Peripheral artery disease (PAD) is the clinical term commonly used to describe stenotic or occlusive lesions in lower extremity arteries due to atherosclerotic or thromboembolic disease. Data from the National Health and Nutrition Examination Survey (1999 to 2004) estimate a prevalence of 5.9% in patients >40 years of age, corresponding to ~7.1 million affected individuals in the U.S.¹ and >200 million people worldwide. Despite aggressive risk factor therapies and recent improvements in medical management of atherosclerotic disease with statins and antiplatelet agents, patients with PAD frequently require invasive procedures to improve claudication symptoms and to prevent tissue loss in those with critical limb ischemia (CLI).²

Endovascular technological advances have made a minimally invasive percutaneous approach the treatment of choice in the initial management of the majority of symptomatic patients over the traditional surgical approach. However, the presence of severe vascular calcification, particularly in the infrainguinal vasculature, presents a significant procedural challenge to current endovascular strategies. Due to a lack of large randomized, prospective trials with independent core laboratory adjudication of device-related acute and late events, operators have used different approaches to treat femoropopliteal or infrapopliteal disease. Percutaneous transluminal angioplasty (PTA) or balloon angioplasty has been traditionally used for treatment of focal lesions. However, early elastic recoil, frequent dissections, and poor primary and secondary patency rates for long lesions, with 40-50% of cases requiring bail-out stenting, limit balloon angioplasty of "severely" calcified lesions, despite the high procedural success rates. Although the use of the last generation self-expanding nitinol stents may be an effective treatment for focal lesions, with high acute procedural success rates, restenosis rates can be as high as 10-40% at six to 24 months, and stent fractures may occur at sites of excessive movement and flexion. Furthermore, the presence of rigid calcified plaques may result in incomplete stent expansion and significant residual stenosis.³ Lack of effective therapy for restenosis has led many interventional cardiologists to seek alternative treatment strategies, such as plaque modification by means of debulking, using an atherectomy device.

Atherectomy is a procedure performed to remove or "debulk" the atherosclerotic plaque from diseased arteries. It is usually combined with low-pressure balloon angioplasty with the goal of minimizing plaque shift while avoiding stent placement. In densely calcified vessels, atherectomy has been used to better "prepare" the vessel prior to stenting in order to prevent incomplete and/or eccentric stent expansion. There are different atherectomy devices designed to cut, shave, sand, or vaporize atherosclerotic or calcified plaques, and they have slightly different indications that depend on the lesion characteristics. Four different methods of atherectomy have been utilized for treatment of femoropopliteal or small-vessel infrapopliteal disease: plaque excision (directional) atherectomy, rotational atherectomy/aspiration, laser atheroablation, and orbital atherectomy.

Directional or extractional atherectomy devices utilize carbide rotating cutter disks that resect and remove the atherosclerotic plaque. These devices have the advantage of avoiding barotrauma, which may decrease the risk of neointimal hyperplasia and dissection. Distal embolization remains a concern with these devices, given that these devices require retrieval of removed plaque, and the use of distal protection devices may be needed, particularly in cases of heavily calcified lesions. The SilverHawk and TurboHawk (Covidien/Medtronic) plaque excision systems are the two U.S. Food and Drug Administration (FDA)-approved directional atherectomy devices in use today, with the HawkOne system recently being FDA cleared as well. The SilverHawk and TurboHawk devices come in various sizes to enable atherectomy in vessels ranging from a diameter of 1.5 mm to 7 mm. The SilverHawk plaque excision system is a forward-cutting, directional atherectomy device that consists of a rotating blade inside a tubular housing with a collection area. The TurboHawk system is similar to the SilverHawk except with a different number of inner blades, allowing for a larger luminal gain. While SilverHawk has one inner blade, TurboHawk has four contoured blades, thus favoring use in highly calcified lesions and achieving more plaque removal per pass. As the name implies, the new HawkOne system is intended to simplify device selection, allowing treatment of lesions with different morphologies (including severe calcification) with one device. The Determination of Effectiveness of SilverHawk Peripheral Plaque Excision [SilverHawk Device] for the Treatment of Infrainguinal Vessels/Lower Extremities (DEFINITIVE LE) study is the largest study to evaluate directional atherectomy, with enrollment of 800 patients worldwide with both claudication and/or CLI across 50 sites in the U.S. and Europe. The device success was reported at 89%, with a post-atherectomy bail-out stenting rate of 3.2%. Rates of distal embolization, dissection, and perforation were 3.8%, 2.3%, and 5.3%, respectively. At 12 months, primary patency rate in claudicants was 78%, whereas the rate of freedom from major unplanned amputation of the target limb at 12 months in CLI subjects was 95%.⁴

