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. 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). 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 (Silver-
Hawk, 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
360º™ Orbital Atherectomy System, Cardiovascular Systems, Inc., St. Paul, Minnesota) now
joins the list of available options.
The Diamondback 360º 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.
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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
(Figures 3a, 3b). A controller allows adjustment of
speed and tracks device run time. It includes a touchscreen
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.) (Figure 4).
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 (Figures 5a–5c).
The wire was redirected to the posterior tibial artery,
and the proximal segment was treated with the 2.0 mm
crown (Figures 6a, 6b). 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 marketreleased
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.
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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 (Figures
7a–7c).
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 360º 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" wirebased
system used in the OASIS trial to a 0.014" wirebased
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
360º 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.
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