Abstract:
Peripheral arterial disease (PAD) encompasses a spectrum of systemic diseases including atherosclerosis, aneurysms, and vasculitis. The term peripheral arterial disease is most often used to describe the result of atherosclerosis in the arteries of the lower extremity, upper extremity, renal, mesenteric, and carotid arterial beds. Patients with PAD are at significant risk of cardiovascular morbidity and mortality, primarily as a result of stroke (from cerebrovascular atherosclerosis) and myocardial infarction (from coronary atherosclerosis). The cornerstone of PAD management includes guideline-directed medical therapy (GDMT) to reduce systemic atherosclerotic risk: smoking cessation and control of hypertension, dyslipidemia, and diabetes. Other implications of PAD and nuanced treatment strategies are predicated by the end-organ perfused. This chapter highlights the evaluation and management of patients with PAD in the lower extremities, renal, subclavian and brachiocephalic, carotid, and vertebral arteries.
Keywords:
peripheral arterial disease, endovascular, peripheral intervention, vascular disease, claudication, critical limb ischemia
Peripheral arterial disease (PAD) encompasses a wide spectrum of systemic diseases including atherosclerosis, aneurysms, and vasculitis. The term peripheral arterial disease is most often used to describe the result of atherosclerosis in the arteries of the lower extremity, upper extremity, renal, mesenteric, and carotid arterial beds. Patients with PAD are at significant risk of cardiovascular morbidity and mortality, primarily as a result of stroke (from cerebrovascular atherosclerosis) and myocardial infarction (from coronary atherosclerosis). Therefore, the cornerstone of PAD management is the focus on system atherosclerotic risk reduction, including smoking cessation, and control of hypertension (HTN), dyslipidemia, and diabetes. The prevalence of PAD increases with age. Of US individuals aged 40 to 59 years, 3% will develop PAD; in those aged 60 to 69 years, 8% will be affected; and in those above the age of 70 years, 19% will develop PAD.
Similar to angina in the coronary vessel, claudication—the symptom associated with PAD in the lower extremities—is related to the mismatch of blood supply relative to demand because of arterial stenosis or occlusion ( Table 5.1 ). Present in 10% to 30% of patients with PAD, classic intermittent claudication is described as exertion-induced calf, thigh, or leg pain that abates with rest. Some patients (10%–30%) with PAD have atypical symptoms of claudication, perhaps due to altered sensation or neuropathy from diabetes, including leg weakness, a sense that the legs may give out, fatigue, numbness, or paresthesia. Patients with PAD may have significant impairment in quality of life, and functional decline has been shown to occur even in the absence of classic claudication symptoms.
| Clinical Presentation of Peripheral Artery Disease | |
|---|---|
| Asymptomatic | No obvious symptomatic complaint (but usually presents with a functional impairment) |
| Classic claudication | Lower-extremity symptoms are confined to the muscles with a consistent (reproducible) onset with exercise and relief with rest |
| Atypical leg pain | Lower-extremity discomfort that is exertional but does not consistently resolve with rest, consistently limited exercise at a reproducible distance, nor meets all Rose questionnaire criteria |
| Critical limb ischemia | Ischemic rest pain, nonhealing wound, or gangrene |
| Acute limb ischemia | The “six Ps,” defined by the clinical symptoms and signs that suggest potential limb jeopardy: pain, pulselessness, pallor, paresthesias, paralysis, and poikilothermia |
Of note, only 1% to 4% of patients with PAD progress to the point of critical impairment of perfusion of the lower extremity resulting in rest pain, ulceration, or tissue loss. This condition of profound hypoperfusion of the lower extremity is termed critical limb ischemia (CLI). Individuals who manifest signs of CLI are at significant risk of the need of amputation unless revascularization is performed and pulsatile blood flow is restored to the foot. Patients with CLI may describe a pain, ache, or numbness in the leg at rest, worsened with elevation of the leg, and relieved with dependent positioning, such as dangling the leg off the edge of the bed. CLI patients have poor outcomes, with an estimated 25% risk of one-year mortality, predominantly because of major adverse cardiovascular and cerebrovascular events. The three risk factors that most dramatically increase the risk of CLI are tobacco use, diabetes, and advancing age.
