Acute Results of Directional Atherectomy for the Treatment of Claudication and Critical Limb Ischemia in the DEFINITIVE LE Study

Original Research

Submitted on Wed, 02/08/2017 - 23:47
Authors

Lawrence A. Garcia, MD1; Michael Jaff, MD2; Krishna Rocha-Singh, MD3; Thomas Zeller, MD4; James McKinsey, MD5      
From 1St. Elizabeth’s Medical Center, Brighton, Massachusetts; 2Massachusetts General Hospital, Boston, Massachusetts; 3Prairie Medical, Springfield, Illinois; 4Universitats-Herzzentrum Freiburg - Bad Krozingen, Bad Krozingen, Germany; and  5Mount Sinai University, New York, New York
 

ABSTRACT: Objectives. Assess the acute safety of directional atherectomy (DA) for endovascular treatment of peripheral arterial disease (PAD) in infrainguinal arteries. Background. Single-center studies and uncontrolled registries have demonstrated 12-month clinical benefit of DA for the treatment of PAD; however, large-scale, independently assessed multicenter data on acute procedural safety have previously been lacking. Methods. DEFINITIVE-LE was a prospective, multicenter, single-arm study. Endpoints were assessed by independent angiographic and duplex ultrasound core laboratories and adverse events were adjudicated by a Clinical Events Committee. For claudicants, the primary endpoint was primary patency at 1 year (estimated by Kaplan-Meier methods). For patients with critical limb ischemia (CLI), the primary endpoint was freedom from major amputation of the target limb at 1 year. Results. A total of 800 subjects with 1022 infrainguinal lesions were enrolled; 201 subjects had CLI and 52.3% had diabetes mellitus. Mean lesion length was 7.4 ± 5.3 cm, mean percent diameter stenosis was 73.6%, and 20.8% of patients had occluded lesions. Periprocedural adverse events included distal embolization (3.8%), perforation (5.3%), and abrupt closure (1.9%). Procedural success was achieved in 89.0% of all lesions treated per angiographic core laboratory assessment, with a bailout stenting rate of 3.2%. Additionally, quality-of-life scores were significantly improved at 30 days compared with baseline. Conclusions. This large, prospective, multicenter, independently adjudicated study produced acute outcomes indicating that directional atherectomy is safe, with low rates of periprocedural events. Results were promising for PAD patients with claudication or CLI, and there were minimal differences between diabetics and non-diabetics.

VASCULAR DISEASE MANAGEMENT 2017;14(2):E21-E33

Key words: peripheral arterial disease, angioplasty, atherosclerosis

_________________________________________________________

Peripheral artery disease (PAD) remains an increasingly common disorder that continues to be a large source of chronic morbidity and mortality worldwide.1-6 The endovascular treatment of PAD has become the first-line therapy in most arterial beds.7-9 The treatment of femoropopliteal and tibial-peroneal disease is one such example. Treatment options in this territory include percutaneous transluminal angioplasty (PTA),10-13 PTA combined with adjunctive stenting, either bare-metal stent (BMS) or drug-eluting stent (DES) implantation,7,12,14-16 drug-coated balloon (DCB),17,18 and atheroablative technologies including directional atherectomy (DA)19-24 with devices such as the SilverHawk and TurboHawk Peripheral Plaque Excision Systems (Medtronic).

No single device is considered the gold standard primarily because of the heterogeneity of the patient population and lesion morphologies being treated and the lack of direct comparisons between technologies. In the DEFINITIVE LE Study, DA was used to treat subjects with infrainguinal PAD. Up until this study, there was limited scientific literature on DA given previous study design limitations and a lack of independent evaluation of outcomes.20,23,24 Further, previous reports have suggested a higher complication rate and inferior durability with DA as compared with other endovascular strategies.21,22

Herein, we focus on the acute 30-day safety outcomes with respect to procedural complications and 30 day quality-of-life outcomes of the SilverHawk and TurboHawk Plaque Excision Systems in the DEFINITIVE LE study in the treatment of lower-limb arterial disease.

