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EP 101 2020: A Virtual Program for Incoming EP Fel ...
Ablation of Atrial Tachycardia
Ablation of Atrial Tachycardia
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We're going to go on to the next video, which is ablation of atrial tachycardias, and Dr. Koop will moderate the discussion for the next session as well. Thank you. Okay, so ablation of atrial tachycardia. So we take atrial tachycardias and we kind of divide them into two groups. We divide them into whether they have a focal pattern of activation or a macro-reentrant pattern of activation. So a focal pattern of activation we see in people with normal hearts, totally normal hearts can have focal tachycardias, but we also see them in disease. Patients with atrial fibrillation, especially after ablation of atrial fibrillation, may have a focal tachycardia. Macro-reentry we typically see in either very heavily scarred or very dilated atria. Small macro-reentrant circuits, which are generally two and a half to three centimeters in diameter, those small circuits typically require very heavy scarring so that you have little conduction channels in between. Very large circuits like going around the tricuspid valve, around the mitral valve, this you can sometimes see in very dilated atria that are not necessarily very heavily scarred. But a lot of times scarring and dilatation go together, they're present in both, and actually big macro-reentry and small macro-reentry actually go together. I want to concentrate on a focal pattern of activation because of the level that where you're at, where you're going to be starting an EP. And I want time to talk to you a little bit about looking at electrograms and timing electrograms. Where do you place the timing? Because how we create a map is very dependent on that. So a focal pattern of activation simply means that activation begins at one site and radiates out in all directions. It doesn't specify a mechanism. So the mechanism probably most often, well, we're not positive, but it's probably triggered firing due to after depolarizations. But it can be abnormal automaticity. Some people even believe you can have very, very, very tiny macro-reentrance circuits they call micro-reentry. Some people believe that. Some don't. But for whatever reason, an atrial tachycardia with a focal pattern of activation, the thing to realize, if you can find where activation begins, ablation there is uniformly successful. And actually, if you localize that spot really very carefully, it's often actually very easy to ablate and very, very quick to ablate. So let's look at electrograms. So here we're mapping a focal right atrial tachycardia in a patient with a totally normal heart. And we're going to be using an ablation catheter to make this map. So the electrograms I like, and the way I like to set them up, is we're going to record the bipolar electrogram between the distal two electrodes. We typically call that the distal bipolar electrogram. Some people will just put a D there. Some people like to call it 1, 2. That's fine. And then the proximal bipolar electrograms is recording the bipolar electrogram between 3 and 4. And I always, always, always record the unipolar electrograms from both the tip electrode, unipolar 1, and the ring electrode. These two electrodes make up the distal bipolar electrogram. Now we focus on the bipolar electrogram. And the reason we do that is magic, okay? Bipolar electrograms eliminate far field. When you see a sharp component on a bipolar electrogram, there's something happening very close to those electrodes that's not very far away. And let's look at why that is. So here is two electrodes laying on tissue. You've got a wavefront that's coming by. So two electrodes make a bipolar electrode. The bipolar electrogram, okay, is the difference in voltage seen at any time as that wave is going by, is the difference in voltage between the two electrodes. How do we do that? We use something called a differential amplifier. A differential amplifier has two inputs, okay? One that's labeled plus and one that's labeled minus. And what a differential amplifier does is it subtracts the voltage of the minus input from the plus input. So the plus is the dominant one, the one that you're typically going to use. So typically, we put the distal or the tip electrode, electrode one, we put in the plus. Two, we put in the minus. And when you start to, when you get in the EP lab, you're going to see that the recording system is going to have two columns, one labeled plus, one labeled minus. And you'll see, you'll plug in the catheters one, two, three, four, five, six. Actually, each one of those pairs is a differential amplifier, okay? Each one is. So there'll be 64 or 128 amplifiers in each recording system or mapping system that you deal with. The key is you always want the dominant electrode is going to be plugged into the plus. Now why does a bipolar electrogram hide far-field signals or minimize far-field signals, okay? So when the wave is far away, both electrodes see essentially the same voltage being generated by that wavefront. And when you subtract them, you get zero. And so the tracing is going to stay flat, and we call that isoelectric, okay? The wave is going to be moving toward the electrode. When it gets to be, yeah, that's why it eliminates far-field signals, because there's no difference in voltage. When that wave gets to about here, you begin to see a deviation. You begin to start to see a signal on the bipolar electrogram, okay? That's