Patients undergoing evaluation for known or suspected cardiovascular disease should also undergo a complete review of systems to assess for all forms of PAD including the following:
- •
Impaired ambulation as a result of cramping, fatigue, aching, numbness, or pain; it is helpful to note the patient’s primary site(s) of discomfort, typically in the buttock, thigh, calf, or foot, along with the relationship of such discomfort to rest or exertion.
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Poorly healing or nonhealing wounds of the legs or feet
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Pain at rest, localized to the lower leg or foot, associated with upright or recumbent positions
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Abdominal pain provoked by eating and associated with weight loss
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Family history of a first-degree relative with an abdominal aortic aneurysm (AAA)
Physical examination for PAD may disclose the following (see Box 5.1 ):
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Diminished or absent pulses (all should be assessed with Doppler if needed)
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Bruits (carotid, supraclavicular, abdominal, and femoral)
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Muscle atrophy
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Dependent rubor and elevation pallor of the feet
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Signs of CLI: hair loss, smooth/shiny skin, dystrophic nails, coolness, pallor, or cyanosis of the foot
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Pulsatile abdominal and/or popliteal masses (aneurysms)
Limb examination includes the following:
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Absent or diminished femoral or pedal pulses (especially after exercising the limb)
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Arterial bruits
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Hair loss
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Poor nail growth (brittle nails)
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Dry, scaly, atrophic skin
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Dependent rubor
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Pallor with leg elevation after 1 minute at 60 degrees (normal color should return in 10 to 15 seconds; longer than 40 seconds indicates severe ischemia)
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Ischemic tissue ulceration (punched-out, painful, with little bleeding), gangrene
It is important to differentiate between other processes with similar symptoms, such as degenerative disc disease or spinal stenosis (pseudoclaudication). In some instances, patients may describe pain that persists while standing still or that is relieved while continuing to walk or leaning forward. These symptoms are less characteristic of PAD and indicative of pseudoclaudication. Diabetic neuropathy, deconditioning, and muscular strain may be difficult to distinguish from PAD. The two most common classification schemes for PAD are Rutherford and Fontaine classifications ( Tables 5.2 and 5.3 ).
| Grade | Category | Clinical Symptoms |
|---|---|---|
| 0 | 0 | Asymptomatic |
| I | 1 | Mild claudication |
| 2 | Moderate claudication | |
| 3 | Severe claudication | |
| II | 4 | Ischemic rest pain |
| 5 | Minor tissue loss | |
| III | 6 | Major tissue loss |
| Stage | Clinical Symptoms |
|---|---|
| I | Asymptomatic |
| IIa | Mild claudication |
| IIb | Moderate to severe claudication |
| III | Rest pain |
| IV | Ulcer or gangrene |
Noninvasive diagnostic testing
With a class I indication in the Peripheral Artery Disease guidelines, the most useful and cost-effective test to diagnose PAD is the ankle-brachial index (ABI). The study is performed by applying a blood pressure (BP) cuff to the calf, then measuring BP at the ankle using a continuous-wave Doppler probe. Ankle pressures at the dorsalis pedis and posterior tibial artery (PTA) pressures are recorded. The process is then repeated with the cuff on the biceps and the Doppler on the brachial artery, quantifying the brachial pressure. The ABI is then calculated by dividing the higher ankle pressure by the higher of the two brachial pressures. A normal ABI is between 0.9 and 1.4. An ABI after exercise is very useful for those patients who have classic symptoms of claudication and/or decreased common femoral pulses and a normal ABI at rest. Resting ABI may be insensitive for detecting mild aortoiliac disease and is not designed to define the degree of functional limitation. In some patients (e.g., those with end-stage renal disease [ESRD] or diabetes mellitus [DM]) with secondary medial calcification, infrapopliteal vessels may become noncompressible. The noncompressible nature may limit the accuracy of the ABI and may lead to the elevated ankle pressure and corresponds to an ABI >1.4. In these cases, a toe-brachial index (TBI) may be considered. The magnitude of ABI reduction has been linked to overall mortality in a U-shaped distribution, with increasing mortality associated with ABIs <1.0 and >1.4. An abnormal ABI in patients with established coronary artery disease (CAD) and DM is associated with an incremental risk of adverse cardiovascular outcomes.
