Ventricular Arrhythmias and Heart Failure: Advances in Pacing

Podcast Discussion With Bradley Knight, MD, and Raul Weiss, MD

In this episode of The EP Edit podcast, we are highlighting the November 10^th session of the Great Debates & Updates in Electrophysiology (GDUEP) conference, which will focus on management strategies for ventricular arrhythmias and heart failure. Brad Knight, MD, and Raul Weiss, MD, are Course Co-Directors of the GDUEP and will be presenting during the November 10^th session. Dr Knight is the Clinical Editor of EP Lab Digest and Medical Director of Cardiac Electrophysiology at Northwestern Medicine in Chicago, Illinois. Dr Weiss is the Director of the Cardiac Electrophysiology Program at Ohio State University Wexner Medical Center in Columbus, Ohio. 

For more information about the GDUEP conference, please visit https://www.ep.greatdebatesandupdates.com/register. This unique, debate-style conference is offered complimentary for clinicians, and all live sessions are also available on-demand through the end of 2022. This episode is also available on Spotify and Apple Podcasts!

Brad Knight: I am Brad Knight, Director of Cardiac Electrophysiology (EP) at Northwestern, starting my 14th year here. I am excited to be joined by my friend, former co-fellow, and colleague Dr Raul Weiss.

Raul Weiss: As always, great being with you. I am looking forward to this conversation! I am in EP at Ohio State University, going into my 16th year, and I am the director of the EP fellowship program.

Knight: The goal is to talk about implantable cardioverter-defibrillator (ICD) therapy and how it has evolved over time from the transvenous to the subcutaneous ICD. You and I were fellows together in the mid 1990s and saw the remarkable development of the transvenous ICD. I remember when these were first done with patches and open heart surgery—it was quite a big deal to have an ICD. Then the transvenous leads allowed those procedures to be taken out of the operating room (OR) and into the EP lab. I remember doing a lot of early defibrillation work with Dr Adam Strickberger at the University of Michigan. Tell me what you remember about those early years.

Weiss: What I remember is that I do not want to go back to those years of defibrillation! It was pretty early on. Even the Multicenter Automatic Defibrillator Implantation Trial (MADIT-I) results were not out yet—as you know, that was the first primary prevention defibrillator trial, which had only 196 patients in 1996. I think that is when defibrillation took off. At that point, if ventricular arrhythmias were inducible during an EP study, we would implant a defibrillator if the patient was not already on an antiarrhythmic medication. But what was important was that many of the defibrillators were placed in the OR, not in the EP lab, so we were a little out of our element. It was not until Dr Strickberger published the first trial showing that implanting a defibrillator in the EP lab was equal in time and safety as doing it in the OR. It is also important to note that at that point, we also moved from epicardial leads, which the surgeons had to implant, to transvenous leads.

Knight: We saw evolution of both the technology and indications. I think a patient had to have survived 2 cardiac arrests to have an ICD in the late 1980s, and the initial indications were all secondary prevention. You talked about MADIT-I and the primary prevention indications that evolved, and we saw some amazing developments in the technology. I think the first transvenous leads we implanted had a 16 French sheath, and we tunneled the lead down into the abdomen. I remember we did a lot of defibrillation threshold (DFT) testing, because the reliability was not as high. Do you recall what the defibrillation protocols were back then?

Weiss: I remember exactly. Let me first say that you are right—the lead was a very thick lead that we put it in the right ventricle. That lead would never move and would tunnel all the way down to the abdomen. At that point, the can was not a hot can, so we would defibrillate between 2 coils. It was not until we moved the defibrillator to the chest and we had biphasic waveform that defibrillation became more reliable. But I remember going all the way to failure. So we would start at 25 joules, go to 20, 15, 12, 10, 8, 6, 4, 2. We would go to one and even sub one, sometimes we would defibrillate 15 or 20 times for the same patient. Not just that, but after the implant we would bring them back in 6 weeks to check defibrillation.

Knight: And then every year.