where there is a difference in voltage seen between the two electrodes. When the wavefront comes in in a perpendicular direction, you're going to have to get closer before there is a difference in voltage seen between the two electrodes. So you can actually draw an oval around the electrode. And no matter what direction the wavefront comes in from, no matter what direction, that wave is going to be invisible to that bipolar electrode. That's the beauty of getting rid of far-field. Until you get to this point, to this oval, I like to call this oval, I make up a name. I call it the recording range, the distance that you can actually record activation on there. So this is where the bipolar electrogram will begin to deviate away from baseline, or you could call it the beginning of the bipolar waveform. Now, that wave is going to come and cross the electrodes. So the sharp part of the electrogram is as the wave is crossing the electrodes, and it's going to cover a much smaller area surrounding the electrodes. So this cross-hatched area will be the area that's going to generate the sharp part of that electrogram. Remember, the center of a bipolar electrode is not at the tip of the catheter. The center of the bipolar is always midway between the two electrodes, okay? Always midway between the two electrodes. Okay, now, I've drawn this to scale. Believe it or not, this recording range with an ablation catheter, this would be an ablation catheter with a 3.5 or 4 millimeter tip electrode and a ring electrode. And believe it or not, you'll see the range across here is huge. It's 2.3 centimeters, 23 millimeters, okay, that you can begin to see a signal, right? This is the 5 to 6 millimeter diameter RF lesion. You can see that you can ablate a lot of places where you can record something, where you see something in the electrogram on a bipolar electrogram and miss. Even the sharp part of the electrogram, that area is much larger than the size of the electrode. Does this make sense? Okay, so what you want to do here, okay, is you want to actually look at what the two electrodes are seeing separately. That's the unipolar electrogram. So, you find the signal you're looking for with the bipolar. That gets rid of the far field, so you know it's a local signal. And you find the signal that you want. And then you position the catheter to get the sharpest part of that potential, to make it as sharp as possible on the unipolar tip electrogram. That's going to mean that that signal is relatively close to that tip electrode. And it's actually fairly close in size to the size of the lesion. So, you find the electrogram on the bipolar electrogram. And then you position the catheter using the unipolar electrogram. So, how do we record a unipolar electrogram, right? A unipolar, oh, I'll come back to that in a minute. All right, so we can do two things, right? When we're dealing with an electrode that has a poor resolution like this, that it sees too big an area to be good for targeting, or really to know for sure what's going on, all right? What we want to do for mapping is we want to record from as small an area as we possibly can. That way, the timing that that electrode sees is definitely right there at the electrode. Does that make sense? Okay, so you want to shrink, you want to shrink these ovals way down. So, how would you change these two pieces of metal to shrink this size down? Make them closer, right? Make the pieces of metal smaller, okay? Make them smaller, but more important, bring them closer together because you're looking at the difference in voltage between the two electrodes. So, the closer they get, the closer a wave has to be to give you a difference in the two voltage. So, the very beginning of the electrogram begins still pretty close to these electrodes, but the sharp part of the electrode is right on there, okay? So, we call this high resolution. What do we mean by that? What is resolution? Resolution is the ability to record a difference in timing between two points. Resolve a difference in timing between two points. So, let's say we have two points here. This wave is coming by. This electrode is going to be activated before this electrode, correct? So, if we have this little electrode, and notice I have the electrode centered right over this point. It's the space right between the two electrodes. If I move the center of this electrode to here, will I see a difference in timing between these two points? I will. I will because there's not even much overlap in the area where the signal is sharp, right? What about here? If I move the center of this electrode, which is right over this point, to this over here, will I see a difference in timing between these two? No, because basically you're going to get the same electrogram on both sides, okay? So, this means this electrode allows me to resolve a difference in timing between these two, and this one doesn't. So, this is higher resolution, lower resolution. Make sense? And actually, actually, Boston Scientific actually puts little electrodes on the ablation electrode so that you get very tight recordings like that to help you do that. So, one possibility, right, is to use the unipolar electrogram to tell what the tip is seeing. The other is to use very closely spaced electrodes to increase the resolution to find that spot. Okay. So, with a regular ablation electrode, right now we're stuck with looking at the unipolar electrogram. So, how do we record a unipolar electrogram? Believe it or not, we use the same amplifier. We use a