Thanks, Nishant, and thanks so much for organizing this. It sounds like it's been a great resource for EP Fellows across the country. And thanks to Brad and Northwestern for hosting. I'll just give a couple of disclaimers. This is a talk I've been giving for many years. So some of the Carto and other maps you see may be a little older looking, but I think the concepts remain the same. It's also a talk I usually give in July or August, to introduce the incoming fellows to what electro-atomic mapping is and how it works. So it's a little bit out of sequence, perhaps, for those of you who are finishing fellowship or finishing your first year. It may be a little basic. But on the other hand, if you're finishing fellowship and haven't been introduced to these concepts, I think it's really important to realize what goes into making a map. Because wherever you are, you may have reps or mappers who are more or less experienced. And really, it's important to understand what goes into putting these colors together that we use on a mapping system. So I will just go ahead and get started. This may not fill up the whole hour, but we'll see. So this was an ATAC we were mapping when I was a fellow. I think Brad and I and some others are probably the last generation of fellows who kind of trained in what I call BC, which is before CARDO. So we actually mapped tachycardias without electroanatomic mapping. And this was an example of a focal atrial tachycardia. Right, and we would pick a fiducial point. So say in this case, the red line at CS56 and say, well, that's essentially zero milliseconds. And then if you see the ABL, that's the ablation catheter. And we'd move the catheter around, in this case, the right atrium. And you could use this with a triggered sweep or just by annotating on the review screen. And we found the earliest local electrogram, once we proved this was focal and not reentrant, is here 24 milliseconds early. Is that early enough? If that's the earliest we found in the right atrium, should we ablate there? Well, again, if you raise a line all the way up to the P wave, which I always will, well, I'll say several times is kind of the cheapest global mapping system you have, you'll see that that early activation, that early electrogram is maybe on time with the onset of the P wave. So we'd say that's probably not early enough to ablate, even though it's the earliest we found in this chamber. So then we go over to the left atrium, do a transeptal puncture, again, with the same reference of zero. I don't know if you can see my arrow. But now we find an electrogram that's earlier in pre-P wave, right? And that's showing this to appreciate that that's all CARDO, NAVIX, RITMIA, all these mapping systems are doing is they're cataloging a point, or these days multiple points relative to some fixed intracardiac reference, and then they're color coding the activation sequence relative to that reference, whether it's early or late, and keeping track of those points in 3D anatomic space. So again, back in the day, we would either map focal tachycardias or macro reentrant using entrainment. These days, obviously, you can do rapid multipoint activation mapping, but it comes down to those basic principles. So again, mapping systems are more sophisticated. This is an older, a little bit of an older slide, but important to realize all the things we can see in the mapping window. Again, I think a lot of times we tend to let the reps run the system and then just look at the map at the end. I always tell our fellows, if you're there watching a case and you have a good rep or mapper, kick that rep out, let them sit next to you and run the system yourself and see how it works, because it really helps you understand how these things work. So obviously you have, in this case, single point mapping. So we have a bipolar electrogram from the tip of the mapping catheter. These days you might have multiple electrograms. You'll often have the unipolar electrogram from the tip. This is important. These days, at least in our lab, the unipolar signals can be pretty noisy on our electrophysiology system, whether it's Cardiolab or EP Lab, whatever you're using. The amplifiers and electrograms on the mapping systems are often better quality. And especially if you're deciding where to annotate an electrogram, obviously the gold standard of when that electrical signal is actually passing underneath the electrode is going to be the negative dvdt of the unipolar electrogram. So seeing that together with the bipolar is helpful. And I think it's something sometimes we lose when we're doing, you know, multi-point 10 or 20 electrograms simultaneous mapping. Again, the reference electrogram, that's the point by which all the other electrograms are being compared in terms of activation time, is important. And again, this is something that typically the rep will pick and often not share with you unless you ask. So one of the first things I'll always ask the rep is what have you chosen as a reference? Because as I'll show you in this case, for mapping an atrial tachycardia, there's a big A on this CS electrogram, but there's also a relatively sharp far-field V. So if the rep told me I was picking CS7-8, I might tell him, well, why don't you actually pick CS5-6 because the A to V ratio is much better there in favor of the system picking the A instead of the V. Obviously, then you have the mapping window. It's going to tell you the tachycardia cycle length, the LAT, the local activation time of the point that you're measuring relative to that reference, right, in this case, 29 milliseconds later. And it's going to tell you typically the bipolar and unipolar voltage, right, for all these systems. We're typically recording voltage simultaneously with activation, whether you're displaying it or not. And then the all-important color bar. I'll talk about some slight differences between CARDO and NAVX, but for CARDO, this is displaying the earliest recorded activity on the map in red and the latest in purple and all the colors in between. So looking at this color bar and whether, you know, what this time interval is between the earliest and latest signal, as I'll point out later, is also important. You know, this is a minor point, but I always like to make it, and that's, again, nowadays there's a separate fill and color threshold, but this fill threshold, which isn't in any particular units, but it's basically the amount of data that's extrapolated around each data point on the map. Again, it may be less relevant these days when we have, you know, 10,000-point maps, but in general, I think you always have to remember that the data are the white dots, right, and the colors in between