Rotational atherectomy is currently available as the Jetstream Atherectomy (currently Boston Scientific, previously Pathway Medical Technologies, Inc.), and the Phoenix atherectomy catheter (AtheroMed). The Boston Scientific/Pathway Jetstream Atherectomy System is a single-use catheter with a reusable, compact console power source and a front-cutting tip that allows it to go through severely stenotic lesions without predilation. It is the only atherectomy device to offer continuous aspiration and active removal of atherosclerotic debris and thrombus. Thus, this device may be particularly useful in lesions of mixed morphologies, particularly those with presence of thrombus (e.g., acute or subacute occlusions). In a multicenter study of 172 patients, Jetstream use had a 99% device success, and six-month and 12-month clinically-driven, target-lesion revascularization rates of 15% and 26%, respectively; with a one-year restenosis rate of 38% based on duplex imaging.⁵ The Phoenix atherectomy device is still under investigation and the Endovascular Atherectomy Safety and Effectiveness (EASE) study is currently evaluating the safety and short-term efficacy of the Phoenix device.⁶

Excimer Laser atherectomy (Spectranetics) uses the high-energy, monochromatic light beam to alter or dissolve (vaporize) the plaque without damaging the surrounding tissue. These devices include a Turbo Elite ablation catheter as well as a Turbo-Tandem system that combines a laser guide catheter with an excimer laser atherectomy catheter. In the Laser Angioplasty for Critical Limb Ischemia (LACI) trial, 155 critically ischemic limbs with above- or below-knee disease that were poor candidates for surgical revascularization were treated with excimer laser-assisted intervention with a limb-salvage rate of 93% at six months.⁷ The excimer laser has an advantage of not only debulking, but also being able to penetrate the proximal fibrous cap in chronic total occlusions. Thus, it may be advantageous for utilization when the intention is to enhance crossing capability as well as further debulk the occluded vessel. Recent results from the EXCImer Laser Randomized Controlled Study for Treatment of FemoropopliTEal In-Stent Restenosis (EXCITE ISR) trial of 250 patients demonstrated the safety and efficacy of excimer laser atherectomy in femoropopliteal in-stent restenosis.⁸ Excimer laser plus PTA subjects demonstrated superior procedural success (93.5% vs. 82.7%; p = 0.01), with fewer procedural complications compared with PTA only (any dissection 7.7%, embolization 8.3%, bailout stenting 4.1%). In the excimer laser plus PTA versus PTA-only patients, six-month freedom from target lesion revascularization (TLR) was 73.5% versus 51.8% (p <0.005). Thus, excimer laser debulking may be particularly advantageous for recurrent in-stent restenosis lesions, given its ability to effectively remove hyperplastic tissue.

Orbital atherectomy is an atherectomy device with an eccentrically-mounted crown that is being used to reduce the total atheroma burden and decrease the vessel-wall trauma, particularly in calcified vessels. Orbital atherectomy utilizes a diamond-coated tungsten crown that orbits 360 degrees eccentrically within the vessel, while employing circumferential plaque removal by differential sanding. The currently available orbital atherectomy devices include the CSI Stealth 360 and Diamondback 360 Orbital atherectomy systems (Cardiovascular Systems, Inc). The CONFIRM registry series evaluated the use of orbital atherectomy in peripheral lesions of the lower extremities and showed that it effectively reduced the degree of stenosis from 88% to ~10% with the use of adjunctive low-pressure balloon angioplasty.⁹ The COMPLIANCE 360° trial compared acute and 12-month results in 50 patients between orbital atherectomy plus PTA versus PTA in calcified femoropopliteal disease.¹⁰ At 12 months, freedom from TLR or restenosis was achieved in ~80% of lesions in both groups, despite rare use of bail-out stenting after atherectomy (5.3% vs. 77.8% in PTA). The peri-procedural adverse events were seen infrequently with orbital atherectomy: perforations (0%), dissections (16%), and embolization (2.6%). Given its mechanism of action, orbital atherectomy may be particularly advantageous in severely calcified lesions, while minimizing vessel wall trauma and need for bail-out stenting. Furthermore, newer low-profile (4 French) systems allow for alternative access options, such as tibiopedal approach.

Despite different choices of atherectomy devices and advanced technologies, there have been no comparative efficacy or safety studies evaluating the four FDA-approved atherectomy devices. Atherectomy devices can reduce the burden of soft atheromatous or calcific plaque, change the vessel compliance, reduce vessel wall trauma, leading to a decrease in the need for bail-out stenting.¹¹ On the other hand, atherectomy devices carry significantly higher capital equipment-related costs, particularly when used in conjunction with distal protection filters, and lead to an increase in procedure duration and exposure to radiation. Given the availability of multiple atherectomy devices, in day-to-day clinical practice, it is important to initially obtain expertise with a single device, paying attention to patient/lesion selection and whether to utilize distal protection. The recent encouraging data from drug-coated balloons (DCB) have renewed the interest in atherectomy devices,¹² and several ongoing randomized trials are currently evaluating a strategy of combining atherectomy and DCB. Additional studies are required to identify subsets of patients benefiting from atherectomy and to establish an optimal, cost-effective therapy, which may include a combination of atherectomy and emerging technologies, such as drug-eluting stents, DCB, and possibly bioabsorbable stent platforms to ensure a more durable patency in complex lesions.