Methods

Study Design

DEFINITIVE LE was a prospective, global, multicenter, single-arm, non-randomized study designed to evaluate the acute and long-term safety and effectiveness of DA for endovascular treatment of PAD in femoropopliteal and tibial-peroneal arteries.25

Candidates for DA in the infrainguinal arteries provided written informed consent prior to screening. Inclusion criteria are listed in Table 1 and included a Rutherford Clinical Category (RCC) score of 1-6, infrainguinal artery stenosis ≥50%, a reference vessel diameter of 1.5-7.0 mm, and a lesion length of up to 20 cm as assessed by the treating physician. Lesions in the superficial femoral (SFA) or popliteal artery separated by more than 3 cm or those separated by more than 2 cm distal to the popliteal artery were considered separate lesions. Major exclusion criteria included presence of severe calcification (defined as fluoroscopic evidence of calcium present in two walls of the lesion that exceeded 1 cm in length), in-stent restenosis, and lesions located within an aneurysmal segment.

Each site’s Institutional Review Board/Ethics Committee approved the study protocol. Subjects were considered enrolled in the study after informed consent was signed and all of the inclusion criteria and none of the exclusion criteria were met.

The study was conducted in accordance with Good Clinical Practice and overseen by a steering committee and an independent Clinical Events Committee (CEC). Angiographic findings (such as dissections, distal embolization, etc) identified and classified by the core laboratory were presented to the CEC for consideration as adverse events. Independent core laboratories conducted analyses of angiographic (SynvaCor) and duplex ultrasonography images (VasCore, Massachusetts General Hospital).

Regular monitoring visits were conducted to ensure that collected data were complete and accurate. Angiographic classification provided by the angiographic core laboratory was final, but the CEC had final say as to relatedness and seriousness of the resulting adverse event.

Interventions

Preprocedure data collection included an ankle-brachial index (ABI) and EQ-5D questionnaire (a patient-reported measure of overall health) for all patients, a Walking Impairment questionnaire (WIQ) for subjects with RCC 1-4, and wound assessment via the Wagner scoring scale in subjects with RCC 5 or 6.

Significant stenosis or occlusion of inflow vessels (iliac or common femoral) required successful revascularization prior to enrollment. Infrainguinal arterial lesions intended for treatment at the time of the index procedure that met the inclusion and exclusion criteria were enrolled and considered target lesions. There was no limit on the number of target lesions per patient. If multiple outflow vessels were present, then the treatment of any outflow vessel was left to the discretion of the operator as to the method of revascularization.

All subjects underwent percutaneous revascularization of the femoropopliteal and/or tibial-peroneal arteries using a DA device. In cases in which the DA device was unable to cross, the lesions were permitted to be predilated, at the discretion of the investigator. Angiographic films, including run-off status, were obtained immediately prior to and after DA to document pre- and post-treatment results. Adjunctive procedures were performed at the treating physician’s discretion; however, if residual stenosis was < 30% post-directional atherectomy, additional postdilation was not recommended. A final angiogram of the target lesion(s) and run-off was performed following adjunctive procedures (if required). Residual stenosis was calculated by dividing the native vessel diameter as measured at the most stenotic segment by the estimated reference vessel diameter (mean of the vessel diameters proximal and distal to the lesion) at that location. Distal protection devices, permitted under the study protocol, were used at the discretion of the attending physician.

Adjuvant Medical Therapy

It was recommended that all subjects receive antiplatelet or antithrombotic therapy per American Heart Association/American College of Cardiology/European Society of Cardiology guidelines before and after the procedure. Anticoagulation during the procedure was left to the discretion of the treating physician to maintain appropriate levels of anticoagulation.