is basically extrapolated. And you can take any map and crank up the fill threshold and the color threshold and make it look like a beautiful map, right? I always, I get upset in publications when someone has a map like this, because it looks like a nice right atrial map, but really you've only got, you know, two data points in this whole area. So usually we'll set it very conservatively at five when our fellows start mapping to be very conservative and force people to fill in the whole chamber. And then if you have a few missing points, you can go up to eight. If you have to go beyond 10 on the fill threshold, it usually means, you know, if you're trying to fill out a whole chamber, you don't have enough density to cover that chamber. And then again, a lot of people will show maps, but nowadays you can turn these points off because there's so many sometimes with, you know, a 10,000-point map that it just becomes distracting. But I kind of force the reps to leave the points on because I want to know, you know, what's an actual acquired point versus what's just extrapolation between those points. So a few words about mapping focal tachycardias, and then we'll talk about reentrant tachycardias, and then finally I'll end a bit talking about voltage mapping. So it's important to realize or remember that focal is a pattern, not a mechanism, right? So focal could be a triggered tachycardia, it could be automatic, it could be a micro-reentrant tachycardia. It is helpful to try and sort that out before you start your mapping, I think. Because again, there are differences in how you might map these tachycardias. If you have, you know, a focal tachycardia that's triggered, you might be looking for a discrete electrogram that's 20, 30 milliseconds pre-P-wave, whereas if it's macro-reentrant, you might be looking for something, you know, mid-diastolic or micro-reentrant, you might be looking for a long fractionated electrogram. You know, one way to sort that out is with adenosine, as Lerman and his group have shown quite nicely. If you have a micro or macro-reentrant tachycardia, you give adenosine, you'll typically get AV block and the tachycardia will continue unperturbed. You know, occasionally it may degenerate to AFib. An automatic tachycardia, you'll get transient suppression and then resumption, whereas you may terminate a focal tachycardia. Again, it's another reminder that termination with adenosine doesn't mean it has to be an AV nodal-dependent tachycardia. Obviously, the other way to sort these out is with entrainment, looking for fusion or progressive fusion. I know a lot of people, it's taboo to paste these days during a tachycardia, but I think that's helpful upfront to get a sense of the mechanism of the tachycardia. Finally, the next thing to start with, as I mentioned, the cheapest global mapping system is always the P-Wave and this 12 ECG, I wanted to make two points. One is just, you know, when people always bring me an EKG and say, you know, where do you think this tachycardia is coming from? It's almost always like some two-to-one atrial tachycardia with the P-Wave on top of the T-Wave. And you can just see here for this stable two-to-one tachycardia, how different the P-Wave looks when it's superimposed on the T-Wave in this case. This is the same P-Wave. So you always have to find, you know, a P-Wave that's unperturbed from the baseline. And again, in the EP lab, that's pretty easy, right? Just put a catheter in the V and add a premature V to bring out the P-Wave. Look at the onset of the P-Wave, because that, as I'll mention, will be important for, you know, a global reference of where you think activation is early enough. But also it gives you a place to start mapping. Again, these days you may say, well, I want to make a pretty map that I can post on Twitter and I'm going to get 10,000 points. But practically, you often only need a region of the atrium. I think I have a question, or I don't think I gave this to Nishant, but I'll just pose it and people can ponder it. You know, where would you start mapping this tachycardia? Coronary sinus, tricuspid annulus, mitral annulus. And again, I think you can see it's negative all the way, pretty deeply negative across the pericordium. So that puts it pretty anteriorly near the tricuspid valve. It's very superiorly directed. And so, you know, somewhere around six o'clock of the tricuspid annulus would be a good place to start mapping. And again, you may get fooled a little by lead I, but the inferior tricuspid annulus can be some fairly apical. So you may have some flat or negative component in lead I with the tricuspid annular A-tach. Okay, I think this question, so again, this is an older map, single point mapping, but just to illustrate a concept. So we're mapping this tachycardia. We've determined whether it's entrainment or pacing that it's focal. And we have an early, you know, red point that's well pre our reference. And then the question is, what's the next step? Are you going to do, I got the map up, we got the questions up there, overdrive pacing from this red area? Are you going to ablate at this area? Are you going to continue mapping or are you going to deliver a late coupled APDs? So I don't know how many people are on, but why don't you go ahead and vote. You want to show them the map again, I can leave. Oh yeah. We're going the wrong direction. Yeah, so only two people are voting, but we got one brave soul that's going to get us ablate. That's good. How much time should I give people? I usually give them about a minute and then, but if they stop voting, I'll end it. Yeah. So those are the results there. Okay. So, you know, late in the years, that's good. So 75% of people are going to continue mapping. And, you know, again, this is just making a small but important point because two people, you know, I think we're just programmed these days to see red and to say, okay, it's red. That's a good spot to ablate. But right, you're missing, you know, you've got this point here, you've got another point over here and another point down here, but for a focal tachycardia, you want not just what's red, but you want red that's surrounded by colors that are later, right? It has to be emanating that from that point to surrounding points. Can I move the poll out of the way? There we go. I don't know if you're still seeing the poll. So, you know, again, this is that same point, right? But now we've mapped more points around there. It still is not high density, but, you know, the earliest point is clearly different and we're gonna continue to get kind of higher resolution in that area to get the earliest point that's surrounded by later points before we ablate. So again, I