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EP Fellows Curriculum: Physiologic Cardiac Pacing
EP Fellows Curriculum: Physiologic Cardiac Pacing
EP Fellows Curriculum: Physiologic Cardiac Pacing
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Absolutely. Can you hear me okay? Yeah, we can. Okay, great. Yeah, thank you so much for having me and particularly for letting me present on this topic, which is, as you know, a hot topic in EP and one that many, many people could speak about. I always start by acknowledging my colleagues at UCLA. I'm one of a massive group of people, both clinicians and physician scientists. And here are my disclosures as well as my funding sources. So, you know, when we use the term physiologic pacing, what we mean is utilization of some aspect of the heart's conduction system to achieve a narrow QRS as best possible. And if you look at this schematic here, hopefully you can see my mouse of, you know, the conduction system starting with the atrial bundles that then funnel into the AV node and then become the proximal His bundle. And as well as actually this distal His-Purkinje system. You can see that there are a wide range of areas that we can target with, you know, pacing leads. And what we're trying to achieve with this really is just to take advantage of the very rapid conduction that you get when you pace the His-Purkinje system. If you look over here at this table, all the way at the right at numbers four through six, which are the bundle of His, the bundle branches and the Purkinje network, you get conduction velocities ranging from over a meter per second to four meters per second. So by activating through the His-Purkinje system, you can rapidly deliver electrical activation throughout the heart. So, you know, there are many different ways that we can achieve physiologic pacing, as you see from this very nice review here by Pugal. You can do His bundle pacing, you can pace an RVOT to try to get narrowing that is contrasted with RV apical pacing. And now folks are doing left bundle branch pacing, as you know, left septal pacing, RV, you know, septal pacing and many other different approaches. And really, I think virtually anyone who needs pacing can be paced with physiologic pacing, especially if they're gonna have a high pacing burden. So that includes CRT, both left and right bundle branch block, as I'll show you some data, heart block and also pacing-induced cardiomyopathy. So what I'll try to do over about the next 45 minutes or so is review the rationale for physiologic pacing, talk about His and proximal bundle branch anatomy, implantation approaches, some initial clinical outcomes, talk about mechanisms of QRS narrowing, which for me is, I think, the most exciting part of doing physiologic pacing, which is this idea that you can, you know, narrow YQRS. And then where we go from here. So this is a very EP audience, so I'm not going to spend a lot of time on the slide. The point of the slide is really just to indicate that many patients need pacing for many different reasons. And pacing obviously has a mortality benefit because if you have a patient who needs pacing, say, for something like heart block, and you're not able to do that, that leads to loss of life. Although pacing is important and very necessary, we have learned from the David trial that it's not so simple. So as you know, the David trial randomized, you know, patients who are receiving an ICD into 256, getting a pacing mode of VVI-40, so backup pacing, and the other group getting paced at DDDR-70. And as you see here, the patients who are in the DDDR-70 group had a higher incidence of death or, you know, heart failure, hospitalization, or worsened heart failure. And the mortality curves for death from any cause was close to significant, not quite. And if you look at, you know, sort of the main, you know, sort of finding between the two groups is the burden of ventricular pacing. You see that those in the DDDR group were paced at, you know, 78% of the time, whereas those in the backup mode pacing only 4% of the time. And that was associated with this, you know, very robust difference in outcomes that I showed you on the slide earlier. And when you decide further and take away the pacing mode, where you look at those who were paced with the same mode, but those who had a, you know, who were paced about 40% of the time versus those who were paced less than 40% of the time, you see, again, this huge, you know, difference in endpoints, making it clear that a high pacing burden is not a good thing, especially if you're pacing from the RV apex. And it's not a mystery why. If you look at LV strain, you know, using echocardiography and look at synchrony, here on the left-hand side, you can see what that looks like in a normal patient where with a normal sinus rhythm, and you can see that the, you know, the different regions here all essentially look fairly uniform versus a patient with left bundle branch block pacing, where you see really here that, you know, the, you know, this loss of synchrony is essentially a lot of dyssynchrony. And especially if you