Weiss: Yes.

Knight: You mentioned the developments of biphasic defibrillation and the hot can that allowed us to not have a superior vena cava (SVC) coil, which was a big deal—we all know the hazards of an SVC coil in terms of extraction. But as far as the average DFT testing, I think our fellows are surprised when I tell them it is only 6J, because it is really not that high. It is just that there are outliers and that is why we used to test. However, we used to test down to failure because if the DFT were 2J, then you would set it to 4J.

The DFT, it was either twice or plus 10, whichever was lowest, because charge times mattered. So if you gave a 4J shot for ventricular fibrillation (VF) rather than a 30J shot, that could mean a 20-second difference in charge time and sometimes efficacy. So we felt like we were doing the right thing with performing all these stepdowns to DFT testing and made a lot of revisions and did a lot of things for patients to get the defibrillators to work. But you must recognize that despite all the powerful data, these devices make patients live longer and are effective at defibrillating, there are problems with the transvenous leads, even in recent years. What do you think the limitations are for the transvenous ICD lead?

Weiss: I think that there are certainly tradeoffs and limitations. In my view, the main limitation to the transvenous lead is the invasiveness into the intravascular space and the risk of an infection that becomes endocarditis or a bloodborne infection. With the extravascular or transvenous defibrillators, you do not have that. Also, the risk profile of implanting a transvenous subcutaneous defibrillator is lower than implanting a transvenous defibrillator. So, other than bleeding and infection with a subcutaneous defibrillator, you do not get the risk of perforation of the heart, risk of complete heart block, etc.

Knight: Yes, there are acute risks of transvenous lead implants and then there are the long-term risks. Although I stopped doing lead extractions about 4 or 5 years ago, I had been doing them for a long time and saw some of the difficult issues related to lead extractions. I know you have been involved in a lot of lead extractions as well.

Weiss: Yes, I am still doing them and I think one of the reasons why subcutaneous defibrillators were so successful is because they happened at a time when there were 2 big recalls on manufacturer leads. So at the same time, transvenous leads were getting a bad reputation.

Knight: What are some of the most difficult transvenous lead issues you have seen?

Weiss: Sometimes you get certain patients in which sensing is not good. Is that what you are referring to?

Knight: Yes, cases that you remember in which there were issues for patients related to transvenous leads.

Weiss: There are certain things that can happen. Sometimes patients have an occluded venous system and you need to dilate the vein, or you need to implant the defibrillator on the contralateral side because you run the risk of having pneumothorax when you try too many times to get access. I am talking about examples in the past, because we use different techniques now to get into the vein and we go to the contralateral side to the right side. You do not want to do it the same day because of the risk of bilateral pneumothorax, so we usually err on the side of caution and bring the patient back the following day.

Another example is vascular access in patients with renal failure, or patients with persistent left superior vena cava. These do not happen as often, but they do happen.

Knight: I think some of the biggest issues we saw were because the technology evolved over time and we did not have everything we needed at the beginning. I remember patients who needed dual-chamber pacing and needed a defibrillator. They would have a single-chamber ICD on one side and a dual-chamber pacemaker on the other side, and we had to worry about device-device interactions. But I think some of the most negative effects on patients were our need to successfully defibrillate. We do not do defibrillation testing very often anymore because the data has shown it is safe and effective. But for patients who failed DFT testing, we would then feel obligated to revise the system. I have a patient who has 2 transvenous right ventricular leads, 2 azygos vein leads for lowering defibrillation, an epicardial coil, epicardial pacing, rate-sensing leads, and a transvenous atrial lead. He ultimately got a heart transplant. However, with pacing and cardiac resynchronization therapy and then high DFTs, patients ended up with a lot of intravascular hardware.

Weiss: That patient is certainly not MRI compatible!

Knight: That is true! You and I were also involved in the early development of the subcutaneous ICD. You were the first author on the IDE trial, and I think that a lot of people in our generation that saw issues related to transvenous leads were big proponents of the subcutaneous ICD. Do you know when that was FDA approved?

