Podcast Transcript: Liquid Embolics: Practical Applications & Techniques

[Dr. Christopher Beck]
I just wanted to widen the lens a little bit and talk about embolics in general, like what are the broad categories of choices? Then what I really want to focus on for liquid embolics is why you like liquid as opposed to coil or beads, or for what applications? All right.

[Dr. Gary Siskin]
One of the things that I think supersedes all of the forthcoming conversation is that we're so fortunate now to have all these tools available to us because I think there's a use case to be made for everything that's out there. By having all these options available, we can really personalize the decisions that we make for a given patient with a particular problem in a particular vascular bed. It's great to have all these options available to us.

Generally speaking, I look at where my target is relative to where my catheter is. If I'm looking at embolizing a vascular bed that is of some distance away from the catheter, then I typically would use particles there or even a less viscous liquid to accomplish that goal. If I'm very close to where the tip of my catheter is relative to the target, then I would use either a more viscous liquid or coils or plugs, or more of a mechanical agent. It really comes down to where I am relative to the target and the size of the vessel that I'm in.

[Dr. Christopher Beck]
What are the points that you consider when choosing a liquid embolic over, well, anything?

[Dr. Gary Siskin]
I think a lot of it comes down to packing density. This is a very interesting concept that all of us as interventionalists are aware of, at least intuitively, but maybe not facile enough to talk about it. Ultimately, no matter what stuff we're putting in an artery to embolize it, we want to make sure that artery is sufficiently filled with the embolic material. For most of the products that we use, it's a combination of embolic material and thrombus that ultimately leads to the vessel occlusion. I think that when we're dealing with liquids, what's interesting to me is the amount of space we can actually fill within the target vessel bed.

Let's take a step back and look at coils, for example. There's some pretty good data out there which talks about a target packing density of around 24% when treating a peripheral or cerebral aneurysm with coil embolization. In other words, we want to fill 24% of the aneurysm volume with coils, and that would be considered an acceptable embolization to reduce the likelihood of future recanalization.

When you really stop to think about it, if you want to just geek out a little bit and look at the volumes of the spaces that we're embolizing and the volume of the coils, [crosstalk] yes, the volume of the coils that we're putting in, the truth is that it's really hard to do that, that it's very difficult to fill 25 or so percent of a target vessel volume with coils. Even in the best-case scenario, you're probably approaching 30%, maybe 40%. A liquid is different. It completely changes the game here when it comes to embolization.

If you have a catheter, let's say, in a pseudoaneurysm, and you want to fill that space, you can fill greater than 90% of that space with a liquid because it's just filling it without the impediments to putting, let's say, a bunch of coils in there because the coils have to fit. They have to fold over on each other. There's going to be gaps between the coil loops, and it adds up to more space than we think. We don't have that problem with liquids. When packing density matters, a liquid is a great choice.

[Dr. Christopher Beck]
One of the other use cases that I've always thought would be very helpful, and they're just some personal cases that come to mind, and also some that I've seen in M&Ms, when you have a patient that's severely coagulopathic, and you put a covered stent in, but that doesn't occlude, and then you try packing that vessel, and that doesn't thrombose, is that something that you guys have seen in your practice or something where you've been leaning heavier on liquid embolics for?

[Dr. Gary Siskin]
Oh, yes. We've all been there, right?

[Dr. Christopher Beck]
Yes. Yes.

[Dr. Gary Siskin]
You're filling the space with coils. You think you've done a great job. You inject a little bit of contrast, and it just flows right through your coil pack. That really relates to what I just said. It's hard to fill the majority of the space with a mechanical agent like a coil. Even if you do the best job, and you have the tightest coil pack imaginable on fluoroscopy, there's still gaps that are difficult to perceive, and you can appreciate those when you inject contrast, and it still goes through.

In order to fill the rest of that space, you're counting on the patient's ability to form clot. That clot has to occupy the space in between those coil loops. Now, thankfully, it happens in most patients. It's not that much of an issue, especially when you're using fibroid coils, let's say, because that even prompts more clot to form. Like I said, we've all been there where it just takes a long time. Liquids are a great adjunct to that. It'll fill those gaps in a way that's not dependent on the way patients can or cannot clot. That's either with coils or just without coils as a de novo agent. If you just take a vessel and embolize it with a liquid, it'll fill the space, and you don't have to worry about the patient's ability to make thrombus.

(2) Practical Applications & Techniques for Liquid Embolics

[Dr. Christopher Beck]
I put out one of the ways in which I thought, like having a liquid embolic as a tool in the tool chest would be helpful. Just curious of how you guys are practicing at Albany. What cases are you using your liquid embolic for?

[Dr. Gary Siskin]
I think first and foremost, we're looking at peripheral hemorrhage. We see a lot of trauma here. It's a busy level one trauma center. I think when we see active bleeding on a trauma angio, so let's say pelvic angio, renal angio, anything like that, we're very quick to grab liquids. I think that the DMSO-based liquids like LAVA, for example, does a really nice job at being able to administer it quickly and to maximally fill the space and stop bleeding quickly.

Now, I think all of us in a quiet moment would probably argue that we're really fast at what we do, but no matter how fast you are, it takes time to put in multiple coils. As people who put coils into vessels, it's pretty rare to have one coil occlude a vessel. It's normally a couple of coils, and that just takes time. Grabbing a liquid and putting it through a catheter that's appropriately positioned, even if you're injecting it very slow. For LAVA, we do advocate that it be used very slowly. The reality is that you're still going to be faster than putting in multiple coils. Therefore, in a patient who needs us to work quickly, this is probably one of the fastest ways we can accomplish that goal.