Follow-Up

Follow-up assessments occurred prior to discharge and at 30 days, 3 months (for subjects with RCC score 5 or 6 at baseline), 6 months, and 1 year following the index procedure. Each follow-up visit included assessment of RCC score, WIQ (for subjects with a baseline RCC score 1-4), EQ-5D, ABI, adverse event evaluations, and wound assessments for subjects with a baseline RCC score of 5 or 6.

Endpoints

Briefly, the study’s primary endpoints were primary patency and freedom from amputation at 1 year; these results were presented elsewhere.25 Prespecified secondary endpoints included: (1) device success, defined as ≤30% residual stenosis following use of the DA device, as measured by angiography, without adjunctive endovascular interventions or periprocedural complications; (2) procedural success, defined as ≤30% residual stenosis following use of the DA and adjunctive endovascular interventions (if required) as measured by angiography without periprocedural complications; and (3) major adverse event (MAE) rate at 30 days and 1 year, defined as clinically driven target-vessel revascularization (at least 70% lesion stenosis or at least 50% with attendant symptoms), major unplanned amputation of the treated limb (resulting in a limb prosthesis), or all-cause mortality.

Statistical Analysis

Data were evaluated for all subjects enrolled regardless of the treatment delivered; all available data for all such subjects were used in primary analyses of baseline characteristics and study outcomes. All target lesions were analyzed as identified by the angiographic core laboratory.

All statistical analyses were performed using Statistical Analysis System for Windows version 9.1 or higher (SAS Institute, Inc). Unless otherwise noted, continuous variables were evaluated using t-tests, binary categorical variables with Fisher’s exact test, and ordinal variables with Mantel-Haenszel x2 test; for continuous variables collected at multiple time points, change scores from baseline were computed and used as the basis for analysis.

Results

Enrollment occurred between April, 2009 and April, 2011 at 47 international centers. Eight hundred subjects were enrolled in the study; however, inadequate informed consent resulted in the exclusion of one subject’s data from all analyses. Baseline demographic information is listed in Table 2. Results are provided for the claudicant cohort (n = 598), CLI cohort (n = 201), and the overall study population (n = 799). The mean age was 70.1 ± 10.7 years and 45.4% of the population was female. Co-morbid conditions included diabetes mellitus (52.3%), hypertension (92.0%), and hyperlipidemia (83.6%). The CLI cohort was older (72.1 years vs 69.5 years; P<.01) and had a significantly higher percentage of subjects with diabetes mellitus (68.7% vs 46.8%; P<.001) and renal insufficiency (23.4% vs 16.7%; P=.045).

Baseline RCC scores are shown in Figure 1. Approximately one-half (49.8%) of the subjects were classified as RCC 3. Baseline lesion characteristics are listed in Table 3. A total of 1022 lesions were treated in 799 subjects (1.3 lesions/subject). The mean baseline percent diameter stenosis was 73.6 ± 18.7%, and 20.8% of lesions were occluded. The mean lesion length was 7.4 ± 5.3 cm; 27.8% were ≥10 cm. The total SFA disease burden, defined as the total of the lengths of all SFA lesions per subject, was 9.4 ± 6.3 cm. 