superimpose heart failure on top of that, it looks even worse. So this is what RV apical pacing does. It mimics this dyssynchrony, and therefore this is why physiologic pacing has come about. To summarize this initial part, again, we've talked about pacing being necessary, life-saving, but a high pacing burden is associated with adverse outcomes, and that's likely due to abnormal myocardial activation, poor energetic use, and abnormal LV pressures, developed pressures, and physiologic pacing enters the picture. So no real talk about physiologic pacing can, you know, go on without really mentioning the work of Ben Sherwide, who was really the person that described his bundle pacing as far back as 1968, if I remember correctly, was when I think his paper was published. And you can see here a tracing from that paper where he showed what the QRS looks like in normal sinus rhythm, and with his bundle pacing, as you see here, the pacing stimulus is here, PI pacing impulse, that looks identical to sinus, and also looks just like atrial pacing. And before moving on from there, I'll go back in time and just talk very briefly about Wilhelm Hiss. This is Hiss Senior, not Junior for whom the Hiss Bundle was made, but the story really starts with him. He was a well-known anatomist in the 1800s, and he was very interested in embryologic development. He actually was credited with building the first microtome, and he really pushed the use of microphotography in anatomical research. And when he looked at cardiac development, he was very interested in this region called the atrioventricular canal. And for whatever reason, he never pursued this himself, but he encouraged his son to do so. So this is Wilhelm Hiss Junior, for whom the Hiss Bundle is named, and he was the third of Hiss Senior's children, and because his father was a well-known scientist and anatomist, he trained at the best institutions at the time. And like a good son, did what his dad told him, and focused on this AV canal. And went on to describe it and describe the embryologic development of this area. But while it gained traction, it wasn't really until Sonal Tawara really actually described the distal conduction system, so the left bundle branch, and then the Hiss-Purkinje fibers, that the real role for the Hiss Bundle actually became clear and made sense. So Sonal Tawara is, of course, credited with describing the left bundle, and here's actually his original depiction here that included the Hiss Bundle, as well as the left and right bundles. So that's really how the anatomic region was described. The anatomy of the Hiss Bundle itself requires getting into, as you know, the Hiss runs along the border in general between the membranous and muscular septum. Here's the atrioventricular portion of the proximal membranous septum. This is where you get a GERBOTE defect, if there were to be a perforation here. And then this is the right and left ventricular portion of that membranous septum. So the Hiss Bundle runs along that crest again between where the membranous septum and the muscular septum meet. This is a view, this is from Marcel Elizari. This is a view from the left side now where the tricuspid leaflet comes in to the septum, septal aspects of tricuspid leaflet. And you see here that, you know, so the head would be up here, the foot's down here, head's up here, foot down here, excuse me. And here's the AV node, proximal Hiss Bundle, and here's where the left bundle comes off. It comes off like a curtain, and then the entire conduction system continues on as a right bundle. I think most people think that the left and right bundles split, but it's really, here's another image of that. It's more like the left bundle comes off as a curtain. And the Hiss Bundle is therefore divided into the penetrating, the common, the common which is the penetrating portion of the Hiss Bundle where it crosses the central fibrous body and then the branching portion, branching Hiss Bundle and penetrating Hiss Bundle. These are just two portions of the Hiss Bundle. The penetrating portion, as you see here, is about five to 10 millimeters in length. It's right-sided, and the branching portion, again, runs along the interventricular septal crest. This is now on the left side, and this starts right when the left posterior fascicles start to come off. So right here would be the beginning of the branching portion of the Hiss Bundle. Now, and then obviously, as you know, divides into the anterior and posterior divisions which go to supply the papillary muscles. You need that tempted down during contraction, and you need electrical activation to get there pretty quickly to tempt that down before the heart starts to contract. A lot of work has been done describing the various morphological, various anatomical variations that they are in this area. This is just to show some of that. And I'll, I think I've made this point pretty clear. I think just that, again, the Hiss Bundle's running right here along the crest of the muscular septum up here, and then, excuse me, the membranous septum up here and the muscular septum down here. So coming back