differential amplifier. A differential amplifier needs two inputs, right? A plus and a minus. So, what we do for a unipolar recording is we plug the electrode, the catheter electrode, into the plus. And we make the minus, we plug an electrode into the minus that's not in the chest. So, it's not going to really see the heart. Okay. And there's two main ways you can do that. One is you can use skin leads like on an ECG, the Wilson Central Terminal. Okay. The other thing you can do is you can use an electrode in the inferior vena cava. So, if you have a catheter coming up ephemeral vein and you have an electrode 25 centimeter from the tip, it's going to be in the inferior vena cava. This is clearly a superior way to do it because the impedance of this electrode is an electrode in blood is the same as this impedance, which is what a differential amplifier needs to see to keep the noise down. When you have a skin leads like the Wilson Central Terminal, you have a difference in impedance and you get a lot of noise. So, this is a better way to do that. The other thing is, as I'm going to show you in a minute, with a unipolar electrode, we can actually tell if a wave is coming towards us or moving away from us. But we can only do that if we don't distort the signal by filtering. So, we want to filter it as little as possible. We have to filter it a little to get rid of the difference with impedance changes with breathing. Otherwise, the baseline drifts. So, you have to filter it a little. And if you filter it way down at 0.5 or 1 Hertz, it doesn't distort the electrogram and it lets you see it. Okay. All right. So, why do we love the unipolar electrogram? Well, number one, it shows us what's right under that electrode. But two, it does give us directional information. Okay. A unipolar electrogram, as the wave moves toward it, the voltage will increase and it steeply increases as it gets very close to the electrode. It goes up very, very steeply and reaches its peak as it reaches the electrode. As it crosses the electrode, it goes from the most positive to the most negative, okay, as it crosses. And then as it moves away, it becomes progressively less and less negative. So, it's the most negative just as it passes and then it gets less and less as it moves away. So, the crossing is what we want to know the timing of, correct? Where the wave crosses the electrode, that is the timing at that exact spot. And we call that the local activation time. So, it's going to be this deep negative component of the unipolar electrogram. Okay. That ends the introduction. So, that was the introduction. And I've got half the time left. Now, we can start to look at some electrograms. Okay. So, we're mapping this focal atrial tachycardia in the right atrium. We're using an ablation electrode. We have the distal bipolar, the proximal bipolar, and always both unipolar electrodes that make up the distal bipolar electrode. So, when we make a map with an ablation catheter, the mapping system is going to mark the position of the catheter at the very tip of the catheter. So, the timing we want is the tip of the catheter, the distal electrode. So, the local activation time is going to be the activation time of the tip electrode or uni-1 or whatever you want to call that. It's going to be the steep downstroke there. That's the local activation time there. If you don't have unipolar electrograms, the best you can do, what we typically do is we simply take the first rapid component, the first steep component on the electrogram as the local activation time. Remember, with two electrodes that are far apart, you often can have, in diseased tissue, two activation times. So you really want to use for timing. You really want to use the unipolar electrodes. OK, so how do you know when you're at, right, we want the site of earliest atrial activation on a focal tachycardia. How do you know when you are exactly at the site of that activation is beginning? A negative deflection on which electrogram? Which you need? The tip, right. OK, right, absolutely. Why? Right, remember, when the wave is moving away, it's negative. And it's most negative just as it begins to move away, just as it's crossing or moving away. So if it's moving away in all directions, everything is going to be a steep negative. Perfect. Now, guess what? I will tell you every map that I have ever made, there's always one place that looks like this that is not the earliest activation. There is a little isoelectric interval right before that signal, OK? And so years ago, what I would recommend is using three criteria instead of one, OK? And the first criteria is you are never at the site of earliest activation until you are at the place where you recorded the earliest far field signal. What do I mean by that? As we move a catheter around, we look at where the first deviation from the baseline is. And we mark where that time is. And the earliest, we keep marking that earlier and earlier. At some point, it'll never get earlier. It stops getting earlier, OK? You're never at earliest activation until you're at that site. And the way I like to do it is the way we do it with a mapping system. I like to take the recorder that we use, the recording system, and set it just like a mapping system on a trigger sweep. I give it a reference electrogram to trigger off of. And that way, the beat is in the same place on the screen every time. And I can see where the far field begins. I'll show you how to do that. And I put a timeline there. And every time I can see it earlier and earlier and