So, let's go back to the basics here. So, I'm gonna tell you the way I think. Although this may be more realistic, this is how I think.
And, we look at the body and you look at the blood vessels in the body. And you can say, "okay, it's kind of like a tree." Right, and people call it the arterial tree or the vascular tree. So there's a couple of different ways
that I'd like you to think about embolization in very general terms. So the first thing is, let's say we want to embolize there in the tree. We'll call that a more proximal embolization, alright. So, what we're gonna do is we're gonna move our catheter
to the exact site of the problem and we're gonna deploy an embolization agent at that exact site. And that's certainly one way to approach an embolization procedure. But, if you look over here, we're going much more distal,
to a much further branch in the tree. This is a little bit different because we may or may not be able to get a catheter all the way out there. So, what we're gonna do is we're gonna get the catheter as close as we can to the target that we're embolizing and we're gonna deliver something to that target
using blood flow. And those are two very different ways that embolize things in the body.
So, the way I like to think about embolic agents is I think we can reasonably classify them into two different categories.
The first is mechanical agents. That first example where we positioned the catheter directly at the site of a vascular abnormality and we deploy the embolic agent at that site. Or there are what we'll call flow-directed agents where we position the catheter near the abnormality
and use flow to get the agent to that site. When we're looking at mechanical agents, we're talking about coils and plugs. And when we're looking at flow-directed agents, we're looking at particles, microspheres, and liquid agents. Alright, so let's talk first about mechanical agents.
So, I think if you think back to the good old days, basically, if you wanted to use a mechanical agent for those that are my age, I just turned 54 for the record, if you are close to me, then you think back where, if you wanted to use a mechanical agent, the only one you were able to use was a pushable coil.
That was it. That was the only thing that was available. There were no other options for using a mechanical agent to embolize things at that site. That was then and this is now. Things are a whole lot more complicated.
So, you can take pushable coils, and there are different sizes of pushable coils. You can take detachable coils, and there are different sizes there, and some of them have fibers, some of them don't, and some of them Hydrogel, and some of them don't.
And so it's just a lot more complicated, a lot more options and a lot more choices to understand when you're choosing what coils to use. So the first thing is pushable coils versus detachable coils. So maybe some of you that are young enough
that they're not using pushable coils in the labs. But, a pushable coil is basically pushed through a delivery catheter with a guidewire or a dedicated coil pusher. You basically, as I'm showing you here, you push the coil into the catheter
and you keep pushing it and comes out. It's not attached to whatever you're using to push the coil out. So, in other words, you can have potential problems with pushable coils. So, what if the catheter is not quite where you want to be?
Or what if the coil you just put into the catheter is not quite the right size which you realize, maybe before or just as you're pushing it in, you're like, "oh my goodness, the wrong sized coil is in there." Well, the reality is that you're screwed
because once the coil is in the catheter, there is nothing you're gonna do about it. You only have two choices, either you push the coil all the way in or you pull the catheter out. Sometimes that's no big deal.
Sometimes it was easy to get the catheter where you needed it to be. But sometimes it's really not a good thing. Sometimes it took you a long time to get the catheter there and, all of a sudden, you're like, "holy crap." So, that's the benefit of detachable coils.
Those "holy crap" moments go away when you use detachable coils. In the case of a detachable coil, the pusher that you use to advance the coil through the catheter is attached to the coil. And it has to be detached by some mechanism
in order to release the coil. In other words, you push the whole thing in, if it's not quite right or it's not quite the right coil, you have the ability to pull it out and start again. So there's value there. And for those of you taking pictures of the slides,
I don't care, but I'll give Stephanie the presentation so she can send it to you if you want. Alright, so don't worry about that, you can just sit and listen if you want. Basically, the use of detachable coils affords a great deal of control
because you can reposition it, you can remove it, I do that all the time. I deploy some of it, I don't like it, I pull it back, I redeploy it. You can make it perfect before you permanently deploy it. So, then the question that comes up is,
how do you release it from the pusher? Well, they're different. Some of them have a separate handle that we attach to the back of the pusher wire and we do some maneuverability, just push it or click it or do something to free the coil.
Some of the, like the Interlock coil or Retracta coil don't have a separate handle, but you either just push the coil out, in the case of the Interlock coil past a certain point, or in the case of the Retracta coil, you can just kind of unscrew it.
