnormal segment, we'll see peak style velocities approaching 500 centimeters per second consistent with a very high grade stenosis.

As we continue to move down into the post stenotic area, we will see that there are dampened waveforms with a classic TARDIS parvis or TP shaped waveform and a decreased velocity of 35 centimeters per second.

Notice that we've lost our normal phasic waveform shape.

Studies on Utility of Duplex and Color Doppler

Let's review a couple of studies that have looked at the utility of duplex and color doppler in the evaluation of peripheral arterial disease.

One of the earliest studies was published in 1987 in circulation by Kohler in his group.

This was before the advent of color doppler and in this study basically used gray scale in duplex doppler in the evaluation for peripheral arterial disease.

They found a sensitivity of 82% and specificity of 92% for the detection of significant stenosis identified as greater than 50% diameter reduction.

In a study published in the Journal of Vascular Surgery, Cosmin, his group utilized Colo Doppler in the evaluation of peripheral arterial disease.

They found a sensitivity of 87% and a specificity of 99% for significant stenosis.

They also described an accuracy of 96% for identifying arterial occlusion.

In a study published by ranking this group, they found there was marked variability in peak systolic velocity measurement.

This is important because we find that unlike the carotid evaluation where peak systolic velocity measurements are utilized to classify arterial stenosis, this study showed that velocity ratios are more valuable for this evaluation.

They were also able to correlate velocity ratios with increasing severity of stenosis.

A peak velocity ratio of at least 2.4 was consistent with about a 50% stenosis.

A ratio greater than four to one was consistent with approximately 80% stenosis and a ratio of seven to one correlated with approximately 90% or greater stenosis.

Color Flow Findings

There are a number of CAU flow findings that are valuable in the evaluation for peripheral arterial disease, and we've touched on several of these already.

We look for evidence of focal color change or aliasing at the site of stenosis.

Another helpful sign of significant disease is the color blue artifact, which is due to perivascular tissue vibration and is typically seen in systole and alize, the lesion, which is usually either a high grade stenosis Pseudo aneurysm or arteritis fistula.

We'll also see a color mosaic pattern when there is post stenotic turbulence.

Here's an example of aliasing in the posterior tibial artery.

Again, notice calcification within the wall.

There's aliasing artifacts seen at the site of the stenosis.

Obviously this is where we'll want to place the sample volume for pulse doppler sampling.

Here in this example, we show that there is a peak systolic velocity of approximately 350 centimeters per second across that stenosis.

Also note that flow is only in one direction through the lesion.

What we see below the baseline here is some ruby artifact.

Here's another example in real time showing aliasing that is occurring across the stenosis in this patient with a bypass graft, and again, the color do is extremely helpful to identify the area of highest velocity so we can place the sample volume in this region.

Here's a couple of examples of color bru artifacts.

Notice here that the artifact is identified across the abnormality and spreads into the superficial tissues and gives a mosaic appearance in real time.

We can actually see this occurring in systole across the stenosis.

Here we have a stenosis in the left anterior tibular artery.

We can see the aliasing occurring in the stenosis and notice these perivascular color blue artifact that occurs during systole.

Here's a patient with a superficial femoral artery occlusion.

Notice that the flow stream is seen in the superficial femoral artery with abrupt termination and no flow.

In the occluded segment, we'll see evidence of a prominent collateral with a mosaic appearance again due to the turbulence of flow from the femoral artery into the collateral and we can appreciate that as well on this CT angiogram where we can see that there is occlusion of the distal superficial femoral artery and that prominent collateral coming off that distal vessel.

Pulse Doppler Findings

Important pulse doppler findings to look for in our evaluation for peripheral arterial disease include elevated peak systolic velocities in the stenosis, loss of diastolic reversal brewery artifact on pulse staler, and of course tardis parvis waveforms distal to the high grade stenosis.

Here's an example of a tight stenosis in the superficial femoral artery.

The sample volume is placed within the lesion angle corrected to the direction of flow at 60 degrees or less.

We notice here that the peak systolic velocity is slightly greater than 250 centimeters per second.

Again, in a high grade lesion, you'd expect to have a monophasic waveform with flow only in one direction.

In systole and diastole, notice again we have this diamond shaped artifact that occurs during peak systole and we see it both above and below the the baseline in peak systole, and this represents a bruie on pulse staler examination.

As we continue to move the sample volume through the stenosis into the post stenotic area, we will see evidence of post stenotic turbulence and again, we'll see uh, a, a tardis parvis waveform with a slow rise to peak systole.

We'll also notice that this flow on both sides of of the baseline because as the red blood cells move through the stenosis, they're going to spin around indirect different directions at distal velocities giving this turbulent flow pattern.

Here's another example of a very tight stenosis here in the common femoral artery.

Notice on our realtime color display that we have a very prominent color brewery artifact.

Again, very helpful sign that there is an underlying lesion here.

Notice also that there's a change in the color pattern that we also notice and that there's mark narrowing of the lumen with plaque causing narrowing of the vessel.

Again, we wanna sample across this segment to obtain the highest peak systolic velocity.

We will then compare that to the velocity in the proximal segment here.

Within this stenosis, we see that the peak systolic velocity is about 414 centimeters per second.

Also, again, appreciate the brewery artifact that we see in peak systole.

As we move down the lower extremity, we notice that the velocity's rapidly decreased to about 93 centimeters per second in the superficial femoral artery below the stenosis, and as we map out the degree of disease in the superficial femoral artery, we'll see that there's a second stenosis just below this sample.

Now the velocity goes from 93 centimeters per second up to 179 centimeters per second, so there's almost a doubling of the peak systolic velocity approaching 50% stenosis, and as we continue to move down toward the popliteal artery, you'll see the very abnormal waveforms at this location.

