Section: New Board Review Category: Imaging

Clinical assessement and Non-invasive imaging and for Critical Limb Ischemia, Diabetic Foot Ulcers and Chronic Wounds

Scott Brannan, MD

Scott Brannan, MD discusses non-invasive testing available for evaluation of arterial disease in patients with diabetic foot ulcerations. Dr Brannan also discusses the criteria to diagnose vascular disease with each given test as well as review current IWGDF guidelines looking at prevention of foot ulcers in at-risk patients with diabetes.

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Goals and Objectives
  1. Review non-invasive tests to evaluate peripheral arterial disease in patients with diabetic foot ulcerations
  2. Review IWGDF guidelines and recent studies looking at prevention of foot ulcers in at-risk patients with diabetes
  3. Define criteria to diagnose peripheral arterial disease with each given non-invasive vascular test
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  • CPME (Credits: 0.5)

    PRESENT e-Learning Systems is approved by the Council on Podiatric Medical Education as a provider of continuing education in podiatric medicine. PRESENT e-Learning Systems has approved this activity for a maximum of 0.5 continuing education contact hours

    Release Date: 12/27/2018 Expiration Date: 12/31/2020

  • Author
  • Scott Brannan, MD

    First Nations Limb Preservation Foundation & Modern Vascular
    Residency: Yale University
    Fellowship: Harvard Medical School, Vascular and Interventional Radiology
    Phoenix, AZ

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  • Lecture Transcript
  • TAPE STARTS – [00:00]

    Male Speaker 1: Dr. Scott Brannan, I believe he works for the IHS, is that correct?

    Male Speaker 2: Affiliated with the IHS.

    Male Speaker 1: Affiliated with the IHS. He is going to be discussing also on vascular disease, Non-Invasive Vascular Evaluation for diabetic for ulcers, chronic wounds and the need for a Non-invasive imaging and diagnostic testing. So let’s welcome Dr. Scott Brannan.

    Dr. Scott Brannan: Alright. So we have one screen everybody sitting in the back. Do you guys want to come up to the front a little bit? You look more curtsy because this is a very interactive lecture if you guys want to get up close and personal. The lecture is about non-invasive imaging clinical evaluation for critical limb. The point of the lecture, the learning the teaching points I’m hoping to get across to you is the importance of vascular evaluation early in the process and the distinction between PAD and CLI. PAD, peripheral arterial disease, CLI critical limb ischemia related but not the same. Their workup is different, the non-invasive imaging and the assessment is different.

    So my disclosures are there. This is just a disclaimer and this is a little slide about PAD. Overall the interventions for PAD from a peripheral vascular standpoint have increased about 4% since 2013. Overall, there is 10 million patients in the United States that suffer from PAD. In those polled, only 26% of adults in the United States are aware of PAD. So everybody is aware of what the pink ribbon is right, if I select anybody out of the audience what the pink ribbon stands for you for example, what does the pink ribbon stand for?

    [02:07]

    Female Speaker: Breast cancer.

    Dr. Scott Brannan: There we go breast cancer. So what’s the ribbon for PAD? Is there a month?

    Kimberley: September.

    Dr. Scott Brannan: Was that Kimberley? Yeah that’s right. September is the month for PAD and there is a grey wristband and a grey ribbon for PAD and I think the grey is meant to represent a modelled foot personally. But I use the breast versus PAD example as an overall lack of awareness. Now does anybody have an idea of what the relative morbidity and mortality rate would be between PAD and breast cancer. Based upon the public awareness, one would think that breast cancer had a far greater morbidity and mortality, but the opposite is true. The morbidity and mortality of PAD is almost twice that of breast cancer and not to diminish the importance of breast cancer, but to highlight the relative under emphasis of PAD.

    So this is a great study 2000 patients, which described the diversity of PAD in terms of lesion characteristic and location. As you can see, this was the task criteria which I’m sure most of you guys are familiar with, it was created in 2007 and then updated again in 2011. And it shows that there is a pretty wide variety of lesions that we have to treat. Some of which are just basic stenoses, a significant percentage of which are CTOs or chronic total occlusions and then there is a smaller percentage of in-stent restenosis and the location is widely varied anywhere from the iliacs down into the pedal arcade. And here is what I think is a very nice graphic describing the location of disease and the different characteristics.