to the development of Hiss Bundle pacing, again, I talked about the work of Dr. Ben Sherlag. The studies were then extended by Dr. Sherlag and other colleagues like Nabil El-Sharif and Ralph Lazara and Chris Windham, where they found that if you looked at a patient with left bundle branch block and you pace the, you know, the proximal aspect of the Hiss Bundle, you don't correct that. You still have the YQRS, but if you pace the distal aspect, you actually get this nice narrowing that you see here. Again, pacing the proximal aspect, pacing distal aspect. And this is where the concept of narrowing the QRS by pacing the distal Hiss Bundle really arose. This was done in animals initially and then followed up in humans. And in terms of, you know, improvement in synchrony, an example is shown here from work by Kronborg and some colleagues back in 2012, where they looked at parahysian pacing and RV apical pacing, and you see here, I think green is the basal septum of the LV and yellow is the basolateral wall of the LV. And you see here that in the same patient with parahysian pacing, both regions reach their peak systolic contraction at the same time, whereas if you pace the RV, this is that dis-synchrony that we're talking about. And they do this in a whole bunch of patients. And show that almost no matter what the index you look at, pacing from the RV septum was associated with worse cardiac contractility and systolic function compared to the parahysian region. That work was extended by Dan Lustgarten, who did this really nice, again, classic study here of looking at Hiss Bundle pacing versus biventricular pacing. And he did this in a crossover design where he took the same patients, had both a CS lead and a Hiss Bundle lead, and was able to compare in the same patients what their EF, quality of life, NYHA class, and six minute hall walk test looked like with Hiss Bundle pacing and biventricular pacing, and basically showed equivalence between the two, again, suggesting that QRS narrowing in this population afforded the same benefits that we have come to associate with resynchronization therapy. So this was really a landmark study that I think really opened this area up and drew a lot of interest into this. Obviously, other people have done work before this, but I think this study was one that really brought this to the forefront. I'll get into some more studies a little bit later. I want to segue a little bit and talk about lead implantation approaches. The, probably, and not to necessarily endorse any company, probably the most commonly used approaches with the Medtronic system where we use the 3830 lead, the Select Secure lead, which is a luminous lead, with one of a number of catheters. These here are the preformed Hiss catheters, C315 family, and also there are two deflectible sheets that can be used as well. And just as a point of mention here that all the other companies are now coming up with sheets mostly, but although Boston Scientific is pushing a lead that's almost like a 3830 lead, except that it does have a lumen, a pretty small lead. A quick primer on the approach. I won't spend too much time on this because there are now many, many videos available online for many people that show how to do this. This is from one of our early cases. This is probably one of my first handful of cases where we were using a CRD2 to mark the position of the Hiss, but in general, we do a left venogram before getting access, and then we put up this lead from the going. And then we drop our wires. In this case, which was a CRTD case, put in the RV defibrillator lead, drop the RA lead into the IVC, and then begin to work to position the Hiss bundle lead. And here's showing the lead with our sheet here. Here's what we see on the programmers. You can see here a nice P-wave, and then the Hiss bundle electrogram, and then the QRS. And again, what you're aiming for is the distal aspect of the Hiss bundle, so you do expect to have a very big ventricular deflection, definitely much bigger than that atria which tells you the distal Hiss. And then we take this position, and this is what it looks like after we screw it in. I think this was the initial tracing here, initial electrograms. And then once we secure the lead, this is what it looked like at the end. And then we essentially pull back the sheet, lead stays in place, and then pull everything back and secure the device. And this is how I did this initially when I started. Now I typically don't use a CRD-2 from the leg, I really just go up from the left upper extremity venous system with the sheet. And here what typical settings look like, the point I want to, what I would like to point out on this slide is really just how making the distinction between the Hiss capture threshold and the local capture. So in this case with the Hiss lead we captured, we lost Hiss, the threshold for Hiss capture was actually three volts here as you see at 0.5 millisecond pulse width, and then the local capture was lost at one. And this is what has dogged Hiss bundle pacing is the fact that you have these high thresholds that could drain battery