think obviously when you start mapping, you're gonna see red on the map and that's only earliest relative to the other points that you've acquired, right? A simple but important concept. And to be comfortable that you're at the earliest point, you know, you have to have either an early point that's surrounded by later points, or you've kind of filled out the whole chamber with high density, and you're confident that it's coming from that chamber and you're at the earliest point. This is just another example on the left. Let me get rid of the poll. Showing a map, again, not super high density, perhaps 82 points. Maybe it looks pretty good here on the superior septal mitral annulus. But again, if you look at the white dots, kind of right at 12 o'clock on the mitral annulus is not quite as densely mapped. And so you add more points and your earliest activations actually a little bit off that area that you had marked initially. So again, the importance of once you find an early point, that's the point to focus on for focal tachycardia, do more high density mapping to eventually find the best point that you wanna target. I'll also argue, you know, entrainment also before you ablate is a good idea. This is kind of a more current high density map. Certainly when you use a multipolar catheter like a grid or a pentarray, and you've got a very high density map, you know, it's less critical. And here you can clearly see a focal tachycardia coming from the base of the right atrial appendage. Again, is that clearly focal? I would argue that it's still important to do some overdrive pacing or entrainment before ablating to prove that. This is also an older map. So again, not super high density. So it's right atrium, tricuspid valve, sort of an LAOV looking out at you. Let's suffice it to say that there were enough points taken in the map that the earliest points are kind of here. And as we know, the HISS is never a single point, right? We typically will make sort of a cloud along the HISS bundle electrograms. And I think we have a question here. And the question is, for this, again, focal tachycardia, earliest, just below the HISS region, what's our next best step? Are you gonna go to a kind of a distal HISS slash right bundle electrogram and cautiously ablate with 20 watts? Are you gonna change to cryo? Are you gonna do a transeptal puncture? Are you gonna do retrograde aortic mapping? Or are you gonna say, you know, maybe this is too high risk. I'm not gonna stop and try flaconide. Okay, so there's the answer. So one person's going to change to cryo. I would say either transeptal or retrograde aortic mapping is appropriate. I think the main point, again, as many of you realized is when you have diffuse early activation in the hysbundle region, especially these days where, you know, transeptal puncture is not really a big deal, you know, you have to map the other chamber and make sure you don't have an early activation before you're going to ablate in that region. Obviously non-carnary cusp for parahysian tachycardia, you know, typically this is earliest a little bit lower below the hys as opposed to above the hys. If it's especially, you know, superior to the hys, then certainly mapping the non-carnary cusp is a good idea. Again, this was a while ago and, you know, we went transeptal and it actually was the earliest spot was actually a little bit off the septum on the left atrial septum. But again, the point is, you know, very important, especially for those who are leaving fellowship, you don't want to start buzzing around the hysbundle with only a right atrial map. You always want to map adjacent chambers and, you know, make sure you don't have an earlier spot at a safer location, which typically, you know, will be the case. I would certainly do that before switching to cryo. This is another case, again, older map where we're mapping and the earliest activation in this case is just posterior to the hys region. And so we went ahead and mapped the left atrium and you can see there's kind of a diffuse early activation in the septum. And so we went back and it turned out that that region posterior to the hys was actually the earliest region. And, you know, we ended up finding a safe spot to ablate there. So, you know, you may not end up ablating in your other chamber. You can make a case, you know, potentially, although the non-carnary cusp could probably be a little too anterior in this case. But again, it always helps to ablate and you can always go back, but you can't go back obviously if you ablate and have a complication. And then, you know, again, rendering remap features. Most maps have this where you can take the anatomy and then if you have a change in tachycardia, you can just use the same anatomy and remap the activation on top of the old map. So you just have to ask your rep, you want to remap the tachycardia because you're watching the electrograms. You see something's changed and you don't have to redo the entire anatomy every time. So a few points now about re-entrant tachycardia. So, you know, we know kind of the hallmarks of macro re-entrant tachycardias are, you know, early meets late or head meets tail re-entrant pattern. Obviously, it's also important that you're spanning all the colors of the color spectrum in the map. And again, typically that your activation covers 95% or more of the tachycardia cycle length. All right. So this might be a typical map. The cycle length of the tachycardia is 384 milliseconds. Again, if we look over to the right on the color bar, we've covered 370 milliseconds. We're spanning all the cycle length of the tachycardia we have in early meets late. So we're pretty happy this is a macro re-entrant tachycardia. Again, personally, I would always entrain just to prove that point, again, I think there's a lot of fear these days that pacing will break a tachycardia. Again, I think if you sense appropriately, start late in the cycle length, and then overdrive pace, it's uncommon to terminate. And if you know the whole tachycardia cycle length, I mean, it's not that big a deal if you terminate, right? You can just re-induce and you know where you're going to ablate either way. We just, you know, we like to see a tachycardia terminate, but most of the time you won't. And again, occasionally you can be fooled as I'll show you in some maps. So this is another, this is a right atrial map of a tachycardia. And what does everyone think of this tachycardia? Again, it looks like perhaps a clockwise right atrial flutter. We have an early, we have colors in the color bar, we have late, we have early meets late. But in this case, again, the tachycardia cycle length is about 400 milliseconds. We've only mapped 170 