    [4:01]

    The most important thing that affects our selection for non-invasive imaging on this slide is the presence or absence of calcification and as you could see based upon the distribution if you have a below the knee lesion, your likelihood of calcification is much higher. In fact the majority of infrapopliteal stenoses are densely calcified and therefore somewhat resistant to most of our non-invasive imaging techniques. That is also true for some of the fem-pop segment lesions, but a smaller percentage and you’re dealing with a much larger caliber vessel, which lends itself better to duplex ultrasound.

    And this is just a clinical slide showing you the diffuse morphology. Here this is what we call a coral reef calcification, it sort of fluffs out into the artery and creates what we’ll call a subtotal occlusion and that’s unique and require special tools, but it’s very easy to image. it’s in the SFA and with the duplex arterial ultrasound, you can easily see it. Where this kind of a lesion will get you into trouble is with your ABI because your ABI with this lesion will be normal. Your ABI will be normal with this lesion because it’s so far proximal that there’s been an opportunity for reconstitution, but the patient is presenting with CLI. so we know that they have a perfusion problem, but the ABI tells us that we’re safe and we’ll also get into ABI here in just a couple of slides. This one is the example of in-stent restenosis. This is obviously partially iatrogenic, we inserted a stent here, it’s foreign body, the body scars around it. This is a chronic total occlusion, so you have a proximal cap, a distal cap, the intervene segment does not opacify. This distal segment is reconstituted from collaterals that branch off of the profound femoral artery.

    [6:00]

    This segment here, the occluded segment, obviously reduces the perfusion pressure right, we still have usually a biphasic polls at the ankle, but the perfusion pressure is massively decreased because of this CTO and this is thrombosis in situ from a low flow state in a patient who had a stent.

    So the question I think from my clinical colleagues on the podiatry side of things is how do we rapidly and accurately triage patients for a vascular specialist evaluation. It’s really not within the purview of wound care or podiatry to be necessarily vascular experts and know what the morphology of the disease and what the best treatment is going to be, but it is, you guys are the just forgive the pong [phonetic] but boots on the ground, you are the people who are in the front line who are seeing patients that have critical limb. So you need to have a reliable system for simply triaging, it’s a binary choice, vascular evaluation, no vascular evaluation, and let’s get into some of the data around that.

    So there are some consensus, guidelines and documents that I’ve used for reference the International Working Group for Diabetic Foot. Everybody is familiar with that, there was a lecture earlier today on it. The guidelines for critical limb ischemia from Europe I think are very, very helpful, although our patient population is a little bit different. There’s a lot of objectivity in these documents. The American College of Cardiology, American Heart Association has documents of 2005, 2011 and 2014 updated, and then there is the task criteria that I used as well as the ADA recommendations. So this is from the International Working Group on the Diabetic Foot. The basic recommendations for PAD evaluation is that a patient be examined annually for the presence of PAD and it should be at a minimum taking an appropriate history and palpating the foot pulses, and this was a strong recommendation but the quality of the evidence is -- as you’ll see most of our evidence for peripheral arterial disease is going to be labeled as low because of the relative paucity of RCTs in PAD. it’s very different from CAD, coronary artery disease, where we’re having abundance of RCTs that give us stronger weight to the quality of the evidence.

    [8:25]

    So the second recommendation was evaluate patient’s diabetes foot ulcers for the presence of PAD, determine as a part of this examination ankle or pedal Doppler arterial waveforms measure both ankle and brachial systolic index. So in your day-to-day practice if you’re going to evaluate the foot and ankle arteries for waveforms, what would be the tool that you guys will use in the office? Anybody? You’d use a blood pressure cuff and a Doppler right, you perform a basic ABI right? Which is a great test for PAD. It is a very suboptimal test for critical limb ischemia and that’s what I’m trying to get across all through medical school, all through fellowship, my entire training ABI, ABI, ABI. And then I became a limb salvage specialist and I started to see the short comings of ABI and how many false negative cases we had, how many times was I able to hear an arterial pulsation that was biphasic at the ankle and then come to find out completely occluded above that and it was shockingly frequent. So how many of you feel comfortable identifying or differentiating monophasic, biphasic, triphasic by show of hands.