Another useful noninvasive vascular assessment is the segmental limb pressure (SLP) evaluation, measuring blood pressure at the thigh, calf, ankle, transmetatarsal, and digits. Identifying the location in the leg where BP abruptly diminishes relative to the brachial pressure determines the corresponding level of arterial obstruction. Additionally, an arterial pressure gradient of >20 mm Hg implies significant obstructive disease. Analogous and often obtained simultaneously, pulse volume recordings (PVRs) may also aid in the determination of arterial stenosis severity and location. SLPs record a pressure and PVRs record a noninvasive arterial waveform at the same anatomic levels. Analyzing the amplitude and morphology of the arterial waveform provides insight into the presence and severity of obstruction.
Limb morbidity and patient mortality
The natural history of PAD with respect to limb morbidity and patient morbidity/mortality varies among patients with and without claudication. Most patients with claudication (∼70%) will have constant stable symptoms for the next 5 years; approximately 10% to 30% will report progressive worsening of symptoms; and few (2% to 4%) will progress to CLI. In contrast, morbidity/mortality is much greater. In individuals with PAD who develops claudication after the age of 55 years, there is a 5-year mortality of 25% to 30%, with the majority (75%) of these deaths attributed to cardiovascular causes. Another 20% of these patients will suffer a nonfatal cardiovascular event. In contrast, in CLI patients there is a primary amputation rate of between 10% to 40%, mortality of 20% at 1 year, 40% to 70% at 5 years, and 80% to 95% at 10 years, mainly from cardiovascular causes.
Noninvasive imaging for anatomic assessment
There are four methods that are commonly used to delineate arterial anatomy, each of which has advantages and disadvantages. These include (1) duplex ultrasound, (2) computed tomography angiography (CTA), (3) magnetic resonance angiography (MRA), and (4) invasive angiography and digital subtraction angiography (DSA).
Duplex ultrasound is useful to diagnose the anatomic location and degree of stenosis. Duplex is frequently used to evaluate infrainguinal vessels and can provide a detailed image of stenosis including the anatomic location within the leg. Renal, iliac, and infrapopliteal vessels can also be imaged using duplex ultrasound, but this is often time-consuming, technique-dependent, and may not be feasible in some patients because of obese habitus or bowel gas obscuring vascular structures in the abdomen and pelvis. Duplex ultrasound is recommended for routine surveillance after femoral-popliteal or femoral-tibial/pedal bypass.
CTA of the extremities may be used to diagnose anatomic location and presence of significant stenosis in patients with lower-extremity, renal, upper-extremity, and carotid stenosis. CTA may be considered as a substitute for MRA for those patients with contraindications to MRA (claustrophobia or presence of pacemaker/implantable cardioverter defibrillator). CTA is noninvasive but confers some risk of contrast-induced nephropathy and poses a small risk of radiation exposure to the patient. CTA imaging of the infrapopliteal vasculature may have limited resolution, and heavy calcification of the vessels may obscure luminal stenosis, making accurate interpretation challenging.
MRA may provide detailed anatomic location and degree of arterial stenosis without the use of radiation or iodinated contrast. MRA most commonly requires the intravenous administration of gadolinium as a contrast agent, which is contraindicated in patients with an estimated glomerular filtration rate (eGFR) <60 ml/min, because of the associate risk of nephrogenic systemic fibrosis (NSF) and nephrogenic fibrosing dermopathy. Alternative, newer imaging agents, including ferumoxytol (Feraheme), may be considered in patients with chronic kidney disease (CKD). MRA may sometimes overestimate the severity of arterial stenosis.
