Non-Invasive Evaluation of PVD
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Hi! This is Dr. Hamden. I am dictating a lecture on non-invasive evaluation of peripheral vascular disease. I am a vascular surgeon at the division of vascular surgery at the Beth Israel Deaconess Medical Center. There, I serve as the director of clinical research and I am an assistant professor at the Harvard Medical School.
Production of this PRESENT lecture was made possible by a generous grant from Huntleigh Healthcare. When you think Dopplers, think Huntleigh.
Peripheral arterial disease is a very common condition. The diagnosis occurs in up to 22% of patients depending on the population you choose, the risk factors, and the diagnostic techniques used. In general, as will be described below, an ABI less than 0.9 gives you the diagnosis of peripheral arterial disease. Within the group of patients with peripheral arterial disease, the ratio of those who have symptoms to those who are asymptomatic is anywhere from 1:1 to 1:6. In other words, a patient may have peripheral arterial disease and not know it.
Another important point related to peripheral arterial disease is, as the population ages, the prevalence increases as you can see here in this table where close to 25% of patients greater than 75%, greater than 75 years old will have peripheral arterial disease. With the ageing of our population, this is becoming a much more important issue.
How patients present with peripheral arterial disease is variable. In general, the majority will either present without symptoms, so you will need to identify them on physical exam or ultrasound test, or will have stable claudication which will be described below. A very small minority of patients will actually present with either chronic limb ischemia or acute ischemia.
The risk factors for atherosclerosis are crucial both from the standpoint of understanding which patients are more likely to have atherosclerosis and peripheral arterial disease, and also on the treatment of those risk factors. If you look at the chart, all the arrows point in towards atherosclerosis. Starting from the left, age is a very important factor. As the population, person ages, their chance of having atherosclerosis increases. Diabetes, as we will describe later, is a huge risk factor for atherosclerosis. Obesity certainly and the other current environment we have where it is almost an epidemic, leads to the metabolic syndrome with hypertension and atherosclerosis. Certainly there is a percentage of patients who have a major genetic component where they have early presentation of progression of atherosclerosis and a number of family members who presented at early ages. On the right, dyslipidemia which includes high triglycerides and high cholesterol levels are certainly well known causative agent. Hypertension the very few percentage of patients who will have true hypercoagulable state and then hyperhomocysteinemia is a recently diagnosed risk factor. In the middle is the most important factor which is smoking. This in and of itself can cause atherosclerosis but with any of the other factors listed to the right or left, there is a synergistic relation and certainly patients have to be treated aggressively and helped to stop to smoke.
When looking at the relations of diabetes mellitus and atherosclerosis, a number of factors are clear. It accelerates both the presentation and the development of the disease 200-400%. The risk of coronary artery ischemic events increases up to 4 times. The age match population, there is a 4 time increase in the risk of stokes and strokes are more severe, and peripheral arterial disease develops a decade earlier. So, instead of seeing a patient in their 60s or 70s, with severe peripheral arterial disease, you may see them in their 40s or 50s. And the cardiovascular risk is equivalent to 3 non-diabetic risk factors if you refer to the chart of the prior slide.
So to review, the diagnosis ranges from 1-22% depending on the population and the risks factors as well as the tests you use. Asymptomatic peripheral arterial disease is very common and it is actually quite important to identify the asymptomatic patients and treat the risk factors before they progress. Probably, greater than 8 million Americans greater than 40 years old will have peripheral arterial disease. So this is certainly on epidemic proportions.
There is a high overlap of patients with peripheral arterial disease and those who have cardiovascular disease and coronary artery disease as well as cerebrovascular disease. When you get into the 70 or older population, the risk of having patient with peripheral arterial disease is 5 times that of when you see them in their 40s, and claudication is much more common in smokers and in diabetics because of the issues related before.