    [10:02]

    Alright, it’s about 25%, which is great, that’s a fantastic number because it’s a very complex physiology for a board certified radiologist to remember. And it’s even more difficult to interpret, if you think you can interpret it, there is a chance that you might not be able to interpret it because a lot of my colleagues can. The only way that we’re able to accurately do that is when we do arterial duplex imaging and we rely on a machine to tell us when the signal goes below the baseline rather than just our ear. And so the handheld Doppler ABI is a great tool for PAD and you should all use it. If you have patients that fall under the rubric of CLI and you guys all know what CLI is, Rutherford IV, Rutherford V, any evidence of arterial insufficiency and rest pain or wound that’s a CLI, then the ABI not that you shouldn’t do it but you shouldn’t rely on it.

    So this is a summary of the International Working Group on Diabetic Foot. This is just sort of a flowchart of what their recommendations are and you’ll see it’s pretty similar across the board. They introduced the TcPO2 for patients with severe PAD and I’m strongly in support of TcPO2’s for patients with severe PAD. I think it has very strong positive and negative value in terms of level of amputation, likelihood of healing, and the likelihood of successful revascularization. There are inherent limitations to TCOMs and TcPO2’s, which I’m sure you guys are aware of and we’ll cover a little bit more in detail here in a second.

    So this is from the European Society 2013 guidelines. Again, their focus is on clinical evaluation and then performance of an ABI, very importantly toe pressures and then lastly TcPO2’s.

    [12:04]

    The toe pressure you’re looking for numbers less than 30 and that’s a pretty reliable indicator even in diabetics with densely calcified arteries, the toe pressure is fairly reliable and then TcPO2 especially in the presence of an oxygen challenge is reliable. Again, this is the continuation of the European Society recommendations and this is a stratification system that they have first, second, third and fourth degree. If you have a patient whose supine TcPO2 values falls between 10 and 30, it's a very good prognosis overall. If the forefoot TcPO2 is less than 10, then you do an oxygen challenge and if there is no augmentation, then that puts them into third degree, which is a TcPO2 less than or equal to 10 and inadequate increase in forefoot with barometric oxygen, so 100% inspired O2.

    And then the fourth category is the TcPO2 less than 10, no augmentation existing wound, very poor prognosis. These are the American College of Cardiology and American Heart Association recommendations, and I think that they’re valuable recommendations as long as they’re titrated with other recommendations that are available, and they all sort of fall within the same range. It relies heavily on ABI as a screening tool. We all know what the normal ranges are for ABI where you’re going to use 0.9 as our abnormal low and we’re going to use 1.4 as our abnormal high. Anything that falls out of that range is abnormal. And again this is really very valuable for PAD, not as valuable for CLI. If this value is abnormal, you put them on a treadmill, exercise them. If it’s a decreased post exercise, what ABI confirmation of PAD means is angiogram, okay that’s the next step is angiogram.

    [14:16]

    So this is from a recent study 2013 was when the data was aggregated, but was presented at the AMP Conference in 2015 by Dr. Mustafa and Dr. Jeff, and it reveals for us the accuracy of ankle or brachial index measurements in evaluating a patient with critical limb ischemia. So the sensitivity of the test is slightly better than a coin flip in a patient with CLI. That’s impactful. This was a study that enrolled over 200 patients. It enrolled patients from a broad spectrum, it was a even distribution in terms of ethnicities, it wasn’t cherry picked to produce a bad result for ABI necessarily, it was anybody who fit those basic characteristics of CLI, which we should all have that [Indecipherable] [15:21] CLI is arterial insufficiency with rest pain or wound that’s CLI and I’m going to imagine that this room is filled with doctors that have offices filled with those patients, I’m going to imagine.

