Cath Lab Digest talks with Raj Dave, MD, Director, Endovascular Medicine, Pinnacle Health/Harrisburg Hospital, Harrisburg, Pennsylvania
What is orbital atherectomy and how does it differ from rotational atherectomy?
Orbital atherectomy is a promising new methodology for treating symptomatic peripheral arterial disease within the major and branch arteries of the leg. It is performed with the Diamondback 360° Orbital Atherectomy System (Cardiovascular Systems, Inc., St. Paul, MN), a new atherectomy device utilizing an orbiting eccentric diamond-coated crown on the end of a drive shaft powered by a pneumatic drive console (Figures 1a and 1b). The shaft and crown are advanced over a pre-placed 0.014” proprietary guidewire, the ViperWire™. The orbital motion of the crown removes plaque from within a diseased arterial segment; as the crown orbits, the debulking area increases, and with increments in speed, the area increases further (Figure 2). For comparison, rotational atherectomy uses a concentrically rotating burr, so luminal gain is as large as the burr size being utilized. Changes in rotational speed of the burr do not result in a significant increase in debulking area as happens during orbital atherectomy. If a larger lumen is desired, a larger burr must be deployed.
Orbital atherectomy is performed over a 0.014” guidewire, in contrast to a 0.009” wire with rotational atherectomy. The larger diameter guidewire makes it easier to advance across a tight stenosis. More support is given, especially when a contralateral approach is utilized or when a supportive guidewire is essential for tracking of an adjunctive device, such as a self-expanding stent delivery catheter. Also, orbital atherectomy allows continuous blood flow through stenosed (but not totally occluded) vessels, which not only continuously flushes particulate downstream but may reduce device-generated heat.
How is orbital atherectomy different from directional atherectomy?
Directional atherectomy is performed using multiple passes with slight rotations of the device to remove plaque in a single plane with each pass. As the atherectomy catheter is advanced, the plaque removed is packed into the nose cone and after several passes, the catheter is removed to empty the nose cone. Orbital atherectomy requires a single insertion, with plaque debulking occurring as the crown is advanced back and forth through the lesion. The diamond coating on the orbital crown is of a fine granular texture and the particles “sanded” from the vessel wall are very small and are less apt to cause significant distal embolization, which can be a problem with directional atherectomy. In my experience with the Diamondback, I have not had angiographic evidence of particulate embolization (no reflow or distal cutoffs).
The orbiting action and ability to increase the orbit circumference by increasing the orbiting speed result in a substantial time saving during the atherectomy procedure. There are other differences in performance specific to lesion characteristics between the two types of atherectomy. The Diamondback, in my practice experience, performs appreciably better in calcified lesions than directional atherectomy.
In what type of lesions does orbital atherectomy perform well?
I have used it with great success in calcified or fibrotic smaller arteries below the knee as well as femoropopliteal vessels. Before the Diamondback was commercially available, there were many lesions that I would not have attempted to cross with atherectomy or other debulking devices that were available.
The ViperWire has good pushability and torque response. The Diamondback does require the use of this proprietary guidewire, which has a 0.023” spring coil tip.
After treating a calcified lesion, I find that the angiographic result is frequently excellent and almost stent-like in appearance. I do use less adjunctive therapy following orbital atherectomy, other than perhaps a simple balloon inflation to finalize a smooth lumen. When using a balloon after debulking with the Diamondback, it is possible to use lower atmospheres and thus reduce the potential for barotraumas.
The Diamondback works for fibrous tissue as well, but luminal gain is not as dramatic in soft plaque.
For total occlusions, what is your technique for gaining access to the distal lumen?