But, again, they're just different. Some require a handle, some don't. I mentioned before, some have fibers, some don't. And that gets interesting. You know, here you have people that feel kind of strongly about this issue.
So different coils have different concentrations of fibers and these fibers really do impact how soft the coils are, how packable the coils are, and how thrombogenic they are. And if you look at some of the different coils that are out there on the market,
you can see that it varies. So something like the Ruby coil has no fibers. Something like Concerto or, excuse me, Interlock, that should be Interlock on the bottom, I apologize about that. But, the Interlock coil on the bottom
has more fibers and the others are somewhere in the middle. You can see the Azur has no fibers. It has Hydrogel. The Concerto has a moderate degree of fibers. And, again, it's just how do you feel about it. Some people don't care.
But, if you care, you just have to realize that the more fibers that are on the coil, the stiffer they are. That's something to think about. So, fewer fibers means softer coils which means you can pack them real tight.
And more fibers means that they're stiffer, they may be increased thrombogenicity so you'll get better clotting in the vessel, but you may not be able to pack them as tight. You'll spaces in between the loops of your coils. So, a couple things to remember
when you're considering a pushable coil versus a detachable coil. One is that the pushable coils are less expensive than detachable coils and there could be quite a difference. A pushable coil may be less than a hundred bucks,
a detachable coil can be five hundred to a thousand dollars depending on what you're using. So, a lot of people have strong feelings about that because of the cost, but I refuse to pretend that detachable coils don't exist. They do.
I personally think they're safer to use, especially when I'm working with any of the residents that are sitting here watching this talk because that's just the way it goes, right? I mean, it's nice to be able to undo the things that other people are doing.
So, I personally select coils based on the margin of error that's at that moment in time. So when there's a high margin for error, and big problems if there is error, then I choose a detachable coil. When there's low probability of error,
I'll using something else. And I think that this translates to me very well with the concept of a filling coil and a framing coil. And so this is how I generally think of most coil embolizations that I do. So, here's my five-year-old drawing of a vessel
with a coil in it and this would be a framing coil. So, a framing coil, conceptually, it's kind of just a very loosely deployed coil that's probably a little bit bigger than the vessel size that I'm embolizing. And I purposely create those gaps
between the different loops of the coil. And then, when I'm filling in the gaps, I'll take a filling coil, and I think, I'm sorry, but for a framing coil, the detachable coil is great. 'Cause you want it to be just perfect
when you have a framing coil. Now, with the rest of it, I'll take a filling coil. And that could be a pushable coil or a detachable coil. All I'm trying to do now is fill in those gaps between the different loops of the coil. So, I'll put one coil in,
then I'll put a second coil in, then a third coil in. And all of a sudden, you're building up that coil pack with the framing coil used to kind of protect it and to hold it in place 'cause the worst thing that can happen
is the thing flies away. So, that's the way in general I think about the use of framing and filling coils. So, when we're using these mechanical agents, just a quick case example, I don't think I have a pointer here,
but, you can kind of see right outside the spleen, there's a little splenic artery aneurism there. And here's what the angiogram looks like. And even though you might look at that angiogram and you can see that round aneurism at the bottom of the image, you might say,
"wow, that looks like it has a big neck "and maybe it would be hard to put a coil in there." But, the reality is with a detachable coil, you can work and get it just right. And you can fill in that aneurism and you can persist with flow to the rest of the spleen.
Same thing with this patient, it was a trauma patient. You can see the big retroperitoneal hematoma on the right side of the lower abdomen. You can see the fracture of the vertebral body that's there or the transverse process, excuse me,
that's sitting right there in the middle of that hematoma. When we do an angiogram, you kind of get a sense, right of the middle of the screen that there's some extravasation of contrast from that lumbar artery. Sorry, I wish I had a pointer, or I'd show you.
But, oh, look a pointer. So there you go. So there's the extravasation from the lumbar artery. Here's the extravasation as well. And so, when we got into that lumbar artery, you can see the extravasation
and I think there's a great place for a mechanical embolic agent because we can go in there and put some coils in the space as well as put some coils back along the lumbar artery and prevent further extravasation. So that would be the situation
where we would want to use some type
of mechanical embolic agent. Nowadays there's plugs. And we look at different plugs that are out there and there are both uncovered plugs like the Amplatzer Plug which is essentially a mesh network of wires.