Table 1: Atherectomy Devices and Where Each Device is Most Advantageous

Atherectomy Type	Directional	Rotational	Photo-Ablative	Orbital
Device	SilverHawk/ TurboHawk	Jetstream	Laser	Diamondback 360
Eccentric, focal calcification	XX			X
Thrombotic lesion		XX	X
BTK lesion	X		X	X
Highly calcific, diffuse plaque	X			XX
In-stent restenosis			XX
In-stent restenosis with thrombus		X	X
Chronic total occlusion	X		XX

References

1. Pande RL, Perlstein TS, Beckman JA, Creager MA. Secondary prevention and mortality in peripheral artery disease: National Health and Nutrition Examination Study, 1999 to 2004. Circulation 2011;124:17-23.
2. Golomb BA, Dang TT, Criqui MH. Peripheral arterial disease: morbidity and mortality implications. Circulation 2006;114:688-99.
3. Rocha-Singh KJ, Zeller T, Jaff MR. Peripheral arterial calcification: prevalence, mechanism, detection, and clinical implications. Catheter Cardiovasc Interv 2014 83:E212–E220.
4. McKinsey JF, Zeller T, Rocha-Singh KJ, Jaff MR, Garcia LA. Lower extremity revascularization using directional atherectomy: 12-month prospective results of the DEFINITIVE LE study. JACC Cardiovasc Interv 2014;7:923-33.
5. Zeller T, Krankenberg H, Steinkamp H, et al. One-year outcome of percutaneous rotational atherectomy with aspiration in infrainguinal peripheral arterial occlusive disease: the multicenter pathway PVD trial. J Endovasc Ther 2009;16:653-62.
6. U.S. National Institutes of Health. Endovascular Atherectomy Safety and Effectiveness Study (EASE) (ClinicalTrials.gov website). 2010-2014. Available at: http://www.clinicaltrials.gov/ct2/show/record/NCT01541774. Accessed 4/12/15.
7. Laird JR, Zeller T, Gray BH, et al. Limb salvage following laser-assisted angioplasty for critical limb ischemia: results of the LACI multicenter trial. J Endovasc Ther 2006;13:1-11.
8. Dippel EJ, Makam P, Kovach R, et al. Randomized controlled study of excimer laser atherectomy for treatment of femoropopliteal in-stent restenosis: initial results from the EXCITE ISR trial (EXCImer Laser Randomized Controlled Study for Treatment of FemoropopliTEal In-Stent Restenosis). JACC Cardiovasc Interv 2015;8:92-101.
9. Das T, Mustapha J, Indes J, Vorhies R, Beasley R, Doshi N, Adams GL. Technique optimization of orbital atherectomy in calcified peripheral lesions of the lower extremities: the CONFIRM series, a prospective multicenter registry. Catheter Cardiovasc Interv 2014;83:115-22.
10. Dattilo R, Himmelstein SI, Cuff RF. The COMPLIANCE 360° Trial: a randomized, prospective, multicenter, pilot study comparing acute and long-term results of orbital atherectomy to balloon angioplasty for calcified femoropopliteal disease. J Invasive Cardiol 2014;26:355-60.
11. Feldman DN. Atherectomy for calcified femoropopliteal disease: are we making progress? J Invasive Cardiol 2014;26:304-6.
12. Cioppa A, Stabile E, Popusoi G, et al. Combined treatment of heavy calcified femoropopliteal lesions using directional atherectomy and a paclitaxel coated balloon: one-year single centre clinical results. Cardiovasc Revasc Med 2012;13:219-23.

Keywords: Alloys, Amputation, Angioplasty, Balloon, Coronary, Angioplasty, Laser, Atherectomy, Atherectomy, Coronary, Barotrauma, Cardiovascular System, Constriction, Pathologic, Cost of Illness, Diamond, Drug-Eluting Stents, Freedom, Goals, Hyperplasia, Lasers, Excimer, Lower Extremity, Nutrition Surveys, Orbit, Peripheral Arterial Disease, Plaque, Atherosclerotic, Platelet Aggregation Inhibitors, Prevalence, Prospective Studies, Registries, Risk Factors, Thrombosis, Tungsten, Vascular Calcification

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