earlier, I keep moving that timeline until I have that earliest far field recording. So activation is only at earliest when it's as early as the earliest far field you recorded. When you're at earliest activation, the distal bipolar and the distal unipolar will begin at exactly the same time. That tells you there's no far field signal earlier than that, OK? So these two things tell you your catheter is very close to the site of earliest activation. The thing that tells you your tip electrode is exactly on the earliest activation is that with both of these met, it then begins as a steep negative. So I use this as the third as the third, OK? So let's do a case. So this is the most common site that you're going to see a focal tachycardia in a normal heart. And this is a very upper part of the crista terminalis, very close to the sinus node. Here are the last two beats of a short burst of rapid atrial pacing inducing the tachycardia. So here's the first beat of tachycardia. And what we did is we used a multi-electrode catheter that's right now positioned along the crista. But we first looked all around that area. And this was the earliest far field signal we ever saw. So I have my timeline up where the very earliest far field is. So now we're working the mapping catheter. And notice here, the mapping catheter, we now see local activation right where the earliest far field was. So that's our first criteria that we're at the site of earliest activation. The second is to compare the unipolar and the bipolar. So here the distal bipolar and the distal unipolar begin at exactly the same time. There's nothing in front on either one. Do you all see that? OK, all right. And that tells us there's no far field earlier. So this tells us we are very, very close to the site of earliest activation. To be sure the tip is exactly on the site of earliest activation, you want to show that it is beginning as a steep negative. Now this gain amplitude is very low. I tend to use pretty low amplitudes, lower than most people, because it makes it easier for me to tell what's sharp and what's rounded. This is actually very, very steep, because this gain is very small on a unipolar electrogram. Usually the signals are very, very large. So this is steep. And we turned on RF, and it was instantaneously successful, because this was very steep, meaning very, very close to that site of earliest activation. OK, you ready for your first exam? Can I ask two quick questions that came up? Yes. Just to clarify for everybody, there's a question that asked, when you say mapping electrodes, do you really mean ablation electrode? Ah, OK. So in the earliest mapping system, really all we had was an ablation catheter, because that was the only catheter that had location information in it that would tell the mapping system where it was. We now can use many different kinds of electrodes and everything. So sometimes people use that term interchangeably. It turns out the ablation electrode is not a great mapping catheter, because the resolution is so terrible, OK? But yes, that terminology still hangs there. And I may have made the error of using those terms interchangeably. I don't know that it's an error necessarily, because they often are the same thing, depending on what you're using. If you're making a map with the ablation catheter, it is the mapping catheter. And I was. Another question that came up is, how can you tell the difference between a catheter-induced PAC and a true native ATAC beat? OK. Actually, that's a very good question. Number one, a bang beat, meaning the catheter hits the tissue and makes a fire, OK? What you're going to see is the electrogram is going to look just like this. It's going to be very sharp unipolar, very sharp unipolar, very sharp bipolar. It'll begin as a steep downstroke, because actually it is beginning at exactly that site. But it is going to be a premature beat. And there's only going to be one beat like that. It's not going to be sustained. So as you're moving the catheter, and a lot of times that's how we tell that premature beats are bangs and not real PACs, is because we look at the electrogram and it looks exactly like that, because activation is beginning right there to recognize the bang beat. OK. All right, you ready for your exam? All right. So here we're mapping another right atrial tachycardia using the ablation catheter, OK? And so here's the proximal bipolar, the distal bipolar, the distal unipolar, second unipolar. So here's the tip, all right? I want to point out a couple of things. Number one, I generally use much lower recording gain than 95%, I think, of electrophysiologists. Again, it's because it makes it easy for me to tell what's rounded and what's sharp. When you turn the gain up too high, everything starts to look sharp. And I think the less gain you use, the easier it is to tell what's sharp and what isn't, OK? Next, you're going to pick a reference electrogram. You want to pick an electrogram that is not going to move. What do we mean by a reference electrogram? We're going to pick something that will be at the same timing during tachycardia every single beat, so we can tell if we're getting earlier or later than that timing. So that beat becomes time zero. That's the zero time, the fiducial point, OK? So you want to pick a very reliable site there. So we're going to use a catheter I like to use in the right atrial appendage. I use this catheter because this is the one where I have an electrode that's in the inferior vena cava. So for myself, I always like to use that