So let's kick up the first talk of Sonny's, and we'll have a question and answer session after his first talk, and again after his second. So we'll see you on the other side. Thank you for the invitation. This is always a lot of fun, and I see new coming, incoming folks. You're entering a field that is remarkably cool. You'll have a lifetime that'll be incredibly exciting. I can't tell you, you made the right choice. Thanks to Boston Scientific for putting this on. Okay, so when you talk about ablation, you always want to be thinking anatomically what your target actually looks like. Accessory pathways can be variable in their course. The majority of accessory pathways, especially left-sided accessory pathways, cross a totally normal annulus. So most people with accessory pathways have a completely normal heart structurally. So the annulus is completely intact, everything is normal, and they just have a strip of muscle that extends around the epicardial side of the annulus. Despite the fact that two or three per thousand people have pre-excitation, and in the 50s and 60s and even into the 70s, there were tons of autopsies done. And lots and lots of hearts have been looked at for all kinds of things. And they looked and looked for accessory pathways. And surprisingly, there actually are very, very few reports in the literature. And what they showed and what they found looked very much like this, with a short accessory pathway that kind of crosses the AV groove perpendicular. The reason there are so very few reports is because very few pathways actually do cross the AV groove perpendicular. They generally cross the AV groove in an oblique fashion. Perpendicular would be like this, with atrium ventricle here you can see, it's oblique. Once we saw this, and this was actually learned by recordings in the EP lab, when anatomists then went back, and the guy who did the most with this is Tan Becker from Amsterdam. And once he saw that these were oblique, looking at the recordings, he went back and actually looked at reports that they even described and said, oh yeah, these things are all oblique. So this is a very typical accessory pathway. So here's a section through the mitral annulus at the site of a left posterior accessory pathway. So this is a trichome stain. These are sections through the mitral annulus. And what you see is a perfectly normal, well-formed mitral annulus. The anatomy is totally normal. In dark brown, you have myocardium, left atrium, left ventricle. And you see here the atrial end of the pathway coming out of this bundle. Then a few millimeters down, you see the mid-body of the accessory pathway. Then a few millimeters farther, you see the ventricular insertion. And when you look at this, you realize it looks like an atrial fiber. And in fact, most of the pathways are left-sided. And I won't have time to kind of go into this today, but there are a lot of features that actually suggest the majority of these, especially the left-sided ones, really are atrial fibers. When you look at this, you get the feeling that in embryology, a little piece of the atrium touched the ventricle. And as the atrium rotated, it kind of pulled this fiber along. And you could understand why we can have pathways that conduct only in one direction, right? Retrograde, the ventricle can easily excite this piece of muscle that can then, as it gets bigger and bigger, as it retrogradely comes up this pathway, it generates more current and excites the atrium. But going antigrade, you can see that this bundle gets very, very thin. And so it generates a very small amount of current that can then get diluted by this big mass of ventricular muscle and not actually be able to excite it. So it kind of explains a lot of the observations that we're gonna talk about. All right, so let's go to ablation. That was my topic. So in the 80s, when we started with radiofrequency current, we thought that we were going to have to ablate from the coronary sinus because we needed to be very close to this bundle. But radiofrequency current is electricity. Electricity goes wherever it wants, right? It's always gonna go where the resistance or the impedance is lowest. So a brilliant electrophysiologist who was a young guy at the time, a guy named Carl Heinz Cook from Humbert, had this really cool idea. He said, what if we stick an electrode underneath the mitral annulus here? We can deliver the radiofrequency current in a bipolar mode between these two electrodes and draw the current, aim the current right at the fiber. So we thought the main electrode was going to be the electrode in the coronary sinus. And when we had a terrific electrogram in the coronary sinus, meaning we actually recorded activation of this bundle, it's telling us we're pretty close, but we didn't see it from, we weren't careful where we positioned the endocardial catheter. And very often the RF didn't work. But what surprised the dickens out of everybody was that when the electrogram here underneath the valve saw the pathway, it always killed the pathway. And so we realized, wait a second, hold on. This is the one that seems to be working. And so the way RF began is it began with an electrode underneath the mitral valve or underneath the tricuspid valve, high up against the annulus, and we used a hard skin patch as the return electrode. And you would get more current because the resistance is lower, the impedance is