November 6th, 2013
Perspective On the First New Atherectomy Device in 20 Years
The 2011 ACCF/AHA/SCAI PCI guidelines give rotational atherectomy (RA) a Class IIa LOE C recommendation as reasonable to use in cases where heavily calcified coronary lesions either cannot be crossed by a predilation balloon or if crossed cannot be adequately predilated prior to successful stent delivery. Furthermore, routine use of RA is Class III, contraindicated, as demonstrated in trial data from the late 1990’s, early 2000’s—In the 1997 DART trial, for instance, restenosis was seen in a quarter of patients, whether they were treated by RA or POBA. The ARTIST trial in 2001 failed to demonstrate benefit for routine RA in diffuse BMS in-stent restenosis.
Modern therapy with paclitaxel DES also failed to demonstrate a benefit with routine pretreatment of heavily calcified lesions in the ROTAXUS trial in 2009 with regards to the predefined primary angiographic endpoint of late lumen loss at 30 days. Though a modest clinical benefit was noted among the secondary endpoints, the trial was admittedly underpowered to make the claim suggested by the data.
Traditional rotational atherectomy systems rely on an in-line, concentric diamond-tipped burr whose end result is debulking of fibrotic and calcific lesions to microparticulate matter of a minimum of 5-10 microns in diameter. Immediate frequent adverse effects include “slow” or “no reflow” phenomenon sometime accompanied by localized myocardial stunning, vessel spasm and transient occlusion, neighboring plaque shift and jailed side branch, dissection or complete heart block in RCA or dominant LCx lesion intervention. Rotablation is therefore not indicated in shock, thrombus, dissection, CTOs, low EF, single conduit, or vein graft intervention.
The Diamondback 360 Coronary Orbital Atherectomy System (OAS), just approved by the FDA, will likely improve these outcomes and hopefully end-user perceptions as well. I was able to get some quality hands-on time with the Stealth© OAS at a recent Interventional Fellows’ Conference last month, and found the device remarkably easy to use with clearly a significant amount of forethought invested in device design and execution. A 1.25mm or 1.50mm diameter crown, eccentrically mounted on a drive shaft, creates an orbit with rotational motion that is manipulated in fine gradations by adjustment of the RPM control knob, mounted on the device console. There is a proprietary stainless steel, spring tip guidewire (not substitutable) with a safety cone that must be kept unkinked so as to ensure no kinks within the guidewire and drive shaft within the body. At the most caudad end of the console is a brake to secure the guidewire and drive shaft in place, preventing both axial and rotational motion in those components. Once the saline infusion pump (nonsterile) is setup and primed (ensuring all air along the line is out and proprietary lipid-enriched Viperslide fluid lubricates the working length), the motor is turned on and low RPMs initiated. Constant to-and-fro motion starting just proximal to the lesion and angiographic guidance of debulking follows as with traditional atherectomy. As with traditional rotablation, any kinks or bends in the guidewire are prohibitive, and the maximum time for the Diamond OAS is 5 minutes in the IFU.
In 2008, ORBIT I demonstrated the superiority of orbital atherectomy. While the purpose of vessel prep remains the same –i.e., reduce plaque shift, facilitate stent placement, reduce calcium burden to allow optimal stent expansion – this new methodology with eccentric orbit allows blood and particulate microdebris to flow past the crown, allowing its continuous washout. Additional benefits include auto-cooling of the apparatus and reduction of thermal injury risk to the vessel. It’s particularly remarkable to note that the particulate matter dislodged are on the order of 2-5 microns in diameter, roughly a quarter to one-half the size of the size of debris from traditional rotablation systems. This matter is in turn auto-phagocytized by the reticulocyte endothelial system, explaining the significantly reduced incidence of slow or no-reflow phenomenon noted with OAS use. Because orbit size can be changed 1:1 with motor speed, there are inherently less exchanges and better conformability to varying / tapering vessel diameters, thereby creating a better reconstruction of the native lumen prior to stenting. The safety and efficacy demonstrated in this year’s ORBIT II trial by 30-day MACE was illustrative of its prior success.
Premarket approval and selective rollout will start the process of iterative discovery. What remains to be seen is not only how quickly the use of this adjunct device takes hold, but what frontiers can be safely breached as the initial steep learning curves are overcome for device fine-tuning. Can OAS be instrumental in diffuse ISR, where traditional rotablation has failed? Can the use of OAS be applied to unprotected left main lesions, where traditional systems have shown significant promise in those with SYNTAX scores >50? Research implications can potentially include the use of IVUS/OCT co-registration of post-ablation vessel diameter, uniformity, and micro-dissection that further inform stent selection, thereby ensuring greater long-term durability and efficacy.
Finally, taking a more ubiquitous global view, how does OAS fare in the periphery? In a large registry of all comers, OAS for PAD endovascular intervention has shown great promise already. In the CONFIRM Registry debulking (above and below-the-knee) was documented in over 3000 pts. Observational data without core lab adjudication of plaque reduction must of course be interpreted with caution, but OAS demonstrated impressive results in an expectedly morbid cohort of patients, where more than two-thirds were diabetic, more than two-thirds had co-existing CAD, and nearly half had critical limb ischemia at the time of intervention. Over the 2 year span from 2009 to 2011, the CONFIRM I, II, and III registry data demonstrated a paradigm shift from attempts primarily at lumen gain to techniques aimed at maximizing vessel compliance, by using shorter spin times, smaller crown sizes, lower rotational speeds, and lower post-ablation maximal inflation pressures. These in turn dramatically lowered slow flow, embolism, and spasm. If the adjunctive use of OAS can help change the operative paradigm from barotrauma and recoil/dissection to one focused on long-term compliance of a smaller lumen, this seems truly worth the wait.