A New Treatment Option for Treating Peripheral Vascular Stenosis: Orbital Atherectomy

Introduction

Peripheral artery disease (PAD) is a manifestation of atherosclerosis that results in compromised functional capacity and an impaired quality of life for the affected individual.^1,2 There are many risk factors for PAD, including diabetes mellitus, current or past smoking history, age greater than 50 years, high blood pressure, obesity, hyperlipidemia, and a family history of heart disease or stroke.³ Classic symptoms affecting the lower extremities include pain with exercise (intermittent claudication) or, in extreme cases, rest pain, infection, ulceration, or gangrene, with these constituting critical limb ischemia (CLI).^4,5 According to the National Institutes of Health, an estimated 12 million individuals in the United States have PAD, although only 2 million of them have been diagnosed with the condition.

Orbital atherectomy is the latest technological advancement available for people with PAD. The concept of atherectomy to treat vascular occlusions has been pursued since the limitations of balloon angioplasty were recognized. Rather than compressing plaque and stretching an artery narrowed by atherosclerotic plaque, proponents of atherectomy have argued for removal of the plaque instead. Although stenting generally has improved upon the results achieved by balloon angioplasty, new challenges have evolved from stenting, including malapposition, underexpansion, and how to treat restenosis and thrombosis. Indeed, one of the potential indications for atherectomy is in-stent restenosis.

Atherectomy has taken several different forms including directional atherectomy or plaque excision (SilverHawk, ev3, Inc., Plymouth, Minnesota), laser atherectomy (Clir-Path, The Spectranetics Corp., Colorado Springs, Colorado), and rotational atherectomy (Rotablator, Boston Scientific, Inc, Natick, Massachusetts). As of August 2007, orbital atherectomy (Diamondback 360^º™ Orbital Atherectomy System, Cardiovascular Systems, Inc., St. Paul, Minnesota) now joins the list of available options.

The Diamondback 360^º OAS has several similarities to rotational atherectomy, as it utilizes an eccentrically mounted “crown” (analogous to the rotational atherectomy “burr”) that is diamond coated and rotates at speeds varying from 60,000 to 200,000 rpm. Rotation is powered by high-pressure air or nitrogen, similar to that utilized for rotational atherectomy. Once in the artery, the crown may be advanced forward and backward using the handle. The system operates on the principles of centrifugal force. As the crown rotates and orbit increases, centrifugal force presses the crown against the lesion or plaque, removing plaque with each orbit. The diamond-grit coating on the orbital atherectomy crown “sands” the plaque as the device comes into contact with the wall.

In contrast to the rotational atherectomy device, the orbital atherectomy crown is eccentric in shape and therefore, orbits on the wire rather than spinning concentrically on the wire. This unique characteristic provides several potential advantages. The crown is only in contact with one part of the vessel wall at any given moment, such that the crown does not obstruct blood flow through a stenosed (but not totally occluded) vessel. In OAS, unlike rotational atherectomy, the microscopic particulate matter that results from the sanding action on the plaque is continuously washed away in the blood stream rather than building up into a large bolus, which is subsequently released downstream when the rotational atherectomy catheter is disengaged from the plaque. The lack of continuous contact with the vessel wall also minimizes heat generation, a potential cause of restenosis.

Perhaps the most unique feature of orbital atherectomy is the variable lumen size that can be created by each device. Since centrifugal force is a function of both the mass of the device and the speed of rotation, faster speeds result in increased centrifugal force, yielding a larger orbit. As a result, a larger lumen can be created with a given crown by simply rotating it at higher speeds. This concept has been demonstrated in animal and cadaver studies, as well as in a carbon block model. A controller allows adjustment of speed and tracks device run time. It includes a touch-screen interface with pre-set device rotational speeds at low, medium, or high.

Thirty-five samples from 8 studies including cadavers, porcine, and carbon block models have been used to study the size of the particulate matter generated by the device. The average particulate size measured is 1.96 microns (99% CI), and 98.8% (99%CI) were smaller than the size of a typical capillary of 9.5 microns. (data on file, Cardiovascular Systems, Inc.).

A single-insertion device, the Diamondback 360^°, is available in Classic Crown and Solid Crown designs. The crowns come in sizes of 1.25 (Classic Crown only), 1.5, 1.75, 2.0 and 2.25 mm in diameter. These crowns are compatible with proprietary .014" guidewires (ViperWire^™, Cardiovascular Systems, Inc.) available in two different degrees of supportiveness: flex and firm. The Classic Crown has less mass than the Solid Crown, and the diamond-coated surface is only on the tangential surface of the crown. The Solid Crown, which received FDA clearance in December 2007, has more mass and diamond-coated surfaces on the tangential surface, plus the front- and rear-tapered sections that assist in the initial crossing of lesions. As a result of the additional weight, the Solid Crown can achieve larger lumens, making it possible to treat larger-sized vessels.

From September 1 through December 31, 2007, more than 350 cases with the Diamondback 360^° were documented (CSI data on file). Results show low rates of dissection (2%), perforation (2.3%), and embolism (2%). These results support the use of orbital atherectomy as a safe revascularization technique. As the Diamondback 360^° is utilized more frequently, the results will further clarify its role in the treatment of occlusive PAD.