milliseconds of the tachycardia cycle length. So this is someone who had an ATAC that was coming from the infralateral tricuspid annulus, had had a relatively lateral CTI line before that, so you have a focal tachycardia that's just blocking coming around the annulus and you have a kind of a pseudo-re-entry pattern. So again, always important to train, but in this case, to interpret not just the colors on the map, but to look at the color bar, have you really spanned the tachycardia cycle length? If not, you know, there's two possibilities. It could be re-entrant, but you're in the wrong chamber, so you need to map somewhere else or you've got a focal tachycardia that's not covering the tachycardia cycle length. And again, the way to figure that out is with some overdraft pacing maneuvers. You know, this is just an example with Navix, and I show this just to point out that there are some differences in how these windows are set up, and I apologize, we don't have Rhythmia, so I don't have that system for examples. But with Navix, as opposed to Carto, where you will only see the earliest and latest points on your map on the color bar, for Navix, the rep will set up the earliest and latest point, and so you'll always have, you know, if you look at this color bar, you'll always have the color bar spanning the tachycardia cycle length, because they've set up the window based on the tachycardia cycle length. And then what you've got to do is to look at the map and say, do I have all those colors in the color bar represented in the map, right? If there's something missing, there's no blue or there's no yellow, then you might say, hey, I'm missing some of this tachycardia cycle length. Maybe this isn't a reentrant tachycardia. But you can't think of the color bar in the same way, because it's not showing the earliest and latest on the map, it's just based on what they've set up as the mapping window. Again, in this map, you'll often see with my maps, there are green dots, so green dots typically are what I've entrained, and that's in the tachycardia circuit. Orange or brown are typically out of the tachycardia circuit. So again, we've confirmed the circuit in addition to having the map. Here you can see it's actually skirting some collision, and then it's kind of skirting over into this connected right lower pulmonary vein, and then down, and this was a roof-dependent flutter after a PVI. So I'm going to talk a bit about setting up a reference. So the reference I use for mapping ventricular tachycardias is typically the proximal CS electrode, the distal CS electrode, the RV apical electrode, lead I, a monophasic electrogram ECG lead during sinus rhythm, or a monophasic surface ECG lead during VT, a lot of options there. Okay, so again, most people pick the monophasic ECG lead during VT, which I'll point out why is the best answer here. And again, I was a little worried when I was looking through this talk last couple of days, like, oh, this is kind of basic for this point in the year. But some people pick, so again, we're mapping VT. So using a CS or HO electrogram probably isn't, or distal CS is not a good reference. Do you use an RV apical electrogram as a reference? Sure, you could. But again, the problem with that is as you're mapping, if that catheter or electrogram moves, your reference is going to mess up the entire map, right? Everything on the map is relative to that reference. Lead one may be good, but may not be. And again, what I'll talk about is the importance of picking a reference that's stable and monophasic during the PVC or VT you're mapping as opposed to sinus rhythm. So most people got the correct answer there. So when mapping these reentrant tachycardias, rule number one has to be to pick the reference correctly. Again, always, always, always ask the rep what you've picked as a reference. Has to be relatively easy for the system to recognize. Something that's not going to move. You don't want far field signals from other chambers. And again, in VT, typically surface ECG is a pretty good reference because you have a large amplitude electrogram. Obviously for atrial tachycardias, the P wave is much lower frequency and it can be used but much harder to use as a reference. Again, you obviously want to pick either a chamber or location for your reference that's not going to be dislodged by mapping. That's why we'll often shadow the CS. So for an atrial tachycardia, you're typically going to use the coronary sinus because it's a stable location and it's something that you're not going to move. If your reference moves, typically you have to redo your whole map unless you can move that reference back to where it was. ECG, missing a G. So for vajricular tachycardia, just use the surface ECG. Don't bother futzing. But again, sometimes in a congenital case, a mustard for example, you might not have a clear CS that you can put a reference catheter in. So you want to choose a location that you think is away from where the action is in terms of the tachycardia. So you're not going to move that reference catheter and pick a V on the annulus instead of an A or have a changing deflection in VT. The rep based on the reference can pick where he's going to annotate as a reference. He can pick the maximum amplitude or the minimum amplitude or the positive dvdt or the negative dvdt. It doesn't matter. This isn't like when you're mapping an atrial tachycardia, you want to map the unipolar negative dvdt. Here the rep is just looking for a reproducible point on the electrogram that's not going to change from time to time. So you can pick any of those that are reproducible. Again, this is just an example on the left of one map of a left atrial tachycardia. And you have this one early point here and you can see the bipolar electrogram, well, it's not so early relative to the P wave, but it's well earlier than the reference. But again, this was an example where the reference chosen had both an A and a far field V. And for this one point, the system has chosen the far field V as a reference. So this one point appears early, but in reality, it's really, you know, it's coming up as 160 minus 160 LAT. But in reality, if you fix that, so the reference is actually on the A, that point's not so early. So again, especially with multipoint mapping these days, I've had a lot of reps who they'll say, well, I'm just going to take all the points or something like confidence, let the system take all the points. I'll go back and edit it later. One or two bad points can really mess up an entire map. And it does take more time, especially when the system's doing it automatically. But you can, you know, display and look at the points as they're being taken and