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His Bundle Pacing 360 Degrees
What is the Future of HB Pacing? (Presenter: Kenne ...
What is the Future of HB Pacing? (Presenter: Kenneth A. Ellenbogen, MD, FHRS)
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So, our next speaker is something of a, the deus ex machina of his bundle pacing and appropriately Ken Ellenbogen will be speaking on what is the future of his bundle pacing. So we're running a little bit behind obviously, so the next speakers are going to try to push it a little bit faster and hopefully we'll get done in time. And I think I can do that. So it's always dangerous to give talks about the future of anything because usually end up coming back two or three years later and every prediction you made is incorrect. So let's see how well I can do here. So the future of his bundle pacing has to do with some of the major issues that need to be resolved in order to further determine what practical role, what realistic role his bundle pacing can play in terms of our pacing armamentarium. And some of the issues that have been raised by folks have been, first of all, what is the long-term reliability of thresholds in QRS narrowing with his bundle pacing? When you think about it, we've been pacing for over 50 years and we have a lot of experience with RV endocardial leads and now we're trying to pace the conduction system often through this fibrous skeleton when we're pacing above the tricuspid valve. So what is the long-term reliability? Secondly, before we get everyone to switch from pacing the myocardium to pacing the conduction system, we need to be able to show we have simple, reproducible, easily taught to new and old implanters way to implant these leads. Third question is hemodynamics. We have to clearly show that hemodynamics and outcomes for selective his bundle pacing, non-selective his bundle pacing, and pacing the conduction system from the septum, left bundle branch block pacing, is good. Of course, none of this is relevant until we have clinical trials of pacing in patients who have heart block and patients who have bundle branch block, and they have to show that the outcomes are better with conduction system pacing. And finally, we need to develop new tools, leads, sheaths for lead implantation. And ultimately, I think most people would agree that the holy grail is leadless implantation in the conduction system. Some sort of device we can implant without transvenous leads that paces the conduction system. So this is going to make my job easier. You've already seen this slide. And the reason I show you this slide, again, is just to remind everyone that the thresholds tend to be higher with selective slide pacing. And of course, it can't be done in 100% of patients. And of course, you can put a ventricular lead in 100% of patients. So the success rate has to be higher. And I think a good example of this is this paper, which was published in Jack in 2018 from Suneet Mittal and his group in New Jersey. Dr. Mittal had come and spent a day with us. We did about three or four cases of his bundle pacing. He went back and tried to introduce this technique amongst a number of people who are well-experienced at implanting pacemakers. And the take-home message was that there is a learning curve. We all know there's a learning curve, although not as striking as you might think. These are 100 consecutive patients, conduction system pacing. And you see the success rate went from 76% to 83%. I don't know whether that's statistically significant, but it's obviously a trend. But you can see that the number of patients who required lead revision was not insignificant in their experience, and it can't be done in all patients. And that is what we have to be able to accomplish in order to be able to convince everyone that pacing should be conduction system pacing. And you heard from Dr. Wong about his technique of using dual leads, but most importantly about his development of a technique that relies upon pacing in the septum of the conduction system, which is often referred to as left bundle branch block pacing. And this is just an example of the patient's underlying QRS. On the bottom is the QRS duration. You can see pacing, pacing, pacing. You can see the left bundle potential here. And you can see the QRS duration goes from baseline to about 110 milliseconds, so minimal widening of the QRS with selective pacing of the conduction system from below the tricuspid valve, from below the tricuspid valve, using this technique of pacing the left bundle branch block. And in this study, and I need to say that there's been a lot of experience with this, using this technique. There have been over 3,000 cases done in China last year. And of course, you'll get the opportunity to see a live cases Friday morning at HRS from Geisinger, and you'll see this technique. But the important thing about this technique is it really changes how we do conduction system pacing. And that is, this is patients who had conduction system pacing shown in the block, left bundle branch block pacing. This is RV septal pacing, or pacing the RV septal myocardium. This is RV apical pacing. What you should see is that the R waves aren't statistically significantly different, whether you pace from the RV apex, whether you pace from this left bundle branch block site. The thresholds are much more similar and overall significantly lower, both at implant, immediately post-implant, and at a three-month follow-up, the thresholds were no different from pacing the RV apex. But here's the amazing thing, the baseline QRS duration, 1-11, paced QRS duration virtually identical, the pacing stimulus to the QRS interval is 31 milliseconds. Now that's not an HV interval. That's more like a bundle branch or some part of the conduction system to the ventricle, but on average it was 30. That indicates you're not pacing septal myocardium, but you're pacing the conduction system. And in patients who had, in whom they could record a left bundle, which in our experience is not everyone, but a minority of patients, the left bundle potential to QRS was 20 milliseconds. So pacing the conduction system can be done with thresholds and R waves similar to pacing myocardium, and this technique is available and is one that can be implemented amongst a large number of patients. Now I said there's a lot we need to learn about hemodynamics. So Friday afternoon at the late-breaking clinical trials, there is a prospective evaluation of feasibility, electrophysiologic and echocardiographic characteristics of left bundle branch area pacing. So some information about hemodynamics. And then is non-selective histbundle pacing good enough? Long-term outcomes, I said we need data about outcomes. Again Friday afternoon, late-breaking clinical trials. So stay tuned. We'll get some of that information tomorrow. This is