When you start examining and talking with patients, you want to identify whether the pain in the lower extremities is at rest or with exercise. This sometimes can be complicated in a patient with diabetes or some other peripheral neuropathy. You want to know whether the pain is reproducible or intermittent. In general, pains that are intermittent are not vasculogenic whereas pains which are reproducible at the proper locations are caused by arterial insufficiency. In regards to claudication certainly, the pain should be in the large muscle group, buttock, thigh, and calf not in the joints. For rest pain, it should be on the top of the foot in the dorsal surface over the metatarsal heads, and certainly, you want to know whether they have a current ulcer or had ulcers in the past.
When you are performing the physical exam, it is important to record pulses at all locations including the femoral, popliteal, and both the posterior, tibial and dorsalis pedis levels. You need to differentiate between exam that is palpable and one that is not palpable but has a Doppler signal. It is not crucial to give specifications regarding the palpable pulse such as 1+, 2+, 3+, 4+, etc, since a number of clinicians use different classifications. I think it is most important to identify whether it is palpable or not. You might characterize it as strong or weak, but other than that those are the numbers that can become confusing. If it is a Doppler signal and not palpable, that needs also to be noted. We generally use a continuous hand-held Doppler and find it the easiest to use and the most accurate. For most purposes, the Doppler signal should be described as monophasic or triphasic. Monophasic indicates either disease proximal to that location or distal to that location. Triphasic is a normal sound that implies maintained inflow to that location and maintained outflow from that location. Also, you want to comment on whether the patient has any ulcerative lesions, eschars, absence or presence of hair, and the presence or absence of rubor. Rubor is a reddish discoloration of the foot mainly that with elevation will go away. This is in differentiation to cellulitis which will not go away with elevation.
With regards to noninvasive vascular tests, the first thing that should be done with every patient is an ankle-brachial index measurement which will be described later, Doppler waves forms which I touched on in the last slide are important when disease is identified, pulse-volume recordings can be helpful in a certain percentage of patients for specific issues, segmental pressure measurements are essentially ABI type measurements done at the different compartments; leg, thigh, calf, etc, treadmill exercise testing is only helpful in patients with the potential diagnosis of intermittent claudication in which there may be some other competing diagnoses.
Non-invasive vascular test generally does not include duplex exam of the arteries themselves. In other words, a standard study is not evaluation of the arteries from the groin down to the foot looking at both the plaque characteristics as well as the waveforms. We generally use waveforms and pressures at different locations to give us the information we need. The duplexes are very specific tests that looks for degrees of stenosis within a specific vessel and tries to visualize a plaque. For the majority of patients this is not required.
The term noninvasive arterial studies or NIAS refers to a group of non-imaging tests that have been described previously. To review, it includes a Doppler waveform of the femoral, popliteal, posterior tibial, and dorsalis pedis arteries, segmental pressures; ankle-brachial index and pulse volume recording.
This is the depiction of an ankle-brachial index which was done in the office with a blood pressure cuff and a hand-held Doppler. The systolic pressures in the left and right arms at the brachial arteries is taken and recorded, then the pressure at both posterior tibial and dorsalis pedis location in each leg is recorded. Then the ankle systolic pressure is placed on top of the brachial pressure for the ratio. For instance, if you have a dorsalis pedis pressure of 120 and an arm pressure of 120, the ABI is 1. The arm pressure is something everyone is familiar with taking. As far as taking the pressure at the posterior tibial and dorsalis pedis level, the easiest way to do this is to identify the dorsalis pedis signal with the hand-held Doppler. Continue the continuous wave Doppler as the pressure cuff is inflated. Once it is inflated to the point where the sound goes away, that is the systolic pressure. This is done at all four locations. By convention, the higher the ABI is, the one that is recorded. For instance, if the ABI at the dorsalis pedis is 1.2, at the posterior tibial it is 0.8, the patientâs ABI is 1.2.