catheter. And that allows me to use the inferior vena cava electrode as my reference for the unipolar recordings. OK, so as we move the mapping, I'm going to call it a mapping catheter now because we're not ablating yet, OK? If we look at the distal bipolar, the far field begins here. On this unipolar, the far field begins here. On this unipolar, the far field begins here. This one is the earliest of the three, and so I'm going to put my timeline here. If ever I see any place that gets earlier, I'm going to move more and more to the left. Does that make sense? OK, so the time 0 is the reference electrogram. So times in front of the reference are minus numbers. Times after the reference are plus numbers. So this is 34 milliseconds before, or minus 34. And it turned out we never found a far field that was earlier than that. That turned out to be the earliest far field, so we keep our timeline up here. Our local activation here, that's not our local activation time. That's where we can see activation. So we can see where the earliest activation is, but we're not there. So the local activation time is going to be the timing of the distal unipolar electrogram. It's going to be that rapid downstroke here, 24 milliseconds before the reference, or 10 milliseconds later than far field. That's too far away to kill that pathway. You have to be within a couple of milliseconds, that tachycardia. You have to be within a couple of milliseconds to reliably, reliably kill that tachycardia. OK, I'm going to move this over to the left to make some room and show you the second site. Look at this. Who wants to ablate here? Show of hands, real quick. Look at this unipolar electrogram. Two people? Three people? Five? Who won't ablate here? That might be a simpler way of saying. Why? How do you know? What am I not giving you here? The timeline. Would I really take that off? Never. I never take it off, OK? Because what you see here is that there is an isoelectric interval before here. This was the one point. It's always one place in the map. There's always one place in the map that you're going to have a steep negative, but there'll be an isoelectric interval in front of it. The actual local activation time is just as late as here. It's also 10 milliseconds after. Let's go to a third site here. Who would ablate here? Show of hands. Bingo. You got it. This is perfect. So here was our earliest far field, and you see local activation on the bipolar beginning there. The second thing is the distal bipolar and the distal unipolar begin at exactly the same time, meaning there's no far field in front there. And then third, the tip. Look at that steep negative at that low gain. Man, that is really steep negative. This was essentially an instant success as soon as we turned on. This will be the last case. Oh, I might be almost on time. So here was a young man who had two prior failed ablations for a focal tachycardia in the left atrial appendage. Not a very common place. The edges of the appendage are frequent sites because they're autonomically innervated, but the actual inside the appendage is not a super common place for a focal tachycardia. And here are the electrograms. So here's the distal bipolar, the proximal bipolar, again on an ablation catheter. We're using it as a mapping catheter. And this was the earliest signal I could find. We looked in this appendage for a while. This was the earliest signal we could find. It was 70 milliseconds before the onset of the P wave. That's pretty early. And whatever. So would you ablate here? If this was the earliest signal we could find, would you ablate here? What's missing? Unipolars. So let me ask you a question. What's the timing of local activation here? Well, the answer is I can't tell you for sure, but it has to be one of the sharp components of the bipolar electrogram. So it has to be either here, here, or here. And this is where the big electrode, being far apart, where it's going to be different in timing between the two electrodes. So now we'll look at the unipolar electrogram. So it has to be one of these three times. So in my mind, I kind of drop a make-believe line down. And I'm going to look for the largest, sharpest downstroke on that. Let's just pretend it's here. The mapping systems that we use today now measure this for us and actually tell us which one it is. But sometimes you need to overread a little bit. So it's important for you to get a feeling for it. What would be the timing of electrode two? We would use the same bipolar electrogram because two comes from this bipolar is seen in this bipolar. It's going to be these same three. And it's definitely this one. It's definitely not here. It's definitely not here. Do you agree? So this one is clear. This one is definite. But you might say, well, wait a minute, Sonny. Hold on. Look, you're using the unipolar electrogram to pick the activation time. Why do you even bother with the bipolar electrogram? Well, what if we did just use the unipolar electrogram on two? Which would be the largest, sharpest, steepest downstroke? It's going to be here, correct? And there's nothing on the bipolar electrogram, which means it's what? Far field. In fact, it might even be coming from where the proximal pair of electrodes are. Do you see that? OK, here's something that's real important. When you start getting into scarred areas of the heart, and we're doing this more and more, our bread and butter is working in scarred tissue. The largest, sharpest signals we record in scarred tissue are far field. So it's critical that we