lower with a big contact electrode here. So we actually got more current here and it worked. And we're off to the races. And the rest is basically history. This was called the retrograde transaortic approach. So we put a catheter in the thermal artery, put it across the aortic valve and up underneath the mitral leaflet. This is a canine heart, a dog heart that's been fixed in formal, and that's why it's brown. And again, so you see the way the catheter would be positioned going across the aortic valve into the left ventricle, underneath the mitral leaflet. Oops, giving away all the punch lines. You can see the mitral leaflet draped over the catheter. We would have to position it up high, right up here against the mitral annulus. And we would get beautiful lesions like this. So here is a canine heart, a section through an RF lesion that was delivered to the mitral annulus. And the dogs were sacrificed to three days to allow time for an inflammatory line to form around, how well does it show there? Do you all see this light? Does it show real well here? This very light coloring, that is the inflammatory line. It clearly demarcates the lesion. Everything inside that is coagulation necrosis. So heat just destroys everything. So everything inside is totally necrotic. There is no structure that will remain. This will form a single dense fibrous ball that will shrink down to about the size of a pea with no structure inside that at all. No surviving bundles or things like that. Now what you would expect, right? Oh, so how did we know where the lesion was actually created? The pathologist would look for the site of the maximum endocardial disruption. And his name is Jan Pita. He would stick an arrow on the slide. So for dummies like us, we couldn't miss it. So here it was perfect where the catheter was positioned. And you see the lesion. And as you would expect, you get necrosis involving the epicardial surface of the ventricle that extends a distance away from the mitral annulus, which would be in here. You can't really make it out. It's all destroyed. What you might not expect or anticipate is that there's also necrosis of the atrium that extends down to the mitral annulus. So basically you have necrosis all the way across here. So remember the key, this is very important because pathways don't go across perpendicular. They go across obliquely. So from underneath the leaflet, you can target the ventricular end of the pathway, the middle of the pathway, or the atrial end of the pathway. You can target any of them from underneath the leaflet. Sometimes the catheter, we thought it looked perfect like it was right up against the annulus, but it was actually wedged in a trabecular recess here. And what we would get would be just a big lesion in the ventricle that did not reach the epicardium. This would not be at all effective in ablating the pathway. And the clue for this is the electrogram. Notice if your catheter is positioned here, you're far away from the atrium. So you'll have a very sharp ventricular potential, but you won't be close to the atrium. And distance on electrogram corresponds to both size, the amplitude of the signal, the atrial potential is gonna be very small and the slope of the signal is going to be small. So you get a tiny rounded or far-field atrial potential, and that tells you you're far away from the annulus. When we were up here, we were very close to the atrium, so we had a very sharp atrial potential. Tells us we're very close to the target. We call that a local signal, or that we're very, very close. Yeah. Sure, and I know he's gonna actually cover one of them in particular. The question came in, since the atrium twists during embryology, does the oblique course always follow in the same direction? As the atrium, it does. And then there is another- And I will show that, yeah. Yeah, I anticipated, I remember. The other question that just came in, as you're showing pictures of this cross-section, what is the risk of damage to the circumflex artery? Actually, we don't see it from the endocardium. There would be from the coronary sinus, and that would be very, very significant. So, surprisingly, from the endocardium, we generally don't hurt arteries. Very, very rarely. On the right side, that's thinner, you can actually ding the right coronary. The only one I've ever seen dinged, actually, there was an atherosclerotic lesion there. So when we occluded that artery, and the angiographer got there, they said, no, no, no, you didn't do this. This was an atherosclerotic lesion. I said, yes, yes, we did this. I mean, that's right where the electrode was. We just heated up a plaque. So, obviously, there's gonna be more danger if you're right at a level where an atherosclerotic lesion is for heating it up and getting an occlusion. But actually, from the endocardium, it is remarkable that the arteries tend to be safe. Okay, there are some advantages to going below the leaflet. The catheter, if you look, is snug up against the annulus. The leaflet actually holds it in place. And that allows you to make, it holds it there, it's stable, and it allows you to deliver current into the tissue. You want the catheter touching all the time to deliver current into the tissue and heat up that muscle. However, I will say that it took a lot of experience to learn to wiggle this thing all the way up against the annulus, where you could get a good, sharp