Invasive vascular angiography has long been considered the gold standard for anatomic imaging. Angiography inherently provides a two-dimensional (2D) image of a three-dimensional (3D) structure. In some instances, eccentric lesions may require multiple angiographic views to determine stenosis severity. Like CTA, invasive angiography requires the use of iodinated contrast, and therefore confers a risk of contrast-induced nephropathy (CIN), particularly in individuals with CKD. To reduce the contrast load and risk of CIN, a 50/50 mixture of contrast and saline may be used for most peripheral angiography. If the use of iodinated contrast is not clinically feasible, gadolinium or CO 2 angiography may also be considered. When angiography identifies an arterial stenosis of indeterminate severity, assessing a pressure gradient has been considered as a potential surrogate for the physiologic significance of a lesion. Some operators may use a narrow caliber (i.e., 4 F) end-hole catheter to measure a translesional pressure gradient; others may prefer the use of a 0.014-inch pressure wire. Assessment of the translesional pressure gradient at rest or following the induction of hyperemia with the administration of peripheral vasodilating medications may also elucidate the hemodynamic impact—and potentially the clinical relevance—of an arterial stenosis. Intravascular ultrasound (IVUS) or optical coherence tomographic imaging may provide additional, detailed anatomic data that may help define the extent and severity of arterial disease and morphologic characteristics such as the presence of thrombus or calcium.
DSA may provide better resolution of vascular structures than conventional angiography by eliminating adjacent nonvascular elements from the image acquired. Since the peripheral arteries are relatively static structures, DSA is technically feasible in this distribution, although the patient may need to stop breathing during image acquisition of vascular structures in the thorax and in the abdomen/pelvis to reduce the impact of motion artifact.
Endovascular revascularization
Overview
Arterial revascularization, whether performed with surgical or endovascular techniques, is reserved for patients who experience lifestyle-limiting symptoms of claudication, rest pain, or tissue loss. Individuals who present with claudication should embark on a supervised exercise program and should receive guideline-directed medical therapy, with consideration of pharmacotherapy for claudication (cilostazol) before being considered for arterial revascularization. In individuals who present with symptoms caused by aortoiliac disease, endovascular revascularization may be considered a first-line therapeutic option. Current guidelines recommend endovascular procedures for individuals with a vocational or lifestyle-limiting disability as a result of intermittent claudication, when clinical features suggest a reasonable likelihood of symptomatic improvement with endovascular intervention and (1) there has been an inadequate response to exercise or pharmacological therapy and/or (2) there is a very favorable risk-benefit ratio (e.g., focal aortoiliac occlusive disease). Revascularization, however, is not a substitute for guideline-directed medical therapy, which reduces cardiovascular morbidity and mortality. Moreover, outcomes from two recent randomized clinical trials indicate that the combination of endovascular therapy (EVT) plus supervised exercise therapy (SET) may provide the best functional outcomes for individuals with lifestyle-limiting claudication.
In individuals who present with CLI, the potential benefit for revascularization is most pronounced. In patients with ankle pressures <40 mm Hg and toe pressures <30 mm Hg, ulcerations will not heal without revascularization: the metabolic requirements for wound healing and for the prevention of infection are much higher than the basal state required to maintain intact skin integrity without ulceration. Without revascularization, loss of skin integrity increases risk of infection, gangrene, and tissue loss.
There is a prevailing practice that emphasizes restoration of blood flow to the angiosome (the infrapopliteal vessel that directly perfuses the affected region of the foot) as a more effective strategy than restoring blood flow indirectly through a different vessel. In some instances, it is not possible to provide direct in-line flow; supplying collateral flow from the peroneal artery or via the metatarsal arch may still be effective, but meticulous observation is critical for wound-healing success.
