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How to Optimize Cerebral Protection During CAS
How many randomized clinical trials of parachutes vs. no parachutes are there? The answer, of course, is none. Not surprisingly, for the same reason, the number of randomized clinical trials of carotid artery stenting with or without embolic protection is also none.
However, an analysis of CAS cases in Germany found that embolic protection devices do, in fact, lower the death rate after carotid stenting. In 13,086 carotid stenting cases between 2009 and 2014, embolic protection devices were used in 67.1% of asymptomatic patients and 48.4% of symptomatic patients, and those who had any embolic protection device used had reduced risk for stroke or death vs. those who did not (crude RR = 0.55; 95% CI, 0.44-0.69).
There are a number of different embolic protection devices on the market. There are various distal embolic protection devices available, as well as a proximal embolic protection device (MoMa, Medtronic). Then there is a newer device that has caused a lot of excitement, the Enroute Transcarotid Neuroprotection System (Silk Road Medical), which provides proximal protection with flow reversal. See the Table for a breakdown of the strengths and limitations of each.
Distal Embolic Protection
Distal protection is still the most popular modality of embolic protection. It is quick, simple and technically straightforward. It allows for treatment with a 6F sheath instead of the 8F one used in proximal devices. Patency of the external carotid artery is not an issue with distal devices, but can be with proximal devices. It also enables carotid stenting with radial artery access, which benefits patients with morbid obesity, sleep apnea or chronic obstructive pulmonary disease.
There are a number of limitations with distal embolic protection. The lesion must be crossed with the embolic protection device. Only emboli 100 µm or larger will be captured. Debris may be lost during capture, and a filter could inadvertently cause dissection. Incomplete apposition in curves is also well-documented.
The newest distal protection device is the Wirion system (Allium Medical); the WISE study of its efficacy in 120 patients was published in March 2017. Unique to this device is a locking mechanism that allows for deployment of the filter at any position or any location on the wire. In WISE, the overall MACCE rate was 3.3%, the overall stroke rate was 2.5% and there was only one major stroke.
The Paladin device (Contego Medical) is another unique way of preventing embolization during the post-dilation phase of the carotid stent using an integrated 40 µm embolic protection filter.
It’s important to remember that distal embolic protection devices are probably not the embolic protection system of choice for string signs, for patients with a bovine or calcified arch or for patients with tortuosity of the common carotid artery or the internal carotid artery. In these situations, a different approach would be mandated. If a filter cannot be placed properly, there is no harm in switching to proximal protection or in sending the patient for carotid endarterectomy.
Proximal Embolic Protection
Advantages of proximal embolic protection include that all steps of the procedure are done under protection and you can use whatever wire you want. But you need a large sheath size and as many as 10% of patients will experience some form of intolerance, especially if their opening stump pressure is less than 40 mm Hg.
We know from studies of diffusion-weighted imaging using transcranial Doppler that there are more hits with distal embolic protection compared with the MoMa device. In a meta-analysis of eight studies comparing proximal vs. distal protection with diffusion-weighted MRI imaging, most studies showed an advantage for proximal protection, but two showed an advantage for distal protection. For the contralateral side, there were fewer ischemic lesions with proximal vs. distal protection.
The MoMa device uses an 8F integrated sheath with a 7.2-cm difference between the external carotid artery balloon and the common carotid artery balloon. It removes debris via aspiration.
An advantage of the Enroute device is that it provides protection for all steps of the procedure, with less cranial nerve injury than that associated with carotid endarterectomy. It also avoids catheterization of calcified or severely diseased arch vessels. Of all the carotid protection device trials in high-risk patients, the ROADSTER trial of the Enroute device had the lowest stroke rate, only 1.4%, all of which were minor strokes. However, it’s important to remember that it may not be appropriate for patients with calcified common carotid arteries, and that it requires a small neck incision, and is frequently done with general anesthesia. Also, a common carotid artery working length of at least 5 cm and a common carotid artery diameter of at least 6 mm is needed.
Future Is Bright
In the future, I think we will see more direct carotid access. Data for mesh-covered stents are quite exciting, with very low stroke rates. These devices are likely to improve the results of CAS. It is hoped that CMS will broaden reimbursement in order to maintain our talent and skill level in CAS procedures.
We can conclude that patient selection, lesion characteristics and arch anatomy are critical factors in determining the type of embolic protection to be used in CAS. Like everything else we do, meticulous technique, good judgment and an experienced operator are crucial for success.
- References:
- Knappich C, et al. JACC Cardiovasc Interv. 2017;doi:10.1016/j.jcin.2017.03.032.
- Kwolek CJ, et al. J Vasc Surg. 2015;doi:10.1016/j.jvs.2015.04.460.
- Scheinert D, et al. Circ Cardiovasc Interv. 2017;doi:10.1161/CIRCINTERVENTIONS.116.004244.
- Stabile E, et al. JACC Cardiovasc Interv. 2017;doi:10.1016/j.jcin.2014.05.019.
- For more information:
- Peter A. Soukas, MD, is the director of vascular medicine and the Interventional Vascular Laboratories at The Miriam and Rhode Island Hospitals, the director of the Brown Vascular & Endovascular Medicine Fellowship Program and associate professor of medicine at Brown Medical School. He can be reached at 208 Collyer St., Suite 100, Providence, RI 02904; email: psoukas@lifespan.org.
Disclosure: Soukas reports he receives research grants from Bard Peripheral Vascular, Biotronik, Cordis, Endologix, Intact Vascular, Juventas, Shockwave Medical, Spectranetics and W.L. Gore and Associates.