Critical Limb Ischemia and the Diseased Popliteal Artery Mohammad Reza Rajebi, MD,* and Constantino Peña, MD† The unique anatomical location and particular biomechanical factors affecting the popliteal artery provide a challenge to determine the proper endovascular, surgical, or combined intervention for patients with critical limb ischemia who often require prompt management in the presence of severe lifestyle-limiting symptoms or of the risk of limb loss or both. Herein, we provide an overview and practical guide for endovascular management of popliteal artery disease in the setting of critical limb ischemia. Tech Vasc Interventional Rad 17:170-176 C 2014 Elsevier Inc. All rights reserved. KEYWORDS CLI, popliteal artery disease, peripheral vascular disease, popliteal stents Introduction Lower extremity peripheral arterial disease (PAD) is a common disease with an estimated prevalence of 30% in patients aged 70 years and older or in those who are 50-69 years of age with a history of cigarette smoking or diabetes.1 Critical limb ischemia (CLI), defined as rest pain or tissue loss or both, is the most severe form of lower extremity PAD. CLI requires immediate medical attention and possible intervention. The exact contribution of isolated or concomitant popliteal artery disease in patients with CLI is unknown, as traditionally superficial femoral artery (SFA) and popliteal artery diseases are grouped together in the medical literature. Chronic occlusive arterial disease is the most common etiology for CLI, while involvement in the popliteal artery is one of the most challenging vascular beds. The popliteal artery serves as the single arterial conduit between the thigh and the calf, presenting a critical inflow vessel into the calf and the foot. The popliteal artery can have a significant variability in diameter from the distal SFA to its bifurcation into the origin of the anterior tibial artery and the tibial peroneal trunk. Before any endovascular intervention, the quality of the popliteal artery proximal and distal to the lesion must always be considered for possible bypass surgery in these patients. Additionally, other disease entities such as popliteal artery aneurysm, entrapment syndrome, cystic adventitial disease, or trauma can also lead to CLI. *Department of Radiology, Mayo Clinic, Rochester, MN. †Miami Cardiac and Vascular Institute, Miami, FL. Address reprint requests to Constantino Peña, MD, Miami Cardiac and Vascular Institute, 8900 North Kendall Drive, Miami, FL 33176. E-mail: [email protected] 170 The popliteal artery has traditionally been considered a “no stent zone” particularly because of the unique biomechanical forces of the area along with the repetitive motion of the adjacent knee joint. Traditional nitinol stents had been thought to lack the flexibility, durability, and conformability necessary. The durability of angioplasty in this region is extremely variable and likely related to the morphologic characteristics of the lesions. As studied in the femoral artery, longer calcified occlusions likely respond worse to angioplasty than their counterpart does. The risk of dissection, coupled with the desire not to stent in this region, has made the popliteal artery an area in which debulking with atherectomy and the use of remodeling balloons (Cryoplasty, AngioSculpt, Chocolate, VascuTrak, Cutting) have been favored. Patient Evaluation The history and physical examination in patients with CLI is important in determining eventual treatment options. The quality of the rest pain, relieving and exacerbating factors, and the other accompanying signs and symptoms should be questioned. The existing ulcers should be investigated, and the etiology of ulceration should be determined. The arterial ulcers usually occur in the toes. They are painful and appear dry and pale. Given the multiplicity of medical conditions in these patients, one should also pay special attention to other diseases that may confound or overlap with CLI, such as diabetic neuropathy. It is important at the time of angiography to correlate the patient's symptoms with the existing vascular disease to determine the revascularization game plan. 1089-2516/13/$ - see front matter & 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1053/j.tvir.2014.08.005 CLI and the diseased popliteal artery Endovascular, open surgical, and combined options should be considered as they apply to the specific patient's symptoms and angiographic findings. In the setting of multilevel disease, the