always start with the bipolar. Always start with the bipolar first, and only look where the sharp components on the bipolar are to find where the unipolar are. You don't look any of the other places where there's not a sharp component. OK, so now. Can I ask a quick question? Yes. Several have come up, but one on this slide. They're asking, why are there so many deflections all over the place here over such a wide time frame? And what do these all mean if you have a bipolar in one location? Does anybody want to tackle that? There are multiple areas of conduction occurring in that range, two that are very far apart from each other. So that means that is a non-homogeneous area. Usually, you see that in a very heavily scarred area. When they're separated by this kind of distance, it usually means there's a line of block in between them. Makes sense? And let me ask one more, because it's come up so many times here. When you say that you can see an isoelectric component of the unipolar signal, what does that physiologically signify, that there's an isoelectric part? And why don't you see a far field deflection if, in fact, it's a wave front that's nearby? OK, the unipolar electrode sees an infinite distance. But as you get farther away from the electrode, the amplitude of any signal is getting smaller, smaller, very, very fast. So in reality, there still is a limit as to how far you see a signal on the unipolar electrogram. It gets so close to baseline, you can't really recognize it as a signal. So you can be far enough away from any activation that you can't really appreciate that there's a voltage there, and it will be isoelectric. OK, so now let's get to the hard part of this. What are we going to do for this guy? Think about this for a second. OK, what's the timing of the earliest far field? I wasn't giving you this, but you know I'm going to have that up there. OK, the earliest far field I can see here would be here on this one, right? Here on this one, but it's way back here on this one. Do you agree? This actually turned out to be the earliest far field that we ever recorded. Now, what's the earliest possible local signal we have there? The first possible local signal would be this one. Do you see that? So 20 milliseconds, man, this is the far side of the moon. 20 milliseconds away is like a mile, OK? You are definitely not going to hit this thing. In fact, the proof of it is, what do you think these double potentials came from? There's a block right there from burning. That's where this was. This was created. So they tried, OK? They tried. You absolutely are never going to get that at that kind of distance. So we looked all over the endocardium of this appendage, and this was the earliest local, was 20 milliseconds later than the far field. Man, where should we look? Or would you just ablate there anyway, because that's the closest you can get? We didn't do that, by the way. We didn't do that. So if you looked all over the endocardium of that appendage, I knew this was a smart group. I knew they could get it. Yeah, look epicardial, sure. OK, so here we put some dye in the appendage. Here's the RAO. Here's the LAO. Here's the catheter going in subxiphoid, or underneath here. And at this position, I'm going to show you the electrogram we recorded here. We're near the tip of the appendage in the RAO, right? We're near the tip. And here is the pericardial catheter here. It's near the outer surface, right? It's kind of lateral on the lateral aspect of the appendage, near the tip. OK, this was, remember, I always, always, always record my earliest far field. This is my reference electrogram. So it's 120 milliseconds from the reference before. So I'm always going to keep that timeline up when I'm mapping the epicardium too. And it turned out we never saw an earlier far field on the epicardium. But we did find a local signal on the epicardium, OK? And let's move it over to the center. So here's a local signal that begins right at the earliest far field, right? The unipolar and bipolar begin at exactly the same time. The unipolar begins as a steep negative. This is earliest activation, right? Now, here's why you need to understand how to look at electrograms. You can't just trust the technology. Our mapping systems are unbelievable today, very high resolution and very good. But what are they going to pick? The mapping systems are going to look for activation in the bipolar signal. But then they're going to go down to the unipolar and take the steepest negative. So where is the mapping system going to select here? It's going to select this. So it's not going to show you this location as the earliest signal. You have to be able to overread and look at this and realize. So on a focal tachycardia, you want to take the first sharp component and override your mapping system to do that. And you need to be able to do that. So do you want to ablate here? Who wants to ablate here? Show of hands. Three people, five? Who wants to ablate here? Come on. I'm dying here. I mean, did I do that bad a job? Did I do that bad a job? OK, let's turn on RF. OK, so we turn on RF here. So here's this little pre-potential, this activation potential here, here. The next one is due right here. But there's nothing, right? This is what I mean by an instant response. OK, what's this be? Sinus, right, exactly. OK, this is when you use these tools, this is the kind of thing that you can sort of expect. So you use the bipolar electrogram to find the possible local signals, as the sharp components. And then you look in the unipolar