Case 1

This case was performed during the Orbital Atherectomy System for the Treatment of Peripheral Vascular Stenosis (OASIS) Trial, which was used to obtain FDA clearance for the Diamondback. Catheters used in the trial included those with crowns measuring 1.2, 1.7, and 1.9 mm in diameter, advanced over a 0.009" rotational atherectomy wire, along with a first-generation controller that allowed manual setting of device rotational speed. Final data from this multi-center, non-randomized, prospective, single-arm trial will be published in the near future.

A 59-year-old woman with insulin-dependent diabetes, coronary artery disease (CAD), and chronic obstructive pulmonary disease presented with CLI. The patient had previously undergone intervention in the superficial femoral artery (SFA) and tibio-peroneal trunk but continued to have problems with wound healing. Angiography demonstrated severe focal ostial stenosis of the anterior tibial artery and severe stenosis of the proximal segment of the posterior tibial artery. The stenoses were approached with a 6 Fr, 90 cm contralateral sheath with bivalirudin for anticoagulation.

A 0.009 RotaWire guidewire (Boston Scientific, Inc.) was advanced to the distal anterior tibial artery. The ostial anterior tibialis stenosis was treated with 1.5 and 2.0 mm orbital atherectomy crowns. The wire was redirected to the posterior tibial artery, and the proximal segment was treated with the 2.0 mm crown. No adjunctive therapy was required for either lesion, as a residual stenosis of < 30% was achieved in both lesions.

Ankle-brachial index changed from 0.73 preprocedure to 0.86 postprocedure. The patient was ambulating at the time of discharge, and wound treatment continued with her primary physician.

Case 2

This case was performed with the market-released orbital atherectomy device. A 75-year-old man presented to the clinic with new wounds to his right foot, with intermittent rest pain. The wounds were on his lateral great toe and on the plantar foot below the 5th metatarsal. The patient was on an insulin-dependent diabetic with CAD, hyperlipidemia, hypertension and a history of carotid stenosis. In September 2005, the patient underwent an excisional atherectomy procedure of the left anterior tibialis, and angioplasty of the left distal posterior artery. Angioplasty of the left posterior tibial artery, left peroneal, and left anterior tibial was performed in May 2006. Post-procedure treatment included amputation of left second and fifth toes.

An angiogram in December 2007 of the right lower extremity showed no disease in the lower iliac with the common femoral artery and profundus femoral widely patent. The SFA had minimal calcification disease, and the popliteal also was widely patent. However, the anterior tibialis was 100% occluded in its mid-distal portion, with minimal filling of the dorsalis pedis via collaterals from the perineum. The posterior tibialis was also 100% occluded.

Orbital atherectomy using the Diamondback 360º of the right anterior tibialis artery was performed. Heparin was administered after passing a 65 cm Pinnacle Destination sheath (Terumo Interventional Systems, Somerset, New Jersey) over the aorto-iliac bifurcation to the mid-portion of the right superficial femoral artery. A Pilot-150 wire (Guidant Corporation) was then used to cross the chronic occlusion of the anterior tibialis artery. The pilot wire was exchanged for a ViperWire^™ guidewire using a Rapid Transit Catheter. A 1.75 Diamondback Classic Crown was run at 80,000, 140,000, and 200,000 rpm throughout the distal portion of the entrance of the tibialis artery and into the dorsalis pedis. This resulted in excellent improvement of stenosis from 100% occlusion to less than 20% residual occlusion, resulting in brisk blood flow.

Follow up at 30 days revealed that the wounds on the right great toe and on the plantar side of the distal fifth metatarsal have healed. The patient reported that his pain and claudication symptoms had subsided.

Conclusions

The Diamondback 360^º OAS is a new approach to treating PAD that overcomes many of the limitations of previous atherectomy devices. The range of crown diameters and rotational speed options allows treatment of stenoses in below-the-knee arteries. The eccentric crown design and orbital path of the device result in a smooth, polished concentric lumen significantly larger than the diameter of the crown using smaller introducer sheaths. The device is highly efficient, yielding “stand-alone” results in many patients. The rapid “sanding” effect and low complication rate contribute to short procedure and fluoroscopy times. The migration from a 0.009" wire-based system used in the OASIS trial to a 0.014" wire-based system now available enhances ease of use and avoids much of the need for wire exchanges.

The Diamondback 360^° is unique because the offset eccentric crown and orbital technology enable the operator to use speed adjustments to maximize the arterial lumen diameter achieved with each crown. This capability reduces procedure time and cost. The Diamondback 360º is able to treat complex plaque morphologies, including calcium, and is capable of generating a lumen that is as much as two times larger than the nominal crown size. The combination of a smooth, concentric lumen created by the orbiting motion and the differential sanding result in a low probability for dissection or perforation. Based on the ease of use, acute procedural success and safety profile, the Diamondback 360^º OAS appears to be another step forward in the interventionalist’s quest for safe and effective tools for the treatment of patients with severe peripheral arterial disease.