treatment of the popliteal artery, when involved, can be critical. The involvement of the popliteal artery disease in patients with CLI has been studied. A landmark study by Graziani et al evaluated and morphologically categorized diabetic subjects with ischemic foot ulcers. In 417 consecutive patients who underwent angiography, there were nearly 3000 lesions. More than 50% of the lesions were occlusions, of which 75% were discovered in the tibial vessels. Of the patients, 85% had popliteal or femoral-popliteal involvement.2 A similar study from the United States with a series of more than 450 patients found most patients with CLI having occlusions of the popliteal or tibial arteries.3 Indications for the Procedure Unlike the patients with claudication, patients with CLI require an intervention for limb salvage or to decrease the extent of amputation. Approximately 40% of patients with CLI who are not able to undergo revascularization will require amputation in the next 6 months.4 As previously mentioned, CLI usually presents a challenge given the multilevel disease and patient's comorbidities. There are 2 major considerations in revascularization of patients with CLI. If tissue loss, ulcer, or gangrene is present, the goal of revascularization is to increase the blood flow to the lower extremity to provide an acceptable tissue perfusion, which is required for the healing process. The required blood flow for tissue repair is more than the flow needed to maintain the intact healthy tissue of the extremity. However, the long-term patency is of less importance in this critical setting. In the presence of rest pain without tissue loss or after the healing of ulcers, the main purpose of the intervention should be improving the patient's symptoms, requiring additional concern about the long-term patency of the diseased vessel. Involvement of the popliteal artery is important in both clinical situations. Patency of the popliteal vessel is essential to provide inflow into the tibial and the pedal vessels. Procedural Steps The patient should be positioned supine on the fluoroscopy table. Antegrade access in the ipsilateral common femoral artery is preferred when possible as it provides better support for the catheters and wires during difficult interventions, decreases the fluoroscopy time to cross the diseased aortic bifurcation and tortuous iliac vessels, and requires shorter catheters and wires. Conversely, antegrade access is more cumbersome and carries a higher risk in obese patients. Furthermore, the use of closure devices is not approved for this access. With antegrade access, the patient's inguinal region as well as the ipsilateral abdominal lower quadrant should be prepared in advance. The access site on the skin is usually more superior to the inguinal region. If excessive 171 abdominal fat is present, the hand that holds the access needle is also responsible for displacing the fat superiorly with its lateral margin. This helps to create a proper angle and to avoid unnecessary soft tissue passage. It is important to identify the actual arterial access site with fluoroscopy. Usually the distal one-third of the femoral head is an appropriate landmark for the arterial puncture site. Ultrasonography is a critical component of our practice in establishing a proper arterial access. After identifying the proper arterial access site on the common femoral artery with fluoroscopic and ultrasonographic guidance, a secure arterial access is established. Initial angiographic evaluation of all of the lesions is important as discussed previously. This provides the angiographic information to assess the number, type, and locations of the obstructing lesions as well as to recognize the distal and proximal edges, identify the collaterals, and evaluate the distal runoff along with the strength and collateralization pattern within the foot. Revascularization Options Revascularization of a stenotic or occluded segment within the popliteal artery follows traditional endovascular principles. Moreover, intraluminal recanalizations are essential to avoid subintimal or reentry passages within the middle and the distal popliteal artery. Subintimal recanalizations within the popliteal artery increase procedural complications, particularly at the level of the knee joint as well as near the bifurcation into the tibial vessels, as they may cause occlusion of vessel branches or dissections. Additionally, a subintimal path limits the opportunity to perform atherectomy. However, maintaining