cut out the ones that are bad or noisy. And I think it's much more worthwhile to do that as you're mapping and have a map that you have confidence in the end, rather than have a map that's garbage. And then you're trying to say, then you're trying to go back and edit 10,000 points. So paying attention to what is coming up on the map and whether the system's picking everything as you expect, I think is important. This is an example of a surface ECG reference for mapping in AfloTrack VT. Again, and so why a good rep will ask you upfront, what's the morphology of the PVC or they'll look over and look at the morphology of the 12 lead for the PVC or VT, right? Because lead one during sinus rhythm may have been a perfectly good monophasic peaked reference. And again, obviously, you can predict if you have eight different VTs. But again, if you're mapping a single PVC, you ended up choosing lead one. In all these three cases, the local activation time relative to the reference, right, is the same. But in this case, compared to this point, if you look at the second versus the third, because there's this biphasic electrogram in lead one, what the system is assigning as the activation time can be very different depending on the reference. So if you have this wobbling going on, again, it completely mess up your map. Okay, the next question I'm going to ask about is setting up the activation window. And so how do you ask your rep to set up the activation window when you're mapping a tachycardia? Do you split 95% so that you have 50-50, so 95% of the tachycardia cycle length, and then you pick 50% early and 50% post the reference? Do you do 90-10, so 90% early, 10% late? Do you pick 10-90, so 10% early, 90% late? Do you take 110% of the window, split 50-50, or 95% and set the window relative to the P-wave? This is mapping an atrial tachycardia. So I know it's probably not a good board question, Brad will say, because it's too complicated. But let's see what people think. Thank you. Yeah, so good. So about half the people said they're going to look at the P wave. Again, in my experience, you know, even very good mapping reps, well, just they just set it 50-50, right? They'll take 95% of the tachycardia cycle and they'll set it 50-50. And maybe 85-90% of the time, maybe 90%. That'll work fine, but occasionally it won't. And again, I think after asking what you're using as a reference, the next question I always ask is what are you setting as your window and how are you setting it up? And again, these are minor points, but I think it's important to pay attention with, especially if you have inexperienced reps. So rule number two is pick your activation window correctly. You don't want to pick points that are outside the window. And again, for focal tachycardias, you want to look at the P wave as we talked about and set the window so that the earliest is 50-70 milliseconds pre-P wave, right? So you want to incorporate early activation and have that show up as red on the window, because that's just sort of the way our brains are used to working. Because if the window is incorrect, you may have an early point that's purple or not red. Same thing with the QRS. Again, it depends, obviously, if it's macro reentrant, it's not going to matter. But if it's a focal PVC that you're mapping, you want to have set up your windows that you're incorporating the time prior to the QRS. It's usually less of an issue for VT because you're using the surface ECG as your reference, not an intracardiac catheter. Again, it's possible if your window is set up and it doesn't make sense, the map that you're looking at, that your earliest signal can be purple. We'll talk about why. For macro reentry, it doesn't really matter how you set your window up as long as you set it 95% of the tachycardia cycle length and then stick to that as you're taking points. And then all the sites, you generally want to take a little bit less than the tachycardia cycle length so that all the electrograms will only appear once within the window of interest. If you set your window too small, you may have electrograms that fall outside the window. That's okay. You just have to decide whether they're early or late. And if it's too big, you may have points that are taken by the system twice. So let's look at this in a little more detail. So this is a surface P wave. Say we're mapping an atrial tachycardia and say this reference ECG is a coronary sinus electrogram. So that's going to be our time zero, right? Everything we're recording with our mapping catheter is going to be early or later relative to that point in time. And let's say this is our atrial tachycardia. So it's going along and this is our mapping catheter recording the local signal. And let's say the tachycardia cycle length is about 310 milliseconds. And so the rep splits the window 50-50, 150 pre and 150 post. Now this electrogram, right, which may be pretty nice, maybe it's a little tall, obviously this is a schematic, but it's pretty early pre P wave. But how is this going to show up in your map? It's going to show up late, right? Because it's falling late in the window. So this may actually show up as purple and not red and that may be confusing. So what I would say is let's look 70 milliseconds pre P wave and then let's make that the earliest part of the window. So we're going to actually set up the window so it's 200 early and 100 late. Now that early electrogram is going to show up as early on your mapping system. Again, there are newer algorithms I'll just mention briefly like coherence for CARDO where you don't need to set a window and it takes these kind of things into account. But with most systems and just for understanding how these systems work, I think it's important to realize that what about if you have a macro re-entrant tachycardia? Well then it doesn't matter where your window is. When you shift the window, what it's shifting is where the early meets late is on the map, right? It'll change that early meets late throughout the tachycardia cycle length. And that's another pet peeve of mine. I know a lot of reps as they're mapping will get really excited and say, Ooh, look, you know, early meets late. You know, this is a good site for ablation. And again, where the early meets late is has nothing to do with the mechanism of the tachycardia or where it's good to ablate. You can have a focal tachycardia with early meets late. If that part of the tachycardia is at the edge of the window, it's just, it really for macro re-entrant tachycardia depends on how your window is set up. It is important though, once you've picked your window to stick with that and, you know, map points that are early is early and later is later. And