life. And I'll get into some of ways of potentially avoiding that shortly. And when we talk about Brady pacing, the Hiss bundle lead is set just like you would RV apical pacing. In terms of terminology, so this is one of our early cases, a patient with depressed LVF ischemic cardiomyopathy, had a prolonged HV and QRS of 200 milliseconds, and with Hiss bundle pacing was able to narrow completely to 99 milliseconds. And this would be called selective capture here. So selective capture, there were a number of terms that were used previously until a paper about four or five years ago agreed to use consistent terms. So these days we tend to favor use of the term selective Hiss capturing, non-selective Hiss capture, in the past things like pure and direct and parahissing and all these terms were used. Selective capture just means that you are getting exactly the Hiss bundle and very little to no local myocardial tissue. So you do get what looks like an HV interval as shown here. And then non-selective capture means that you do capture some local myocardium in addition to the Hiss bundle. And then you get what looks like a delta wave, which reflects that local myocardial capture. Most cases of Hiss bundle pacing are non-selective Hiss capture, but that's still associated with significantly improved outcomes. This was my very first Hiss bundle case here, 74-year-old woman who had hypertrophic cardiomyopathies and underwent AVR and septal myomectomy and then initially had heart block, which resolved, but she was left with a pretty wide left bundle branch block over six months, her EF dropped, her NYHA class increased and she went from having only exertional dyspnea to dyspnea at rest. She'd been optimized on medications and obviously met class one indication for CRTD. At this point, this was one of our, as I mentioned, my very first case. We explained to her that Hiss bundle pacing is new, but had potential benefits, including a more natural activation of the cardiac induction system. And she agreed to it. And this was her case here. Again, you see here CRTD-2 from the groin. This is her aortic valve here, CRHV interval was 64 milliseconds measured. And this is what we got with her. Again, big ventricular potential here. You can see the Hiss bundle electrogram here. We secured here and we actually ended up with non-selective pacing, non-selective Hiss bundle capture, as you see here. We did narrow her QRS from 198 milliseconds to 123, which wasn't perfect. We hoped we could completely normalize it. But even with that, just improving to 123 and not complete normalization, her EF went from 15% to 55%. And this was my first case again now about six or seven years ago. And she's still doing really well today. Until today, she's now seen by one of my partners. And this really got us going on this. This led us to design this study here. I mentioned that Dan Lustgarten had used a crossover approach to examine the feasibility of Hiss bundle pacing. We put our series together where we looked at patients where we just used Hiss bundle pacing lead alone for CRT to assess the feasibility of that. And we took patients who had indication for CRT, either they had failed CS lead or suboptimal coronary venous targets, or a handful of patients who opted for Hiss bundle pacing from the start. We recruited about 17 patients. We were unsuccessful in four. And of the 13 that got the lead here, there are characteristics here. You see that we had a pretty wide QRS, again, about 180 milliseconds. And here were our results here. Again, this is now published. We're able to narrow the QRS significantly from about 175 plus or minus 30 to 122. Most mean narrowing about 53 milliseconds in most patients, which again, you may not see as often with the traditional coronary sinus pacing. Here again are selective versus non-selective. Most of our patients were non-selective capture. And even with that, you saw the EF substantially improved, the LV internal dimension and diastole also significantly improved. And one thing that was interesting that we saw was that the wider the QRS, the greater the narrowing that we saw. This hasn't been replicated as often in the other studies, but we thought this was really quite interesting. And here are outcomes. We did have one patient that had a pneumonia and passed away shortly after the implant, and another got septic and actually needed device exploitation, but all the other patients doing pretty well with no arrhythmias or shocks in the one-year follow-up that we had. So switching gears to mechanism here, to me, again, this is one of the most exciting parts of his bundle pacing is how does it work? How do we narrow the QRS in his bundle pacing? And we put together this review a few years ago with a resident of mine who's now a fellow at UCSF, where we sort of reviewed all what has been noted in terms of how his bundle pacing manages to narrow the QRS. And the predominant concept is this idea of longitudinal dissociation, the idea that fibers that will become the right or left bundle are predestined within the his. And so that if you get block within the his in the