Weiss: If I remember correctly, it was 2012.

Knight: September 2012! So, what are the advantages and disadvantages of the subcutaneous ICD now?

Weiss: The advantage is that it is totally extravascular. The device senses and defibrillates very well. I think that the disadvantages are that it does not pace, so for patients who may benefit from antitachycardia pacing (ATP), for example, or for patients who need bradycardia support, they do not have that. We also take the implantation technique for granted. How you implant the defibrillator is important, because that reflects on impedance. If you place the defibrillator too anteriorly or the lead too far to the left, you may have low impedance, but you will have quite a bit of energy shunting out of the heart. The other issue that is particular to the subcutaneous ICD is the T-wave oversensing. Even though we have the filter and we are smarter in how we program the device, we still have inappropriate shock, in particular due to T-wave oversensing.

Knight: Yes. The recent data would suggest that the inappropriate shock rate is far lower than it used to be, but it is still unfortunate when a young patient gets a shock with exercise, for example.

Weiss: Yes. It is quite equivalent to the transvenous ICD.

Knight: I think the other obstacle to widespread adoption is the size, particularly in thin patients. But I am a big proponent for this device in young patients. It avoids the long-term issues related to lead implantation. I am surprised it is not implanted more often in young patients. But we still encounter preauthorization denials from some insurance companies who consider it to be experimental. Despite the data that has been published showing it is comparable to a transvenous ICD, we still run into that. It is also true that physician reimbursements are not at the same level as a transvenous device. I would hate to think that is a factor when doctors and electrophysiologists consider implanting the subcutaneous ICD, but the reimbursement is lower than the transvenous device.

There was a concern that the charge times were going to be longer and we would have more patients with syncope, for example. But it turns out, based on all the data from transvenous devices, that waiting a long time to deliver a shock lowers both inappropriate and even appropriate shocks to let it terminate spontaneously. But another obstacle is just getting anesthesia or doing DFT testing. Can you tell me what you do at Ohio State for anesthesia? Are you still performing DFT testing?

Weiss: We use anesthesia for those cases. It does not need to be general anesthesia—it can be MAC anesthesia. We also use quite a bit of local anesthetic. There is a class I indication for DFT testing for the subcutaneous ICD, so I am doing it on almost every patient unless there is a contraindication. For example, a patient who was in atrial fibrillation and not taking his oral anticoagulation.

Knight: Yes, I think we routinely still do DFT testing with implant. But I think we learned over time that low impedances were predictive of success. Do you perform DFT testing during generator changes?

Weiss: Not on everyone, but yes I do it in some cases.

Knight: For some of the early implants, we were not putting the device as posteriorly and we were not putting them intramuscularly, so that is a good point. Sometimes I will even make the pocket a little more posterior when I do a generator change and then at least check the impedance.

Weiss: If the impedance is less than 95 ohms, the likelihood of success is 95% or higher. If on top of that, if you do a posteroanterior and lateral chest x-ray, and follow the PRAETORIAN score, you certainly get pretty close to the 95% or higher percentage.

Knight: Right, it becomes a practical issue. If the first shock does not work at 65J, it is not like the days where you could add a subcutaneous array and attach it to the device. So you could put the device more posteriorly perhaps, but you have to look at it from a practical standpoint.

Weiss: Yes. There are no tools to decrease, other than repositioning. You have only one pin in the header.

Knight: If we could get the size down with some other techniques, adding additional leads or some other tricks, different vectors, I think that would potentially help adoption of the subcutaneous ICD.

Weiss: Yes, I think there are 2 reasons at this point why people may shy away from it. One is tunneling—not everyone was trained with tunneling. The second one is DFT testing, which again, not everyone used to do down to failure.

Knight: Yes.

Weiss: Testing is becoming pretty easy to do.

Knight: What is the experience with the subcutaneous ICD in South America? Is it available?