then you'll end up with your re-entrant pattern on the, on the map. The one other point I always like to make is sometimes you will have a few windows, a little small, an electrogram that's right on the, on the edge of the window. And, you know, the rep may ask you, should I take this point as early or late? If it's re-entrant, you know, again, it doesn't matter. Just stick to the same approach, whether it's early or late in the window. If it's focal, you know, you can pace. So you might pace, overdrive, pace the tachycardia. And then after the last captured beat, look at whether that electrogram is early, comes back early before the P wave or comes back late. And that can help you tell the rep whether that should be an early or late point. This is just an example on the left of a window that's too wide. So the tachycardia, the window here is set to 350 milliseconds, but we can see that the tachycardia cycle length is 250. So again, especially if it's automatic mapping, the system doesn't know whether to take a point that's early or late because the points are represented twice. And again, that can make the map look very different. So again, that's why you want the window generally 95% or a little shorter than the tachycardia cycle length. This was a map from a case I did probably eight or nine years ago. It was one of our outreach hospitals. It was using Navix. The patient was referred for flutter. Of course, they're two to one, so it's hard to see the flutter wave. And we did this map with Navix and, you know, it looks pretty reasonable. It looks like counterclockwise flutter. And so what's the next step for this arrhythmia? Do you ablate the CTI? Are we going to overdrive pace? I'm going to try to use the term overdrive pacing rather than entrainment because entrainment is really a response to overdrive pacing. We're going to overdrive pace from the septum, the CTI, or we're going to give adenosine. Ed, do you mind if I have you just explain that point about seeing exactly where the P-wave is a little more? You know, if you can't see it, what methods do you use to unmask the P-wave so you know where it is? Yeah, no, I think that's, I mentioned it briefly initially, but it's always good. So the easiest, again, when you're in the lab is just put a catheter in the V and deliver a premature V and move the V out of the way so you can unmask the P-wave and look at it. You could give adenosine, obviously, to look at the P-wave, but often you're worried about tachycardia terminating. So that's another way if you want to bring it out, but I would say the easiest is just to add a premature V, move the V out of the way, and then you can look at the P-wave both for timing and for morphology. Okay, so only five people are answering, but at least they all picked the correct answer, right? So a map is just a map, and in this case, so we, you know, this is this halo catheter with the tip that was in the CTI, and we're overdrive pacing, and I mean, I think everyone can appreciate, I mean, this is nowhere near the tachycardia circuit, right? You have complete, you have massive fusion, and you have a hugely long PPI. It looks like we're not even getting into the CS, so, you know, what the heck is going on here? We had a map that looked pretty good. We have someone in flutter, and yet you pace from the CTI. Patient hadn't had prior cardiac surgery, and, you know, why are we so far off? So one thing that, let's get rid of this, Navix does is, it has this feature called re-entrant, and that, again, is to help it map re-entrant tachycardias, you know, basically any mapping system, when it has an early and a late point, is then going to interpolate all the points between that early and late point and make what's called, like, a reverse rainbow pattern. The re-entrant button forces it to bring the early and late together, so it looks like more of a re-entrant pattern to our eye. So the rep had turned that on. All I did is turn that off, and now you look at this same map, and you might say, huh, that's not quite as convincing. It could be, you know, it could be that you just don't have a dense map, and it's kind of clockwise flutter, but not quite as convincing. So what I did next was just, you know, with Navix, you can shift the window, so I shifted the window later so that the earliest was, you can't see the P-waves that clearly here, but earlier relative to the P-wave onset, and then re-annotated all the electrograms based on that window, right? And now you can appreciate that there's an early region breaking through the septum that's just passively coming around and colliding. So, you know, again, in this case, we went from this map to this map just by turning the re-entrant button off and shifting the window. Again, just showing that it's, again, another reason why I always like to entrain, I'm glad everyone picked Entrain, because a map are just colors. It may be correct, but again, you can be fooled by some of these algorithms and by how your window is set up. Again, the third point, it's probably not as critical these days with the multi-point mapping, but it's just to, I still like to, again, oversee and make sure that the system is picking the points correctly, even when you have multiple points. You know, the difficult situations are obviously when you have these complex, long fractionated electrograms. If you have a split If you have a split electrogram where one is clearly near field and higher amplitude and sharper, you know, typically that's what you would pick as the annotation. If there's a split and it's unclear or a long electrogram that's unclear, I'll often tell them just to leave it out, right? Making it a floating location only point, and you can go back and annotate it. You know, the other thing you can do is look at the surrounding points and pick early or late based on the surrounding points. But importantly, again, when you're mapping on the annulus where you have both A and B signals, you want to make sure you're picking the A and not the B for an ATAC. And again, this is harder when you get to multi-electrode mapping where you're using a pentarray or a grid, but you can, at least with the pentarray, you know, display all the points and unclick the points that you don't like, so you're only getting accurate points in the map. Again, this is just an older map, but long fractionate electrogram. You know, you could debate the biophysics, but practically, we end up taking typically the onset of the long fractionate electrogram, which tends to work for atrial or ventricular tachycardias. And again, in this case, based on the one point, you know, you can totally change a map from focal to reentrant, depending on how it's chosen. But