fibers that will be going to become the left bundle, then you would get left bundle branch block. And the idea is that if you then pace in this region, either by pacing at very high outputs, you can get a larger area of capture, or pacing beyond the side of block as shown here, you can then narrow that QRS. And we go on to show the different pacing wavefronts that you can get here. But the, again, predominant concept is this idea of longitudinal dissociation. And speaking with Ben Sherlock, who published the initial paper on the concept, it doesn't quite work as well in diseased tissue. But if you acutely put in a lesion in the left bundle, as they did in normal animals, it made sense. So there's some idea that this may not completely explain all cases, but at least this is the best that we have at this point. And here's another image of that. Here's actually an image of the proximal his bundle region. And you can see here again, these tracks here that go through. So in pink here, that's the tissue, and then the, excuse me, the pink here is the tissue, conduction system tissue, and then blue here is the central fibrous body, and you see it penetrating here. So work by Ratong and Gaurav at University of Chicago was very, very helpful in helping us understand a couple of things. One, potentially how to select patients for his bundle pacing, and two, the potential mechanisms of narrowing. So what they did was, in a whole bunch of patients, some of whom did not necessarily need his bundle pacing, they mapped the right and left sides of the septum, and essentially were able to identify patients with intrahistian blocks, so this might be more akin to that longitudinal dissociation that I mentioned, versus patients who had block more within left bundle, so this would be true left bundle branch block, versus patients who had intact his furkinje activation, and this might indicate that this is more nonspecific IVCD or some other mechanism for writing QRs, maybe just severely diseased hearts with very poor muscle-to-muscle conduction. And what they showed is that the more proximal the blocks of the patients that had left intrahistian block, which were 46% of the patients, you were able to narrow the QRs in 94% of those patients, whereas in patients with left bundle branch block, that was more within the left bundle, that was 18% of their patients, you could narrow in fewer of those patients, 62%, whereas in those with more distal block, you could not narrow any of those patients at all, which, in a way, tells us what we sort of already knew, but again, just the idea that block can be in the proximal left bundle or can be in the his bundle, and this makes sense for why we are now doing left bundle branch area pacing, which I'll get into just a little bit here. Some other really interesting concepts with regards to his bundle pacing, this is data from Parikh Sharma, next to you, you got your neighbor there in Chicago, who looked at his bundle pacing for CRT in patients with right bundle branch block. All the data I've shown you till this point has really been in left bundle, and they show that, indeed, you can narrow the QRs even in right bundle branch block, they had a narrowing of about 158 to 127, and in their patients, whether they were severely low EF or modestly low EF or all comers, you see EF improvement in all of their patients, and these are kind of their patient characteristics here. So his bundle used for right bundle branch block, again, I thought this was a very exciting study in that it shows that it wasn't just the left bundle branch that can be narrowed, you can also do that for right bundle, and patients, as you know, with right bundle branch block and heart failure, traditional CRT with a coronary sinus lead doesn't really help those patients, so the idea of being able to do this, I think it was really quite interesting and a great contribution. The other area where this, I think, is interesting is in AV node ablation, and the way that, I'm not sure how most people do their AV node ablations with pacing, the way we tend to do it is to put the lead in first and then come back and ablate later just to make sure that the lead is healed into place appropriately. And you see here in this paper from Pugao where they showed here the sites around the his bundle lead where they ablated, you might be worried that by ablating so close to the lead you might dislodge it, and what if something happens, but that actually didn't happen, and I've done several of these cases myself, and it really does look like you're ablating right on the his bundle lead, which is a little nerve-wracking, but that tends to be pretty safe. And so here's a fluoroscopic image of that. Again, if you look at projections here of where you're ablating, it looks again like you're right on the lead and you might be worried about damaging the lead, but they showed in this one patient here who had pacing-induced, excuse me, who had tachycardia-induced cardiomyopathy, you could again achieve a very narrow QRS with avian node ablation and his bundle pacing, and they showed here 19 months follow-up, very, you