And you can look at the covered plugs that are available right now like the MVP Plug and the EOS Plug that's made by Artventive. And you can see that these are covered, they have some type membrane that looks like a little parachute
that sits in the vessel and is able to occlude flow. I think generally, plugs are used for similar indications as coils. I think that you all can consider plugs as just bulkier, fancier, and more complicated versions of detachable coils.
In general, you can pull a plug back into the catheter before you deploy it. So the plugs occupy more space within a vessel than a single coil. And each plug, like a detachable coil, is attached to the pusher wire
and is released by rotating the pusher wire until the plug is detached. And, the nice thing about a plug is it has the potential of being the only thing needed for vessel occlusion. So a lot of people like plugs as they're a little faster.
So I want to jump in now into the other type of embolic agent called flow-directed agents. Remember that these agents are all used to embolize a vascular bed that's distal to the tip of the catheter. So, it's not right where the catheter is,
it's a little bit more distal. So, in other words, if you're standing there, if you're standing right here and you want to embolize there, instead of trying to get the catheter and navigate this whole thing,
just put something in the water and have it drift down to the part where you want to embolize. That's what we're trying to do. So, PVA particles represent the standard for particulate agent. So these are irregularly shaped PVA particles.
The problem with PVA particles is they work, there's no doubt about that, but they have the potential to aggregate. So, in other words, even though you guys might pull out a vial that says 355 to 510 micron PVA, the reality is those PVA particles
are going to fit together like pieces of a jigsaw puzzle and be effectively larger than the advertized size. So what that means is that you may embolize a little more proximally than you intend to embolize. They also have a tendency to occlude microcatheters.
So sometimes they can be a little bit difficult
to administer. So that brought about microspheres. So, if you think about it, if the PVA particles look like little pieces of a jigsaw puzzle, they have the chance to fit together and aggregate.
But, if you put two balls next to each other, they're not going to aggregate and so they tend to stay a bit more true to size and are able to get to a targeted vessel. And there are a number of microspheres that are available, the Embosphere product, the E-block, Embozene,
these are all different variations on a theme where you have different size microspheres that get you to different places in the vasculature. So microspheres no doubt are easier to administer with a microcatheter. They don't proximally aggregate
and we know that because pathologically, we find them in smaller blood vessels than PVA particles even though we might use larger spheres. They travel to size matched vessels which at least allows in theory for a more targeted embolization,
meaning, if I know that I want to embolize a 500 micron vessel, I could actually use a 500 micron bead and get it to exactly the right place. The biggest problem, as I mentioned early on in my talk, is that we don't necessarily know all the time
which vessel we're targeting. So I think in this case the technology may actually have accelerated beyond our ability to always effectively use that technology. The manufacturing process, which is great,
assures size uniformity. So, in other words, it just gives us the ability to target particular vessels with particular sizes. And uterine fibroid embolization is one example. I think you can certainly see here, as I think my daughter can,
which vessels look funny. So here's a pelvic angiogram. Here are the abnormal uterine arteries right here. And as we selectively catheterize these vessels, we're gonna put a catheter kind of right here but, in reality, it's really difficult to get a catheter
to go all the way through here, all the way up here. There's no reason to do that. We'll just leave the catheter down here and inject these microspheres to do the work for us and travel all the way out to the distal vasculature of uterine artery.
And, at the end of the day, we can get it from here to here. So that's the concept of a flow-directed embolic agent. Here's another case of what looks like an angiomyolipoma. This is a, sorry I just put that one picture
so I'm going to bypass that.
I don't think I finished putting the pictures in. So the other example of flow-directed agents are liquid agents. And there a couple of different examples of liquid agents.