I think it should be the part of any initial office visit unless the patient clearly has no vascular disease, has strongly palpable pulses, and does not have any lesions indicative of concern. As stated, it should be performed at both posterior tibial and dorsalis pedis levels. One important thing is that patients with atherosclerosis often have left subclavian artery stenosis at much higher rate than they do on the right side. In that case, the patient may have a blood pressure of 80 on the left and 140 mm of mercury on the right, in that case I would use the 140 for both of the brachial portions of the ratio. For instance, if on the left arm the blood pressure is 80 and at the foot it is also 80, you would get a falsely elevated ABI in that side of 1 when in fact, it really should be 80/140 which will give you a markedly decreased ABI which would be correct. Also, this will be noted because it would be important to identify that the patient likely has subclavian brachial artery stenosis.
The ABI is incredibly sensitive but it is not specific, in other words it does not identify what location the problem is. It just notes that throughout the leg or frankly throughout the arterial system on that side from the common iliac artery down to the dorsalis pedis artery there is some level of disease. Pre and post exercise values are important in patients who have a normal resting ABI but either symptoms or lesions. In the patient population that I often work with, which is highly a diabetic and patients with end-stage renal disease, they get what is called medial calcific disease where the artery is not necessarily stenosed or blocked, but has calcification of the wall which makes it very difficult to compress. What you will see in those patients is that their arm pressure will be anywhere from 120-180, but when you try to compress their dorsalis pedis artery, you will be getting numbers in the 300-350 mm range. By definition, any value greater than or equal to 250 mm of mercury is non-compressible. The only caveat would be in the very odd patient who would have such a very high blood pressure, say 220-230 mm of mercury in their arm or their foot pressure may in fact be that high. In the cases where the patients have non-compressible vessels, you cannot rely on the ABI and you often get false elevation. In a number of cases, patient have been sent to me who were told they have normal circulation because they had an ABI and in fact when you look at it, their ABI is 1.6, which is higher than normal, which raises eyebrows, and then you look at the actual numbers and it took 300 mm to compress them when in fact their ABI is probably somewhere in the 0.5-0.6 range. Other tests which will be described above are then helpful.
These are the standard interpretations of the ABI. Normal is considered 0.9-1.3, but more data has come out in the recent years and probably anything less than 1.1 is abnormal. ABIs between 0.7 and 0.9 are considered mild disease although you will have a number of patients who will claudicate in the 0.7 range. When you get into 0.4-0.7, that is moderate disease. Patients will claudicate and often have ulcers. Less than 0.4 is severe disease. Patients will have rest pain and ulcers generally. This is certainly a spectrum of disease and these numbers are not as I stated before specific. So, a patient might have an ABI of 0.8 and an ulcer and on the other hand might have an ABI of 0.4 and not have any symptoms and you have to take that into perspective. And as stated before, ABIs generally greater than 1.3 are usually due to non-compressible vessels and should be thrown out as a standard value.
So, you can see here, ABI is incredibly important as it predicts mortality in patients with peripheral arterial disease. As you see in the blue, these are patients with very low ABIs which would often have rest pain and ulcers and you can see their survival over months is very diminished as compared to the patients who have abnormal but higher ABIs on the top curve.
Doppler waveform in the lower extremities should be triphasic at all levels. This indicates normal blood flow in a high resistance bed. On the contrary, if you were looking in the cerebrovascular or carotid circulation, a triphasic waveform would be abnormal since that is a low resistance bed. Monophasic waveforms are never normal in the legs. A triphasic waveform includes a rapid upstroke as systole occurs, then there is a decay and a reversal of flow in the arterial bed. This is basically, if you can envision, elastic muscular arteries recoiling as they are hit with a large blood volume, and then at the end of diastole as the vessel recovers, it returns to its normal configuration and pushes some blood forward and that is forward flow. So, a triphasic waveform would be rapid upstroke forward flow, short reversal flow, and then small additional forward flow where monophasic would only have an upstroke and then decay. Monophasic waveforms are generally described as a whoosh, whereas triphasic waveforms are described as crisp and you can hear actually three sounds.