know, essentially very stable lead positions, no change in the QRS duration here as you see. And, you know, some increase in the lead threshold, again, a known issue with his bundle pacing, and stable to slightly improved LVEF as you see here in functional class. Now, you know, we're always taught that, you know, if a patient has advanced conduction system disease and you start pacing that ventricle, that the remaining wisps of fibers in the conduction system essentially go away or that you lose that. And this paper was really nice in showing that that's not necessarily the case. So what they did here was to look at his bundle pacing in patients with long-standing AV block and chronic right ventricular pacing. Again, the patients that you would expect that you could no longer find a hiss or any aspect of the conduction system. And here's an example of one of those cases. You see here the PACE QRS in this patient who'd had complete AV block for eight years. So she'd been paced for eight years and developed pacing-induced cardiomyopathy. And with careful mapping, PACE mapping here, they were able to identify a site and capture there led to non-selective capture of the hiss and narrow the QRS dramatically. And they showed in their series of 60 patients that, you know, with some patients, again, look at the duration of RV pacing here, out to 80 months, that you could substantially narrow the QRS. You see, look at the difference here between the RV pacing QRS and HISS bundle QRS. Substantially narrow the QRS and improve the LV function. So, you know, really nice study showing that, you know, we shouldn't just give up on patients who've been pacing for a long time. And HISS bundle pacing still potentially has a role in these patients. In one patient, they've been pacing for up to 22 years. I mean, this is really remarkable that someone took the time to really map out the conduction system and pace this patient. So this is, again, yet an impressive study. And looking across at all the studies, this has probably been updated by now, you know, about eight or so studies here, looking at when the studies were published, the implant success rates and the types of leads that were used. And you see that, in general, success rates with HISS bundle pacing is high, and you tend to get substantial improvement in the LV function, as you see here. So, really exciting way to move forward. Now, I'll spend a little bit of time on left bundle branch block pacing. As I mentioned, HISS bundle pacing is associated with high pacing thresholds. Sometimes you don't get QRS narrowing. As I showed you in the paper from Gaurav Upadhyay and Ratan, you can actually have block in the proximal left bundle. So HISS bundle pacing would not correct those patients, right? You could also have infernodal AV block. And there are issues with lead stability and, again, thresholds over time. And so, this was really developed by Weijian Wang out of China, also a big HISS bundle pacing expert. And he's been doing this for some time, actually. And he, I remember, would always put in his HISS lead and then go distal to that to see if he can find a better site. And he kept going distally until he actually started bordering into the septum and pacing the left bundle branch. And that's where left bundle branch area pacing came from. And he's written, with Bogal, this very nice piece here in Heart Rhythm about a hands-on approach. They actually showed, I think it's easier to see on this slide here, they looked for this W pattern. So here's an example in their recently published series, multi-center series, where they look prospectively at patients with left bundle branch block and non-ischemic cardiomyopathy. Here are the patient characteristics you see here. And so, in these patients, you see this is the native QRS here. And when you, and panel B here is actually pacing the septum, so not quite capturing the conduction system tissue. And you see this W pattern here, which is sort of what they look for. And then by burrowing deeper and deeper into the septum, you see this progressive change here. And all of a sudden, you get to a point where your stim to peak QRS actually narrows. And that tells you that you have captured the left bundle branch. They actually captured it here, but there was some output dependence. So by increasing from three volts to five volts, they were able to actually get more selective capture of the left bundle branch, as you see here, and you see substantial QRS narrowing. And in their study, they went from about a mean of 165 milliseconds with left bundle branch pacing to QRS of 104 milliseconds. And here are their patient outcomes here. Again, at six months and at 12 months, increase in LVEF and reduction in LV and systolic volume, again, showing that you do get, with left bundle branch pacing, you get that reverse remodeling that you saw with his bundle pacing. So now we have these two approaches, his bundle pacing, left bundle branch, left bundle branch area pacing. How do you pick? I thought this perspectives and contrast between Ken Ellenbogen and Santosh Padala at VCU and Gaurav