For patients with CLI, revascularization is an essential element for limb salvage. The choice of whether to pursue an endovascular or surgical approach depends on patient- and institution-specific features. In addition, the revascularization approach may depend on the technique that will provide the most robust straight-line flow, incurring the lowest risk for the patient. Patient comorbidities, anatomic features, presence of surgical targets and venous conduit, physician preference, and overall candidacy for safe performance and recovery from surgery must all be considered in this decision. Endovascular options are minimally invasive and, when compared with surgery, confer a lower risk of perioperative stress and adverse cardiovascular events. Endovascular therapy has historically been plagued by high restenosis rates. Restenosis may have limited clinical impact, however, if the vessel stays open long enough to promote wound healing. In the Bypass versus Angioplasty in Severe Ischemia of the Leg (BASIL) trial, there was no difference in amputation-free survival for up to 3 years among patients treated with an endovascular-first (as compared with a surgical-first) strategy at 3 years. Although surgical bypass has been long held as the gold standard treatment for patients with CLI, endovascular approaches may emerge dominant in the coming decade. Currently, the choice of revascularization approach remains patient and institution specific.
Endovascular therapy offers several distinct advantages over surgical revascularization, including (1) reduced morbidity and mortality (same-day or short-stay procedure), (2) ease of repeat procedure if needed, (3) future surgery not precluded in optimal outcomes, (4) general anesthesia unnecessary, and (5) decreased infection rates. A small arteriotomy, compared with the large wound from an open surgical approach, confers a lower risk of infection and typically permits return to normal activity within 24 to 48 hours after an uncomplicated procedure. This has led to widespread adoption of an endovascular-first approach, depending on the anatomical substrate and patient.
Endovascular therapy, however, is associated with risk for vascular injury (vascular dissection, perforation, abrupt closure, or thrombosis), bleeding (access, retroperitoneal, and potentially gastrointestinal from dual antiplatelet therapy), and exposure to radiation and nephrotoxic contrast. In addition, depending on the vascular bed, endovascular therapy has a high rate of restenosis and need for repeat revascularization. The Trans-Atlantic Inter-Society Consensus (TASC II) document provides anatomic and lesion guidance on which revascularization strategy may be most efficacious for a particular lesion. In general, TASC A and B lesions are felt to be amenable to endovascular therapy, whereas more complex lesions such as long occlusions (TASC C and D) might be better served with surgical revascularization. This document, however, was generated before the advent of technologies that, in experienced hands, permit successful crossing and treatment of even the most complex lesions using advanced endovascular techniques and is generally considered outdated. Each vascular bed ( Fig. 5.1 ) and the corresponding angiographic techniques and data for revascularization, are reviewed in detail in the following sections.
Appropriate use criteria (AUC)
In 2014, The Society for Cardiovascular Angiography and Interventions (SCAI) developed the first expert consensus document establishing appropriate use of peripheral vascular intervention for the renal, iliac, femoropopliteal, and infrapopliteal arterial beds. This document was updated in 2017 and provides operators guidance for when and how to revascularize lesions in these territories. As has become customary when considering coronary intervention in the era of AUC documents, operators considering peripheral intervention should be familiar with the appropriate indications for revascularization and should document the rationale for considering intervention in detail.
Iliac interventions
As noted, the TASC classification was generated for aortoiliac lesions ( Fig. 5.2 ), with general recommendations for an endovascular approach for TASC A and B lesions and a surgical approach for the more complex TASC C and D lesions. This classification system provides a simple schema to categorize lesion complexity. The evolution of endovascular technology and outcome data, however, has rendered the guidelines less relevant to contemporary clinical practice. In fact, recent expert consensus documents from the SCAI advocates for an endovascular-first approach to most aortoiliac lesions, with surgery recommended for endovascular failures. Current American College of Cardiology/American Heart Association (ACC/AHA) guidelines recommend endovascular revascularization of aortoiliac disease when a favorable risk-benefit ratio is present, depending on patient- and lesion-specific determinants.