atrial potential. And then when we had to move the catheter along the annulus, what you have to do is push the catheter in to free the tip up, rotate it, and wiggle it back up again. So, there is really a pretty long learning curve to this. Once you get it, you can actually do pretty well, and it's incredibly effective. But it is hard and much harder to learn as a fellow. In the early 90s, John Schwartz introduced the transeptal approach. So, you go across the septum, and you can maneuver all along the annulus pretty easily. That is a big help there. But now, then we're responsible for maintaining good contact against the tissue. We don't have anything holding us against there. If you deliver the lesion down low with very good contact, you get a beautiful lesion that involves the epicardial surface of the atrium by the annulus. But it might surprise you to learn that you also get the epicardial surface of the ventricle along the annulus. So, you can ablate anywhere across the accessory pathway from above the leaflet. You can ablate the atrial end, which is what people typically think about doing from above, but you can do the middle of the accessory pathway, or you can do the ventricular end of the accessory pathway from above. Sometimes, we thought we were in perfect position, but we were too high, and when you're too high, the lesion may not reach all the way to the annulus. And so, this is not going to kill the pathway. Worse, you're close enough that you may stun the pathway so that it's blocked, and it may stay blocked long enough that you think the pathway is ablated. You pull the catheters out, and in four days, the patient's back, conduction recurs, and patient's back in tachycardia. So, you really want to avoid this. I travel a lot and get to Proctor a lot of cases in a lot of places, and I will tell you, almost uniformly, I see people position the catheter very, very high. It is the rule rather than the exception, so you don't want to do this. And the way you know that you're too high is you're far away from the ventricle, which means that when you look at the electrogram, you're gonna have a sharp atrial potential, but the ventricular potential is gonna look far away, meaning the ventricular potential's gonna be small, rounded, it's not going to be steep. Steepness is closeness, and that's absolutely critical. So, when you're down here in a good position, close to the annulus, you're very close to the ventricle, you're gonna have a large, sharp ventricular potential. So, if you're above the leaflet, you want the sharpest ventricular potential you can have. If you're below the leaflet, you want the sharpest atrial potential that you can have. So, here's the deal. The deal is the lesions are perfectly adequate. They're effective, they're going to do the job, and the key to ablation of accessory pathways is the same thing as real estate, right? What are the three main rules of real estate? Location. What's the second one? And what's the third one? And it's absolutely identical in accessory pathway ablation. All three rules are critical, okay? All right, so that's what we're gonna talk about. Now, if you go to the literature, they're gonna tell, the literature will tell you how to find the accessory pathway, and almost everybody in this room was taught this is the way you're going to find the accessory pathways, okay? And these criteria come from the early 70s, and they came from what information was available. And the very few histological sections that were available suggested that accessory pathways were short and they crossed the AV groove perpendicular. So when criteria were created, okay, if you look at antegrade, antegrade means the atrium, you activate the atrium, the atrium activates the accessory pathway from the atrial side toward the ventricular side, then that's going to activate the ventricles. In a perpendicular pathway, if you find the site of earliest ventricular activation, that's where your pathway is going to be located. It's also going to be the site where when you look at how close the atrial and ventricular potentials are to each other, we call that the shortest local AV interval, it's going to be right there, okay? And it doesn't matter what the direction of activation is, whether the wavefront's going this way or going this way, that's where it's going to be. The other thing that people look for is fusion between the atrial and the ventricular potentials. It's perfectly logical, okay? The electrodes are large enough and the pathway conduction time based on the way these pathways were perceived would be short enough that when you have ventricular activation beginning, you'll still be recording the atrial potential. So the atrial activation will be about here when ventricular activation begins. So from this catheter, you'll still see atrial activation, so you'll have fusion between the atrium and the ventricular potentials. So this was thought to be very important, okay? And it was also thought, my teacher was taught by the greatest accessory pathway electrophysiologist, well, one of the two greatest on earth, a guy named John Gallagher from Duke, and John told my teacher, Eric Prostowski, you can't record accessory pathway potentials, okay? He tried it in the operating room and he said, you can't do it. So I was taught you can't do it. So what happens when you tell a little kid you can't do it? As soon as I became an