Weiss: Yes, it is available in all countries. I believe adoption is low, though, and I think part of the reason may be because the subcutaneous ICD is more expensive than the transvenous ICD.

Knight: That is probably true. The extravascular with the substernal ICD lead study, sponsored by Medtronic, was just published in the New England Journal of Medicine, and we were fortunate enough to participate in that and I was on the steering committee. I have limited experience with implants. We only enrolled one patient, but I was very involved in the development of the lead and the technique to place it there. I think it is important to emphasize that that device during that trial was implanted by electrophysiologists who had extensive training, including cadaver training and animal training, and were scrubbed in with their surgeon to help them get access to the substernal space. Can you comment a little about what you think about that technology?

Weiss: I think we have done a few patients here, 4 patients were done in the pretrial—I was not involved. We would do the testing in the OR.

Knight: Right—you did acute testing, but not chronic implants.

Weiss: Yes. Which by the way, there is nothing wrong with that. I think the subcutaneous ICD was done the same way. There are a few good things about it. One of the things, as you alluded to, is that the device size is much smaller because now you are under the bone. So the energy requirement should be relatively less. One concern I may have is that now an infection may be a mediastinitis but I have not seen a significant problem, so maybe more a theoretical than practical consideration.

Knight: Like anything, there is going to be a risk of infection. These may be more difficult to manage, but it does seem to be feasible once you get under that substernal space—it is a lot of fat. So it is not very difficult if done properly with fluoroscopy to take a tunneling tool and place a lead, as long as you hug the back of the sternum and do not get too close to the right ventricle. It does require significantly lower defibrillation energy. And if there is not too much fat between the pericardium and sternum, then you can capture the heart to provide ATP and brady pacing.

Weiss: Yes, of course.

Knight: The big question is how many people, particularly recent graduates in EP, are going to be comfortable going in a space where we never have been before.

Weiss: It is another step that remains to be seen. As you mentioned, training is everything. If people are well trained and receive training by the manufacturer, it should be okay.

Knight: Yes. I remember in the late 1980s, I was a medical student at Ohio State University and I remember getting special-order ICDs that were custom made for individual patients and having to wait weeks for these to be delivered for epicardial implants.

Weiss: Yes, they were made in Pittsburgh. They were made on demand and sometimes patients would wait in the hospital 5 to 6 weeks to have their device delivered.

Knight: Things are better now! It is great to hear your experience with the evolution of the defibrillators over the past 30 years. Final comments or thoughts?

Weiss: Yes. We went from 1 wire on the transvenous to 2 wires and now to biventricular (BiV). With BiV, or left bundle branch area pacing, I have a little bit of concern about the pull back from the apex on the fibrillation. So if you implant in that area, it would probably be a good idea to test those patients, at least at the beginning. When you have a defibrillator that can provide therapy, you may be more inclined to use it in patients who are not as sick and they may have some benefit.

The last thing I will say is about the battery. I think battery life on the defibrillators used to be 3 or 4 years, and now we can get up to 17 or 18 years on a defibrillator. The reason for that is we do not call it “end of life” when 70% of the battery is used, because the last portion of the curve may be unpredictable. Now that you can get up to 90% of battery usage, as well as good software in the device, I believe that is why the longevity of the defibrillator is probably 4 times what it used to be when we first started implanting. It is really good.

Knight: I liked your comment about physiological pacing and your concern about taking the coil and not putting in the apex, because in the early days when we did a lot of defibrillation testing, how apical we were was really important to get successful defibrillation. Even companies would compete to get the coil a little closer to the tip to gain a few more millimeters. I think that if we start doing that, we will have to go back to some defibrillation testing.

Weiss: Yes, I agree. Well, as always, it is wonderful talking with you!

Knight: It is great talking with you, too! I want to remind everybody to join us on November 10th from 7:00 to 9:00 PM Eastern Time for another GDUEP.

Weiss: Thank you, Brad!

Editor’s Note: The transcripts have been edited for clarity and length.