A Refresher on the Percutaneous Treatment of Lower Extremity PAD

Key words: peripheral arterial disease, atherosclerosis, atherectomy, claudication, kissing technique, dissection, debulking, recanalization, subintimal, restenosis Atherosclerosis is a systemic disease affecting all major vascular beds. In the cerebrovascular system, atherosclerosis can result in stroke; in the coronary system, it can result in myocardial infarction, and in the peripheral arteries, atherosclerosis can result in claudication or acute limb ischemia. Peripheral arterial disease (PAD) affects 12-20% of Americans age 65 and older with only 50% of that age group being symptomatic.¹ Approximately 12 million people in the U.S. alone have PAD.² Risk factors for atherosclerosis, and therefore, for PAD, include active smoking, dyslipidemia, diabetis mellitus, and hypertension. Risk is higher in patients with diabetes mellitus. It is estimated there is a 3-fold greater risk for PAD in those with diabetes also over the age of 50.² The International Diabetes Federation estimates that somewhere in the world, a leg is lost to diabetes every 30 seconds.³ Each year there are 150,000 lower-extremity amputations, with a $270-million price tag.⁴ PAD greatly impacts quality of life, making walking difficult or worse, and increasing the risk of heart attack, stroke, leg amputation, and even death. PAD, symptomatic or asymptomatic, is a powerful independent predictor of coronary artery disease (CAD) and cerebrovascular disease (CVD) (Table 1).⁵ In the Coronary Artery Surgery Study (CASS) Registry, for patients with known CAD, the presence of PAD increased cardiovascular mortality by 25% during a 10-year follow up.⁶ Recognizing the symptoms and early diagnosis of PAD, therefore, is very important. In a 2001 study, only 49% of those receiving amputations had any diagnostic vascular evaluation prior to amputation.⁷ PAD treatment options include medical therapy, endovascular therapy, and surgery. Medical therapy includes risk factor modification, exercise, and drug therapy. Endovascular therapy includes peripheral transluminal angioplasty, stenting, atherectomy, and thrombolytic therapy. Surgical options consist of bypass grafts, endarterectomy, and amputation. Over the past decade, percutaneous revascularization therapies for the treatment of patients with PAD have evolved tremendously, and a great number of patients can now be offered treatment options that are less invasive than traditional surgical options. In this article, we will discuss the percutaneous treatment of PAD. Percutaneous treatment of lower extremity obstruction can be divided into three anatomic zones:⁸

Inflow tract: Common iliac arteries (bilateral) External iliac arteries (bilateral) Outflow tract: Common femoral arteries Superficial femoral arteries Popliteal arteries Runoff bed: Tibialperoneal trunk Anterior tibial artery Posterior tibial artery Peroneal artery

Inflow Tract Area Interventions

Atherosclerosis affecting iliac or aortoiliac vessels manifest as hip or leg claudication. Atherosclerosis in these vessels can also result in erectile dysfunction. In 1999, the Trans-Atlantic Intersociety Consensus (TASC) group developed treatment guidelines based on lesion location and characteristics (Figure 1).⁹ The recommendations were for treating TASC-type A to B lesions with an endovascular approach and type C to D lesions surgically. However, with the rapid evolution of endovascular techniques, type C and D lesions can now be treated percutaneously, with long-term patency rates comparable to surgery, and without the associated morbidity and mortality.¹⁰ Iliac arteries have a higher rate of dissection and elastic recoil. Therefore, primary stenting is the preferred strategy in iliac artery disease, although some operators are still using provisional stenting.¹¹ A meta-analysis of 14 studies performed since 1990 involving either percutaneous transluminal angioplasty (PTA) or stenting reveals higher procedural success with stenting (39% lower risk of long-term failure with stenting).¹² Iliac arteries can be stented with balloon-expandable or self-expandable stents, with 80% primary patency at 1 year with self-expandable stents.¹³ Balloon-expandable stents have an 87% primary patency at 1 year¹⁴ and have great radial force, allowing for increased placement precision in ostial lesions. Self-expanding stents have no risk of external compression or deformation. They are flexible and can be delivered from the contra lateral approach, allowing normal vessel tapering. If atherosclerosis of the common iliac arteries also involves the terminal aorta, then balloon-expandable or self-expandable stents can be used with either the “hugging” or “kissing” technique. The hugging technique should be used if atherosclerosis is affecting the terminal aorta and ostia of common iliac arteries to minimize the risk of aortic dissection. The hugging technique uses two self-expandable stents, deployed simultaneously from the terminal aorta into each common iliac artery. The kissing stenting technique (Figure 2) is used if atherosclerosis mainly affects ostia of both common iliac arteries and minimally affects the terminal aorta. It offers excellent procedural outcome (100%) and patency (92%).¹⁵ The 3-year assisted patency rate for stenting of occluded iliac arteries is 80% to 90%, which compares favorably to surgical revascularization (5-year patency of aortobifemoral grafts: 91% for claudication and 88% for critical limb ischemia).¹¹ Surgical treatment is also associated with 8.3% morbidity and 3.3% mortality.¹¹ The main complication after endovascular intervention is embolic phenomena, which are estimated to be 4% but may be as high as 24% when treating longer-segment occlusions.¹⁶ Lower primary patency with endovascular revascularization of iliac arteries has been noted in the presence of diabetes, length of lesion, poor distal runoff, renal insufficiency, and female gender.

