Avoiding the Aortic Arch and Using Flow Reversal: Carotid Artery Stenting with the Silk Road System to Reduce Stroke

Are there specific points during the (traditional femoral access) carotid artery stenting procedure that carry an increased risk of stroke?

One of the real baggage items with traditional carotid artery stenting (by “traditional carotid artery stenting”, I mean transfemoral percutaneous with a distal protection device strategy) is the endovascular highway “across the arch” phenomenon. Endovascular manipulation in the arch is probably the reason that elderly patients have a documented higher complication and stroke rate with traditional carotid artery stenting. The points in traditional carotid artery stenting where stroke is likely to occur are with catheter and sheath manipulation in the arch of the aorta, irrespective of the use of a distal filter protection strategy. There is inferential evidence, in the form of the ARMOUR¹ and EMPiRE² trials, that flow reversal is a better protection strategy than distal filters. The experience worldwide with the Silk Road system (Silk Road Medical), which is now close to 400 cases, has shown an incredibly low overall stroke risk, in the 1% range typically achieved with carotid endarterectomy. Many of the cases have been done in Europe, in both Toledo, Spain and by Ralf Kolvenbach in Dusseldorf, Germany, who published results of a small study in the Journal of Vascular Surgery.³ The cumulative experience of these 400 cases suggests that the Silk Road variation on carotid stenting may be the technical improvement or evolution that makes carotid artery stenting equivalent in perioperative outcomes to carotid endarterectomy, which is the holy grail that carotid stenting has been seeking.

Can you describe the ROADSTER trial?

The ROADSTER trial is a single-arm trial of the Silk Road device or strategy, which incorporates transcarotid access with a flow reversal system, and it is a trial investigating same in high-risk patients. The parameters are rather broad in this trial, but it is a single-arm, high risk as opposed to low risk trial, including both symptomatic and asymptomatic patients. 

Why include both asymptomatic and symptomatic patients?

CREST⁴ ultimately enrolled both symptomatic and asymptomatic patients, and one of the goals of ROADSTER and its largely vascular surgeon investigators is to mimic real-world practice, where surgeons might be looking for an alternative compared to traditional carotid endarterectomy. The surgeon investigators in this trial by and large would use carotid endarterectomy as the gold standard in most of these patients.

What are the endpoints of the ROADSTER trial?

Thirty-day stroke and death is the principal endpoint agreed upon by the FDA, so later outcomes are not crucial to the pivotal trial per se. We already know from CREST that if you get the patient over the hump of the procedure, long-term stroke prevention in CREST with endarterectomy versus carotid artery stenting was equivalent. It is getting over the periprocedural stroke risk that has been the rub for traditional carotid angioplasty and stenting; multiple meta-analyses of the available trial data indicate a 2-fold risk increased stroke/death risk for carotid artery stenting as opposed to carotid endarterectomy. 

Is this procedure being done in a hybrid OR?

Yes, we do all of our procedures in a hybrid operating room. I think that any environment with appropriate imaging would suffice. While the appropriate lighting, room and set up is required, the surgery, when performed by vascular surgeons, is really rather simple and straightforward. 

How is access with the Silk Road system performed?

The system requires a direct transcarotid cut down, low in the neck in the common carotid artery. There are certain technical/surgical nuances to securing the artery and positioning the sheath. The single most important technical and anatomic consideration is that the system does require a certain length of reasonably disease-free common carotid artery in order to access the artery and position the sheath. Patients need to have a fairly detailed ultrasound distance measurement between the clavicle and the carotid bifurcation that must equal about 5 cm of disease-free artery. 

Is tortuosity an issue?

It indeed can be an issue, although tortuosity at that level in the common carotid artery is not a particularly common problem. Such tortuosity occurs either in the mediastinum or up in the internal carotid artery, beyond the bifurcation. The tortuosity in the internal carotid and/or around the lesion, sometimes an obstacle in distal filter placement, is not an issue with the Silk Road system and procedure. There is a learning curve and we certainly did our first few cases under general anesthesia. Now we have done about 15 cases using only local anesthesia in the base of the neck, and that more than suffices for the carotid cut down in most patients.

What are the possible risks with a transcarotid cut down?

Where you access the common carotid artery with the Silk Road system, there is, at least in theory, a risk to the 10th cranial nerve, but all of the other cranial nerves that are involved in carotid surgery, such as the hypoglossal, glossopharyngeal, and spinal accessory, are a non-issue, because you are nowhere near any of those structures with this procedure. 

Some like to use the argument that if you add in cranial nerve injury, the neurologic event rate of endarterectomy is no better than carotid artery stenting. In our own practice, cranial nerve injury after carotid endarterectomy is vanishingly rare. 

What happens after the transcarotid cut down?

The common carotid artery is accessed low in the neck. Under appropriate anticoagulation, a purse string suture is placed in the anterior wall of the common carotid artery. One important technical point is to make sure that the access area of the common carotid artery is disease-free, because you do not want to use a purse string suture and put in a 10 French sheath in a diseased artery. We have had a couple of complications in patients with just that issue. Surgeons attempted to introduce this hardware into a diseased portion of the artery and had local dissections occur. After the purse string suture is placed, the artery is accessed with a micropuncture system. Presuming that the external carotid is patent, a stiffer wire is put in the external carotid, and the sheath and flow reversal system is introduced. The flow reversal system relies on the sheath pumping blood from the carotid artery through a little high-flow reversal system. The blood goes through a filter and then is returned to the patient via a femoral venous sheath. Once the flow reversal is activated, our experience has been similar to the paradigm in traditional carotid artery stenting in terms of paying attention to the time the filter is deployed. The duration of flow reversal is usually under 5 minutes. It certainly has been reported that there are patients who will not tolerate flow reversal. Experience has shown that even if the patient develops neurologic symptoms, or if the procedure is done under general anesthesia with electroencephalographic (EEG) monitoring, for example, the period of flow reversal is so brief that you can usually proceed by driving up blood pressure and moving along. We have done close to 20 cases and haven’t yet seen a patient who didn’t tolerate flow reversal; this includes some patients with contralateral high-grade carotid artery stenosis. 

