COMMENTARY

New Leads on Leadless Pacemakers and SubQ ICDs

Jeffrey Geske, MD; Paul Friedman, MD

Disclosures

May 04, 2016

Editorial Collaboration

Medscape &

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Dr Jeffrey B. Geske, MD: Greetings. I'm Dr Jeffrey Geske, cardiologist and assistant professor of medicine at Mayo Clinic. During today's Trending Topic recording, we'll be discussing new devices for arrhythmia management, specifically leadless pacemakers, with Dr Paul Friedman, professor of medicine and electrophysiology specialist here at Mayo Clinic. Greetings, Paul.

Dr Paul Friedman, MD: Jeff, great to be here.

Dr Geske: Well, I am excited to talk about today's topic with you. As you know, you're my go-to person when we have an interesting case or are looking for a novel solution, and I'd like to learn a little bit more about need for leadless pacemakers.

Leadless Pacemakers: The Basics

Dr Friedman: Sure. As you know, pacemakers are used to treat bradycardias with symptoms, and they're extremely effective. But over the years, we've identified a number of potential complications. The first is that there's a surgical pocket, and that pocket can develop a hematoma or can become infected—and of course, it's a wound that requires management.

Second, the lead is a foreign body that travels through a vein, across a valve, to the heart, and that lead can become infected. It can dislodge. It can erode. It can cause thrombus in vessels. Our own data suggest that, in patients who have a [patent foramen ovale] PFO, there's an increased risk of stroke over years because thrombi may form on those leads and then go flying paradoxically and affect the brain or other organs.[1,2] So for those reasons, there's been an increasing interest in finding a way to pace the heart without a lead traversing through the vasculature. A leadless pacemaker is just that.

Dr Geske: Paul, tell me a little bit about these leadless pacemakers. How long do they last, and are you able to take them out or revise them?

Dr Friedman: The battery life will, typically, be somewhere between 8 to 10 years. That's what's projected. It depends on how much they're pacing. It could even be a little longer. They are designed to be removable. There is a little hub at the back. There's a special tool that lets you go in and essentially lasso it, dock to it, and then remove it, either by unscrewing it (in the one that's active fixation) or covering the tines and pulling it out. Human experience in removal is limited to a couple of years. So we don't really have good long-term data about removability, and that's one of the unknowns at this time.

Differences From Subcutaneous Defibrillators

Dr Geske: I know there have been a lot of changes in device management, and one of the things that I've come across is that of a subcutaneous defibrillator. How does a leadless pacemaker differ from a subcutaneous defibrillator?

Dr Friedman: Great question. The leadless pacemaker, as we saw, is a small bulletlike metal object that is entirely within the heart that it paces. The subcutaneous defibrillator has no vascular leads, like a leadless pacemaker; and in fact, it has nothing touching the vasculature. The entire defibrillator sits near the left axilla, and it does have a lead on the outside of the ribcage where it senses far-field signals. If it detects [ventricular tachycardia] VT or [ventricular fibrillation] VF, it can give a shock and defibrillate the heart. It can very briefly pace for up to 30 seconds after a shock to treat postshock bradycardia, but it often will stimulate pectoralis and other muscles with pacing. So, it's not a viable long-term pacemaker.

In fact, while the two technologies are very different, it's envisioned that, in the future, they may be used together. So, if there's a patient who needs defibrillation and needs pacing, you could address both needs with a leadless pacemaker, providing the antibradycardia support—potentially antitachycardia pacing support—and the defibrillator, of course, to defibrillate when needed.

Who Should Get a Leadless Pacemaker Now?

Dr Geske: Well, that sounds like a great future target, but who would you envision getting a leadless pacemaker now?

Dr Friedman: Currently, the leadless pacemakers are VVIR. They do have rate response. The two different models use different modalities. One looks at changes in temperature, because when we exercise and breathe harder, there's a change in blood temperature, and it uses that to increase the heart rate. The other one has an accelerometer, and it demodulates cardiac motion to determine overall body motion so that it can then activate the heart rate based on physical activity.

But as I mentioned, they are VVIR. Currently, VVIR pacemakers are used in about 10% to 15% of people who need pacemakers: patients who have chronic atrial fibrillation who will never need an atrial lead; patients who need very infrequent pacing and don't need atrial ventricular synchrony.

Two trials have just been published on the device in the New England Journal of Medicine. One trial included 525 patients[3]; the other included 725 patients.[4] Essentially, those were patients who had a VVIR indication for pacing. The Nanostim study of the active fixation device excluded patients with recent cardiac surgery or pulmonary arterial hypertension.[3] The devices are approved in Europe. In the United States, it's still part of a protocol [Editor's Note: since this discussion was recorded the Micra Transcatheter Pacing System has been FDA approved.

Dr Geske: What insights have we learned about these devices?

Dr Friedman: First, the question that comes up is: How do they fare compared with standard devices for complications? And the short answer is: Favorably. They actually had, on average, fewer complications. The rate of dislodgement was essentially similar to historical controls, 0% to 1.5%, depending on the study you look at. The risk of perforation is also similar, about 1.5%. Obviously, the leadless pacemaker, because there's no pocket, has no hematoma, no pneumothorax. We're not putting needles near the lung apices.

We don't have long-term follow-up, of course, and it's important to remember that the historical controls were often dual-chamber pacemakers. So they may have had a slightly higher risk because there's an atrial lead, although any complication that was clearly attributable to the atrial lead was excluded in the analysis.

What's Ahead in Devices?

Dr Geske: Well, where do we go from here? What do you see in the future? As we look at the information that we've learned from these recent trials, as we look at the technology that we have, what's the next step?

Dr Friedman: First, as we mentioned, combining leadless pacemakers with subcutaneous defibrillators will almost certainly happen over the next few years. The next big goal is dual-chamber pacing. That's a little trickier. You now have two devices to deploy. The atrium is a smaller, thin-walled chamber. So there will have to be some design changes, and there will need to be a form of communication between the two devices so that they can coordinate their pacing activity. Nonetheless, that should probably come out over the next couple of years.

Beyond that, there's the question of cardiac resynchronization therapy. It may include a current leadless pacemaker, as we see, deployed in the [left ventricle] LV. Questions there about thrombogenicity need to be addressed. The other possibility is if there's some early human data using ultrasound-triggered seeds. A tiny seed is placed in the LV endocardium—it's very small—and then a subcutaneous device delivers an ultrasound beam to activate it. The ultrasound is converted by this passive element into electrical energy, which then paces the heart. A lot of exciting technology is on the horizon.

Dr Geske: Wow, that sounds fantastic. Thank you so much for joining us here today. Paul, it's been a pleasure speaking with you. And thanks to all our viewers for joining us at theheart.org on Medscape.

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