First you have Onyx which is used most prominently in the brain. But the reality is there's a growing number of people that are using this more often in the periphery. So this consists of an ethylene vinyl alcohol
and a suspension of tantalum powder that allows us to see it. And there are two different concentrations that are different based on the viscosity. And, we have to mix Onyx with DMSO, that's a polar solvent and that prevent it
from essentially hardening in the catheter. Most microcatheters these days are DMSO compatible even though Medtronic and Covidien won't necessarily endorse the use of different catheters, I will tell you that the vast majority of microcatheters on the market today
are DMSO compatible. Glue is another potential agent to use that's usually given in combination with ethiodol and potentially tantalum powder although people are using ethiodol often. The ethiodol is used as a vehicle for the glue
and it also acts to slow the polymerization down. And again the tantalum powder is what's radiopaque and it also slows down the polymerization. So the glue, what happens is the glue incites an acute inflammatory reaction in the vessel wall. That leads to chronic inflammation and fibrosis
and that polymerization occurs once it comes into contact with blood. And by changing the ratio of glue to ethiodol, you can change how quickly that process occurs. And finally, some people will use absolute alcohol. That's a very aggressive sclerosant.
It usually causes rapid precipitation of proteins from the vessel wall and rapid clotting of the vessel. We are using this more often, we use it in combination with lipiodol to allow us to see the alcohol
and we use typically a seven to three ratio. So we use that quite often in angiomyolipomas. So you can see this fatty tumor at the upper pole of the left kidney. Here we are with the angiogram. You can see the vessels
that are constituting the angiomyolipoma and the reason why we're embolizing those is to reduce the risk of bleeding which can happen in these larger, but benign tumors. And so once we complete it, what you're seeing here,
is the final picture and this is the ethiodol mixed with the alcohol in the vasculature of the angiomyolipoma. And that's a really effective way to occlude these blood vessels. But, again, the point is that it's the flow
that carries that stuff out and not necessarily the catheter itself.
So the next question that comes up is what about Gelfoam? You know, people forget about Gelfoam. It's been around for a long time
and the reality is Gelfoam is certainly still an effective agent. It can kind of be classified as both mechanical agent and a flow-directed agent depending on how we use it. So if you essentially cut it up into real small pieces
and create a slurry, mixing it with some contrast and saline, then you can make it almost like a pasty liquid and it will travel well beyond the catheter tip. Or you can cut it into big pledgets and that's going to be more of a mechanical agent
and stay pretty close to the tip of the catheter. So that is the original resorbable agent. A lot of people talk about how Gelfoam is temporary. And we know from pretty early work done out of Yale that vessels embolized with Gelfoam usually recanalize
within a couple of weeks or months. But, lately I think people are starting to rethink that a little bit and are coming to appreciate the aggressive inflammatory reaction that may be associated with Gelfoam and that could potentially lead to a permanent occlusion.
So the Gelfoam may go away but the occlusion may be persistent.
So it's more of a how you use your words. So, to finish up the question is what's new with embolization agents? And I think there's two things that are kind of new.
The first is visible microspheres. So you ask yourself, "wouldn't it be great "if we could see the embolic microspheres "under fluoro and not have to use contrast?" Certainly, it's a no brainer if someone maybe has a contrast allergy or renal failure.
You want to minimize or avoid the use of contrast. But, as this picture shows from the LUMI website, this is no contrast here. These are actually beads accumulating in a tumor vascular bed. So, wouldn't that be great?
But, and you can see it on CT, and no contrast here, you see exactly where the beads went and everyone's happy. But, the other question is, would it be great if you could actually see
where those microspheres went because, keep in mind, they don't always go where you think they're going to go and do you necessarily want CAT scans for the rest of time showing your beads in the left lobe instead of the right lobe or too high or too low.
So there are people that really do think that way and are wondering if this is a tool that where the benefit of the tool outweighs the risk of the tool. And these days, we all have new technology available to us. These are colon beam CT to make sure
that the particles we're injecting are going where we want them to be. And you may or may not need these radiopaque beads. So there's good and there's bad and people are gonna have different opinions about that. So the reality is that there's ongoing development
in the area. And there are smaller beads that are being released which are certainly easier to deliver but, again, they may not carry a survival advantage and it just depends on how important you think being able to see the beads are.
I think resorbably microspheres are a much more interesting new frontier when it comes to embolic agents. To me, it makes sense to use an embolic agent that's not a permanent implant and these are being developed now.