and Rod at U of Chicago was a really nice way of overview of looking at both. I mean, at the time that this was published, there was only one study with outcomes up to 12 months with left bundle branch area pacing, and that was Weijian Wang's paper. So there was no experience outside of China at that point. But they very nicely, if you look at the, on this right side of the screen here, the paper from Ken and Santosh, very nicely actually looks at, in terms of the differences between the two, anatomy, histology, physiology, et cetera. But I think one way of, a nice way of summarizing the potential issues with left bundle branch area pacing, I think was nicely captured here, where Gaurav and Rod essentially outlined that at this point, there's of course a lot more data for his bundle pacing than left bundle branch area pacing. And some of the advantages for his bundle pacing are that you can completely recruit intrinsic left conduction system activation. So again, by pacing and recruiting native conduction within the his bundle, you are getting both bundle branches. There's obviously, there was, at least at the time this was written, much more evidence for his bundle pacing. And at that point, again, we didn't know as much about left bundle branch area pacing. So the criteria weren't as developed and the generalizability was unknown or unclear. Now with the paper that I just showed, one slide before this, which is a multicenter study, an international study, we now have more data outside of China with left bundle branch area pacing. So the way I think it's going to likely boil down is that most people will try his bundle branch, excuse me, his bundle pacing first. And if you don't get QRS narrowing or complete QRS narrowing, you might try left bundle branch area pacing and see if you narrow completely there. Of course, that takes time. That's more radiation exposure, et cetera. So it remains to be seen how people will use these two techniques. And when we have better tools as well that allow us to get into the conduction system more reliably and faster, I think that that may also change. As I wrap up here, I'll just call your attention to this nice compendium that was published, wow, now four years ago in the Journal of Electrocardiology where a number of different folks contributed different articles to the concepts of his bundle pacing, including anatomy, physiology, et cetera. One point to mention is that physiologic pacing or his bundle pacing is now making it into the guidelines. Again, class 2A and 2B for patients with AV block who have an indication for permanent pacing and EF between 36 and 50% that you expect to pace more than 40% of the time. Again, this was from the David sub-study here that you can consider his bundle pacing. And then class 2B in patients with AV block at the level of the AV node that you obviously they have an indication for permanent pacing, you may consider his bundle pacing to maintain physiologic ventricle activation. And I think that over time as more data come out and more people use this, this is likely to rise in terms of guidelines. Lots of studies in the works. This is a search from today. Every time I give a his bundle talk, I update this. These are a number of studies that are actively recruiting for his bundle pacing and left bundle branch area pacing. So again, more data will be forthcoming. So to conclude, physiologic pacing is an important option for many pacing indications, including forward synchronization. It's associated with significant clinical and cardiac structural improvement. And of course, this is especially true in patients who need pacing and have depressed LD function. The mechanisms of QRS narrowing, which again I think are just fascinating, are incompletely understood. But I think over time as we learn more and more, I think that this will, one, teach us not only what bundle branch block is or what conduction block really means, I think that it will also expand our use of physiologic pacing. The next point is just to again highlight that this is now making it into the clinical guidelines for pacing. And as we get more and more tools, again, being developed and get smarter about using this, I think that more patients will derive benefits from physiologic pacing. So with that, I'll go ahead and stop and again acknowledge my UCLA colleagues and my funding sources, and I will be glad to take questions. All right, thanks, Olu. That was great. A few questions maybe I could ask. Maybe you could just clarify when you're putting in a HIS bundle lead, selective versus non-selective capture, or do you make an effort to get one versus the other? Does it not really matter? Yeah, so that's a good question. I used to have a slide, you know, that was actually put together by Sivam Mopura from Mayo where he actually, you know, showed the different sort of anatomic, you know, sort of locations of the HIS bundle running over the crest of that muscular septum. So the HIS bundle can be pretty superficial. They call that the naked HIS bundle or can be buried very deep. So even if you try as hard as you can for those situations