    As you can see the specificity is a little bit better, but still much lower than what we would expect from a comparative diagnostic study. The negative predictive value of 63% is pretty amazingly poor for a screening test right? That’s what ABI is supposed to do is be a binary screening test if it’s negative then you’re good, if it’s positive then let’s go and do some further evaluation.

    [16:03]

    The negative predictive value of this screening test is 63% in a CLI patient. So arterial duplex imaging is our next fallback for a non-invasive form of imaging and it is absolutely the next best thing to angiography. And in some cases if you have a great tech, it’s better than an angiography because angiography won’t tell us about the elastic recoil of the artery, which is extremely important for maintaining laminar flow in the vessel. The angiogram gives us flow characteristics, but it doesn’t give us the dynamic characteristics of elastic recoil after systole as does the duplex arterial ultrasound.

    So in my opinion, duplex arterial ultrasound is actually probably better than digital subtraction angiography as an evaluation of arteries if you have a highly experienced, highly qualified, vascular certified ultrasound tech, which a lot of us don’t have rapid access to. The other place where the arterial duplex starts to breakdown is below the knee. We have very small vessels, very densely calcified, a relatively large quantity of soft tissue is separating the probe from the artery itself, and so there are very severe limitations especially at the mid-calf level and so what you’ll frequently see are images obtained in the proximal tibials, which demonstrate a patent vessel and a biphasic waveform, and then you’ll see the distal waveforms are monophasic, the velocity is decreased but the interpretation is patient tibial arteries, but the truth is that the intervening segment between the proximal tibials and the ankle very, very difficult to image arterial duplex unless it's a thin patient and experienced tech.

    [18:01]

    It’s relatively time consumptive to do one of these exams and it requires a cooperative patient. Transcutaneous oxygen measurement, this is an example of what it looks like for the patient. It has a lot of advantages in my mind. The way it works it measures local O2 delivered to the skin via the capillaries. It’s a representation of the metabolic state of the limb. For the patients that we treat, which is a lot of patients with calcified arteries and a lot of patients that are missing toes, the TcPO2 can be very helpful because our toe cuff measurements aren’t possible in those patients. We use this for wound healing prediction, for determining the level of amputation, for qualification for hyperbaric oxygen therapy and also for predicting the likelihood of success for revascularization. Limitations are those decreased accuracy in edematous and inflammatory states. You can overcome that with an oxygen challenge in some cases and the requirement of prolonged motionlessness with the patient for an accurate reading.

    So this is an oxygen challenge where the patient is breathing a 100% O2 at one atmosphere. Most patients should correct to greater than a 100 mmHg when breathing 100% O2 at one atmosphere. If this is what your oxygen challenge says, then there is unlikely to be significant macrovascular disease that can be fixed with minimally invasive techniques or even a bypass. If your response to O2 is poor, meaning that the total attention of oxygen remains less than 30 mmHg even in the presence of 100% inspired O2 at one atmosphere then there is a high likelihood of significant arterial disease that could be assisted by minimally invasive or a bypass. Right, so again this is the point, CLI is not equivalent to PAD.

    [20:02]

    In CLI, there is a maldistribution of the skin, microcirculation in addition to a reduction in the overall pressure head. These are the criteria for TcPO2 measurements, which I think as our machines become more sophisticated as our technology becomes a little bit more user friendly, I do believe that TcPO2 is going to permeate more and be a little bit more useful, right now it’s relatively limited because of the cost, because of the patient motion limitations, and because many of our patients are edematous or inflamed.

    And lastly digital subtraction angiography remains the goal standard and it is not a massive surgical procedure, it does not require an overnight admission. Over the last 10 years, we’ve really demystified the whole angiographic process and I hope one day to be up here lecturing you guys on how to do your own foot and ankle angiography that’s my goal. Aright, I’ll take any questions. Kimberley you have to have a question. Yes please.