So, here's just an example of one of them which is made of more of a chitosan or a carbohydrate type of material where you can see from Day 0 to Day 14. What happens over time is the bead begins to kind of fall apart and degrade
and ultimately it just goes away. And it's a real interesting angiographic work that's been done pre-clinically in animals that have shown the angiographic appearance to start to look normal as well over time. So it's really interesting
and while there are a number of studies that at least show proof of concept in animals, no significant work has been done in humans to date. We've implanted some of these in a couple of patients who've gone onto surgery and the results have been interesting
but there's no large scale clinical trials that have been done. And they really do need to get done because you're gonna hear a lot about resorbable agents probably over the next year or two because I'm aware of a couple
that are gonna be out to market. And the real question that I would hope the docs that you work with remember to answer is does it work? Because there's a coolness factor to delivering something that's temporary,
that will go away in time. But there really is no cause or no reason to utilize it for embolization if it's not as effective as more classic embolic agents that have the experience behind it. So I do think clinical trials are gonna have
to be done to prove efficacy and to compare them against the available embolic agents. But, I do think that it seems like a good idea and you can get that just by looking at the tattoo industry where a lot of people aren't so happy with permanent tattoos.
And so I think if people have the opportunity to do something temporary, that would go away over time, I bet a lot of people might choose that option.
So it's the same thing goes with the temporary agents. So a couple of tips to close it down here. One is know your catheter.
Understand that not every embolic agent that I talked about can be delivered through every angiographic catheter. As a result, I think you need to pay attention to the catheter that you're using before you open the packaging
for a particular embolic agent. It happens a little more often than I care to admit where someone opens an embolic product and then we realize what catheter we actually have in the patient.
And we can't deliver that embolic agent through that catheter. And that requires obviously either opening another embolic agent or changing out the catheter. So just pay attention before it's used.
It's better to administer particles through a larger inner diameter microcatheter, you know, an O2-7 or and O2-8 inner diameter catheter. Remember that Interlock and Concerto coils as examples of detachable coils require a smaller ID microcatheter
while a coil like a Ruby needs a larger ID microcatheter. That's one reason why we stock all of these coils in our lab because sometimes we use different microcatheters and we want to be prepared to embolize through either of them. Remember Onyx requires a DMSO compatible microcatheter.
And, if you're using plugs, that Amplatzer 4 Plug which is the newer one can be placed through a five French angiographic catheter, but the older and larger plugs like the Amplatzer 2 usually requires a guide catheter or a sheath.
That's not an uncommon mistake that I will confess to you that some of our docs run into. That they want to use a particular plug and they just have the wrong delivery catheter in there. The other thing I'll suggest is to do the job once. As a technologist, you're probably standing there,
you're watching the cases go by and maybe you're helping the cases and your doc says, "ah, that's good enough, "I'm sure it's going to thrombose in time." It's very common, "we've done enough, "you know, it'll be fine."
That's a fail in my mind. You cannot count that it's gonna do that. My opinion is when you set up to embolize a vessel, embolize the vessel. Alright, the idea that you can incompletely embolize it and that clotting is going to occur in time
is an unreliable strategy. That's like best case scenario. So, to me, I encourage the people I'm working with and myself to take the time to definitively embolize a target vessel and not to leave anything to chance.
You will hear that a lot. Your docs will say, "oh, it's good enough, "you know, it'll be fine." And a lot of times, it's not fine. Tighter is better, okay. So, we seek to get tight coil packs
without any visible spaces. So, when I showed you that framing coil, if that's how you leave it, in all likelihood, that's not gonna be an effective embolization. Personally, that's how I grade my fellows is I give them points for artistry.
So the tighter the coil pack, to me, the better the job is and I think that is an important point to remember. And usually, I can achieve that by using coils of different sizes. So I like that concept of using a framing coil
that's slightly larger than it needs to be and then filling in the spaces with progressively smaller coils. So we might use a 10 millimeter coil and then go down to an eight, a six, even a four to fill in some gaps.
So that's how we like to coil vessels in general. So, in conclusion, there are a large number, I don't think I touched on all of them, but I touched on a lot of them, a large number of embolic agents that are available to us as intervention radiologists
for embolization procedures. And I can't stress enough to you that it's important for everybody involved in a case to understand the nuances of every agent before you use it to understand how it benefits every patient,
how technically you need to pull it off and how we can do the best job for the patients that we're treating with embolization procedures. So thanks. (applause)v
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