Table 4 describes the procedural characteristics. The average procedure time (from arterial access to catheter removal) was 70.9 ± 34.3 minutes, with shorter times observed in the claudicant group (67.7 minutes vs 80.6 minutes; P<.001). Predictors of a longer procedure time included patients with CLI (vs claudication), longer target lesion treated, greater baseline severity of stenosis, the number of lesions treated, and the presence of arterial calcification. Predilation to allow passage of the DA device was performed in 8.3% of lesions in subjects treated for claudication and 15.8% of those in CLI subjects (P<.001), typically using PTA balloons, which were predominantly (75.0%) ≤3 mm in diameter. There was no significant difference in the percentage of lesions predilated in femoropopliteal vs tibial-peroneal arteries (10.1% vs 11.6%). After initial therapy with DA, adjunctive therapy was performed in 35.3% of the target lesions. The majority of adjunctive therapy was PTA; the adjunctive stent rate was 3.2%. Distal embolic protection (DEP) via a filter device was used in 22.2% of subjects, with the SpiderFX Embolic Protection System (Medtronic, Inc) used in 97.2% of those cases. DEP use was significantly more frequent in conjunction with the TurboHawk device than with SilverHawk (39.8% vs 14.2%, respectively; P<.001) and in CLI subjects than in claudicants (27.4% vs 20.4%, respectively; P=.049) and occurred qualitatively more often with longer, more heavily stenotic, and calcified lesions. Device success (defined as ≤30% residual stenosis following use of the DA device) was achieved in 74.9% of all target lesions and did not differ significantly between the claudicant and CLI groups or between femoropopliteal and tibial-peroneal lesions. Procedural success (defined as ≤30% residual stenosis at the conclusion of the procedure) was achieved in 89.0% of target lesions, including 91.2% of lesions in claudicants compared with 83.0% of lesions in the CLI subjects (P<.001) and was more often achieved in femoropopliteal lesions than in tibialperoneal lesions (90.1% vs 84.0%; P=.02). Following DA, the mean percent diameter stenosis was 24.3 ± 13.3%. For those lesions treated with adjunctive therapy, the residual stenosis was 18.7 ± 11.5%. Predictors of greater procedural success included female gender, SFA lesion location, lower baseline percent diameter stenosis, absence of vascular calcification, and shorter lesion length. Table 5 shows the periprocedural adverse events in the study. The most common event noted was arterial perforation (5.3%), which occurred more frequently in the claudicant group than in the CLI group (6.2% vs 2.5%, respectively; P=.04). Abrupt closure occurred in 15 cases (1.9%). Distal embolization was noted in 30 of 799 subjects (3.8%) as adjudicated by the CEC and angiographic core lab. This includes 24 events in 542 subjects (4.4%) with evaluable angiograms of run-off and 6 additional embolic events adjudicated by the CEC in the remaining 257 subjects without evaluable run-off angiograms. In total, 13 subjects (1.6%) had distal embolizations that were subsequently treated. The use of DEP devices was at the discretion of the implanting physician. No significant differences were noted in the rate of distal embolization by use of DEP (22/622 without DEP [3.5%] vs 8/177 with DEP [4.5%]; P=NS]. Moreover, within the group of subjects treated without DEP, the embolic event rates were not statistically different between patients treated with TurboHawk or SilverHawk devices (4/150 [2.7%] vs 18/472 [3.8%]; P=NS). There were no significant differences in rates of periprocedural events between femoropopliteal and tibial-peroneal lesions. Rates of distal embolization were also not significantly associated with other lesion characteristics, although greater rates of embolization in smaller target vessels, longer lesions, calcified lesions, and cases with multiple target lesions were observed.

The 30-day MAE rate was 1.6% including 4 deaths (0.5%), 6 clinically driven target-lesion revascularizations (0.9%), and 3 major unplanned amputations (0.4%; 1 above the knee, 1 below the knee, and 1 Syme’s), all in CLI patients. MAEs were more common among CLI subjects, with a rate of 3.5% vs 1.0% among claudicants (P=.02). None of the 4 deaths within 30 days were adjudicated as related to either the study device or the index procedure by the CEC (3 were due to myocardial infarction and 1 was due to cardiogenic shock).

All secondary outcomes are listed in Table 6, including ABI, RCC, the WIQ and EQ-5D questionnaires, and wound healing. Each outcome demonstrated statistically significant improvement at the 30 day follow-up visit compared with baseline. Procedural success and adverse events were no greater among patients with diabetes (Table 7). A small but significant difference favoring non-diabetics was found in improvement in RCC from baseline to 30 days (P<.01), but was not seen in ABI measurements.