Do you use a support catheter or combination support catheter, and specialty crossing guidewires before placing the ViperWire guidewire? After performing several hundred cases with total occlusions, I have become fairly consistent with the use of a support catheter such as Spectranetics QuickCross (Colorado Springs, CO) and a Terumo Glidewire (Ann Arbor, MI). These two devices have provided me great success in gaining access in more than 90% of cases in which I needed to access the distal true lumen. In rare instances, I use a reentry catheter such as Outback (Cordis Endovascular, Miami, FL) or Pioneer. For below-the-knee lesions, I consistently rely on the Asahi family of guidewires (Miracle Bros, Confienza and Pilot, distributed by Abbott Vascular, Redwood City, CA), with close to 95% success. Recently, I have been very impressed by the ability of the Safe Cross reentry system to cross total occlusions in peripheral vascular cases. This device is extremely useful in complex plaque due to its ability to deliver radiofrequency energy while the wire is being advanced. After gaining access to true lumen, I utilize either a 0.035” QuickCross support catheter or 0.020” catheter to exchange for a ViperWire guidewire, and then perform orbital atherectomy.
The Diamondback has a range of crown sizes and operates at three preset rotational speeds. How do you determine the appropriate size crown and what is your current technique in terms of initial versus final rotational speed?
It is very important for the operator to be familiar with the two types of crowns available with this system — classic and solid — as well as the controller touch screen interface and the displayed information. The controller has preset speeds (low, medium and high). I start at low speed, followed by medium and then high, if needed, and advance the crown slowly (1 cm per second). Figures 3a and 3b demonstrate the speed and expected lumen diameter for each device size and type. It is critical to realize that lack of resistance in a vessel during an orbital atherectomy procedure does not mean device orbiting and sanding are not occurring. In other words, even after resistance is no longer felt, the device will continue to sand until a maximal lumen is achieved for the selected crown size and arterial lumen in which it is orbiting.
I usually start with a small crown and use it up to its maximum speed to achieve the largest lumen possible before upsizing to the next crown size, if necessary. Especially in below-the-knee lesions, orbital atherectomy will frequently produce a very acceptable standalone “stent-like” result. Hypothetically, preventing additional barotrauma may add value to long-term durability of the procedure by preventing restenosis. Verification of patency will likely evolve as we continue to see growth in the atherectomy device market and treatments addressed at preventing or reducing restenosis in the peripheral vasculature.
How do the solid and classic crowns differ?
The solid crown addresses the issue of additional luminal gain in larger vessel (Figure 3a). The 2.25 solid crown can achieve up to a 4.5 mm lumen, whereas a similarly sized classic crown will achieve a 3.8 mm lumen (Figure 3b). Certainly, having the diamond coating cover the entire crown increases the sanding surface area for debulking. In addition, having the diamond coating at the tip of the device improves its penetrating capacity through a difficult chronic total occlusion. The classic crown has a 1.25 mm crown, which is useful in treating smaller, more distal arteries. There are future crown design improvements underway to improve penetrating capacity and to address various types of plaque morphologies.
What is the risk of dissection and perforation?
More than 350 cases with the Diamondback were documented after the product was released in September of 2007 through the end of the year (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.
I do find that I use adjunctive therapy in fewer cases. When I do use adjunct therapy, I have found it is more successful when it is preceded by orbital atherectomy. Fibrocalcific plaque jeopardizes stent expansion in many lesions, and it is my opinion that an atherectomy procedure improves long-term results regardless of whether you plan on stent placement. Plaque reduction and the smooth lumen created with orbital atherectomy will improve the ability of the stent to expand and therefore maximize luminal gain. In calcified lesions, where stent mal-expansion and fractures are more common, the Diamondback can improve stenting results.
If I can get a stent-like result, as shown in a recent superficial femoral artery (SFA) case (Figures 4a–4e), I will avoid stenting. There are multiple other patient subsets, such as diabetics with small vessels or patients with challenging femoropopliteal segments, in which stenting is undesirable. In these cases, orbital atherectomy provides an excellent tool to achieve an acceptable result, without the need for adjunctive therapy.
Have you used this device in above-the-knee arteries — the SFA or popliteal?
Yes. I have found it extremely helpful in complex calcified SFA/ popliteal arteries. With the availability of the solid crown, my experience is growing in above-the-knee vessels. Fibrocalcific disease is extremely common at the adductor canal and in the popliteal artery where stenting results are poor. In fact, all nitinol stent trials exclude patients with popliteal disease at the knee joint. The Diamondback is an excellent tool to address that subset of patients — especially the diabetic patient with calcific disease — above, at and below the knee.
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