Outflow Tract Area Interventions

The common femoral artery lies over the hip joint and placement of a stent is suboptimal. Restenosis or stent thrombosis can be associated with limb-threatening ischemia as circulation to both the superficial femoral artery (SFA) and the profunda femoris can be compromised simultaneously. Endovascular stenting at this site may make future vascular access (for diagnostic and interventional procedures) and bypass surgery (aortofemoral, femoropopliteal bypass) at this site impossible. Atherosclerosis in this artery is best treated with bypass or endarterectomy with patch angioplasty. Debulking with atherectomy devices can be done for patients who are poor candidates for surgery.¹¹ Different atherectomy devices are available, such as the SilverHawk device (ev3 Endovascular, Inc., Plymouth, Minn.), laser atherectomy (Spectranectics Corp., Colorado Springs, Co.), and cutting balloon atherectomy (Boston Scientific Corp., Natick, Mass.). Atherectomy devices do have a role in locations where stenting should be avoided, such as ostial SFA lesions or disease that extends into the popliteal artery. Atherectomy using the SilverHawk device with adjunctive low-pressure angioplasty may be preferred in these locations. Some small trials have shown favorable technical and clinical results after SilverHawk atherectomy for de novo femoro-popliteal lesions, but not for restenotic lesions.¹⁷ Similarly, laser atherectomy may increase limb salvage rates in patients with limb ischemia, but is rarely used. In a randomized comparison of excimer laser angioplasty (ELA) versus angioplasty for the treatment of long SFA, ELA was associated with decreased use of bailout stenting, without any improvement in 12-month patency.¹⁸ One small study has also shown the benefit of using the AngioSculpt scoring balloon (AngioScore, Inc., Fremont, Ca.) in infra-popliteal segment disease.¹⁹ Orbital atherectomy is a promising new methodology for treating symptomatic peripheral arterial disease within the major and branch arteries of the leg. It is performed with the Diamondback 360° Orbital Atherectomy System (Cardiovascular Systems, Inc., St. Paul, Minn.), an atherectomy device utilizing an orbiting eccentric diamond-coated crown on the end of a drive shaft powered by a pneumatic drive console. The shaft and crown are advanced over a pre-placed 0.014” proprietary guidewire, the ViperWire. The orbital motion of the crown removes plaque from within a diseased arterial segment; as the crown orbits, the debulking area increases, and with increments in speed, the area increases further. Rotational atherectomy uses a concentrically rotating burr, so luminal gain is as large as the burr size being utilized. A small study showed benefit in femoral and tibial segments with excellent procedural success (92.5%) and a favorable safety profile.²⁰ None of the atherectomy devices have been studied in head-to-head, randomized, controlled trials to determine the superiority of any one device. The superficial femoral artery (SFA), especially mid-SFA, undergoes multiple stresses, including extension, contraction, compression, elongation, and flexion torsion. SFA lesions are diffuse and often occluded. Recanalization devices have been used for chronic total occlusions. These include the Frontrunner® XP CTO catheter (Cordis Corp., Miami, Fl.), Outback® LTD® Re-Entry catheter (Cordis), and Pioneer catheter (Medtronic, Inc., Minneapolis, Minn.). The Frontrunner XP CTO catheter is a blunt microdissection device that takes advantage of the elastic properties of adventitia versus inelastic properties of fibrocalcific plaque to create fracture planes. The Outback LTD Re-Entry catheter is a 6 French (F) catheter with a hollow 22-gauge cannula used for re-entry. The device is placed subintimal, adjacent to reconstitution of the vessel, and two orthogonal views are taken. An L-shaped fluoroscopic marker provides reproducible orientation of the tip towards the re-entry target site. The “T” fluoroscopic marker, combined with a 90˚ orthogonal view, confirms the desired alignment with fine-tune positioning at the target re-entry site. Finally, the 22-gauge, nitinol re-entry cannula is plunged into the distal vessel to re-enter into the true lumen.²¹ The Pioneer catheter is a 6F catheter with two wire ports, each 0.014-inch compatible. One port has a hollow-core nitinol needle that is guided by intravascular ultrasound (IVUS). It is connected to a console (Volcano Corporation, San Diego, Ca.), enabling vascular imaging. The device placed subintimal at the distal tip at the level of the SFA re-entry site; IVUS is maneuvered until the tip of nitinol needle is directed towards the true lumen at the 12-o’clock position. The needle is plunged into the lumen at the controlled depth and 0.014” wires sent through the needle.²¹ None of the above-mentioned devices have been tested in head-to-head, randomized, clinical trials; even registry outcome data with these devices has not been rigorously controlled or monitored.¹¹ For long, segmental lesions (up to 10 cm), self-expanding nitinol stents may be better than angioplasty alone.²¹ Self-expanding drug-eluting nitinol stents have also been investigated for use in the SFA in a randomized trial, but did not reveal significant differences in an angiographic or clinical outcomes.²³ For focal, non-calcified lesions, angioplasty alone often provides excellent angiographic results. For heavy, calcified lesions, a low threshold for primary stenting is reasonable because of the poor angiographic results achieved with angioplasty alone. For ostial SFA lesions or SFA disease that extends into the popliteal artery, debulking with atherectomy with low-pressure angioplasty may be the preferred initial strategy, while surgery (aortofemoral, femoral-popliteal bypass) would have long-term patency.¹¹

