Hi, this is Eric Brestovsky. Welcome to another segment of EP on EP, and I'm delighted today to have with me a colleague for many years, Dr. Bradley Knight, who's the Director of Electrophysiology at Northwestern University. Brad, I'm going to welcome you here, even though you're a Tar Heel and I'm a Dookie, but we're going to put those behind us. We'll keep that aside. Keep that aside. You've done so much work in the cryoablation area, and what I'd like to talk to you about today is kind of what's new, but maybe you can start with the standard cryoablation, what you've learned, and what maybe the things that need fixing are, and then tell us where we're headed. Sure, sure. We adopted the cryo balloon for pulmonary vein isolation with the first generation device. So at Northwestern, we have seven faculty doing AFib ablation on a routine basis. We've all trained in different programs, and we have different techniques and different ideas, but once we took on the cryo balloon, all seven of us now have adopted it as kind of our go-to for first procedures for pulmonary vein isolation. And now with the second generation cryo balloon, there was a significant improvement. I think it's a very efficient way to isolate the veins. It's a very effective way. It's very safe. We participated in the Stop AFib post-approval trial, where there were 340 patients followed for three years, and the success rate, as defined as freedom from AFib, was 68%. And then we looked at the redo rate kind of as a surrogate for, you know, who had AFib that was to the degree they needed to have another procedure, and the freedom from a repeat procedure was about 82%. The circuit dose study just came out comparing RF to cryo. They were comparable, but I think what that showed us is that these definitions we use of success may be a little strict, and they demonstrate, as you probably know, there was a 99% reduction in AFib burden. Yeah, that's, well, you know, from the beginning of the guidelines for AFib ablation, I've been that one guy who never got his way, but I said 30 seconds is ridiculous. No clinician in the world cares about 30 seconds, nor do any patients, right? So I think we have undervalued for the public how successful ablation is, because we have The public and our peers, our general cardiology colleagues. Yeah, who say, well, it doesn't, you know, if it works in 40%, then you realize, no, someone who's had a terrible sort of quality of life now feels good, even though they had the odd episode. Right. So I guess at least as comparable as RF, I think there's some other advantages. I think patients do better in the first couple months after the procedure that's not quite captured in some of these trials, that blanking period is important to patients. But it could be better. You know, we just, you know, we routinely used a cryo balloon, but it has some limitations and I think it could be improved upon. So when we do a cryo balloon, we in general need to have occlusion of the vein to get a successful circumferential lesion. You can get a lesion wherever you have contact, but you really need to have a good occlusion to easily, with a single shot, isolate the pulmonary vein. And when you freeze it, it becomes very noncompliant and can back out a little bit. There's two sizes. There's a 23 and a 28 millimeter balloon, but we never use the 23 millimeter balloon. And sometimes even the 28 millimeter balloon is just not big enough. It doesn't fill a common ostium. Sometimes it will slide into the vein a little bit. So there's room for improvement with different balloon sizes, making it more compliant, avoiding the need to do touch-ups and gaps. There also remains to be issues related to dosing. You know, how long should we freeze, how many lesions should we give, how many freezes should we give. And there's still issues with collateral damage. We looked at the bronchus, freezing the bronchus when we freeze with the balloon. So things could be improved upon. So let's go through a couple of those. My understanding is that people are moving away from multiple freezes and there's even a movement to a shorter initial freeze, as I understand it. So what are you currently doing in your lab? I think it's clear that a four-minute freeze that we were doing with the first-generation cryo-balloons is not needed with the second-generation balloon. So we limit almost all of our freezes to three minutes. And we strive to look at time to isolation. So if you have the circular mapping catheter deep in the vein to provide a stiffer rail, you're not going to see when you isolate the vein. There's value to bringing that achieve back to the balloon and looking at the pulmonary vein potentials so that, number one, you can determine how quickly you isolate the vein. And if we isolate the vein in less than a minute, we usually don't give a second freeze. There's other value, too, because if you isolate the vein, you'll see PV delay and isolation. It helps you be more confident that what you're seeing at the end is not PV potentials. They could be far-field from the appendage, for example. So I think it's important to look at the PV signals when you freeze. So you've moved to a new methodology with the balloon you're using and still getting good success. Yes. So what about new technology or new, if it's not a new balloon, just new ways of doing things? Do you have some thoughts on that? It's a good way to categorize. I think there's two areas of development. There are areas that are trying to help us use the current balloon better. And then there's developments in new balloons. So why don't you take us through both of those? Well, I think that right now, the standard mapping systems, you can't visualize the balloon. There's no electrodes on it. So with the current generation 3D mapping systems, you can't see the balloon. You can use the BioSense CARDO system, and you can use CARDO sound. You can see the balloon, and you can make circles around it and display that on your map. It doesn't tell you where you're in contact, but it does show you where the balloons are. For people that are doing a lot of extra pulmonary vein ablation with the balloon, people are trying to make roof lines, isolate the whole posterior wall, you can categorize on that. Yeah, we won't talk too much about that. But you can see where you've placed the balloon with the CARDO sound system. What about ice? Does ice help at all? Well, this is their version of the ice, but we routinely use ice. So yes, we use ice to determine occlusion. We don't routinely use the 3D sound, but an ice image allows you to look for occlusion with color flow before we give contrast. It's a way to minimize contrast. But you raise a good point. We want to minimize it. A number of times, we have to give contrast, it requires fluoro, it requires contrast injections. So there are techniques that will allow you to do that with standard ice. There are other mapping systems that are being developed that may allow you to do that. So Philips has an EPD system called Codex, which has a lot of potential because it uses a different way of creating the images. So it uses dielectric imaging, and it has the potential to image the balloon. And they even have a