Liquid Embolics in Practice: Clinical Applications & Technical Considerations

[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]
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.

[Dr. Christopher Beck]
We talked about endoleaks peripheral hemorrhage. Any other use cases that you guys have liked and are thinking about using it more or introducing the different parts of your practice?

[Dr. Gary Siskin]
Yes. Certainly, peripheral hemorrhage is the proven indication for this. This is on label. It's got a lot of data behind it. I think it's a very justified approach to that problem. When we start veering that off, just realize now it's just-- does it make intuitive sense to you? Is there some data that supports its use? We've really liked the way it behaves in portal varices. I think as an adjunct to a tips procedure, let's say, where you just feel like there's a persistent varix and you want to fill it up, we've had a lot of nice success using LAVA to fill that space. It's very opaque. It's very easy. I'm not worried about the catheter getting stuck, and I know exactly when to stop. It's not then rushing through the tips I just created. I've been very happy with that.

Endoleaks is another off-label indication where I think there's a lot of utility for liquids. We can all appreciate that in many of those cases, there's a space to fill in the native aneurysm sac, and there are vessels that are providing both inflow and outflow to that endoleak. It's difficult. It always looks like it should be easier, but it's difficult to navigate these catheters into either all or some of those vessels. I love that liquids can get there for me. When I see that I'm in the area of the sac where contrast is accumulating, and I inject a liquid, usually the less viscous liquid, it will make its way through the sac into the outflow vessel. I will feel like I've really done a complete job for that patient. I think endoleaks are a great place for this

There is some data supporting that when it comes to Onyx at least, but it's going to take a little time for some of the newer products to receive that literature-based support. I do think that some of the Venus applications that we're used to using, maybe it's a varicocele or pelvic venous disease in women, where I think there is at least opportunity to explore the role that a liquid like LAVA can do in these patients. Many of us will go distal in those patients. Certainly, let's say in women, you might sclerose some of those varices first, then create some coil-based occlusion at the very lower inferior end of the gonadal vein.

Then many people will just try and fill space. They'll either use a sclerosant all the way up to the renal, maybe cap it with a plug, do things like that. Think about how easy it is to just take a solution like LAVA and just fill the space and go all the way up. It can find its way into some of those branch vessels that we're trying to find with venograms, as we're progressing in the embolization case. I think there is definitely utility for using this material in either varicoceles or pelvic venous disease, but it is both off-label and not really described right now. I think you're flying a little bit on your own when it comes to work like that. I can tell you, it's going to be effective. It's just a matter of demonstrating and proving it.

[Dr. Christopher Beck]
This is the question that I had in that people have been using liquid embolics in the neurospace for a long time. Then a lot of interventional radiologists have been using things off-label for a very long time in the peripheral space. Why was it so long to bridge that need for just regular interventional docs who weren't in the neuro interventional space?

[Dr. Gary Siskin]
It's probably a question that has a lot of different answers. The first is to have industry support, to fund the appropriate trials, to gain peripheral approval for particular embolics. I think, LAVA was very, Sirtex and LAVA were very committed to getting that done. I think that was a very important step for us as interventionalists. When you use a product off-label like that, you can't get the appropriate education to use it.

What I said years ago, it was my neuroendovascular partner who taught me how to use it. I didn't have a company representative or someone who really was well-schooled in learning the nuances of that product. Teach me like we learn everyday new products that we get. We have company reps come and show us the way we're supposed to use it, but we were never able to do that. It was never really quite the widespread confidence for using liquids in the periphery. I think that diminished people's appetite for that product. It was a lot of self-teaching. I think that ultimately, as people became more comfortable using these products, there began to be more of a demand for them because once you use them, you just see, you know that it's a good addition to our toolbox.

Now people want products that have been tested and that they can be appropriately educated on for use in the periphery. That is the best part about having these newer products available to us is that we can really learn the right way to use them and have conversations like this, that we can really start talking about how to do it, what our experiences are, and have people worry less about the potential implications of not learning how to do it the right way right from the beginning.