Discussion

The DEFINITIVE LE study was undertaken to establish clinical and scientific data for DA using the SilverHawk and TurboHawk devices as treatment of infrainguinal PAD in both claudicants and CLI patients. The trial, although not randomized, was prospective, and all outcomes were determined by an independent CEC as well as adjudication of events by independent core laboratories (both angiographic and duplex ultrasonographic), which provides a scientific basis for the efficacy and outcome of DA in one of the largest prospective registries in the lower limb to date.

The overall trial results have already been published,25 and the outcomes demonstrated that DA was safe for the treatment of either claudicants or patients with CLI out to the endpoint of 12 months. However, several questions remain regarding the acute safety and results. Therefore, we report herein the specific outcomes with regard to acute and periprocedural outcomes to 30 days. These outcomes of this heterogeneous group of patients enrolled support the early positive findings seen elsewhere.19,20,24,26 However, these results were the first to be reported with independent core lab and clinical events committee adjudication not seen in prior single-center and multicenter registries. Additionally, despite having more adjunctive therapy in the longer-lesion subset and less in the shorter-lesion subset, there was no difference in acute complications or 30-day outcomes. The overall procedure time was longer for the CLI group, as could be expected with the multilevel nature of PAD in this patient population, but did not differ in fluoroscopy time or iodinated contrast dose. Unsurprisingly, more than 2 lesions and multilevel disease were independent predictors of longer procedure times. Furthermore, calcified lesions resulted in longer procedure times, although the use of DEP in these patients did not affect the 30-day outcome. The embolic events were very low at 3.8% overall. No significant difference in the rate of distal embolization by use of DEP was noted. However, the study was not powered to detect such differences and the use of DEP with more complex lesions, which tend toward greater rates of embolization, makes direct comparisons difficult. Within the group of subjects treated without DEP, the embolic event rates were not statistically different between patients treated with TurboHawk or SilverHawk devices (4/150 [2.7%] vs 18/472 [3.8%]; P=NS). Within the group of subjects treated with DEP, the embolic event rates were 4.0% (4/99 subjects treated with TurboHawk) and 5.1% (4/78 subjects treated with SilverHawk; P=NS). While no statistical differences can be detected, the embolic rates were slightly lower in subjects treated with TurboHawk than in SilverHawk models despite the treatment of more complex lesions. This event rate, which is lower than those reported elsewhere,21,26,27 and importantly, independently reported by the angiographic core laboratory, is acceptable for this device when compared with other devices used in the infrainguinal arteries. Perforation rate for this study was 5.3%, and all events were associated with wire passage, DA use, or adjunctive therapy to include PTA and/or stenting. We did not delineate the complication from one device to another in the process of the procedure because completion arteriography may not have been performed after each step. Therefore, the event was adjudicated as an event regardless of primary cause. Effective debulking to ≤30% diameter stenosis using DA alone was achieved in 74.9% of all procedures and in 89.0% of patients requiring adjunctive therapy. Average post-DA diameter stenosis was 24.3% and 18.7% following adjunctive therapy. The need for predilation to facilitate the passage and use of an atherectomy device occurred in 9% of lesions. This was noted in subjects with longer and more calcified lesions at baseline. Our findings suggest that optimal debulking in a challenging lower-limb location of the infrainguinal segments can be achieved using DA and that this method of revascularization is a viable alternative to PTA and stent approaches, with excellent safety and 30-day results for the treatment of patients with PAD.

Study Limitations

There are several key limitations to this trial and report. First, this study is a non-randomized registry. However, given that this protocol was not driven for device approval and more toward the scientific pursuit of the objective outcomes from therapy, it becomes noteworthy and makes this trial unique to other registries. Also, this report only details the events to 30 days. Furthermore, any complications that may occur after 30 days are not captured here. However, it should be noted that no further anatomic complications (aneurysm, etc) were reported in the final 12-month report. Lastly, these data and acute outcomes should not be extrapolated to other FDA-approved or pending approval atherectomy or atheroablative devices. Any potential inference should be performed in a direct fashion with direct comparator trials.