attending, what's the first thing I tried to do? You got it. I mean, I'm still 10 years, my therapist thinks I'm growing a little bit, but 37 years ago when I started my job, right, I was about 10. So yeah, and it turns out that it was thought you couldn't record a pathway potential and you shouldn't be able in this situation because the atrial wavefront is going to be so big, it's going to mask this completely. If you look retrograde, ventricular activation activates the accessory pathway. With a perpendicular wavefront, the pathway is absolutely going to be located at the site of earliest atrial activation. It will also be the site of the shortest local VA interval and it won't matter what the direction of activation is, okay? And the ventricular potential is a big potential. You're still going to be recording it at the time atrial activation begins. So people believed that it was important to record fusion of the ventricular and atrial potentials and that you shouldn't see a pathway potential because that ventricular potential is going to hide it. These criteria are absolutely legitimate. They're absolutely legitimate and are correct when you are dealing with a perpendicular accessory pathway. There's nothing wrong with these. The only issue is that almost all accessory pathways are oblique. In all locations, free wall, septal, makes no difference. They're all twisted. And the distance on average is probably more than a centimeter across here. And here's the problem. When you look at earliest retrograde atrial activation on an oblique course where you record it is here. This is where the shortest local VA interval is. It's out here. When you look at earliest anterograde ventricular activation, it's out here. I'm going to come back to this in the workshop. So we'll deal with this a lot more completely in that workshop. But notice, so what does that mean? With an oblique course, the classic criteria will get you near the accessory pathway. They won't put you directly on the accessory pathway. What is cool though is that the oblique course actually does allow you to record an accessory pathway activation potential. And that is the target. And if you make this the target every time and only look for earliest activation when you can't find a pathway potential, you're going to be surprised at how often that pathway is going to be ablated very, very quickly. Okay, so there was a question about are the pathways oriented in the same direction as the atrial fibers are located and absolutely are. So the left atrium twists this way. So the atrial end of left-sided accessory pathway is about 80% of the time the atrial end is going to be located lateral and superior or anterior by the old name in that direction. If you look at the electrograms in the coronary sinus, if you have a catheter in the coronary sinus and the great cardiac vein, the atrial end is going to be distal to the ventricular end. The ventricular end will be proximal in the coronary sinus. Now how do you know you're dealing with an oblique course? It's actually pretty simple. All you have to do is paste the atrium or the ventricle from two sites on opposite sides of the accessory pathway. So let's say we're going to paste the atrium on opposite sides here. If we paste the atrium here from the great cardiac vein, we're going to get a wavefront that's going to come around like this. As that atrial wavefront is coming around, it's going to enter the accessory pathway. And so as the atrial wavefront comes this way, the accessory pathway wavefront is going to propagate this way. And so the local AV interval at the site of earliest ventricular activation is going to be very short. They're going to both arrive at the same time. Does that make sense? If you reverse the direction of activation, if you paste the atrium from the very proximal CS on this side of the accessory pathway, the atrial wavefront is going to go around like this and it's going to go past the accessory pathway. So the atrial wavefront is going to pass the ventricular end where you're going to measure the local AV interval very early. It's going to go past the accessory pathway, turn around. What's going to happen to the local AV interval? So it's not fixed, correct? It's not going to be the same. It's the same if the pathway is perpendicular. It's never the same, basically. And it's always going to change. It'll surprise you how much it will change. It'll about double, usually, most of the time. You can do the same thing looking retrograde, okay? You can get a ventricular wavefront going around the mitral annulus this way by pasting the very bottom, the very inferior aspect of the right ventricular septum very basally, very, very close to the tricuspid annulus. That'll give you a wavefront going like this. So let's just imagine we have an accessory pathway out here and we're looking from the lateral aspect. We're looking from the epicardium. So the atrial end is going to be lateral or anterior, right? And the ventricular end here is going to be sort of septal or posterior. Is everybody oriented okay? Cool. So if we're pacing the RV at the base inferiorly, we're going to get a wavefront that's going to come around like this. And what's going to happen is that wavefront is going to enter the accessory pathway very early. And where we measure the local VA interval is right at the site of earliest atrial activation, okay? Now, notice two