[Dr. Christopher Beck]
One of the things I wanted to unpack, Gary, was DMSO. You mentioned DSMO liquid, and I was curious of how that plays into LAVA.

[Dr. Gary Siskin]
Yes, so DMSO, it has two roles when it comes to the use of products like Onyx or LAVA. It's a component of the embolic itself. The reality, it's just part of the material, but it's also a solvent that we put into the catheter almost like as a primer before we administer the embolic. We're greasing the wheels for lack of a better word, right? We're understanding what the internal volume of the catheter is. We call that the dead space volume. If you look into the instructions for use for any of the microcatheters that you use, you certainly want to make sure that they're DMSO compatible. You also want to understand what that volume is. We will fill that space with DMSO and then follow it with the embolic. That really prevents any of that from polymerizing or precipitating in the lumen of the catheter. It allows us to inject it a little bit more easily into the target vessel. It's an important component of what we're doing both as part of the product and as part of the process of injecting it.

[Dr. Christopher Beck]
You also mentioned injecting slowly, like how slowly, is it just a feel? What is slow?

[Dr. Gary Siskin]
The way I was taught was inject it as slow as you possibly can and then go slower. The reason for that is, it's not that crazy. There's actually a reason. The reason is that you want the control. If you administer it that slowly, then what you're doing is you're having it almost imagine dripping out of the catheter, but staying together. The agent is coming out as one growing mass of embolic. It has a leading, almost like a leading membrane or a leading shell that comes out.

As you continue putting that slow forward pressure on the embolic, you start to crack that shell and that allows it to sludge forward. You have this very controlled injection of the material. You can see it well, you can see exactly where it's going, but you can also appreciate when it starts to reflux. If you inject it too quickly, it'll run away from you a little bit. You'll either push it too far forward or you'll cause it to reflux too quickly. That's when you run the risk of non-target embolization. The slow injection is really to take advantage of its controllability, is what I would say.

[Dr. Christopher Beck]
Let's say you're in a tiny branch, like it's a renal trauma, and you got a little pseudoaneurysm and you're deep into the vessel, maybe a two-miller vessel. How slow? How long would it take you after you have the solvent in to embolize that vessel?

[Dr. Gary Siskin]
If my catheter is well into that target vessel, then I would use a higher viscosity formulation. When it comes to LAVA, there's two viscosity formulations. One is called LAVA-18, one is called LAVA-34. Those are actually the units of viscosity, they're millipascal seconds. If I get my catheter right where I need it to be, I would slowly administer the LAVA-34. I would have it reflux back or pull my catheter back until the space was completely filled and I avoided refluxing into a vessel that I wanted to preserve.

If my catheter could not get that far, let's just say I couldn't make that last turn or that last division, and I'm in more of the parent vessel for that branch, then I would use the lower viscosity formulation because I would want that to do the work for me. That's a phrase I like to use. I don't have to go all the way out there because the lower viscosity formulation will do that work for me. It will travel, it will bridge that gap between the target and the tip of my catheter. That's how I make that decision, but that's how I would handle it.

One of the things that a new user would probably be surprised at, and I remember being surprised at this, is how little you actually need. When you're talking about a two-millimeter vessel, maybe it's a centimeter, maybe two long, that's it. You're going to use 0.1 ml, maybe 0.2 tops. It is a remarkably small amount of material that you need to treat a vessel like that.

[Dr. Christopher Beck]
Getting into that. What do you inject with? 1cc syringe, 3cc syringe? Because if you just need 0.1 ml, like that's pretty controlled.

[Dr. Gary Siskin]
Yes. Very. These materials come packaged with 1 ml syringes. Typically what we're talking about for dead space volume or the internal volume of the catheter is about 0.5 ml. You're first filling that microcatheter with 0.5 ml of DMSO, and now you're then going to be chasing it with the LAVA, let's say. What you're doing is initially first pushing out the DMSO, and we do that just as slowly as the embolic. That could be a source of error for some people because you might be thinking, "Well, it's not the embolic yet, it's just the solvent. Let me just push that in." That can because spasm and it can hurt patients. Patients feel that.

We want to go very slowly. We want to avoid that. Some people will use nitro first to help prevent that. Whatever you're doing, you're first pushing in the DMSO, and now you're going very slowly. You know that the first things coming out of the catheter are the DMSO. You don't have to fluoro right away until you get close to completely injecting that dead space volume. Then you start looking, and if you go slow enough, you'll see it begin to accumulate near the tip of the catheter, and you'll see it push forward as your injection force increases. It does not take a lot. You're right, it's a 1 ml syringe. It's very controlled. For most of the bleed cases that the average person is going to do, it's less than 2 ml of product that you need to administer. In fact, I would say less than 1 ml.

[Dr. Christopher Beck]
How far can you get the embolic to run, I guess, like if you're using the lower viscosity formulation?

[Dr. Gary Siskin]
We've done a lot of cases, and it's not always easy to predict. There's a lot of variables. Because slow to me could mean something different than slow to you, and slow to the next person. I would say it's not predictable. I'd love to give you an answer that it's going to go 3.5 centimeters from the tip of the catheter. I have not found that to be the case. There have been times where I'm maybe a little disappointed that it doesn't go as far as I want, and there have been times that I'm potentially surprised that it went as far as it did.

I think the way to account for that is to get your catheter as close as you can to the target. That's going to take care of all of that, because now you'll be able to put the material in. As it starts to reflux, you can begin to pull your catheter back while you're injecting to fill all that space.

(3) Handling Catheters To Prevent Complications