Conclusion

In summary, the findings of the DEFINITIVE LE registry establish the periprocedural and acute safety of the SilverHawk and TurboHawk systems for DA. As the primary outcome from DEFINITIVE LE provided evidence of a primary patency similar to other trials of stenting and drug-coated balloons, DA may provide an additional primary strategy for PAD without implantable scaffolds in this challenging anatomic territory.

Acknowledgments

The DEFINITIVE LE investigators would like to recognize and thank the patients involved with this clinical study for their participation. The authors would like to acknowledge Scott Brown, PhD, for statistical support, and Meghan Schadow, MS, Azah Tabah, PhD, and Bridget Wall, PhD, for assistance with technical aspects of the article.

ClinicalTrials.gov identifier: NCT00883246.

Funding: Medtronic, PLC, Santa Rosa, California.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. Dr Garcia reports that he is the principal investigator for the present study. Dr Jaff reports non-financial support from Abbott Vascular, Boston Scientific, Cordis Corporation, and Medtronic; compensated board member for VIVA Physicians (501c3 not-for-profit education and research organization); equity investment in PQ Bypass, Vascular Therapies, Primacea, and Embolitech. Dr Zeller reports grant funds to his institution and personal fees (advisory board) from Medtronic.

Manuscript submitted October 24, 2016; Provisional acceptance given November 18, 2016; Final acceptance December 20, 2016.

Address for correspondence: Lawrence A. Garcia, MD, St. Elizabeth’s Medical Center, Division of Cardiology, 736 Cambridge Street, Brighton, MA 02135. Email:  Lawrence.Garcia@steward.org 