We've lost the phasia configuration.

It is flow only in one direction in systole and diastole, and there is a slow rise to peak systole consistent with the TARDIS configuration.

Also recognized that the peak systolic velocity is normally low at 32 centimeters per sec.

Upper Extremity Evaluation

We expect to see similar findings in lesions involving the upper extremities.

Here's a patient that presented with right arm pain and we notice from samples obtained in the right subclavian artery that we've lost, our phasic waveform velocities are abnormally low about 46 centimeters per second.

Again, we have a slow rise to peak systole, continuous forward diastolic flow.

This certainly has a tardis looking waveform indicating there's likely a proximal lesion as we move distally a little bit.

We also know that the flow is abnormal in the axillary artery, which has a persistent TARDIS appearance, so clearly the lesion must be more proximal than this subclavian artery.

As we look more proximally, we see a very turbulent abnormal flow pattern and this has the appearance of post diotic turbulence.

So I don't think we actually find the lesion here on this study, but we clearly see that there is a very abnormal biphasic waveform, uh, very shaggy appearance consistent with a post stenotic waveform.

When we compare this to the contralateral side, we can see that the left subc playin artery has a nice normal phasic waveform and if we go back to the right and look at the carotid artery, we can see that that has, uh, a normal appearance with a rapid systolic upSo.

So clearly the lesion must be near the origin of the subclavian artery because if it was involving the no artery, then the common carotid artery should have been involved and have an abnormal waveform shape.

So to further characterize this lesion, we looked at the patient's CT scan and we were able to identify a very tight stenosis right at the origin of the right subclavian artery, helping us to determine the location of the stenosis at the origin of the right subclavian.

Waveform Analysis Quiz

So here's a little quiz for you.

Here's a patient that presents with leg pain, and I'm gonna give you two wave forms for your analysis.

One from the right common femoral artery, one from the left common femoral artery.

So where do you think the lesion is?

As we look at the waveforms, we can see a normal phasic waveform on the right.

The peak systolic velocity is approximately 90 centimeters per second, so clearly there's no evidence of of a lesion on the right side, and we notice that there's a rapid systolic upstroke, which indicates that the inflow should be fine and it's relatively high resistance, which lets you know that there's probably good distal perfusion.

When we look at the left side, we can see that the velocity's low, it's only about 25 centimeters per second.

We also don't have that nice normal rapid upstroke that we see on the right here.

We could d, we could easily drop a perpendicular at the onset of systole, which crosses the baseline by about 90 degrees.

We can't do that on the left side.

If we would drop that perpendicular here, we would be off axis.

So this indicates that there's probably an inflow lesion is that we have a delayed peak systole and also we see continuous forward diastolic flow suggesting there's distal ischemia and low resistance.

So if we were to take a guess where the lesion should be, we'd expect it to be above the level of the left common femoral artery.

And as we moved up the lower extremity, we can see that there's a very tight stenosis that occurs at the, in the left external iliac artery with the peak STO velocity aliasing at over 450 centimeters per second.

So by analyzing the waveform not only can determine that there is the presence of significant disease, but we can also save time by knowing where that that lesion should be located.

Criteria Following Intervention

Let me finish up by talking about some of the criteria that we can use following intervention.

Here are criteria published by Dennis Band and his group that look at peak systo velocity and velocity ratios in patients with bypass graft.

Typically, we will follow patients, uh, after bypass to look for evidence of recurrence stenosis and Dr.

Bandi proposes that a peak systolic velocity in the stenosis greater than 300 centimeters per second likely warrants intervention.

He also suggests a velocity ratio of greater than 3.5 for indicating significant disease.

And again, we utilize this ratio similar to the ratio we use for the detection of native peripheral artery stenosis by looking for the velocity in the stenosis and comparing it to the proximal segment.

Here's an example of a significant stenosis at the distal anastomosis of this bypass graft.

The color doppler tells the whole story.

We can see evidence of aliasing at the distal anastomosis and the p systolic velocity in this location is almost 600 centimeters per second.

Dr. Bandi also proposed criteria for significant stenosis following angioplasty, and he suggests that a PXI style velocity between 180 and 300 centimeters per second suggests at least a 50% stenosis And a velocity ratio between two and 3.5 would also indicate at least a 50% lesion.

For a severe stenosis greater than 70% diameter reduction.

They recommend looking for a peak systolic velocity greater than 300 centimeters per second, a LOC velocity ratio greater than 3.5 to one and an end diastolic velocity greater than 45 centimeters per second.

And of course, with, with a severe lesion, you'd expect to see damp monophasic TARDIS waveforms distal to the stenosis following.

There are also criteria proposed for the evaluation of peripheral stents for a, for a stenosis associated with a stent greater than 50% diameter reduction.

It has been suggested that the peak STO velocity ranges from 190 to 275 centimeters per second with a velocity ratio between 1.5 and 3.5.

For a high grade greater than 80% diameter reduction, the peak STO velocity should be greater than 275 centimeters per second with a velocity ratio greater than 3.5.

Here in the example on the left, we see tight stenosis and a femoral artery stent.

The velocity in this example is approximately 270 centimeters per second.

Here's an example on the right of an occlusion of a distal stent.

Stents are usually easily recognized because they're quite echogenic, and in this particular example we can see that there's no flow through the stent and it's filled with a low level internal echoes.

Conclusion

So in conclusion, in our evaluation for peripheral arterial disease, we find the indirect test to be extremely helpful for screening for arterial examination and help determine the approximate location of peripheral arterial disease.

We then utilize duplex in colo dola to help characterize these focal lesions to location, degree and extent.

We can use this test to monitor the disease progression, help direct appropriate intervention and assess the therapeutic response to treatment.

Thank you.