things. Number one, the ventricular wavefront is propagating across at the same time as the pathway wavefront. So if you pace the RV like that, do you think you're going to see the pathway? No. This potential here is going to hide it, totally mask it, okay? You won't see it. You know, people say, oh, Sonny, I never see pathways. Well, yeah, if you pace on that side, it's going to hide it, okay? And what about the local VA interval at the site of earliest atrial activation? It's going to be very short, correct? You always want to measure it at the site of earliest atrial activation, but you see these two are going to arrive at the same time. If we reverse the direction of ventricular activation, and we can do that by putting the pacing catheter out the coronary sinus and great cardiac vein, stick it in a vein, just like you're going to learn to do. Isn't there some technique for heart failure or something, I don't know, pacing, yeah, okay. But you can actually pace the base of the left ventricle very distally out here in a vein. You can get a wavefront coming this direction. Watch what's going to happen. The ventricular wavefront is going to cross the site of earliest atrial activation very early. And here's the magic, that you're not going to be activating the accessory pathway until the ventricular wavefront is moving away, away, so that at the time the pathway is activated, the ventricular wavefront has moved away, now you can clearly see the accessory pathway. You could say, oh, it's unmasked, okay? And then atrial activation here is going to be very late, because you cross the V early, the local VA interval. As you see, the local VA interval pacing the other way was very short. Here it's very wide. That tells you you're dealing with an oblique course, okay? So the key is, the oblique course is what lets you see the accessory pathway. But the oblique course, but the pacing site will either separate the ventricular and atrial potentials and show you the pathway, or it'll bring them together and hide the accessory pathway. So the direction of pacing is the thing that lets you either see the pathway or prevent you from seeing it. The same thing is true for atrial pacing. For instance, if we pace the atrium in this direction, the atrial wavefront and the pathway are simultaneous, the atrial potential is going to hide it. But if you pace the atrium this way, the atrial wavefront goes past the pathway as it turns around and activates the accessory pathway. So in one direction, the AV interval becomes fused. You don't see anything. In the other direction, it separates it, and you can see the pathway potentials. So let's do a case. Where's my time? Oh, my goodness. Oh, boy. Okay. All right. Okay. Oh, did... Oh, you... Okay. Okay. All right. So here is a young man with a concealed left free wall pathway. You find the site of earliest retrograde atrial activation. In his case, it was straight lateral here. Now, normally you want your CS catheter crossing that, but this was a different patient. We can get a wavefront going in this direction by pacing the inferior septum on the right and very, very basal. I like to use a deflectible catheter here just to be able to pace very basally. Okay. Notice if we pace here, the ventricular wavefront in the CS is going to be proximal to distal. If you look, the ventricular potentials are proximal to distal. And if the pathway is slanted in the usual way, as the ventricular wavefront goes by, it's going to activate the pathway. They're going to go together. It should give us a short local VA interval. When we look here, actually, the ventricular potentials overlapping the atrial potential. It's really short. You can't even see the A at all. Okay. So this is not going to help us. Let's reverse the direction of activation. The easiest way is to just put a catheter. You can sometimes wedge the CS catheter into a vein distally. I like to just take the pacing catheter because it's deflectible and just put it in a vein distal to the pathway. That gives me a beautiful wavefront propagating in this direction. You can also do this. It's a little more difficult. Put your catheter out the pulmonary artery, curl the catheter down tightly against the floor of the PA, pulmonary artery, pace at high output, and you won't capture anything. And as you pull the catheter back very slowly, the first place you capture ventricle, you'll actually get a ventricular wavefront coming around in this direction. And that's what we're doing here. So the ventricular wavefront should be distal to proximal in the CS. Does that make sense to everybody? Okay, and you see we did reverse the direction of activation. Now ventricular activation is distal to proximal, and we should have to go past the pathway and turn around and come back. So the local VA interval should increase. Did it increase? Yeah, striking increase, right? Now you can truly see the atrial activation sequence. You can see the site of earliest atrial activation. But more importantly, now that we've separated the ventricular and atrial potentials, do you see anything else? Loud, I'm half deaf. Pathway potentials, right, exactly. So what did we do? We found the proximal site of earliest atrial activation, and we paced the ventricle on opposite sides. In one direction, the V and the A were very short. I can't see anything there. In the other direction, the VA interval widened. What did that