References

  1. Dormandy JA, Rutherford RB. Management of peripheral arterial disease (PAD). TASC Working Group. TransAtlantic Inter-Society Concensus (TASC). J Vasc Surg. 2000;31:S1-S296.
  2. Pentecost MJ, Criqui MH, Dorros G, et al. Guidelines for peripheral percutaneous transluminal angioplasty of the abdominal aorta and lower extremity vessels. A statement for health professionals from a special writing group of the Councils on Cardiovascular Radiology, Arteriosclerosis, Cardio-Thoracic and Vascular Surgery, Clinical Cardiology, and Epidemiology and Prevention, the American Heart Association. Circulation. 1994;89:511-531.
  3. Second European Consensus Document on chronic critical leg ischemia. Circulation. 1991;84:IV1-IV26.
  4. Weitz JI, Byrne J, Clagett GP, et al. Diagnosis and treatment of chronic arterial insufficiency of the lower extremities: a critical review. Circulation. 1996;94:3026-3049.
  5. Smith GD, Shipley MJ, Rose G. Intermittent claudication, heart disease risk factors, and mortality.  The Whitehall Study. Circulation. 1990;82:1925-1931.
  6. 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;326:381-386.
  7. Schillinger M, Sabeti S, Loewe C, et al. Balloon angioplasty versus implantation of nitinol stents in the superficial femoral artery. N Engl J Med. 2006;354:1879-1888.
  8. Scheinert D, Scheinert S, Sax J, et al. Prevalence and clinical impact of stent fractures after femoropopliteal stenting. J Am Coll Cardiol. 2005;45:312-315. 
  9. Laird JR, Katzen BT, Scheinert D, et al. Nitinol stent implantation versus balloon angioplasty for lesions in the superficial femoral artery and proximal popliteal artery: twelve-month results from the RESILIENT randomized trial. Circ Cardiovasc Interv. 2010;3:267-276.
  10. Schillinger M, Haumer M, Schlerka G, et al. Restenosis after percutaneous transluminal angioplasty in the femoropopliteal segment: the role of inflammation. J Endovasc Ther. 2001;8:477-483.
  11. Adam DJ, Beard JD, Cleveland T, et al. Bypass versus angioplasty in severe ischaemia of the leg (BASIL): multicentre, randomised controlled trial. Lancet. 2005;366:1925-1934.
  12. Laird JR, Katzen BT, Scheinert D, et al. Nitinol stent implantation vs balloon angioplasty for lesions in the superficial femoral and proximal popliteal arteries of patients with claudication: three-year follow-up from the RESILIENT randomized trial. J Endovasc Ther. 2012;19:1-9.
  13. Gruentzig A. Percutaneous transluminal angioplasty. AJR Am J Roentgenol. 1981;136:216-217.
  14. Matsumura JS, Yamanouchi D, Goldstein JA, et al. The United States StuDy for EvalUating EndovasculaR TreAtments of Lesions in the Superficial Femoral Artery and Proximal Popliteal By usIng the Protege EverfLex NitInol STent SYstem II (DURABILITY II). J Vasc Surg. 2013;58:73-83.e1.
  15. Dake MD, Ansel GM, Jaff MR, et al. Paclitaxel-eluting stents show superiority to balloon angioplasty and bare metal stents in femoropopliteal disease: twelve-month Zilver PTX randomized study results. Circ Cardiovasc Interv. 2011;4:495-504. 
  16. Dake MD, Scheinert D, Tepe G, et al. Nitinol stents with polymer-free paclitaxel coating for lesions in the superficial femoral and popliteal arteries above the knee: twelve-month safety and effectiveness results from the Zilver PTX single-arm clinical study. J Endovasc Ther. 2011;18:613-623.
  17. Tepe G, Laird J, Schneider P, et al. Drug-coated balloon versus standard percutaneous transluminal angioplasty for the treatment of superficial femoral and popliteal peripheral artery disease: 12-month results from the IN.PACT SFA randomized trial. Circulation. 2015;131:495-502.
  18. Rosenfield K, Jaff MR, White CJ, et al. Trial of a paclitaxel-coated balloon for femoropopliteal artery disease. N Engl J Med. 2015;373:145-153.
  19. Ramaiah V, Gammon R, Kiesz S, et al. Mid-term outcomes from the TALON Registry: treating peripherals with SilverHawk: outcomes collection. J Endovasc Ther. 2006;13:592-602.
  20. McKinsey JF, Goldstein L, Khan HU, et al. Novel treatment of patients with lower extremity ischemia: use of percutaneous atherectomy in 579 lesions. Ann Surg. 2008;248:519-528.
  21. Keeling WB, Shames ML, Stone PA, et al. Plaque excision with the SilverHawk catheter: early results in patients with claudication or critical limb ischemia. J Vasc Surg. 2007;45:25-31.
  22. Yancey AE, Minion DJ, Rodriguez C, Patterson DE, Endean ED. Peripheral atherectomy in TransAtlantic InterSociety Consensus type C femoropopliteal lesions for limb salvage. J Vasc Surg. 2006;44:503-509. 
  23. 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;16:653-662.
  24. Zeller T, Sixt S, Schwarzwalder U, et al. Two-year results after directional atherectomy of infrapopliteal arteries with the SilverHawk device. J Endovasc Ther. 2007;14:232-240.
  25. McKinsey JF, Zeller T, Rocha-Singh KJ, Jaff MR, Garcia LA, Investigators DL. Lower extremity revascularization using directional atherectomy: 12-month prospective results of the DEFINITIVE LE study. JACC Cardiovasc Interv. 2014;7:923-933.
  26. Zeller T, Rastan A, Sixt S, et al. Long-term results after directional atherectomy of femoro-popliteal lesions. J Am Coll Cardiol. 2006;48:1573-1578.
  27. Sixt S, Rastan A, Beschorner U, et al. Acute and long-term outcome of SilverHawk assisted atherectomy for femoro-popliteal lesions according the TASC II classification: a single-center experience. Vasa. 2010;39:229-236.