where the HIS bundle is buried deeper, you almost always capture some local myocardium. So what I do is I look for as much QRS narrowing as I can get, and I don't really care so much about whether it's selective or non-selective. I, of course, go in looking for selective, but after you've been in there for a little while, I think you're just happy to get something that's much narrower and that's better for the patient. And are there any patients that you, what patient characteristics do you use to decide on physiologic pacing versus putting in an apical lead? Yeah, so that's also a good question. I think in general, if you're going to have a patient who is going to pace a lot, I start to think about physiologic pacing in those patients. Of course, if it's a much older patient that you may not want to have them on the table for too long, then I think that I may not necessarily pursue HIS bundle pacing, especially if it's taking too long. But in general, I try to use HIS bundle pacing or physiologic pacing in any patient that I think is going to pace a lot. And that's my very simple criteria. And I tend to use HIS bundle pacing more for CRT because I personally just have more of an interest in that. I think it's fascinating that, again, we can narrow the QRS with physiologic pacing, with HIS bundle pacing. But to answer your question directly, it's more so pacing burden for me. And then I guess on the heels of that comment, so your thought process for CRT, do you start with the LV lead? Do you start with HIS lead and then move to left bundle? How do you think about that? Yeah, so I'm actually quite aggressive with physiologic pacing. I pretty much, every single patient of mine who is a resynchronization patient is approached with physiologic pacing. I mean, it's what I tell the patient. It's the discussion we have in clinic or in a hospital before the procedure. And I tell them that if I cannot narrow the QRS with physiologic pacing, then I do coronary sinus lead. And of course, that can lead to slightly longer procedures, but I believe that this truly is what's better for the patient. They are, the heart was never meant to be activated from the epicardium, as we get with the coronary sinus lead. And so I think that for that reason, and I'm sure you're familiar with data where patients with ischemic cardiomyopathy, especially those with lateral scar can actually get VT from epicardial pacing in terms of coronary sinus. So I pretty much off the bat plan to do physiologic pacing and only if HIS bundle and left bundle branch area pacing fail, do I do a coronary sinus lead. Okay, and then I guess my last question, what tools are you most excited about coming out in this field? Yeah, hopefully this isn't seen as an endorsement of any particular company, but I've seen and played around a little bit with the Abbott HIS Pro sheath, the deflectible. I'm not sure if you have it at your center. We actually don't have it at UCLA yet, but I think the idea of being able to map with the same sheet that you're going to deploy the lead with, I think I'm excited by that. And the fact that it's deflectible. So I'd say that's, again, this is not a particular endorsement. I think that, again, I know Biotronic is coming out very soon. I think they're about half a year out with their preformed sheets. And I know Boston has their sort of sheets out as well. But the ability to map with the, and because what that's going to do is it's going to really help you for those patients where either maybe they've been chronically paced and there's no antegrade conduction so you can't find a HIS, that might help you with those patients.
Video Summary
Physiologic pacing refers to the utilization of some aspect of the heart's conduction system to achieve a narrow QRS complex. This can be achieved by targeting different areas of the heart's conduction system using pacing leads. The aim is to take advantage of the rapid conduction that occurs when pacing the His-Purkinje system. His bundle pacing is one approach where leads are placed in the His bundle region to achieve QRS narrowing. This can be effective for patients with conditions such as heart block or pacing-induced cardiomyopathy. Left bundle branch pacing is another approach that targets the left bundle branch in order to achieve QRS narrowing. This can be useful for patients with left bundle branch block or right bundle branch block. Both approaches have been shown to improve cardiac function and provide clinical benefits. The mechanisms of QRS narrowing are still not fully understood, but it is thought to involve longitudinal dissociation and recruitment of the intrinsic left conduction system. Physiologic pacing is being increasingly recognized in pacing guidelines and is seen as an important option for many pacing indications. New tools and techniques are being developed to improve the success and outcomes of physiologic pacing.
Keywords
Physiologic pacing
heart's conduction system
narrow QRS complex
pacing leads
His bundle pacing
left bundle branch pacing
QRS narrowing
cardiac function
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