In contemporary practice, most iliac occlusions and complex lesions can be treated with endovascular technique with high procedural success rates and excellent long-term patency. Two recent meta-analyses confirmed that technical success rates for aortoiliac intervention exceed 90%, and confer 4- to 5-year primary patency rates of 60% to 86%, secondary patency rates of 80% to 98%, and limb salvage rates of 98%.
Aortoiliac lesions are generally treated with stent insertion, since stenting may minimize vessel recoil and prevent abrupt occlusion. However, a provisional stenting strategy may also be used in simple lesions. This approach has been shown to be safe and cost-effective over a 5-year period. The current ACC/AHA guideline supports primary stenting over provisional stenting of the common and external iliac arteries with a class-I recommendation (level of evidence B) and should likely be considered at the preferred approach in complex iliac lesions.
Technical details
When considering revascularization for lower extremity PAD, using preprocedural noninvasive imaging may aid planning a favorable access and treatment strategy for these lesions. The preferred site for arterial access depends on several factors, including (1) location of the target lesion(s), (2) presence/absence of any lesions in the contralateral iliac artery, (3) need to treat infrainguinal vessels, (4) presence of common femoral artery (CFA) disease, (5) angulation of the aortoiliac bifurcation, (6) severity of target lesion (occluded or not), and (7) availability of radial or brachial artery access. When treating unilateral disease within the proximal iliac system (e.g., the common iliac artery), ipsilateral access is preferable to permit direct delivery of equipment. A contralateral approach is possible but will often be met with challenges of establishing adequate coaxial support to deliver a balloon/stent to a lesion that is proximal in the common iliac artery.
In contrast, if the target lesion is in the distal common or external iliac artery, contralateral access may be preferred, particularly in situations where external iliac disease extends distally to the common femoral region, compromising ipsilateral sheath placement. If entire reconstruction of the aortoiliac bifurcation is required, bilateral femoral access permits simultaneous bilateral iliac stent placement and kissing balloon postdilatation. More than one access site (a second site could be femoral or brachial/ radial) may be required to approach chronic total occlusions (CTOs) ( Fig. 5.3 ) in order to facilitate both antegrade and retrograde crossing and for better visualization of the extent of occlusion. Initial arterial access via the radial or brachial artery is also an attractive option, but lesion location and equipment length should be taken into account during treatment planning.
Angiographic technique
Initial DSA angiography (with a breath hold) of the iliac arteries should be performed in the contralateral oblique, using either a pigtail or omniflush catheter with or without power injection ( Table 5.4 ). Contralateral oblique imaging opens up the common iliac and bifurcation into the external and internal iliac arteries. In the setting of iliac occlusions, the pigtail should be proximal enough in the aorta (i.e., near the level of L4 to L5) to opacify all of the lumbar vessels that typically provide collaterals through various branches. The imaging should be engaged long enough to permit the outflow from collateral vessel and determine whether the occlusion involves the CFA and/or lateral circumflex iliac vessel. If the CFA is not involved and the lateral circumflex iliac or another side branch is patent, ipsilateral access can often be obtained under roadmap function with use of these side branches for wiring to provide enough support to place a sheath. This then permits a retrograde approach that affords greater support for advancement of interventional equipment.
