Endovascular Health 101 for the Outpatient Wound Clinic

Appropriate endovascular care can begin in the wound center with proper assessment and testing for vascular comorbidities. This article discusses current guidance, examines emerging trends, and offers a primer on helpful jargon commonly used when communicating with interventionists. 

Not surprisingly, the ever-increasing number of patients who are living with diabetes mirrors the increase in those in the outpatient wound clinic who live with comorbidities that are commonly associated with the disease. Among those conditions is peripheral arterial disease (PAD). Approximately 8.5 million people in the United States live with PAD, including 12-20% of individuals older than age 60, according to the Centers for Disease Control and Prevention. Meanwhile, awareness of PAD among the general population is estimated at 25%.¹ 

The team approach to lower extremity amputation prevention and wound management is recognized as a necessity due to the complex nature of patients afflicted with limb-threatening PAD or critical limb ischemia (CLI) — the more advanced form of PAD for which there are 500-1,000 new cases seen in the U.S. per 1 million people each year.²  Communication within the interdisciplinary team is essential in expediting care for this patient population, yet an even larger challenge is in the early detection of PAD and in the prevention of PAD subsequently deteriorating into CLI, which is associated with an excessively high risk for cardiovascular events (including myocardial infarction) and death.^3-5

The first steps in lower extremity amputation prevention lies in a greater understanding of the disease and how to better assess these high-risk patients throughout the course of their disease management. Simply stated, regular and ongoing assessment is essential in treating any lower extremity wound patient, regardless of the underlying etiology. Knowing how to better assess these patients will certainly improve outcomes in addition to reducing potential pain and suffering. This article will discuss the vascular testing pertaining to arterial disease in an attempt to help providers avoid lower extremity amputations among their wound clinic patients. (Venous disease, while a significant issue, relies on basic ultrasound testing for diagnosis and will not be covered.)  

EPIDEMIOLOGY OF CHRONIC LEG WOUNDS

Chronic leg ulcers (CLUs) affect 0.6–3% of those older than 60 years of age, increasing to more than 5% of those older than 80. CLUs are a common cause of morbidity, and its prevalence in the community ranges from 1.9% to 13.1%.^6,7 It is thought that the incidence of ulceration is rising because of the aging population and the increased risk factors for atherosclerotic occlusion, such as smoking, obesity, and diabetes. In the course of a lifetime, almost 10% of the population will develop a chronic wound, with a wound-related mortality rate of 2.5%.^6,8 Approximately 65,000-75,000 of major amputations (above the knee and below the knee) are performed annually for CLI. Within five years, approximately 70% of CLI patients die, which costs $11 billion (with Medicare and Medicaid paying almost 80% of the bill).⁹ 

AVOIDING THE “AMPUTATION LOTTERY”

Studies have determined that at least 50% of lower extremity amputations are performed in the U.S. as a first-line intervention and without prior vascular testing, meaning the decision to amputate is often based on subjective opinion versus objective findings. A patient’s fate, then, where amputation is being considered, may rest upon whether the provider whose care they are under is cognizant of the importance of lower extremity preservation and willing to see that process through. Hence the term, the “amputation lottery,” a phrase this author has coined to describe the too-quick-to-amputate mentality that too many clinicians follow. The SAGE Group has further validated the economic impact that amputation has on the healthcare system and found that minor amputees experience adverse events at the same rate as major amputees (re-amputation and cardiovascular death).¹⁰ 

To better appreciate the perspective of the interventionists, whether they be vascular surgeons, cardiologists, or radiologists, a review of some basic terminology will help bridge a gap between podiatrists in the wound clinic (and those receiving wound clinic referrals) and their vascular specialists. Interventionists, as with all other specialists, tend to use acronyms and references to anatomy and procedures that may seem confusing. A better understanding of some basics will help in overall vascular assessment and knowing the type of tests to perform (and/or to order). Here are common terms and basics (beyond PAD and CLI) that will assist wound care providers in their efforts:

• CTO (chronic total occlusion): a common heart disorder in many patients living with coronary artery disease (CAD). With CTO, one or more coronary arteries are completely blocked and present for at least three months.
• Inflow disease: also referred to as aortoiliac disease, a form of central artery disease involving the blockage of the abdominal aorta as it transitions into the common iliac arteries.
• Outflow disease: also referred to as infrainguinal disease and involves the femoral, popliteal, and tibial arteries; tends to cause more significant tissue damage than inflow disease.
• Femoropopliteal occlusive disease: involvement of the femoropopliteal arteries in patients living with PAD.
• PTA (percutaneous transluminal angioplasty): a procedure that opens a blocked blood vessel using a small catheter with a balloon at the end of it.
• Atherectomy: restoration of blood flow in an artery with the use of a device designed to shave or sand occluding plaque.
• Stent: a metal device implanted into an artery to regain or maintain patency of the vessel.
• DES (drug-eluting stent): metal stent coated with a pharmacologic agent that is known to suppress restenosis.
• MAC (medial arterial calcification): a condition that leads to the stiffening of the elastic layer of the arterial wall, but in contrast to intimal artery calcification does not obstruct the arterial lumen.
• EVAR (endovascular intervention): treatment that offers a lower risk alternative to open surgery in many patients living with multiple comorbidities.
• Antegrade approach: a routine technique for percutaneous treatment of lower extremity vascular disease.
• Retrograde approach: has recently become an essential complement to the classical antegrade approach.
• Rutherford classification: a commonly used clinical staging system for describing PAD based on stage and severity. 

Several of these highlighted terms and acronyms need no further explanation in the context of this article. However, a further examination of inflow and outflow disease, antegrade and retrograde approaches (to endovascular intervention), and the Rutherford classification are all warranted for a greater understanding of the vascular assessment process. Inflow disease refers to aortoiliac occlusive disease and can also be known as Leriche’s syndrome. It is characterized by diminished pulses bilaterally and slow-to-heal wounds when present. Other symptoms are impotence and gluteal or thigh claudication. Conceptually, inflow disease is found in the thighs and above, with pain in the hip, thigh, and buttock as key indicators. Outflow disease is also known as iliofemoral occlusive disease and is associated with arterial segments found below the superficial femoral artery. Outflow disease is characterized by unilateral leg with diminished pulses. Buttock claudication may be present. Femoropopliteal occlusive disease is characterized by thigh and calf claudication and normal femoral pulses in the groin. Rest pain is an indicator and rest pain upon elevation is indicative of advanced stenosis or occlusion, leading to CLI. Rutherford classification system (or Rutherford-Becker classification system): categorizes the severity of PAD based on clinical presentation and symptoms. The levels of symptoms and severity are:

0 – asymptomatic
I – mild
II – moderate
III – severe
IV – ischemic rest pain
V – minor tissue loss (toe ulcer, focal gangrene)
VI – major tissue loss (above transmetatarsal level)

When EVAR is utilized to restore blood flow to a tenotic or occluded lower extremity artery, access to the diseased vessel is typically achieved with the use of a wire-guided approach, with balloon angioplasty, stents, and atherectomy commonly used to restore flow. The interventionist gains access through the traditional antegrade approach and, when warranted, the retrograde approach. The antegrade approach is an endovascular approach into the leg and foot that originates with access to an artery, typically in the groin. The retrograde approach is an endovascular approach into the foot that originates with access via a pedal artery. The dorsalis pedis and posterior tibial arteries would be the typical vessels with targeted lesions for such procedures. 

ANGIOSOMES

The concept of angiosomes was introduced in 1987.^11,12 Conceptually analogous to neurological dermatomes, angiosomes provide a vascular mapping of the body, showing anatomical regions between the skin and bones that are supplied by specific arteries and veins. Location of an ulcer can help determine the likely location of an arterial stenosis or occlusion when considering the corresponding angiosome. Angiosome-based revascularization is a concept in which the target artery for reperfusion is the one associated with the ischemic angiosome. This direct revascularization approach is associated with higher limb-salvage rates than indirect revascularization, in which a non-angiosome vessel is the target.^11,13 Whether used in conjunction with attempts at revascularization or not, angiosomes may provide an initial screening modality in arterial (and ulcer) assessment.

COMMON ARTERIAL TESTING METHODS

Before examining specific lower extremity testing methods, it is worth reviewing guidelines published by the Wound Healing Society (WHS) for assessing vascular status in the diabetic foot:¹⁴

• Clinically significant arterial disease should be ruled out (Level I).
• Examination of the patient as a whole is important to evaluate and correct causes of tissue damage. This includes factors such as systemic diseases and medications, nutrition, and tissue perfusion and oxygenation (Level I). 
• Risk status: age; sex; ethnicity; tobacco use; diabetes; previous coronary, stroke or leg event; body mass index; and hypertension.
• Clinical foot exam: condition of distal hair growth, skin texture, and color, as well as changes in skin color with elevation and dependence, temperature of skin, and femoral/popliteal/pedal pulses.
• Noninvasive vascular testing exams: ankle-brachial index (ABI), pulse-volume recording (PVR), skin perfusion pressure (SPP), transcutaneous oximetry (TCOM).