an intraluminal access may be practically impossible in some lesions, especially given the presence of a hard cap in the proximal end of the lesion. Retrograde pedal or tibial access may be helpful in these situations to maintain an intraluminal path. Nevertheless, when a subintimal recanalization is performed, maintaining a small proximal loop with the hydrophylic guidewire is crucial to control the length of the subintimal dissection. Additionally, reentry devices are available to not only address the technical challenge of reentry but also help control the location where reentry occurs, allowing the protection of the middle and the distal popliteal artery if it is patent. Surgical bypass is generally considered the treatment of choice for lesions involving the middle and the distal popliteal artery if the patient is a surgical candidate and there is sufficient venous conduit. Traditionally, balloon angioplasty is the primary endovascular treatment for the popliteal artery lesions (Fig. 1). Similar to the femoral artery, the use of plain old balloon angioplasty (POBA), particularly for short, noncalcified lesions, appears to have similar patency, target lesion revascularization (TLR) rates, and symptom improvement scores when compared with nitinol stent placement if the vessel responds well to the initial angioplasty. This was demonstrated in a study that included 246 patients with popliteal artery stenosis who were randomized to POBA M.R. Rajebi and C. Peña 172 Figure 1 A 60-year-old man with a nonhealing ulcer of the left fifth toe (Rutherford category 5). (A) Digital subtraction angiogram (DSA) demonstrates a long segment occlusion of the popliteal artery and the tibioperoneal (TP) trunk with reconstitution of the proximal posterior tibial artery (PTA) (arrowhead) and the peroneal artery (arrow). (B) The lesion was crossed with the aid of a wire and a catheter, and the TP trunk and the PTA were treated with a 2.5-mm 120-mm balloon catheter (arrow). (C) The popliteal artery was treated with a 4-mm 40-mm balloon catheter (arrow). (D) Postangioplasty DSA demonstrates resolution of occlusion without flow-limiting dissection. (127 patients) or nitinol stent placement (119 patients). The study included 21% patients with CLI and 33% patients with popliteal occlusions. The average popliteal lesion measured 42 mm. Highlighting the risk of an acutely unsuccessful angioplasty requiring stent placement in the popliteal artery, 25% of patients in the POBA group crossed over to receive nitinol stent placement because of dissection or residual stenosis greater than 30%. Figure 2 A 78-year-old woman with a left first toe ulcer (Rutherford category 5). (A) Angiogram demonstrates a short segment occlusion of the proximal popliteal artery and stenosis of the TP trunk. (B) The lesions were crossed with the aid of a wire and a catheter, and a 6-mm 150-mm nitinol stent was deployed in the proximal popliteal artery (arrow). (C) The distal popliteal artery and the TP trunk were treated with a 3-mm 120-mm balloon catheter (arrow). (D) Postprocedural angiogram demonstrates resolution of occlusion and stenosis without flow-limiting dissection. TP, tibioperoneal. CLI and the diseased popliteal artery 173 Figure 3 An 84-year-old woman with rest pain involving the right lower extremity (Rutherford category 4). (A) Angiogram demonstrates a short segment occlusion of the supragenicular popliteal. (B) The lesion was crossed with the aid of a wire and catheter and treated with a 4-mm AngioSculpt balloon (arrow). (C) Postangioplasty angiogram shows a spiral dissection involving the treated lesion (arrow). (D) A 6-mm 4-cm drug-eluting stent was deployed in this region. Interestingly, based on the actual treatment received, patients who underwent POBA had similar results when compared with those who underwent provisional nitinol stenting (failing POBA first) as well as those who underwent primary nitinol stenting.5 In case of unsatisfactory response to angioplasty, heavily calcified severe lesion, or a flow-limiting dissection, stent implantation can be used for restoration of proper blood flow, especially in the supragenicular segment of the popliteal artery (Fig. 2).6 The opportunity to perform a safer and more effective angioplasty has led to the creation of specialty angioplasty balloons that aim at reducing dissections and improving luminal diameter by scoring the plaque or controlled dilatation of the vessel. These include the Chocolate balloon (Cordis [J&J], NJ), AngioSculpt balloon (AngioScore, Inc, CA) (Fig. 3), and VascuTrak balloon (CR Bard, AZ) (Fig. 4) among others. However, there are no randomized trials comparing the true value of these balloons in the popliteal artery. Debulking of the popliteal artery lesions with the use of atherectomy has been used successfully as a method to improve the vessel lumen and flow. In a study that compared atherectomy with balloon angioplasty, investigators concluded that both techniques offer similar midterm patency, limb salvage, and freedom from intervention despite a discrete pattern of complications, with dissection being more common with angioplasty vs a higher rate of thromboembolic events with atherectomy.7 Additionally, atherectomy may be an option to adapt the vessel wall so that it can better respond to angioplasty (Fig. 5). As drug-eluting technology becomes more popular, the use of drug-eluting balloons may help increase the patency of popliteal artery angioplasty, whereas drug-eluting stents may increase the patency of those lesions requiring Figure 4 A 70-year-old man with a necrotic right third toe (Rutherford category 6). (A) Angiogram demonstrates severe stenosis of the proximal popliteal artery and multifocal stenotic lesions in the distal popliteal artery. (B) The lesions were crossed with the aid of a wire and catheter and a 6-mm 8-mm drug-eluting stent was deployed in the proximal popliteal artery (arrow). (C) The distal popliteal artery was treated with a 4-mm 40-mm VascuTrak balloon (arrow). (D) Postprocedural angiogram demonstrates significant improvement of the lesions without flow-limiting dissection. M.R. Rajebi and C. Peña 174 Figure 5 A 79-year-old woman with a right foot ulcer (Rutherford category 5). (A) Digital subtraction angiogram (DSA) demonstrates occlusion of the proximal popliteal artery. (B) The lesion was crossed with the aid of a wire and a catheter, and debulking was achieved using an orbital atherectomy device. (C) The popliteal artery was then treated with a 6-mm 120mm balloon catheter (arrow). (D) Postprocedural DSA demonstrates resolution of stenosis without flow-limiting dissection. stenting by reducing the risk of restenosis (Fig. 6). Studies focusing on these trends as well as the actual effect of drugeluting technology on patients with CLI and limb salvage rates will be helpful. The effect of drug-eluting balloons after atherectomy to improve patency, particularly in calcified vessels, has also been studied8; however, data on the popliteal artery are limited. Self-expanding covered stent technology (VIABAHN, WL GORE, AZ) has been studied extensively for long femoral occlusive lesions as well as for the treatment of popliteal artery aneurysms. The covered stents appear to have responded well to the constant biomechanical motion of the popliteal artery. The covered stents with heparin coating have demonstrated improved patency and target lesion revascularization rates in the femoral-popliteal segment, especially when they are appropriately sized and expanded to the underlying vessel (Fig. 7).9 Although a significant correlation between the number of patent runoff vessels and stent patency is under debate, patients' underlying tibial disease as well as the concern for occluding collateral vessels has spurned many away from using covered stents in popliteal lesions in patients with CLI. The Supera stent (Abbott Vascular, CA) is a uniquely woven nitinol stent that has demonstrated significantly improved radial strength and crush resistance when compared with the traditional nitinol stents. Recent trials in the popliteal artery have demonstrated superior patency rates to traditional nitinol stents in the popliteal artery. The rate of stent fracture with this type of stent has been reported as extremely low.10 The data from the randomized Surgical Versus Percutaneous Bypass Trial are pending publication. Recognizing and Treating Complications Thromboembolic events, restenosis, stent stenosis, and stent fractures are the main complications of endovascular CLI and the diseased popliteal artery 175 Figure 6 A 63-year-old man with a nonhealing ulcer of the left fifth toe. (A) DSA demonstrates occlusion of the genicular popliteal artery. (B) After an unsuccessful attempt via an antegrade access, the lesion was crossed with the aid of a wire and a catheter via a pedal access through the dorsalis pedis artery. (C) A 6-mm 80-mm drug-eluting stent was deployed in the popliteal artery (arrow). (D) Postprocedural angiogram demonstrates