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Stent Retrievers, Aspiration Catheters & Promising New Devices for Stroke Thrombectomy

Author Gabrielle Gard covers Stent Retrievers, Aspiration Catheters & Promising New Devices for Stroke Thrombectomy on BackTable VI

Gabrielle Gard • Feb 16, 2022 • 631 hits

With a variety of equipment for stroke thrombectomies, choosing the optimal techniques and equipment remains a difficult and ambiguous decision for providers. The most commonly used equipment are the stent retriever, double stent retriever, aspiration catheter, balloon guiding catheter, or a combination thereof. To better patient outcomes, it is necessary to factor in the thrombus location as well as the anatomy of the patient before deciding on therapy. Additionally, challenging strokes remain difficult to target and treat with current thrombectomy equipment. However, there are promising new technologies that will help elucidate clot composition and better resolve tough fibrin rich clots.

Dr. Hannes Nordmeyer, head of the Neurointerventional Department at the St. Lukas Hospital in Solingen with radprax, and Dr. Matthew Gounis, director and co-founder of the New England Stroke Center, discuss how to determine the optimal techniques for patients and the future of challenging thrombectomies. We’ve provided the highlight reel in this article, but you can listen to the full podcast below.

The BackTable Brief

• Current technologies, such as stent retrievers and aspiration catheters, result in high success rates of TICI 2b/3 for stroke thrombectomies, but a first pass TICI 2c/3 should be the new standard of success.

• Clot composition, anatomical layout, and clot behavior are critical factors in determining which equipment will result in the best patient outcomes.

• Future technologies, such as large bore aspiration catheters and new neurovascular imaging, will help resolve and reveal difficult anatomy and clot composition.

• Tough fibrin rich clots evade current technologies, but the Cerenovus Nimbus geometric clot extractor shows promise for successful treatment.

Stroke stent retriever device Cerenovus Nimbus geometric clot extractor

Table of Contents

(1) Selecting the Optimal Stroke Equipment: Stent Retriever, Aspiration Catheter, or Balloon Guiding Catheter?

(2) What To Do When Tough Clots Won’t Budge: Alternatives to Stent Retrievers and Aspiration Catheters

(3) The Future of Aspiration Catheters & the Importance of Clot Composition

Selecting the Optimal Stroke Equipment: Stent Retriever, Aspiration Catheter, or Balloon Guiding Catheter?

With recent technological advances, standard stroke thrombectomies have diversified beyond the original Penumbra system with aspiration. With this advancement comes the difficulty to choose the best stroke therapy for a given patient. Operators must now choose between a stent retriever, double stent retriever, aspiration catheter, balloon guiding catheter, or a combination of solutions. Dr. Gounis and Dr. Nordmeyer offer their approaches to selecting the optimal stroke equipment. Dr. Gounis discusses how changing the definition of a successful recanalization as first pass TICI 2c/3 will help to determine the optimal techniques. Further, Dr. Nordmeyer discusses how the anatomical layout of the patients’ vessels, the thrombus location, and the clot’s behavior should be used to choose the appropriate equipment.

[Dr. Michael Barraza]:
All right. So both of you have clearly played an integral role in the evolution of optimal stroke therapy, and so the question is today, what do we consider optimal in terms of technique and equipment and doing stroke thrombectomy? And I learned with stent retrievers first, specifically the solitaire, and then it changed practices. As you know, the vast majority of these were done with aspiration first with the penumbra system, and more recently with imperative care zoom catheters, which Dr. Gounis is familiar with having published a paper on the efficacy of those. They're fantastic catheters, but the point of all this is that I didn't really notice any difference in terms of efficacy in technical or clinical success between these two different systems, and I don’t know if that’s anecdotal, but it's really not just me. And, you know, we have all these case series and trials with catchy names (my favorite being the BADASS technique, CAPTIVE, and SAVE), and they all propose some combination of stent retrievers, balloon guides, and aspiration catheters as the best way to remove clot. But to me, it seems like there's no real convincing data that establishes any of these is superior. Do you guys agree or am I missing something?

[Dr. Hannes Nordmeyer]:
So I think we're still struggling with the most effective method to pull clots, right? So, we tried out anything: pure stent retriever in combination with balloon guiding catheters, double stent retriever techniques, SAVE techniques, pure aspiration. And I had the fortune to work with René Chapot for many years, and we went for double retriever techniques. Really in the early years of thrombectomy, when we failed to retrieve the clot within the first two or three maneuvers, we deploy two stent retrievers in parallel to untangle the clot in between of them. And we had really high success rates with that, and, yes, I think nowadays, the need is really to have one retriever that makes it all, right?

[Dr. Matthew Gounis]:
I can elaborate a little bit on that, in that, I think at estimate, we had the good fortune to hear the SWIFT DIRECT study. And what I took away from that is that it was really compelling that up to 97% of successful recanalization, which is defined as TICI 2b/3. So the techniques and the equipment have gotten remarkably good. I think we need to change the definition of success, which is what Dr. Nordmeyer just said, and that should be first pass TICI 2c/3because that's what we know is going to impart the greatest benefit to the patient.