technique under development where you can determine occlusion by determining flow from the electrodes on that circular mapping catheter in the vein and determining if you have occlusion without giving contrast. And there's other systems. The system Jesse Sra is developing, the NAVIC 3D system, is a way to take advantage of your standard x-ray equipment to develop a three-dimensional image of the balloon and then overlay that with the CT scan. So most of the new research is not, we'll get to the balloons, is really trying to figure out how you can really be sure you've got exactly the kind of occlusion you want and to get the most optimum chance at isolation. And it sounds like there's a variety of things going on that will help the electrophysiologists in that regard. Right, right. So how about different balloons? Right. Well, the current balloon is under development to make it potentially better, potentially. I think we talked about the ways of trying to image it. Maybe if you put electrodes on the balloon, you could see it with standard mapping systems. You could take the current balloon and come up with different sizes. You could make it more compliant. I think the current Medtronic balloon will have future iterations that will be different sizes and give you more flexibility for things like that. There's other companies developing cryo-balloons. Right. So it's become, and I think the numbers, my understanding is that they have about half the market for first-time pulmonary vein isolation. So I think there's a pretty impressive adoption of the cryo-balloon and there's really no competition right now for it. So Boston Scientific has a cryo-balloon program. The advantages potentially of their balloon is that it's compliant. So when we put the balloon in there with the current Arctic Front balloon and freeze, it gets very rigid and can back out. Boston Scientific balloon is made of an elastic substance so that it remains at low pressure and remains more compliant, which theoretically could help you get pulmonary vein occlusion. Some of that data was presented at the Heart Rhythm Society last year. So it seems to be an exciting new competitive balloon. So let me switch then just to the end. This is a very nice update. Thank you very much, Brad. What is your, you said that, I know that as much as you're saying everybody's in lockstep at Northwestern, I'm sure that's not actually true because I know a lot of your colleagues at Northwestern, they wouldn't necessarily be in the same line. So there must, do people have different views, not on the paroxysmal, but the persistence? I mean, that's a huge area of debate now. Do you routinely do every persistent with cryo or is there at some point you pick and choose? We do a lot of persistence with cryo, particularly patients that are early persistent or patients whose left atrial size is normal. If our objective when we go into the case is to just isolate the veins, which I can make a strong case for, for the first time procedure for persistence, if that's the objective, we'll often use the cryo balloon. But for the redos and for longstanding persistence, I think we all feel with limited data that we should be doing more than just PVI, but I think it's still important we come up with a tool that gives durable, safe pulmonary vein isolation before we really know what else needs to be done. So let me ask you one last thing. I would say as a clinician, because I'm not in the lab doing ablations for AFib anymore, I still do some to BSVD. So if I have a patient that comes to me and has documented flutter and fib, I think that's important information to when I send that patient to my colleague. And usually I will tell them, listen, this is a patient you're going to have to probably do RF in, unless you really want to use two separate catheters and as a director of a lab and a youth director, that's expensive. I mean, there have to be some economies for your lab. No, you raise an important scenario where it doesn't become a cost issue. Often I'll still use a cryo balloon and I'll use RF. You will. You'll use two different RFs. I'll use a cheap RF catheter. There is no cheap RF catheter. I still use an eight millimeter catheter to ablate a CTI. Okay. Maybe that's a cheap one. But yeah, some of my colleagues will stick with RF in that scenario. We don't routinely do CTI lines, by the way, for patients who have seen a documented flutter. And I know you could argue, and I understand this argument, that if you got rid of the fib, you'd probably get rid of the flutter. Yeah. Okay. And there's maybe a 30 to 50 or 40% chance you won't get rid of the fib. And if the flutter was really bothersome to the patient, you don't want to deal with the flutter as a recurrence. No, I agree. I think you can't rely on PVI to solve the typical flutter that they had clinically. I don't think so. Yeah. Yeah, I don't think so. So that's interesting. So you'll still be stubborn and go ahead with the PVI with the cryo. Yeah. And it's not stubborn. I shouldn't say stubborn. I think when we first looked at our early experience, we were saving about a half an hour of time per case on average. And I think it removes some of those outliers where you struggle. Now the RF technology has gotten a lot better since we started doing cryo, so I accept that. But I put it this way, if cryo balloon was first and you could isolate the pulmonary veins and someone came to you with a single point-by-point ablation catheter and said, we want you to isolate the pulmonary veins with this, would you switch? I think RF came first. And so it's- Well, and that's the problem if you're good at what you do and you feel comfortable with it. But I totally, for me, I think they're equal. I mean, the studies have shown they're equal. And I think it comes down to preference of the operator and make sure they're skillful at what they're doing and correct patient selection. I mean, I don't know if I had a persistent AFib that was a 5.2 sonometer left atrium that I would just tell my guys to go in there and do a cryo of the veins and get out. Because they're probably going to find something. We don't do lines and crazy things, but they may find another source when they're in there. I guess you could cryo it, but you know, if you're going to stick by the rules. But I think as long as you're good at it, you do what you're good at. But I'm excited that there's advances. And yeah, personally, they've won me over. I mean, I think the cryo data are very strong. Yeah. Right now, I think it's a pretty safe energy source. I mean, we talked about cryo balloon, but there's also other cryo-based linear ablation catheters that are being developed. Right. So, we'll tell you this, and I think everybody knows it. I'm an RF guy when it comes to AV node re-entry. I'm never going to change that. I just want to tell you. Me too. Oh, good. I'm glad to hear that. But everyone tries to tell you, oh, you have safety if you know what you're doing. You don't cry. You're talking about focal cryo? Yeah. No, we don't use focal cryo. Okay. There you go. Brad, thank you so much. Yeah. Thank you, Eric. Thank you.

cryoablation

pulmonary vein isolation

atrial fibrillation

AFib treatment

effectiveness