electrogram, and you position the tip catheter to get the sharpest you find the signal here that you want, and you position it to get the sharpest component you can get on the unipolar electrogram, and that's going to work for you. Thank you so much, Sonny. Every time I see that talk, I learn something, and I redouble my efforts when I go back to the EP lab to do better. Because the pearls that you give are always so valuable to people at every level of training. So thank you for that. There are wonderful questions that have come in. And let me start with one from Dr. Bronstein. He asks, why do you need to set the high pass filter so low on the unipolar EGM if you're looking for a rapid downstroke, which is a high frequency signal? Because when we change filters, it affects the electrogram. And it can even change rarely. It can even affect polarity. So we do this. We filter. By the way, the high pass is the first number, is the low number. It means it allows the high frequencies to go through. It minimizes the low frequencies, is the high pass filter. So we use that on the bipolar electrogram because we want to filter out far field so that we can just see what's local. And if we add additional glitches or additional sharp components, we're not going to time the electrogram from the bipolar. But the unipolar, we will mess up. We will change the electrogram to see what's coming towards you and whatever. So you always want to filter it as low as you can. You can't really go below about half a hertz, half a hertz or one hertz, because one electrode is in the chest and one electrode is out of the chest. And as you breathe, the air coming in and out of the chest makes the baseline swing up and down. And so we have to filter that out. Fred Wittkampf taught me about 30 years ago that you could go up to about one hertz without ruining the unipolar electrogram, but you really don't want to go higher than that. Gotcha. Dr. John asks about the local activation time in unipolar 1 versus 2, and which local activation time would you use? You look at both of them, because they're telling you when the wave is crossing that electrode. But when it comes to positioning for ablation, all you care about is the recording on the tip electrode. That's why the two unipolars are important. They help you recognize why you're seeing the bipolar, why the bipolar looks the way it does. You need to see both unipolar electrograms. But for picking the ablation target, it's just the unipolar 1 electrogram. Yeah, and this was just a wonderful extension, by the way, of a talk from yesterday that talked about electrograms in their basic recording. And then this goes far beyond it to show the practical applications of that. So to extend Dr. John's question, if you saw an earlier local activation time on uni 2 versus uni 1, what would that tell you about moving the catheter? Perfect. You want to move the catheter to put the tip exactly where electrode 2 was. Generally, that's pulling the catheter back a tiny bit. And years ago, some savvy people, when we were only recording bipolar electrograms, if people would have the target on the bipolar electrogram, and they would ablate and nothing would happen, they would pull the catheter back a little bit and ablation would work. And that's because they were recording the bipolar electrogram that was showing you that beautiful potential. That beautiful potential was being recorded from electrode 2. But if you record the bipolar and the two unipolar electrograms that make up the bipolar, you can instantly see that that good bipolar was coming from electrode 2 to pull the catheter back to position the tip where electrode 2 was. Another follow-up question to that from Dr. Fu is, if you do indeed have an earlier local activation time on uni 1 versus 2, should you try advancing the catheter further forward to see if you can get earlier than that? OK, if you are, and we're talking about a unipolar, we're talking about a focal tachycardia, you absolutely want the earliest. So in this case, what you would see is, if the sharp downstroke is earlier on electrode 1 than 2, but the downstroke is not where the earliest far field was, meaning there's still a little bit of a positive component before the downstroke, yes, you're going to keep moving that electrode forward to get to where that downstroke begins right at the site where that earliest far field was recorded. If you're at the site where the bipolar and the unipolar are beginning at exactly the same point, and the unipolar is steep negative there, don't move it. Even if electrode 1 is earlier than electrode 2, if you push it forward, it's going to get later. You already know you are at the site of earliest activation. You don't move it. You ablate right there. But I guess if you were to see a far field signal on the bipolar channel that's a little bit earlier, and your uni 1 is earlier than uni 2, but not as early as the far field, then, of course, you would still fine tune. Right, because that would mean you're at that one rare place where the unipolar 1 is seeing an isoelectric interval before the downstroke. Right, exactly. Absolutely. Another question talked about the spacing of electrodes. And the question was, does it matter if you get electrodes really closely spaced if the catheter is moving along with the heart anyway? What does that matter? I guess the point is, if the resolution, if you're trying to improve the resolution of your recording, but the catheter is still moving in 3D space and sliding around in the myocardium, is