This is just a review of the last slide. There is a rapid upstroke and decay, reversal flow as the elastic vessel recoil, and then very small forward flow at the end of diastole.
This is a depiction of a waveform in the lower extremity; the femoral level, the superficial femoral popliteal, posterior tibial, and triphasic. This is an elderly person so there is quite a bit of artifact but you can identify the triphasic pattern where there is upstroke and decay, then flow below the baseline, and then some additional forward flow. The triphasic waveform as I stated is normal in high resistance, i.e., lower extremity.
Pulse volume recording is a very important study especially in patients with non-compressible vessels. It is a plethysmograph. It actually measures the change in volume of blood in a leg compartment, not the blood flow itself. Itâs really a very qualitative test; it is not quantitative. In other words, it gives you a general idea of different levels of blood volume within a compartment and not an actual percentage. It is generally good to compare within a patient but not between. In other words, comparing the left leg to the right leg at the metatarsal level is useful but comparing Mr. Jones to Mr. Smith at the metatarsal level is generally not helpful.
It is important to know the pulse volume recording is very temperamental so to speak it can be affected by wrong cuff size, temperature in the room, and the patientâs blood pressure. It is notoriously poor in healthy young patients who have very reactive vessels, i.e., those young women with Reynaud disease if they are evaluated for improper reasons and end up getting a pulse volume recording that might look terrible and precipitate another test.
It is often helpful as a supplemental test when you are trying to decide on whether an ulcer will heal on its own without an angioplasty or bypass, or whether a foot procedure such as a toe amputation or a transmetatarsal amputation would heal.
This is a depiction of a pulse volume recording in a patient with severe tibial artery occlusive disease, right greater than left. If you look at the waveforms at the high thigh, low thigh, and calf level; on the right they are pretty normal, on the left the calf level starts to diminish. Then on the right, there is a decrease at the ankle level bilaterally, worse on the left. Then on the right, there is very limited deflection and essentially flat line at the metatarsal and the digits, so this is a patient who would often have rest pain or ulcers and would not heal an ulcer primarily and would certainly not heal on amputation, if itâs done without revascularization.
Segmental pressures are essentially the blood pressures in a specific leg compartment, thigh, cuff, etc. Using these numbers instead of the ankle-brachial index, you can get a thigh brachial index or a calf brachial index. However, in general, these are just things that you would just eyeball to get a general sense whether the circulation is normal at a location, each location on the leg, and also gives you some clue as to where the disease may be apparent, i.e. is it in the superficial femoral artery or is it more of distal or tibial location. For matters of physics that I will not describe here since frankly I do not understand them that well, pressure increases as you go down the leg and that is why the ankle-brachial index is greater than 1.
Treadmill is important when you are trying to differentiate vasculogenic or arterial causes from other unknown causes. These causes could include neurogenic such as a spinal stenosis. It would be especially important in a patient who had a normal ABI and waveform at rest, but clearly had pain that was developing in the large calf muscles at a certain distance that was reproducible. It is not particularly useful if there is a clear abnormality at rest. If you refer to that prior patient who had very abnormal pulse volume recordings starting at the ankle down, there probably would be no particular use in having him exercise and likely that patient would not be able to exercise. Also, if they have a foot lesion or an abnormal ABI or abnormal waveform, there is no reason to exercise them.
This unfortunately does not show very well from the number standpoint, but as you can see in the lower 2 curves, when the patient exercises the ABI drops significantly from the systolic pressure in the 100 range to lower than 50, and as you follow the curve, it starts to recover towards the 60-70 range but never goes back to a 100. That represents someone who has claudication and severe arterial stenosis that is exacerbated by exercise. Basically what happens, with the stenosis is at rest, it may not cause symptoms because there is enough of a pressure head generated to get the blood down to the foot so to speak. As the patient exercises, first of all there is more demand for blood below the stenosis, and above the stenosis, the collaterals and the large arterials such as in the thigh will dilate and siphon off blood so you both get a decreased pressure head and an increased demand and that leads to a functional hemodynamic problem.
