Cath Lab Digest

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” (Figure 1) (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 (Figure 2). 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.