some data on an issue that I think will come up down the road. And that is a direct comparison of pacing the conduction system in patients with heart failure compared to CRT pacing, paper published about a year ago. And you can see, in fact, as one of our prior speakers pointed out, that pacing the conduction system may, in fact, we may, in fact, be able to show an improvement compared to pacing biventricular pacing. This is just looking at systolic blood pressure compared to AEI pacing in patients that have left bundle branch block. That is AEI versus pacing the left ventricle through the CS, or AEI pacing versus the histbundle. There's a greater improvement in systolic blood pressure with histbundle pacing compared to biventricular pacing. There is some data on pacing and patients that have bundle branch block, retrospective, not sequential patients. And that is an area that future clinical trials are going to have to address. Long-term results of selective site or conduction system pacing over time. Some of that data has just recently been published. Here's an EKG from a patient who had histbundle pacing, and here you can see their baseline QRS. You can see one year later a 12-lead electrocardiogram, and this is certainly quite impressive. This is selective histbundle pacing. And then five years later, their electrocardiogram. And note, this is selective histbundle pacing. It's an isoelectric interval between the stimulus and QRS, and the QRS morphology and duration are unchained from baseline to one year to five years. So I think we're beginning to collect information that says you can pace the conduction system. The results are long-lasting. You can pace the conduction system with good pacing thresholds. And just finally, long-term lead performance and clinical outcome. This is from the paper in Heart Rhythm. Large number of patients. Really great QRS long-term. Ejection fraction is great, but look at the incidence of pacing-induced cardiomyopathy in patients who have conduction system pacing. One patient for an incidence of 2% compared to an incidence of 22% with just conventional pacing. So dramatically better outcomes, which should translate into decreased heart failure, et cetera. And you've all seen this paper. This is based on the intention to treat analysis. I won't belabor this. Not a true randomized controlled clinical trial, but the type of evidence that suggests that we're not that far from being able to do a trial. We'll have to see what the results show. You saw this trial presented this morning at Late Breaking Clinical Trials. Clearly a small pilot trial, but the results of this trial, I think, give us hope that a larger trial, particularly with this technique of pacing the left bundle branch block, is feasible, can be done, particularly with clinical equipose. As you heard from one of the speakers, there are large numbers of clinical trials that are in process. This is one particularly interesting one, looking at AV optimization delivered with direct tissue bundle pacing in a group of patients we don't know what to do with. Patients with long PR intervals without the bundle branch block. It is a randomized multicenter trial looking at a clinical outcome. It's being done in England. The primary outcome is an improvement in objective exercise capacity. Maybe not EF, maybe not heart failure hospitalizations, but I think that will be coming next. It's one of the really good prospective trials. We need more trials. Dr. Wang is doing a trial in China. This is a particularly important trial, patients with an EF less than 40%, narrow QRS, persistent AFib with RVR, randomized multicenter trial, small trial, his bundle pacing versus by V pacing for nine months, with an end point being the change in EF. There is a trial called His Alternative being done in Denmark. Another small trial, but again, I think it's going to be one of those very important trials. HeF-REF, heart failure with reduced EF and left bundle branch block, 50 patients in each arm, randomized, double blinded outcomes for six months, and end points are success in maintaining narrow QRS and change in LV and systolic volume as a primary end point, comparing his bundle pacing to by V pacing, like the clinical trial you saw this morning. I think we're just testing the waters. So in conclusion, we are limited by largely observational data from small numbers of centers. The clinical variables that are measured vary greatly between studies. The duration and size of studies is limited. Impact of left bundle branch block pacing may dramatically, will dramatically change our field. Device and tools are not really geared for his bundle pacing, but new tools are emerging. There's a new tool that was just introduced over the last week, and there are several new tools that will come out over the next six months. I've seen them. I've played with them. They look interesting. We need large-scale, multi-center trials assessing safety and efficacy. Remember, pacing is lifelong therapy. We need outcomes data, important outcomes data. A randomized trial of conduction system pacing versus RV or versus by V pacing in the appropriate patient population is where the field will be going. Once those trials are done, we will have basically the type of evidence that gives conduction system pacing a class one indication with a good level of evidence. Thank you very much.
Video Summary
Dr. Ken Ellenbogen discusses the future of his bundle pacing, highlighting the major issues that need to be addressed. Firstly, the long-term reliability of thresholds and QRS narrowing with his bundle pacing needs to be determined. Secondly, a simple and reproducible method of implanting leads in the conduction system needs to be established. Thirdly, the hemodynamic outcomes of selective his bundle pacing, non-selective his bundle pacing, and pacing of the conduction system from the septum need to be demonstrated. Clinical trials are needed to compare the outcomes of conduction system pacing in patients with heart block and bundle branch block to determine if it is superior to conventional pacing. Furthermore, there is a need for new tools and leads for lead implantation, with the ultimate goal being leadless implantation in the conduction system. Dr. Ellenbogen also mentions ongoing clinical trials and emphasizes the need for large-scale, multicenter trials to assess the safety and efficacy of conduction system pacing. Once these trials are completed, conduction system pacing may receive a class one indication with a good level of evidence.
Meta Tag
Lecture ID
5340
Location
Room 155
Presenter
Kenneth A. Ellenbogen, MD, FHRS
Role
Invited Speaker
Session Date and Time
May 09, 2019 4:30 PM - 6:00 PM
Session Number
S-039
Keywords
bundle pacing
QRS narrowing
implanting leads
hemodynamic outcomes
conduction system pacing
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