[Dr. Michael Barraza]:
Yeah, I think that's a really important point. Dr. Nordmeyer, for a standard large vessel occlusion what is your normal setup in terms of equipment?

[Dr. Hannes Nordmeyer]:
We have mainly two setups. In patients with straight cervical vessels, we go for balloon guide catheter and a stent retriever technique. If there is any anatomical reason, like extremely torturous ICA, where a balloon guiding really doesn't make any sense because aspirating from below, with all the vasculature distal to it, having been stretched and being in a ventralposition, doesn't make sense. We go for a triaxial access with a guiding catheter, aspiration catheter, and the microcatheter for the stent retriever. So, this is mainly the approach for easy and difficult anatomical situations, and then it's really up to the location of the thrombus and the behavior of clot within the first one or two maneuvers, whether to change the method or to go on with the stent retrieving approach.

Listen to the Full Podcast

Challenging Stroke Thrombectomies with Tough Clot with Dr. Matt Gounis and Dr. Hannes Nordmeyer on the BackTable VI Podcast)
Ep 178 Challenging Stroke Thrombectomies with Tough Clot with Dr. Matt Gounis and Dr. Hannes Nordmeyer
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What To Do When Tough Clots Won’t Budge: Alternatives to Stent Retrievers and Aspiration Catheters

Regardless of technology, success relies heavily on the embolus composition, especially for fibrin rich clots, which evade the stent retriever and the aspiration catheter. Dr. Gounis details how the stent retriever and the aspiration catheter work to resolve tough clots and the differences between them. The Cerenovus Nimbus geometric clot extractor has been showing promise on resolving tough clots due to its unique angles and stronger radial force. Dr. Nordmeyer discusses how he has switched to using the Nimbus on fibrin rich clots that do not respond well to a stent retriever in order to get a high success rate.

[Dr. Matthew Gounis]:
I thought it was a very thoughtful approach to looking at thrombectomy, and what we've learned in today's existing technology, forgoing what is to come, is that the success of the procedure relied largely on the composition of the embolus, the thing that occludes the vessel. And so, it's been shown that groups in Germany, the collaborations like the STRIP registry, that clots that have a lot of fiber (they're typically from cryptogenic strokes or from a cardio embolic source), essentially the stent retriever or an aspiration catheter, can't get them. And it's because with a stent retriever, there's less integration with this tough fibrin structure, so that's the way stent retrievers work is by kind of acting like a cheese grater and getting some of the clot in the interstices of the device. So that as you pull it, you have mechanical clamping of the clot, and if you don't get that integration, what happens is the clot simply rolls off the stent. That's why it was really an interesting analysis from the STRATIS that they found longer stent retrievers are more effective, and it's just because you're giving the clot less opportunity to completely roll off the stent. With aspiration catheters, you can't get adequate ingestion if it's very fiber rich, so you can't get adequate amounts of clot into the catheter, so that when you pull it, you can't get the entire clot out. So these fibrin rich clots are kind of like the tough clots, and it’s probably around, Dr. Nord Meyer can clarify, 20% of the time. That's why with today's existing technology, like different stent retrievers, I have a different mechanism of action, like a Nimbus type device. We've shown that with the technique Dr. Nordmeyer invented, which is kind of to pin the clot with the microcatheter and the Nimbus device, what we've shown in vitro studies doing high resolution CT is that there's less relaxation, or loss of integration, with the stent retriever and using a technique like that.

[Dr. Michael Barraza]:
In terms of design, is the Nimbus any different from a standard stent retriever?

[Dr. Matthew Gounis]:
Yes, it's fundamentally different. So, it's got a unique series of angles on the proximal end that are smaller in diameter. It has a stronger radial force. and so, yes, it's fundamentally a different concept and that's why it's probably working better with these fibrin rich clots. I don't know if Dr. Nordmeyer would like to elaborate.

[Dr. Hannes Nordmeyer]:
Yes, it's really impressive to see the Nimbus device acting in a model with a fibrin rich clot, where you can see under camera guidance, how the proximal spiral part of the device grips the clot and, really, pinches the clot while the struts close if you resheath it a little bit by advancing the microcatheter over the proximal part of the device. And we've seen that in the lab. And then we really felt that in real life in patients, it worked the same way. So whenever we found that the clot was fibrin rich, just by pulling out tiny fibrin, rich white or yellow fragments, or just by getting the feeling that the clot is not reacting to a stent retriever, we switched to Nimbus and performed this pinching maneuver and really had high success rates.