tell me? That the VA interval was not fixed at the site of earliest activation. What does it mean if you reverse the direction and the VA interval? It means there's an oblique course, right? So all I care about, I'm going to throw, this is of no value to me. Pacing from the direction where they're fused is of no value. I'm going to use the site where we get separation, and that's going to let me see the pathways. So where do we ablate? A lot of people say, well, why not just ablate right there? Well, we're going to talk in the next talk about the resolution a little bit of an ablation catheter. It's not very good. Oh, I forgot to add a little something to that one, something called MIFI, but I guess I have time to edit. But the resolution of the ablation catheter is not actually very good. And so when you think you're here, you might actually be here. So the safest thing to do is go to the middle of the accessory pathway. That way, if you think you're here, but you're here, the pathway dies. If you think you're here, but you're here, the pathway dies. That's our business, right? I'm from the Wild West, right? Oklahoma, we have real cowboys there. That's no joke. Actually, it's a very cool culture. It's a very cool culture. OK, all right. So the last thing I want to mention, and I'll stop after this. The last thing I want to mention is, take a look. So we're going to target here near CS5, OK? Now by the way, most people call this 1, 2, electrode 3, 4, electrode 5, 6. I just call it by the bipole. So these are the distal two pairs, the distal pair, the second pair, the third pair. So we're going to ablate here, but I want you to notice something. Look at the timing of atrial activation here, right? So if this is pathway and this is atrium, this is the junction between the pathway and the atrium here. Do you see that? All right, so this would be earliest atrial activation. If we extend this line up, look at the timing of atrial activation here. On the bipolar electrogram, the timing is at the first rapid. Okay, the first rapid is this downstroke right here. You see where I timed that? That's 20 milliseconds. If you told your attending, well, today let's go ahead and ablate an accessory pathway where the site, at a site where retrograde atrial activation is 20 milliseconds later than the earliest activation, they might tell you, maybe you should go home today. But there is a reason. Why is it late there? It's actually to be expected. What you're going to see, which we'll talk about in the workshop, is retrograde. Remember the oblique course is because these are atrial fibers. It's the direction the atrium is twisted. So the longitudinal direction of the cells is like this. The longitudinal direction of the cells in the atrium is the same way. So the conduction velocity is very, very fast in this direction. That's why earliest activation, when you look from the endocardium, looks like it's here. Turning around takes a long time. Why? The fibers are oriented like this. Turning around, you're going transverse rather than longitudinal. So there's a big delay in turning around. And then it'll pick up speed coming back this way. But you're aiming right here. So you have this big delay here before you get back to where you want to ablate. And what I want to mention to you is the longer the oblique course, the later the timing is going to be here. And because the longer the oblique course, the steeper the angle is going to be turning around. So the longer the delay here, okay, on average, it's going to be about 10 milliseconds or so. So maybe I should stop here. The rest of the slides or the other half will be in the slide set. Let me ask a couple follow-up questions that have been coming in. One that has to do with the retrograde aortic approach. And is there a risk of damaging the mitral valve apparatus when you're tucking the catheter up and ablating there? Actually, no. Going underneath the mitral leaflet, mechanically, it doesn't hurt anything. The RF doesn't seem to hurt the leaflet. It doesn't perforate it or whatever, probably because the resistance in there is high. So current doesn't go there. Current goes where the resistance is low. So the mitral leaflet is fine. You don't see perforation or whatever. The thing you have to be careful of is crossing the aortic valve. You can actually stretch and damage the aortic valve, especially in young children. And most people don't do this. And I like this for VT too. I like to use a long sheath and cross the valve with a guide wire and put a long sheath across. But most people will come up the aorta, will loop the catheter and push the loop across into the LV. And usually that's okay. But be aware, it's not the mitral valve you worry about. It's the aortic valve. Another question came up with, do you see a fanning out of the end of the pathway more on the atrial side versus the ventricular side? By fanning out, do you mean branching? Yeah, branching. So should you target a narrow portion or a fanning out portion and how does that play a role in deciding where to ablate? You know, it's really interesting. I actually don't call pathways separate unless they're three centimeters apart because you will see parallel components. But usually the branching does not influence the ablation when you aim at the middle of the accessory pathway. You would think with branching, you'd get an atrial end and you'd see a shift in