    Male Speaker: [Indecipherable] [21:18]

    Dr. Scott Brannan: CO2 angiography is a useful adjunct. It doesn’t really fit into the rubric of this lecture because it’s an invasive technique, it’s an invasive imaging technique, but we can talk about it, it’s a great time to talk about it. So what CO2 angiography does is instead of injecting iodinated contrast, we forcefully inject CO2, which displaces the blood inside the vessel and provides us an air contrast instead of an iodine contrast. It is very effective by using a lot for lesions above the knee. It is less effective for below the knee, however, with sub-selective catheterization, CO2 angiography below the knee, so infrapopliteal, can be very accurate but you have to have sub-selective meaning into the origin of the AT or into the tibial peroneal trunk with a good 5-French diagnostic catheter and somebody who knows how to do a CO2 angiography.

    [22:20]

    It’s a great test. Thankfully, we now have technology, which is much, much better in the form of endovascular ultrasound. So we will be discussing this tomorrow. It's a revolutionary tool that’s been around for a long time in the coronaries, but was never really specifically tooled for the periphery. And we now have 0.014-inch catheters that go down to 1.8 mm that give us beautiful images everywhere from the common femoral artery down through the pedal plantar loop without any contrast. I’ve done pedal reconstructions on Alan’s patients and Keith’s Patients and Kimberley’s patients with less than 5 cc of contrast for a complete artery construction with using IVUS. So CO2 is helpful, but it’s becoming historic, IVUS is a lot more useful. Good question, thank you.

    Male Speaker: One last question before we have to close this. Although it’s not diagnostic of anatomic obstructions, I find it post volume recordings are really a great way to diagnose impaired perfusion or PAD in the foot or whatever level you do and I just want to know your opinion on that.

    Dr. Scott Brannan: Yes especially for the toe pressures I feel like toe pressure cuffs are extremely accurate, extremely helpful. The other segmental recordings of the thigh, the calf and the ankle, I find those to be less reliable but they’re great for determining where you think the level is and for treatment planning, but what I’m trying to talk about right now is more of a binary system of how do we chunk these patients to either their fine vascularwise or they need specialty evaluation.

    [24:19]

    Male Speaker: Very simple you see a flat PVR waveform, you send them on to your vascular surgeon.

    Dr. Scott Brannan: Amen, yes, yes exactly. Okay, anybody else? Keith, yes.

    Keith: Okay this does work. We’ve had many discussions about lowering the barrier of entry for podiatrists and their office space to get patients to you that they are concerned about and a lot of podiatrists who are in the office and we don’t have a lot of these modalities available to us and we had a discussion about what is the value of looking at an x-ray because all of us can do an x-ray at our office. If you see calcification of varying degrees and varying locations on an x-ray is that enough information to call you and in your experience how much calcification on an x-ray correlates with degrees of occlusion that you’ve seen. So in other words, I would love it to make it easy for everyone in this room not to be embarrassed to send a patient to you based on calcification on an x-ray without wasting the patient’s time trying to find an arterial ultrasound.

    Dr. Scott Brannan: Yes, so it’s a very cogent point. A practice management tool for the majority of podiatrists in the country as three views of the foot and ankle, just about every patient gets that. And there’s a wealth of information on that film and there is vascular information in the form of vascular calcification and there have been some very, very good initial relatively small population 54 in one study and like 150 in the other about correlating the severity of pedal arterial calcification with the presence or absence of hemodynamically significant arterial disease.

    [26:02]

    Now, the studies were somewhat limited because they did not use the gold standard to evaluate. They use the combination of arterial duplex and TcPO2 as they’re determinant of who actually had disease and who didn’t. So it didn’t include angiography and angiography or IVUS endovascular ultrasound frequently gives us something different than our non-invasive testing.

    But even given that, the percentage of in accuracy was small enough to warrant inclusion of pedal arterial calcification has a significant risk factor for hemodynamically significant stenosis. Are we going to be wrong sometimes? Yes, we will, but if there is even a 30% correlation that’s a much stronger correlation than hypercholesterolemia, yet we have not used this tool, this information that you all have in your three views of the foot and we’re working on a study right now. Thankfully it’s been funded to do retrospective and then prospective evaluation correlating directly to gold standard angiography with the severity of pedal arterial calcification. So it’s going to be a recommendation I think very soon for you guys. Thank you, good night.

    TAPE ENDS: [0:27:28]