The Future of Aspiration Catheters & the Importance of Clot Composition

While current equipment and therapies have led to high recanalization rate of TICI 2b/3 from the SWIFT DIRECT study, developing technologies may pave the way towards better patient outcomes with more instances of first pass TICI 2c/3. Dr. Gounis sheds light on a new class of the large bore aspiration catheter, 088 aspiration systems, and the millipede catheter currently undergoing testing in Ireland. While existing optical coherence tomography and IVUS systems are not suited for intracranial use, a new neurovascular technology that uses an 014 wire with an optical engine will be able to determine vascular etiologies for successful thrombectomies. Dr. Gounis and Dr. Nordmeyer discuss how new imaging techniques will reveal difficult anatomy and prove another useful factor in determining optimal equipment.

[Dr. Michael Barraza]:
Same with me. Are either of you aware of any techniques or equipment on the horizon that looked like they could distinguish themselves over the rest?

[Dr. Matthew Gounis]:
Yeah, I'd be happy to respond to that one. There’s a new series of aspiration catheters that are very, very large bore, like 088 aspiration systems. And I think the newest technology that we're evaluating and it’s in its beginning in terms of clinical experience with the millipede catheter being tested in Ireland and the route 92 catheter being tested in the United States. I think that reliable navigation of these super large bore catheters to the middle cerebral artery is going to be realized in the near future. And I think, again, it's lending us towards what I said as the definition of success, which is TICI 2c/3 at the first pass.

[Dr. Michael Barraza]:
That's interesting. Dr. Gounis, you've also done a lot of research on intravascular imaging. With either optical CT or even more traditional like IVUS, can you tell if that, clot composition or anything from them, before we start trying to remove these clots, which ones are going to be harder to pull?

[Dr. Matthew Gounis]:
Yes, so, we've looked into it. So just to be clear, the existing optical coherence tomography technology that's clinically available and the existing IVUS systems are really not designed and not appropriate for intracranial use, so anything beyond the carotid siphon. You'll see scattered case reports of OCT being used in the intradural space, but nothing ever distal to the siphon, and the reason is because of the tortuosity. Those catheters, essentially the fiber that spins the lens, it can't work in that extreme tortuosity, but we are introducing a new neurovascular technology that'll be available probably within a year. It's a very exciting system. It's basically an 014 wire that has the optical engine in it. And we have looked into it, and I think it's going to be primarily useful in the setting of stroke when you have multiple failed passes, and it's not a tough clot, but rather there's an underlying atheroma or a dissection. That's where I think this technology may be particularly useful is to look at those underlying vascular etiologies that are not cardioembolic or large artery, generated emboli.

[Dr. Michael Barraza]:
Dr. Nordmeyer, what other tactical or patient specific elements can result in a challenging or unsuccessful thrombectomy?

[Dr. Hannes Nordmeyer]:
As I said, anatomy is really an issue. So if we have very tortuous vessels, like an elongated and one segment that is really dipping downwards and then pointing upwards again, we know that all techniques available on the market have a high percentage of failure in these occlusions. So if the anatomy is against us, there's still really the need to go again and again and again for the retrieval and to escalate the therapy by switching to a more aggressive device that has higher radial force or another architecture like the Nimbus or to go for double retriever techniques and really trying to advance a large bore aspiration catheter as close to the thrombus as possible to apply as much aspiration force to the thrombus as you can. But I think what Dr. Gounis just said thrombus imaging with an 014 wire is giving us some information on whether there's atheroma or just tough a clot, for example, that could be a real game changer. So if we're having had four or five or six unsuccessful passes, and we know that the reason for it is the atheroma, we would straight go for stenting, of course. So it still might be very challenging to get up a PTA balloon up there in torturous anatomy, but having early information on the reason of the occlusion that can accelerate the whole procedure and prevent us from spending time on several thrombectomy maneuvers, if we know that stenting and angioplasty would be the right thing to do.

Podcast Contributors

Dr. Matt Gounis discusses Challenging Stroke Thrombectomies with Tough Clot on the BackTable 178 Podcast

Dr. Matt Gounis

Dr. Matt Gounis is a biomedical engineering professor at the University of Massachusetts Medical School.

Dr. Hannes Nordmeyer discusses Challenging Stroke Thrombectomies with Tough Clot on the BackTable 178 Podcast

Dr. Hannes Nordmeyer

Dr. Hannes Nordmeyer is an interventional neuroradiologist in Germany.

Dr. Michael Barraza discusses Challenging Stroke Thrombectomies with Tough Clot on the BackTable 178 Podcast

Dr. Michael Barraza

Dr. Michael Barraza is a practicing interventional radiologist (and all around great guy) with Radiology Associates in Baton Rouge, LA.

Cite This Podcast

BackTable, LLC (Producer). (2022, January 10). Ep. 178 – Challenging Stroke Thrombectomies with Tough Clot [Audio podcast]. Retrieved from

Disclaimer: The Materials available on are for informational and educational purposes only and are not a substitute for the professional judgment of a healthcare professional in diagnosing and treating patients. The opinions expressed by participants of the BackTable Podcast belong solely to the participants, and do not necessarily reflect the views of BackTable.



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