The clinical guidelines recommended by the WHS and several of the modalities endorsed by the organization are presented. Most of these modalities have been readily available and in use for a significant time. That said, simple palpation of pulses may not be utilized in a typical clinical setting. Baseline vascular assessment should be performed during any new wound patient evaluation, and repeat testing should be ongoing in the high-risk patient where PAD or CLI is present. Pre- and post-revascularization assessment should also be administered during any wound care patient encounter, with more extensive testing, such as arterial doppler and waveform, being performed every 3-4 months post-revascularization. The following is assessment guidance parameters: 

Palpation and general assessment: The presence of dusky digits, dependent rubor, or a suspicious-appearing ulcer or eschar on a digit does not require a special skillset beyond observation to raise concerns for worrisome PAD. The following statement by Lee C. Rogers, DPM, cannot be emphasized enough: “Absent pulses can be an indicator of no flow, but palpable pulses are never an indicator of sufficient flow.”  

ABI: The ABI is a widely endorsed noninvasive test that is easy to perform in an office setting. However, there are inherent problems. To review, the ABI compares pressures in the brachial arteries to lower extremity pressures in the posterior tibial and dorsalis pedis arteries.  The ratio between these pressures is the ABI. Where the ABI loses its usefulness is when noncompressible vessels falsely elevate pressure readings. (Noncompressible refers to the presence of calcified or blocked vessels.) This phenomenon is seen in many patients living with PAD and diabetes. Also, variations in the administration of ABI testing make the results less reliable than other available tests.  

Duplex arterial ultrasound: A noninvasive test that allows for visualization and quantification of a lesion. It is user-dependent, and calcification may limit the quality of the image.

PVR: Utilizes cuffs at multiple levels, including toes, transmetatarsal, calf, and thigh, to assess quality of blood flow through arteries. The test utilizes air volume plethysmography to evaluate changes in arterial blood volume during each cardiac cycle. The PVR reveals the level as well as the absence, presence, and severity of arterial disease (and is a qualitative assessment). The test is performed on both legs for comparison as well as for future reference and comparison.

TCOM and SPP: A previously published article in Today’s Wound Clinic by Caroline Fife, MD, FAAFP, CWS, provides an excellent, in-depth overview and comparison of both TCOM and SPP technologies, concluding they are complementary in their obtaining objective information regarding tissue perfusion. In short, TCOM measures oxygen molecules present in tissue (TcPO₂) while SPP is a pressure measurement or measure of reactive hyperemia. Both modalities are recognized as having relative ease of use and are often found in wound clinics. They both hold value in assisting in the prediction of potential success of an amputation and optimal level, and for pre- and post-revascularization efficacy.¹⁵

Magnetic resonance angiography (MRA), computed tomographic angiography (CTA), and digital subtraction angiography (DSA): When advanced PAD is suspected or already confirmed by clinical presentation (for example, a Rutherford III-VI), additional vascular assessment is required to determine, with greater specificity, the location(s) of arterial stenosis or occlusion. MRA, CTA, and DSA are three such methods typically utilized. Each has pros and cons: DSA is considered the “gold standard” of arterial imaging. It has high resolution and is typically used to guide intervention. The greatest drawbacks are that ionizing radiation and iodinated contrast dye are used. It produces two-dim0ensional images. CTA is noninvasive and provides three-dimensional imaging. Ionizing radiation and iodinated contrast material are used. Imaging is limited in the presence of densely calcified vessels. MRA is noninvasive and does not use radiation or contrast dye. It produces three-dimensional images.  Drawbacks include lower spatial resolution than that of CTA. Prior stent placement may cause image artifact.

CHANGING LANDSCAPE & WHAT’S ON THE HORIZON

Fluorescence angiography: One of the recent technological advancements in lower extremity vascular assessment has been the use of fluorescence angiography to assess tissue perfusion. Fluorescence angiography uses indocyanine green, a water-soluble injectable dye that is roughly 98% protein bound after intravenous injection. The benefit of this technology is the quality and specificity of the images produced in determining tissue perfusion. Applications in diabetic foot ulcers (DFUs) have enabled surgeons to determine, with greater accuracy, the comparative success of pre- and post-revascularization procedures. When amputation is indicated, fluorescence angiography can provide a greater predictability of the outcome based on uptake of indocyanine green by viable tissue. NOVADAQ Technologies Inc. (Toronto, Ontario) has been the developer and distributor of this technology, with applications extending into areas beyond cardiovascular disease and wound care. Cardiac and colorectal surgery, breast reconstruction, and laparoscopic cholecystectomy are among the specialties where this technology has been successfully utilized.

