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Andò et al. Vessel Plus 2023;7:15 https://dx.doi.org/10.20517/2574-1209.2023.26 Page 11 of 22

advancement (with the corresponding lack of advancement observed under fluoroscopy), and, above all, the
lowering of the pitch of the burr sound that is generally associated with decelerations > 5,000 rpm and
indicating an increase in resistance encountered. There are technical algorithms for managing and resolving
burr entrapment [74,76] that go beyond the scope of this manuscript.

Orbital atherectomy
The Diamondback 360° Coronary Orbital Atherectomy (OA) System (Cardiovascular Systems Inc., St. Paul,
MN, USA) is a percutaneous device currently indicated to facilitate the placement and implantation of
coronary stents. The OA system uses a single-size (1.25 mm) diamond orbiting eccentric crown that runs
eccentrically on a dedicated guidewire (ViperWire, Cardiovascular Systems Inc.); the system is compatible
with 6 Fr guide catheters and is operated by an electric console; a special knob allows to control the forward
and backward movements of the crown. The system involves a washing solution (ViperSlide,
Cardiovascular Systems Inc.) which reduces friction while the orbiting crown ablates calcium; the system
can operate at low or high speed (80,000 or 120,000 rpm, respectively). The mechanism of action of the
orbiting crown is bi-directional differential sanding, which uses centrifugal force to ablate the hard calcified
tissue and deflects the normal tissue, leaving it intact. The high speed creates a larger sanding diameter by
increasing lateral pressure, while the slower manual advance of the orbital crown increases the radius of the
[77]
orbit, eventually creating fractures of calcium . Coronary OA can be assimilated to RA but has several
potentially advantageous technical aspects that distinguish it. The orbiting crown allows a bidirectional
ablation of the calcium, both in forward and backward motions, to reduce the risk of device entrapment. In
addition, the orbiting eccentric crown creates pulsatile forces that affect deeper calcium and contributes to
[78]
change in vessel compliance . Thanks to the small dimensions of the crown, the blood flow is maintained
during the calcium ablation, and this reduces thermal injury and allows the continuous washout of the
micro-particles produced by ablation (which, however, are smaller than 2 microns, therefore smaller than
those produced by RA), and therefore a lower risk of no-reflow. The specificity of orbital atherectomy is the
variable lumen size that can be obtained with the single 1.25 mm crown according to the duration of
ablation, the number of passes, and the rotational speed. Since centrifugal force is a function of both the
speed of rotation and the device mass, faster speeds result in increased centrifugal force and ultimately a
larger orbit. As a result, a larger lumen can be created by the same crown simply by rotating it at higher
speeds. The OA system is currently used in the USA and Japan and has been clinically introduced in Europe
in the last couple of years. Data on OA clinical outcomes are derived from the single-arm ORBIT I, first-in-
[80]
man studies of 50 patients in India and ORBIT II, 443 patients in the USA , and from a retrospective
[79]
real-world registry of 458 patients, which confirmed the safety and efficacy of OA with low rates of
angiographic complications and MACE . Long-term results report a 3-year target lesion repeat
[81]
revascularization (TLR) incidence of 7.8% and MACE of 23.5% in the ORBIT II study . The ECLIPSE
[82]
[83]
study , the largest ever randomized study in patients with severely calcified coronary lesions
(clinicaltrials.gov: NCT03108456) has recently completed the enrollment of approximately 2,000 patients
receiving OA or conventional angioplasty to prepare coronary arteries for stent implantation. Studies with
OCT have shown that OA results in more profound tissue modification than RA and a lower incidence of
malapposed stent struts . Basically, this theoretically better vessel preparation could be associated with
[43]
clinically superior long-term results; however, no randomized study has ever compared OA with RA. Post-
marketing data from the USA report a not negligible incidence of complications, including both vascular
(perforations related to excessive straightening of the ViperWire and dissections) and general events
(arrhythmias, and death). The most reported failure modes included detachment and/or structural damage
[84]
of the device components and device entrapment . On this background, high speed is now generally
avoided in tortuous lesions, severe angulations, and vessels smaller than 3.0 mm in diameter . Not
[84]
differently than with RA, attention to meticulous procedural technique is the key to effective safe utilization
of OA.