if it's unclear, again, tell the rep not to take that point, and then you can always go back and annotate those points afterwards. This is just another example, older biatrial map. So here's, you know, potentially, is this a focal tachycardia from the right atrium? Well, this one point, the system, you know, this is actually annotated the V and not the A. So is this a right atrial tachycardia? Well, if you go and correctly annotate the A, it's actually a left atrial tachycardia. Finally, the fourth rule I like to use is, you know, if you have, now you have contact force, if you're in contact with the chamber and you don't have signal, you know, label that as SCAR. I still don't like, one of the things I don't always like about NAVX is it has the low voltage ID. You can set that also with CARDO. So anything below some cutoff, it's going to label automatically as gray or SCAR. And you have to ask the rep, well, what did you set the low voltage ID to? Because they may set it to one millivolt, and then you may have small signals that are just showing up as gray that you want to annotate that aren't showing up on that map. So I'll set it pretty low, you know, 0.05. You can always make it higher, but I want to pick up and annotate all those small signals. With CARDO, you can set a low voltage under the tool SCAR settings, below which it'll make all that gray. But what I prefer to do is just, you know, annotate as you go. And if you are on a site that has no signal, you have to tell the rep, you know, mark the site gray. You know, obviously in this case, you've got split potentials. You've got a, this was a post-tetralogy FLO, you know, free wall, re-entrant tachycardia. But, you know, when you're deciding where you're going to ablate, it really helps, obviously, to have SCAR and boundaries annotated on the map. And, you know, I see a lot of people just moving their catheters around and not paying attention. But if you have your catheter in a location, and the rep or the system is automatically annotating something at that point, because it has to pick something, again, you're getting erroneous points in the map. So just tell them, make that SCAR. And then, again, the last point is probably anyone who follows our Twitter discussions is anatomy doesn't equal EP. Again, just start pacing late in the cycle length. If you have the circuit mapped out, again, it's not that big a deal if it breaks. It usually won't, but at least use the EP and, you know, prove where the critical isthmus is before you start ablating. Again, we have, obviously, more sophisticated maps. So this is a, this coherent map is one of the biosense maps where you can now, you know, you don't have to set a particular window. You have conduction velocity and arrows that can help you look at the activation patterns. And I actually like these. You can look at the voltage on the right next to the activation, and it's a little more intuitive. But again, I think you still have to keep track of what the information is that goes into the map. So I'll go quickly. I'm just going to end with a few points on voltage mapping. So this is also an old slide from Frank Marsalinski, and this is how, for those of you who weren't around when this was established, you know, kind of the usual cutoffs we use for mapping a post-infarct cardiomyopathy. So this was, and I thought about editing the slide, but I didn't. You know, at the time, this is around 2000, detailed mapping, so greater than 80 sites per chamber, right? You're, you know, Nishant would probably throw you out of the room if you only had 80 points in the right ventricle. But this was single-point mapping, and all, you know, Frank did is mapped 10 normal patients, and then he looked at the fifth percentile of normal amplitude in those 10 patients, and it was around 1.5, and that's it. That was one paragraph in his 2001 CERC paper on linear ablation for poorly tolerated VT. You know, this probably wouldn't get into most journals these days, but that simple observation has really stood up over time as the upper boundary of normal voltage for post-infarct cardiomyopathy. You know, where does the lower bound, the 0.5, come in? It really was never studied. It comes from the days of Josephson mapping in the OR, where less than 0.5 was typically a scar. So again, 1.6, you know, we generally use 1.5. There have been a lot of studies after that, you know, trying to fine-tune that number using MRI, but in general, if you set it at 1.5 in normal parts, obviously, you'll have purple. This is an ischemic post-infarct cardiomyopathy, where less than 1.5 is scar normal, and then you have borders on between 0.5 and 1.5, and those numbers have generally held up. This is just the RV cardiomyopathy patient. So another question, voltage settings I use for an epicardial bipolar Okay, well, good. I feel like I'm teaching people. Don't worry, this is too basic. So that same, you know, there was a separate paper once we started doing epicardial map. I have to remember, I think it was Mark Dayall who was the fellow who did this paper, looking at the same thing where we did epicardial maps on, you know, 10 people with idiopathic PVCs. And actually the fifth percentile, again, this is for bipolar voltage, was actually 1.0 as opposed to 1.5. You know, is that going to make a critical difference in your map? Probably not. But when we're doing epicardial voltage maps, we typically use 1.0 as the upper bound and not 1.5. Some people guess 5.5 and that will come, I'm just going to move this here, apparent here. So again, you know, this was Matt Hutchinson's paper, a looking at unipolar mapping, which because the unipolar electrode is more of an antenna, and this is not perfect, but it can be a surrogate for when you have epicardial scar. So on the top is from Matt's paper, epicardial or endocardial bipolar voltage, 0.5 to 1.5 in a normal heart. For unipolar LV voltage, and again, there have been some papers that have debated this a bit, but for unipolar, the top number is 8.3. That's the fifth percentile of normal unipolar voltage. Doesn't matter so much what the bottom number is. And then again, this is the epicardial map with the upper cutoff of 1.0. This is a normal heart up top. In the bottom, we have a bipolar endocardial map and some with a non-ischemic cardiomyopathy. Again, the bipolar map looks pretty normal when we use the unipolar map at a cutoff of 8.3. Again, you see this ghosting in, in this inferior lateral basal area that turns out to be scar on the bipolar epicardial map. So you have a non-ischemic myopathy. Again, these days, we'll typically have an MRI. We might have a sense of where the scar is, but if you have a normal endocardial map