| Artery or Vascular Territory | Angiographic View (Degrees) |
|---|---|
| Aortic arch | 30 to 60 LAO (with slight cranial angulation) |
| Brachiocephalic vessels (origin) | 30 to 60 LAO |
| Subclavian | AP, ipsilateral oblique with caudal angulation |
| Vertebral origin | AP, ipsilateral oblique with cranial angulation |
| Carotid extracranial | Lateral, AP, ipsilateral, 45 oblique |
| Renal arteries (origin) | AP, 5 to 25 LAO |
| Mesenteric arteries (origin) | Lateral or steep RAO |
| Iliac artery | Contralateral, 20 to 45 oblique |
| CFA, SFA, and PFA arteries | Ipsilateral, 30 to 60 oblique |
| Femoropopliteal | AP, ipsilateral, 20 to 30 oblique |
| Infrapopliteal trifurcation and runoff | AP |
Stent types
Two types of stents are available for endovascular interventions. Balloon-expandable (BE) stents offer greater precision of placement and superior radial strength; they are therefore better suited for calcified vessels but may be less desirable in segments that involve excessive tortuosity. They are often used to treat common iliac lesions and with aortoiliac kissing stents. Self-expanding (SE) stents, characterized by their flexibility and ability to conform to varying vessel diameters, are the optimal choice for vessel size mismatch across the lesion. These stents have less radial strength compared with BE stents, but in vascular segments inherently prone to flexion or extrinsic compression or in tortuous vessels, the superior flexibility of SE stents may outweigh the compromise in terms of radial strength. Recent data comparing these two stent types in the aortoiliac arterial bed suggest that SE stents may have an enhanced patency rate over BE. There has been debate on whether stent architecture or composition (i.e., nitinol vs. stainless steel) has any effect on restenosis rates. However, the CT Perfusion to Predict Reponse to Recanalization in Ischemic Stroke Project (CRISP) trial failed to show any differences in clinical outcomes 1 year between nitinol (S.M.A.R.T. Nitinol Stent System; Cordis Corporation, Miami Lakes, FL) and stainless steel (Wallstent, Boston Scientific Corp., Watertown, MA) iliac artery SE stents.
Polytetrafluoroethylene (PTFE)-covered stents are also available in BE and SE formats. Whereas covered stents were previously reserved for the treatment of iliac aneurysms, arteriovenous (AV) fistulae, and iatrogenic perforations, recent studies suggest that covered stents may be used for primary treatment of stenotic lesions as well. The comparison of covered versus bare expandable stents (Covered versus Balloon Expandable Stent Trial [COBEST]) for the treatment of aortoiliac occlusive disease trial demonstrated a significantly lower restenosis rate with the use of the covered stent when compared with bare-metal stents. In a subgroup analysis of these data, the outcomes from treatment of TASC C and D lesions with covered stents were superior to those treated with bare-metal stents, although in part this finding might be attributed to operator confidence in providing higher-pressure balloon postdilatation following covered-stent placement, resulting in greater luminal gain. One disadvantage of expanded PTFE (ePTFE)-covered stents, however, is the slightly reduced deliverability because of the scaffold stiffness and the need for larger sheaths, although this has recently changed with 6-F compatible covered stents. PTFE-covered stents may also occlude any spanned side braches, including major vessels, such as the internal iliac artery and/or major collaterals, potentially obliterating collateral flow in the event of stent occlusion.
Anticoagulation
Unfractionated heparin (UFH) is most commonly used for intraprocedural anticoagulation during aortoiliac intervention and offers the benefit of acute reversibility (using protamine sulfate) in the event of serious adverse bleeding events, such as iliac perforation. Direct thrombin inhibitors, such as bivalirudin, have been used for peripheral intervention but are more costly, are irreversible, and have not achieved widespread adoption.
Procedural techniques
After selection of the vascular access site and placement of a sheath (4 to 8 F or larger), wiring techniques are similar to other interventional procedures. It is imperative that operators be familiar with equipment compatibility among stents, balloons, crossing catheters, and covered stents, because they may use 0.035-, 0.018-, and 0.014-inch systems. For the greatest degree of support and trackability, especially if vessel tortuosity or calcification is encountered, 0.035-inch wires may provide the best option. Small profile systems, compatible with 4-F to 6-F sheaths, are available for balloon and stent treatment of most aortoiliac lesions, if desired. In clinical situations where the potential for vessel perforation is a concern, it may be advisable to use a 7-F to 8-F sheath system, to permit the delivery of PTFE-covered stents. Larger caliber sheaths are often required for the delivery of specialized crossing and reentry catheters, which may be necessary to complete complex interventions in totally occluded vessels, and may improve procedural success rates to more than 90%.