Spatial frequency domain imaging: The reflection of light off an object or material can provide information about that material. Modulated Imaging (Irvine, CA) has taken the concept known as spatial frequency domain imaging and developed several products whose applications will allow practitioners to determine oxygen levels in tissue and other indictors of tissue health. This concept enables the measurement of the amount of oxyhemoglobin (HbO₂) and deoxyhemoglobin (HbR), and reports an accurate measure of mixed arterial/venous oxygenation in the tissue below the epidermis. With this modality comes the ability to determine the true health status of tissue. At present, the focus of the company’s efforts is a device (Ox-Imager CS^®) that provides noninvasive diagnostics to assess tissue viability. The device also measures important indicators of tissue health, specifically tissue blood oxygen saturation, HbO₂, and HbR, as well as providing a surface-color photograph. The device is indicated for use to determine oxygenation levels in superficial tissues for patients with potential circulatory compromise and is designed with future growth in mind. Its flexible architecture allows for onsite software upgrades and rapid factory component changes, as new indications for use are approved. Future products will reportedly be compatible with Windows, iOS and Android hardware, with models designed to be suitable for all point-of-care environments, from hospitals and wound clinics to home healthcare. n

Desmond Bell is founder and president of the Save A Leg, Save A Life Foundation. He is dedicated to lower extremity preservation and has a private practice in Jacksonville, FL, where he specializes in wound management. 

References 

1. Roger VL, Go AS, Lloyd-Jones DM, et al. Heart disease and stroke statistics - 2011 update: a report from the american heart association. Circulation. 2011;123(4):e18-e209.

2. Norgren L, Hiatt WR, Dormandy JA, Nehler MR, Harris KA, Fowkes FGR. Inter-society consensus for the management of peripheral arterial disease (TASC II). J Vasc Surg. 2007;45(1 Suppl):S5-S67.

3. Murabito JM, Evans JC, Nieto K, Larson MG, Levy D, Wilson PW. Prevalence and clinical correlates of peripheral arterial disease in the framingham offspring study. Am Heart J. 2002;143(6):961–5.

4. Criqui MH, Langer RD, Fronek A, et al. Mortality over a period of 10 years in patients with peripheral arterial disease. N Engl J Med. 1992;326(6):381-6.

5. McKenna M, Wolfson S, Kuller L. The ratio of ankle and arm arterial pressure as an independent predictor of mortality. Atherosclerosis. 1991;87(2-3):119-28.

6. Vinayak Agale S. Chronic leg ulcers: epidemiology, aetiopathogenesis, and management. Ulcers. 2013;1-9.

7. Rayner R, Carville K, Keaton J, Prentice J, Santamaria XN. Leg ulcers: atypical presentations and associated comorbidities. Wound Pract Res. 2009;17(4):168-85.

8. Chatterjee SS. Venous ulcers of the lower limb: where do we stand? Indian J of Plastic Surg. 2012;45(2):266-74.

9. Allie, DE. New advances in critical limb ischemia. the staggering clinical and economic cost of CLI. Presented at New Cardiovascular Horizons CLI Summit, Miami, 2006. 

10. The sage group estimates the economic cost of critical limb ischemia amputations at $25 billion. 2014. Accessed online: https://www.vasculardiseasemanagement.com/content/sage-group-estimates-economic-cost-critical-limb-ischemia-amputations-25-billion  

11. Bell D. Can angiosome-based revascularization have an impact in limb salvage? Podiatry Today. 2012;25(3). Accessed online: www.podiatrytoday.com/can-angiosome-based-revascularization-have-impact-limb-salvage

12. Taylor GI, Palmer JH. The vascular territories (angiosomes) of the body: experimental study and clinical applications. Br J Plast Surg. 1987;40(2):113-41. 

13. Singh K. New treatment paradigm: the angiosome concept. Podiatry Today. 2012;25(Suppl 2):4-7.

14. Lavery LA, Davis KE, Berriman SJ, et al. WHS guidelines update: diabetic foot ulcer treatment guidelines.  Wound Repair Regen. 2016;24(1):112-26.  

15. Fife C. Non-invasive vascular testing and the wound care clinic. TWC. 2010;4(8):30-6.