asking, you know, you're collecting unipolar together with bipolar, look at the unipolar LV map. Cutoff is 8.3 for the LV, and that can kind of clue you in. Again, this is another older case where we had a bipolar map showing a small endocardial posterolateral scar. But if you look at the unipolar map, you see a much bigger area of low voltage. And then when you look at the epicardial map, you have a much bigger scar than endo, and this is a predominantly epicardial scar. I'm just going to keep going because time is running low, but it's sort of a factoid. This was Glenn Pollan, I think, who did this paper. But the unipolar cutoff of the right ventricle is 5.5. Again, the left ventricle is 8.3. Again, there have been papers that suggest that it may be lower. And I'm going to cut off this one, too, just so we finish on time. So what about for the atrium? There have been papers now looking at – Sanjay Dixit had one looking at atrial voltage. We looked at this briefly, and the fifth percentile of normal atrial voltage in a paper I wrote about nine years ago is about 0.5. So we typically use 0.05 or 0.1 to 0.45 as voltage for an atrial map. And it's really helpful, again, I think, especially in these post-PPEI flutters where you can really nicely with high-density mapping see before you've really done any activation recordings where you have gaps in pulmonary veins or in prior ablation lines and where prior ablation lines have been performed. I kind of like now Biosense has this upper and lower threshold for early meets late. So you used to just use the upper threshold to avoid that reverse windowing effect. The lower threshold you have to play with. But it basically will find adjacent areas that have conduction block. So in this case, if it's more than 20 percent of the cycle length between adjacent areas, it'll mark that with this white line. So you can see areas perhaps a block. And again, in this case, the other mapping that's nice to play with is the ripple mapping, and I spent a lot of time on it. That basically is annotation independence. You don't have to worry about annotating. It's just basically displaying the amplitude at each point over time. But you can clearly see just looking at the substrate and sinus rhythm that you've got activation that's breaking through the roof and the floor. So this patient had a roof and floor line that's reconnected and colliding on the posterior wall of the atrium. And then if you look during the actual flutter in the same patient, you can see how activation is kind of hugging those lines of block and resulting in a roof-dependent flutter that's kind of breaking through in the left atrial roof. So I think using this upper and lower bounds to kind of define sort of local conduction block as well as looking at the activation, looking at the scar altogether, looking at the substrate and sinus rhythm and with propagation can be helpful these days. Just another example of a right atrial atypical flutter in someone who had a surgical maze. Again, you can make out by the high-density map where a gap is. And then again, during a flutter, you have activation that's traveling around and through that gap. This is sort of a question, again, you can just think of in your head. I won't take a poll. I'm not sure if it does everyone. I tend to always like imaging before AF ablations. I think a lot of people have left that off. I'm just going to make a point, again, this is more for mapping that although not doing imaging, you know, the maps are so good these days that you can get away with not doing imaging for many cases. But don't forget about these variants like veins on the roof. You know, if you're trying to, you can imagine doing a WACA wide area ablation in this patient and your catheter is going to sit really well in this little roof vein and it's just going to ablate it and occlude it. So I think even if it's 5% of cases, I still like to do imaging because you will occasionally get these weird anatomies like this in one upper vein and all the other veins are kind of merged into this area in the back. And you know, because we knew about this, we ended up doing a wide area box kind of around all the veins or a left-sided SVC. And this is a case where we ended up doing a left-sided SVC isolation. So knowing what you're getting in for, I think also is helpful in terms of preablation mapping. So again, to summarize, our mapping systems, again, they're creating a 3D catalog of color-coded activation or voltage relative to a fixed reference, pick a stable reference, pick a mapping window that fits with the surface QRS or P wave, annotate the points, look at what the rep is doing, learn how to do that yourself, label scar, and use entrainment to confirm what you found before ablating. So I will wind up there hopefully on time. And I don't know, Nishant, if you do questions at the end or we wrap it up. Yeah. That was great. Thank you so much. I think there's like a lot of really fundamental points there. There was one question. We tend to stay away from industry stuff, but there was this question about whether you prefer one system for a particular type of case, like do you do NAVX for atrial tach and CARDO for VT? And then do you have any preferences in terms of your high-density mapping catheter? Yeah, I use both systems. I tend to use more CARDO for VT partly because I like the anatomic. I think they've both gotten much closer. It used to be the impedance mapping, the ventricle always ended up looking more pancake-like. I think with the magnetic catheters, they've gotten closer and certainly either is fine. When I train, we use a lot more CARDO. So I tend to use more CARDO for VT. Sometimes it depends on the hospital. So at one outreach hospital, they only have NAVX, so I'll use anything. If I'm using CARDO and I'm mapping VT, I actually use the Decanav. I like that a little better in the ventricle than the PentaRay I found. I know the PentaRay, the splines can get mixed up and at the base, you don't get quite as good contact. So both for the RV and the LV, I've actually used the Decanav to get sort of rapid maps. And if we're doing an endo-epi case, I use the Decanav on the epi and you can move that around and get really quick points. You're not giving fluid. If I'm using NAVX, then I'll usually use the grid. I like the grid. So we'll use that on the endo-epi. I like the grid, especially for post-PBI, atypical flutters. I think it gives really nice coverage. If I'm doing an atypical flutter with CARDO, I'll use the PentaRay.

electro-anatomic mapping

atrial tachycardia

ventricular tachycardia

3D map

reference point

activation window

entrainment

ablation

high-density mapping catheters

scar tissue