Complications of iliac endovascular intervention
Although major complications during iliac interventional procedures are rare, the interventional team must always be vigilant for evidence of contrast reaction, arterial perforation, dissection, embolization, and access site complications. The two most dangerous complications are distal embolization (DE) and iliac perforation. DE has been reported to occur between 0.4% and 9% and may be treated with mechanical or rheolytic thrombectomy, balloon inflation, stent placement, and, occasionally, surgical embolectomy.
One of the most acutely potentially catastrophic complications is iliac artery perforation or rupture, the incidence of which ranges from 0.5% to 3%. As proceduralists continue to address increasingly complex lesions, the risk of major complications such as iliac perforation and rupture correspondingly increases. During balloon inflations, patients should be monitored for the report of pain, especially during postdilatation of stents, since pain may indicate stretching of the adventitia, which confers the potential risk of vessel rupture. Given the fact that the retroperitoneal space may rapidly expand with blood if the iliac artery is ruptured, which can lead to exsanguination and potentially fatal consequences, the operator must keep at the ready a full complement of covered stents and aortic occlusion balloons during any iliac intervention. Special attention should also be paid to sheath and guidewire compatibility of occlusion balloons and covered stents. All iCAST covered stents are 7-F sheath compatible. Viabahn covered stents: 7 to 8 mm: require 8-F sheath; 9 mm: 9 F; 10 to 11 mm: 11F; and 13 mm: 12 F compatible. Coda balloon need a14-F sheath and Tyshak balloons 18 to 25 mm, a minimum 9-F sheath.
Perforation may result from manipulation of guidewires, reentry devices, crossing catheters, or during balloon/stent deployment. The report of acute low back or abdominal pain, especially during balloon inflation, should indicate to the operator the potential for impending vessel rupture. If there is a concern for rupture, careful attention should be paid to the arterial pressure waveform. If a precipitous drop in pressure occurs, an angioplasty balloon should be inflated proximal to the possible site of rupture to tamponade the bleeding. Once tamponade is attained, an appropriately sized covered stent should be considered. There is rarely time to proceed with open surgical repair in these patients, but if the patient is stable, this may be also considered if technically necessary.
Femoropopliteal interventions
Compared with intervention in the aortoiliac distribution, the outcomes following endovascular treatment of the femoropopliteal segment have considerably higher rates of restenosis. There are several pathophysiologic differences that explain this discrepancy in outcomes: (1) Femoropopliteal atherosclerosis is often more diffuse, heavily calcified, or totally occluded than are lesions in the iliac segments; (2) the femoropopliteal segment is uniquely exposed to major extrinsic forces, including repetitive flexion, torsion, and compression along its length; and (3) the engineering challenge is great for creating a scaffold or platform that can withstand the biologic nature and physical forces unique to the femoropopliteal segment.
In the TASC II document ( Box 5.2 ), the complexity of femoropopliteal disease is categorized as A, B, C, or D, reflecting severity on the basis of lesion length, presence of total occlusion, and territory involved. Although more severe TASC C and D lesions have historically been considered best amenable to surgical revascularization, recent advances in endovascular technique and device technology have dramatically improved acute procedural success rates with endovascular treatment. Despite these advances, however, the long-term patency following endovascular therapy remains suboptimal. Appropriate treatment decisions for disease in the femoropopliteal territory require careful consideration of patient, lesion, and operator-specific factors. Patient factors include age, systemic comorbidity, availability of endogenous conduit, and whether disease is associated with CLI versus claudication. Important anatomic features include extent of disease, involvement of points of flexion less amenable to stent treatment and historically preserved for bypass anastomosis (common femoral and popliteal arteries), and presence of calcification. Operator experience with advanced techniques may also play an important role in procedural outcomes and durability.