the side of earliest atrial activation or whatever. If you aim for the middle, it doesn't happen. Aiming for the middle is what works. And we didn't get to it. But if you do this, if you find, if you either pace the atrium or pace the ventricle and find the direction that separates the two potentials and see the pathway and aim for the middle of the pathway, you're going to find that more than half the time you'll actually kill the pathway on the first burn. This is over several thousand pathways since 1988. We've been doing this and it's legitimate. I mean, this is the way to win. This is the way you win. And the last question I'll ask deals with the electrograms. There's a question about how do you tell the difference between the pathway electrogram and the atrial electrogram and also when you're pacing from two different sides, do you see an inversion of the electrograms where you're recording? No, you don't see an inversion of the electrograms because it doesn't matter which direction you're going to come. The pathway is still going to go the same way. But the way, yes, you can have double atrial potentials that look like atrium and pathway, no question, especially in people that have had prior ablation. In fact, it's the rule. I'll even show that to you in the workshop. The way you differentiate a retrograde pathway potential from the atrium is you pace the ventricle and deliver an atrial extra stimulus. The first thing to move is the atrium. And so that second potential should move, but the first one that you think is pathway will stay fixed. Antigrade, you can separate them by pacing the atrium and delivering a ventricular extra stimulus. When you pace the ventricle with the ventricular extra stimulus, you're going to retrogradely activate the pathway and you'll pull the pathway potential in and leave the atrial potential still. That's for next year for you guys. It's not a difficult technique to do, but it'll take me 20 minutes to go over it with you. Okay. Well, Sonny, thank you very much for that video. And we're now going to open things for questions. Let me just remind the attendees that you do have the chat box. You can put questions in at any time. And Sonny, there are a number of them that came in that really covered something that you actually talked about during the video itself in response to a question about the potential for damage to the annulus, the mitral, the chordae. And perhaps you might just elaborate on the fact that even though it's low flow, the current tends to go where the impedance is lowest. So do you look for an impedance change in those locations? Maybe you could just answer a couple of questions that came in, one from Dr. Neville at the Lahey and another one from Mexico City as well. Sure. We were actually quite surprised in the beginning. The annulus really seems to be very resistant both to the motion of the catheter. I mean, we always tried to be gentle, so it's hard to know. But we really didn't see a lot of injury to the chordae, injury to the mitral annulus. Again, you want to be careful with the aortic valve in that you can stretch that out, especially in young children. But for some reason, the fibrous tissue really seems to be very resistant. And I mean, we can make the assumption that that's simply because current is always going to go where the impedance or the resistance is the lowest. And fibrous tissue is where it's going to be the highest. But I can't tell you that's what it is. It may be that it's heat resistant as well. I don't know. But that's not been a problem. Excellent. A question came in from Dr. Taha about really the relative merits of the retrograde versus the transeptal. And perhaps to expand on that a little bit, are there specific patients or specific types of anatomic considerations in which you would prefer to go retrograde as opposed to transeptal? Not really. The first four or five years, or at least the first three years, we did everything using the retrograde approach on the right side as well. We went underneath the leaflets on the right side as well. It works remarkably well. It's very stable. It is technically challenging. To maneuver the catheter under the valve is hard because it gets stuck. And it takes a gentle touch to be able to push it in, rotate it, and wiggle it a little bit and take a lot of practice. By being above the leaflet, you can move the catheter along the annulus very, very well. The issue there is contact. Then we're responsible for contact. The biggest error that I see is that most people try to come perpendicular to the annulus. If you can maneuver the catheter parallel to the annulus, you do a lot better. Actually, the original sheaths, the Schwartz sheaths, the SLSR sheaths, were designed to allow you to be parallel. That helps a lot, and I like that. Most of the people today are used to deflectible sheaths, and that will bring you straight perpendicular. It is more difficult to stabilize the catheter. You want to use anything you can to tell you that you're laying properly. If you can measure contact force, if you can measure impedance, depending upon your mapping system, whatever system you're using has a way to help you with that. When you're above the leaflet, which is the transition that almost everyone has done, again, the issue is being low enough. I mentioned this in the lecture. Most of the people, as I watch, have a very large sharp A, and a