there a limit in terms of electrode spacing that that will actually help you? Because if you're moving back and forth, sliding several millimeters, and your resolution is submillimeter, how does that help you if you get that fine and real resolution? Well, with the higher resolution, with the closer spacing, if the catheter is sliding, you will, in fact, see big changes in that bipolar electrogram. If you're sliding on and off the tissue, when the electrode spacing is very close, that signal would become a far-field signal, and then a close signal, and a far-field signal, and a close signal. When the electrodes are far apart, you may not actually recognize that you're moving on and off the tissue. So the closer the electrode spacing is on the bipolar electrogram, the more you will recognize that there is movement on that electrode, because you will see greater changes in the electrogram on a beat-by-beat basis. You can get rid of a lot of those changes by eliminating respiratory motion. If the patient is under general anesthesia, you can turn the ventilator off. If you ventilate with 100% oxygen and the patient is paralyzed, they don't generate much CO2. You can turn the ventilator off if their lungs are good for a couple of minutes, and you get rid of a lot of that motion. And I like to do that. But you will see that the closer the electrode spacing, the more you will see a difference if the electrode moves. The question came up regarding catheter orientation and tissue. You've talked a lot about the catheter being parallel to tissue, but what if you're directly perpendicular? How does that impact the electrograms on Uni 1 and Uni 2? You have to be a little bit careful of what's marketing and what's real. If you had a wave going exactly perpendicular to your two electrodes, it would only disappear if the wave was perfectly straight and the current was exactly the same all along that wavefront. But there are no wavefronts that are perfectly straight and the current is the same all the way along. Even if you played out cells on a single layer of cells and you make a wavefront, it's always curved. So you don't lose the wavefront being perpendicular. You will still see it. It will be smaller and less sharp than when it's coming parallel to the electrodes. But you don't actually lose it. You have to be careful with what's real and what's marketing. I'll ask one last question before we move on to the next lecture. The question came up, does it matter in a bipolar recording if the tip electrode is a negative or positive? I think you had talked about how unipolar electrodes, the electrode itself is an anode, is a positive pole. With bipolar, if you were to have reversed the two, you had mentioned the tip was positive and the ring was negative. What if you had reversed the two? How does that impact the recording? It will reverse the potentials. They'll be upside down. And so something coming toward the tip is going to be negative. Again, I don't tell whether something's coming toward or away from a bipolar. I always use the unipolar electrograms for that. So it's not as critical. On the bipolar, you're really taking the negative components or the sharp components. So instead of them being negative, they'll be positive. And as long as you're just looking at the sharp components to be the local, possible local activation on the bipole, you're OK. But it's generally a good idea to be careful and look at your recorder setup. And typically, it's good to make the tip the negative. But you just have an upstroke that's sharp instead of a downstroke that's sharp on the bipolar electrogram if you've reversed them. Perfect. Sonny, amazing as always. Thank you so much for participating in our virtual EP101 this year. To stay on time, I'm going to move on and have them queue up the next video, which will be on AV node reentry. So one last parting words, Sonny, and then we'll move on to the video to move on to the next topic of AV node reentry. Thanks for having me, Arjun. Always a pleasure.
Video Summary
The video discussed the ablation of atrial tachycardias and the different patterns of activation that can be observed. A focal pattern of activation means that activation begins at one site and radiates out in all directions. This type of tachycardia can be seen in people with normal hearts, but also in patients with atrial fibrillation. In contrast, a macro-reentrant pattern of activation is typically seen in heavily scarred or dilated atria. The video emphasized the importance of careful electrode placement and interpretation of electrograms in mapping and successfully ablating atrial tachycardias. It explained the use of bipolar and unipolar electrograms, with the bipolar electrograms being used to eliminate far-field signals and the unipolar electrograms providing directional information. The video also discussed the importance of high-resolution recording and the use of filters to minimize baseline drift. It provided examples of mapping and ablation procedures for atrial tachycardias in the right atrium and left atrial appendage, highlighting the importance of accurate electrode placement to target the site of earliest activation. The video concluded by discussing the limitations of catheter movement and the impact on electrogram recordings.
Asset Subtitle
Warren “Sonny” Jackman, MD
Keywords
ablation
atrial tachycardias
activation patterns
focal activation
macro-reentrant activation
electrode placement
electrograms
mapping and ablation procedures
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