resolution of the occlusion without flow-limiting dissection. DSA, digital subtraction angiogram. interventions in patients with CLI. The length and diameter of the balloons and stents, the crossing of distal collateral vessels, and the number of patent runoff vessels have been described as important factors for patency. Additionally, patients' comorbidities such as diabetes and end-stage renal disease as well as the inability to tolerate dual antiplatelet therapy are thought to increase the risk of stent failure.11 Figure 7 A 77-year-old woman with left fifth toe gangrene (Rutherford category 6). (A) Digital subtraction angiogram (DSA) demonstrates severe stenosis of the proximal popliteal artery and occlusion of the distal popliteal artery. (B) The TP trunk reconstitutes distally. The anterior tibial artery also reconstitutes but again occludes proximally (arrow). (C) The lesions were crossed with the aid of a wire and a catheter, and the popliteal artery was treated with a 5-mm 50-mm covered stent graft (arrow). (D) The distal popliteal artery, TP trunk and proximal PTA, and peroneal artery were treated using 2 kissing balloons of 2.5 mm 120 mm. (E) Postprocedural DSA demonstrates resolution of the proximal stenosis and interval establishment of flow in the distal popliteal artery and the TP trunk. TP, tibioperoneal. M.R. Rajebi and C. Peña 176 Acute thromboembolic events can be managed with thrombolysis. Restenosis after angioplasty may respond to repeat angioplasty or stent placement. Angioplasty and stent relining can be effective methods of treatment. Surgical interventions should be reserved for severe cases of stent fractures and failure of endovascular options. Clinical Follow-Up In our practice, the patients are evaluated with a noninvasive arterial duplex study with pulse volume recording at rest after the procedure on the same day or the day after the intervention. The patients are placed on proper antiplatelet therapy based on the intervention they received and the type of stent implanted. Dual antiplatelet therapy with aspirin and clopidogrel for 6 months is prescribed for patients with stent grafts. The initial postprocedure visit is scheduled at 1 month after the procedure with a repeat noninvasive study. After the initial visit, the patient is followed up at 6 months and 1 year after the procedure. The patients are instructed to contact our office in case of worsening symptoms or new ones. Conclusion Management of popliteal artery disease in the setting of CLI presents an extremely controversial topic. This is partly related to the lack of randomized clinical trials specific for the popliteal artery given its unique anatomical and biomechanical characteristics, which discerns it from the SFA. Today, most interventionalists only treat the popliteal artery when there is a clear indication. Balloon angioplasty and, when possible, surgical bypass remain the best options. Nonetheless, with the advent of drug-eluting balloons and stents as well as the introduction of more durable stent designs and new atherectomy devices, there will likely be more options available to be offered for patients with severe PAD. Further investigations comparing these advanced options and balloon angioplasty with focus on popliteal artery are required to establish an evidence-based approach. References 1. Hirsch A, Criqui M, Treat-Jacobson D, et al: Peripheral arterial disease detection, awareness, and treatment in primary care. J Am Med Assoc 286:1317-1324, 2001 2. Graziani L, Silvestro A, Bertone V, et al: Vascular involvement in diabetic subjects with ischemic foot ulcer: A new morphologic categorization of disease severity. Eur J Vasc Endovasc Surg 33:453-460, 2007 3. 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Lammer J, Zeller T, Hausegger KA, et al: Heparin-bonded covered stents versus bare-metal stents for complex femoropopliteal artery lesions: The randomized VIASTAR trial (Viabahn endoprosthesis with PROPATEN bioactive surface [VIA] versus bare nitinol stent in the treatment of long lesions in superficial femoral artery occlusive disease). J Am Coll Cardiol 62:1320-1327, 2013 10. León LR Jr, Dieter RS, Gadd CL, et al: Preliminary results of the initial United States experience with the Supera woven nitinol stent in the popliteal artery. J Vasc Surg 57:1014-1022, 2013 11. Johnston PC, Vartanian SM, Runge SJ, et al: Risk factors for clinical failure after stent graft treatment for femoropopliteal occlusive disease. J Vasc Surg 56:998-1006, 2012