After the system is introduced, flow reversal is begun, and at this point, a small-diameter predilatation can be done, although this is not required very often. Primary stenting and a gentle post deployment angioplasty, during which we generally never use anything bigger than a 5 mm balloon, is really the way to go. The Silk Road system theoretically carries the same risk of hemodynamic consequences as traditional carotid artery stenting, and we prophylactically administer glycopyrrolate, not atropine, to our patients. We haven’t had any significant bradycardia or hypotension result.

What have you observed in the cases you have done so far?

In the 20 cases we have done, the results have been good. We have had no complications. The Silk Road procedure is less of an operation for the patient than a traditional carotid endarterectomy. Circumstances where the Silk Road procedure is especially helpful include radiated necks with tissue rigidity and scarring, and redo carotids (there are a high percentage of redos in our cases). This procedure is substantially less of an operation for the patient than a redo carotid endarterectomy.

How would you describe the learning curve?

There is a learning curve, but it will be very different depending on the operator. Let’s restrict it, for example, to vascular surgeons, because I am going to assume that one operator would do the cut down and do the endovascular portion of the procedure. For an endovascular-competent vascular surgeon, the learning curve for this procedure is rather gentle. For a surgeon who has done very little endovascular work or no carotid stenting, that curve, of course, is steeper.

Do you anticipate that the system use will always be done with a single operator, or that some institutions might decide to have the surgeon do the cut down, and then have an interventionalist come in and place the stent?

I am certain that will happen. As a matter of fact, there is at least one of our trial sites where that is the modus operandi. Some of the ROADSTER trial sites have, for example, neurosurgeons doing the entire procedure themselves, and there are one or two sites where surgeons are teamed with interventionalists and they do the procedure together. You could use the analogy of who is doing thoracic aortic endografting at your institution. Across the country, that varies, from vascular surgeons who do the procedure by themselves, to places where cardiac surgeons and vascular surgeons do it together, to places where cardiac surgeons and cardiologists do it together. There are certainly a number of endovascular procedures where different specialties will either perform it in isolation or in tandem, and those things are usually governed by local practice, local expertise, and local politics.  

Timewise, how does the Silk Road system compare to traditional carotid stenting?

It is a variable of experience. We have done this procedure, start to finish, in an hour. It could be equivalent or I can certainly envision that in many patients, this would be more expeditious than traditional femoral access, depending on how easy it is to place a sheath across the arch. 

What do you anticipate for the future?

The first thing that we have to do with this trial is get FDA approval and an indication. Not even getting into the whole morass of CMS reimbursement, I think that both traditional transfemoral and the newer transcarotid high-flow reversal with the Silk Road system will be available for some time. My personal opinion, and why I agreed to be the national co-principal investigator of the ROADSTER trial along with Chris Kwolek, MD, is that the transcarotid high-flow reversal system is the next step in the evolution of carotid stenting. I believe it has the potential to make stenting of equivalent safety to carotid endarterectomy. Carotid artery stenting with traditional distal filter placement is a failed experiment, in my view. It got as good as it’s going to get in the CREST trial. CREST was confined to expert operators, yet even then, the stroke/death rate of angioplasty and stenting was twice that of carotid endarterectomy. It is possible the Silk Road system will prove to be the next step in the natural evolution of the carotid stenting procedure, but it all depends on the results of the trial. 

Disclosure: Dr. Richard Cambria reports that he receives clinical trial support to conduct the ROADSTER trial from Silk Road Medical; similar trial support has been received from W.L. Gore, Cool Medical, and Medtronic.

Dr. Richard Cambria can be contacted at rcambria@partners.org

References

1. Ansel GM, Hopkins LN, Jaff MR, Rubino P, Bacharach JM, Scheinert D, Myla S, Das T, Cremonesi A; Investigators for the ARMOUR Pivotal Trial. Safety and effectiveness of the INVATEC MO.MA proximal cerebral protection device during carotid artery stenting: results from the ARMOUR pivotal trial. Catheter Cardiovasc Interv. 2010 Jul 1; 76(1): 1-8. doi: 10.1002/ccd.22439.
2. Clair DG, Hopkins LN, Mehta M, Kasirajan K, Schermerhorn M, Schönholz C, Kwolek CJ, Eskandari MK, Powell RJ, Ansel GM; EMPiRE Clinical Study Investigators. Neuroprotection during carotid artery stenting using the GORE flow reversal system: 30-day outcomes in the EMPiRE Clinical Study. Catheter Cardiovasc Interv. 2011 Feb 15; 77(3): 420-429. doi: 10.1002/ccd.22789.
3. Pinter L, Ribo M, Loh C, Lane B, Roberts T, Chou TM, Kolvenbach RR. Safety and feasibility of a novel transcervical access neuroprotection system for carotid artery stenting in the PROOF Study. J Vasc Surg. 2011 Nov; 54(5): 1317-1323. doi: 10.1016/j.jvs.2011.04.040.
4. Brott TG, Hobson RW 2nd, Howard G, Roubin GS, Clark WM, Brooks W, et al; CREST Investigators. Stenting versus endarterectomy for treatment of carotid-artery stenosis. N Engl J Med. 2010 Jul 1; 363(1): 11-23.