Runoff Bed Interventions

Obstructive disease affecting the popliteal and infrapopliteal vessels is treated percutaneously or with medical therapy. Percutaneous treatment is usually reserved for patients with critical limb ischemia, where inflow is required to help an ulcer or ischemic pain. It also required in patients who have severely symptomatic claudication unresponsive to medical therapy. Angioplasty is usually the primary treatment, using balloons specifically marked for the treatment of tibial disease. These balloons come in lengths up to 120 cm. The results of angioplasty in tibial disease are usually stable;²⁴ however, some operators also deploy a stent after angioplasty to decrease the chances of restenosis or if the angioplasty results are not satisfactory, and in bailout conditions. A variety of stents have been used to treat infrapopliteal disease, including bare-metal and drug-eluting coronary stents, and more recently, self-expanding nitinol stents. Although these stents provide excellent immediate angiographic results, there is a paucity of long-term data regarding the benefit of this strategy. Sirolimus-eluting stents appear to restrict neointimal hyperplasia in the infrapopliteal vascular bed and seem to have a low restenosis rate, leading to the approval in Europe of a balloon-expandable sirolimus-eluting stent for infrapopliteal disease.²⁵ Regardless of the interventional technique employed, most series report procedural success rates of >90%, and amputation-free survival at 6-12 months is usually >85%.²⁶

Summary

Atherosclerosis is the leading cause of occlusive arterial disease of the lower extremities. The pathogenetic mechanisms that lead to PAD are similar to those of coronary artery disease (CAD). Treatment options include medical therapy, percutaneous intervention, and surgical revascularization. Percutaneous revascularization is a less invasive option in the management of peripheral vascular disease (PAD). Over the past 30 years, there has been steady growth in the use of percutaneous intervention, and it has become the first-line therapy for PAD. Increased emphasis on containing and reducing health care expenditures has also led to an increase in the use of percutaneous intervention (as compared with surgical procedures), because it can be performed as a same-day procedure, thus reducing overall cost.

References

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———————————————————— The authors can be contacted via Dr. Syed Ahmed at: sahmed@iowaheart.com