V is there. There is a ventricular potential there, but it is not sharp, so you know it's far away. Usually, you're five, six millimeters above the annulus. You really want to be sure that you have a sharp ventricular potential, especially when you look at the unipolar electrograms. Sharpness corresponds to closeness, and that's critical. Thanks, Sonny. Excellent question came in from Dr. Pashonis. How do you differentiate between a stun accessory pathway versus a successfully enduring ablation of an accessory pathway? You can't know for sure, but basically, the thing that correlates best is how quickly the pathway is ablated when you turn on RF. If you get to the middle of the pathway so that you have an isolated pathway potential, and you position the catheter so that the unipolar tip electrogram has the sharpest signal on it, generally, that pathway will disappear, and you have a stable contact. If you have those three things, even if it's not a high force number, but the stability of the contact that the catheter is laying properly on there, that pathway will usually disappear within the first couple of beats. When it disappears within the first couple of beats, if it stays stable there, and you get a long, you're able to put enough current in, you have a, remember, the injury, the lesion is based, is a function of contact force or contact power and time. It's going to go away. I see a lot of patients referred with failed ablation, and they'll say, oh, it went away within the first 10 seconds. For me, if something takes longer than two seconds, I really worry about that, and I will make sure I hit that area again and again. It should go within the first couple of beats if you've picked the electrogram properly. Again, you want a pathway potential, not earliest activation, and you want it sharp on the unipolar electrogram. The longer it takes, the less likely it is to be permanent. Excellent. Sonny, a question came in from Dr. Cancharla, Kristin Cancharla, one of my colleagues here, about the posterior, I'm sorry, the slant of the septal pathways in your experience. What's the slant of the septal pathways? About 80% of the time, an antireceptal or right anterior paraceptal pathway that we still call that antireceptal region is going to be slanted with the atrial end anterior and rightward of the atrial end. The atrial end very often will be very close to the hiss, but the ventricular end is very often going to be 5 to 10, as much as 15 millimeters to the right of that. A mid-septal pathway is the opposite. The ventricular end is on a right mid-septal pathway, and the little bit we can tell for the rear left mid-septals, it looks the same. The ventricular end is inferior to the atrial end at least 70% of the time. Right posteroceptals, the atrial end is going to be high, just like the mid-septals. It'll be the same. The right mid-septal and posteroceptals are slanted the same with the ventricular end inferior and the atrial end superior. The left posteroceptals, probably 90% of them, the atrial end will be distal in the CS or more lateral, and the ventricular end is going to be rightward. But in every location, you don't know the slant. You may be dealing with the 10% to 20% or 30% that are oblique in the opposite direction. It only takes a few minutes to find the site of earliest activation and pace on opposite sides and find the direction that separates the A and the V, and that will let you find the pathway potential. Excellent. Sonny, we have just about a minute left, but a couple of questions came in about where you actually ablate. You always ablate where you see the accessory pathway potential, how frequently you're able to see it, and what you might do too in the remaining several seconds is to clarify the role of cryoablation. When do you use it, if at all? So are you able to look at an accessory pathway potential, and when do you use cryo? Okay. You can find an accessory pathway potential over 90% of patients. If you find the site of earliest activation, and you pace on opposite sides, and you look where you separate the A and the V, and you always pace from the site that separates the A and the V, you should find the pathway potential, and the critical thing is that the two electrodes of the ablation catheter are far apart, and you must be recording the potential from the unipolar tip electrogram. So you find it with the bipolar electrogram, but then you reposition the catheter to get the sharpest signal you can get on the unipolar tip electrogram. If you do that, more than 50% of the patients, the pathway will ablate with the first RF, and usually within the first few beats. Cryoablation, cryo is not quite as powerful a killer, sucking heat out as putting heat in. So, and plus the electrode is much bigger, so the recording resolution is poorer. So I use it, I use it only when I'm in an area where heat is going to create adjacent damage, and that is usually within a vein. If I'm afraid I'm going to be near a coronary artery, like in the middle cardiac vein or whatever, and I shoot the angiogram, and the artery is within five millimeters, I will use cryo. That's really the only place I use for accessory pathways. Excellent. Sonny, thank you very much.

Sonny Jackman

ablation

accessory pathways

anatomical considerations

retrograde transaortic approach

transeptal approach

electrode placement

oblique course of pathways

cryo-ablation