Some general rules: If the patientâs pulse is not palpable unless there is severe foot deformity or incredible amount of swelling, that is not normal except in probably about 3-4% of patients who may not- who may have a congenital absence of a dorsalis pedis or congenital absence of a posterior tibial artery, but if it is not palpable it is not normal. If there is a lesion or an ulcer, this is ischemia until proven otherwise. A number of patients will be sent to me who have been treated for months for so-called neuropathic ulcer just because it is in the proper location when in fact, there is a patient with neuropathy but the reason to have an ulcer because there is no blood supply.
As with any patient, you want to start with the history, then the physical exam, and a documentation of ABI. If the findings are unclear at the initial evaluation or you are planning a certain treatment as described before where you might want to know whether a toe amp will heal, then noninvasive arterial studies can be helpful but they certainly do not need to be done in every patient. The exercise treadmill is really only if the patient is normal at rest and you are trying to differentiate the causes of pain with walking.
In addition, this is my personal opinion, high-tech studies such as TCPo2, nuclear medicine exams, etc are very institution specific and I think only in certain hands are helpful. In most settings, they are more information than you need and probably do not allow you much more benefit than a standard physical exam and some of the noninvasive arterial tests that have already been mentioned.
Some other tests that may be helpful. An MRA which is a magnetic resonance angiogram done with a contrast agent called gadolinium. This is more of an anatomic study where it will identify degrees of stenosis and also at the specific anatomic locations. This is certainly only in patients who you are planning either a bypass surgery or angioplasty type procedure. They are really quite expensive and would not be considered in the standard routine screening panel.
CTA which is a CT scan with IV contrast gives similar results to MRA and is institution specific where which test is of most benefit depends on where you work. Often a conventional contrast angiogram performed through the groin is the standard evaluation before planning a major treatment.
Some conclusions about the non-invasive evaluation: every patient does not need extensive testing. They need a good history and a good physical which includes an ABI.
Non-invasive arterial studies; however, are good to identify baseline for the patient to rule out a significant vascular component. Say in a patient who continues to have pain with walking and no one can find a cause, if you rule out a vasculogenic component then other things can be looked at such as a spinal stenosis, etc. It is also good but sometimes difficult to be a 100% sure whether someone will heal an ulcer or a toe amputation. What it may do in a patient say who cannot undergo a bypass or angioplasty, if the pulse volume recordings are flat line at the metatarsals and the ABI is 0.5, you know that there is no point in doing a transmetatarsal amputation. You just have to be honest with the patient and say at best you will be able to undergo a below-the-knee amputation, and it will save you and the patient a waste of procedure.
In order of importance, these are some of the take home messages from the lecture. ABI should be done as a baseline in most patients unless they clearly do not have any history or physical findings of vascular disease. The Doppler waveform is very important to identify whether it is triphasic or monophasic for the reasons described before. Segmental pressures are also helpful because they can determine whether the occlusion or stenosis is in the thigh or below the knee. And then, pulse volume recordings are supplemental especially in patients who have non-compressible vessels such as diabetics and those with end-stage renal disease where you cannot compress the vessels.
Production of this PRESENT lecture was made possible by a generous grant from Huntleigh Healthcare. When you think Dopplers, think Huntleigh.
|Goals and Objectives|
After participating in this activity, the viewer should be better able to:
1. Recognize the presentation of PVD.
2. Perform a thorough history and vascular examination.
3. Utilize laboratory testing to evaluate PVD.
4. Utilize noninvasive vascular testing.
Estimated time to complete this activity is 50 minutes.
Physicians, diabetes educators, and other health care professionals who treat patients with diabetes.
Complete the 4 steps to earn CE/CME credit:
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