Secrets Of Micra: How Medtronic Reinvented The Pacemaker

By Doug Roe, Chief Editor

I recently read that the term “disruption” is being overused by those who are describing more incremental or evolutional change, and I agree. But the concept, and required technology, of the Micra Transcatheter Pacing System (TPS) may end up in Webster’s Dictionary as a true example of disruptive innovation.

When it comes to implantable devices, smaller is usually better. But with Medtronic’s Micra TPS, smaller ­is groundbreaking. Since the introduction of the first implantable pacemaker in the late fifties, the race has been on to shrink it. But in nearly six decades, there have been only nominal improvements to pacemaker size. The challenges with size reduction include materials, electronics, and power supply. Today’s average pacemaker is the size of a tea bag and is connected to several feet of leads, electrical cables which connect it to the heart. On the other hand, the Micra shares similar dimensions with a large vitamin — that is one-tenth the standard size!

As opposed to traditional pacemakers, The Micra does not require a surgical incision in the chest for pocket placement, making it cosmetically invisible. There are also no attached leads to run. The miniature pacemaker is placed directly into the heart. Its small, capsulized form allows it to be implanted using a catheter through the femoral vein, similar to how a stent is inserted. The Micra uses small “tines” to attach inside of the heart.

I sat down with Mike Hess, VP, Bradycardia R&D CRHF Division at Medtronic, to discuss the origin and development of this device.

Med Device Online: What initial drivers led to the development and introduction of Micra?

Mike Hess: It has been a consistent effort for about seven years. We were looking at the opportunity to make pacemakers safer for the patient, easier to use for the physician, and to eliminate some of the potential complications that come with implantation. There have been a number of attempts to make a small pacemaker that could go on or in the heart. The idea has always been a neat little science project that would fizzle away because the technology was not mature enough to make it a real product.

[Medtronic’s] team began realizing that, by leveraging our company-wide technologies and therapies, we finally had the building blocks to make it feasible. Then, it was a matter of knocking out all the technology hurdles, one by one, to build confidence that we could actually build it.

MDO: What are the advantages of the miniaturized technology?

Hess: I think the reduced invasiveness of the implant procedure brings the biggest advantages. It eliminates so many sources of patient complications, and we saw this large complication reduction in our clinical trial. Also, patient comfort, cosmetic improvement, and overall patient satisfaction are big benefits. It helps, psychologically, not to have that physical bump. Patients don’t have that constant reminder under their skin, that they have a cardiac disease and that there is always something for them to watch out for.

MDO: How was this disruptive development team fostered inside Medtronic’s more traditional R&D group?

Hess: It started in an incubator-like environment to keep it protected from being overwhelmed by the mainline business, which is the biggest challenge with anything really new and disruptive in an established business.

At the time this project started, we had a dedicated R&D group that was working on more long-term, more risky projects. It was really incubated there. There was a fair amount of debate internally, early on: Is it really going to work? Is it a good idea? Should we stay the course and keep doing what we always do, or should we pursue this new approach?

I think, over time, as more of the questions were answered and more proof of concepts were developed — from the original plastic slug with paper clips we used to visualize what it would look like, to the real products being placed in animals and working — internal enthusiasm started to build. Also, once our customers got excited by seeing the early prototypes, we really started getting a lot of momentum.

MDO: Was it championed by upper management, driven by the science down low, or some combination of both?

Hess: There was debate at multiple levels. At the business level, this is a pacemaker like other pacemakers. So the question was, is it really going to add to the market and be substantially better? From the technical perspective, it is going to do things very differently, which generates questions about the physiology and the performance of the device. We had all the healthy debate you want to have for such a disruptive product, happening at multiple functional and department levels.

MDO: What core competencies comprised that innovation team?

Hess: They had pretty much the same engineering disciplines we see on other teams. There was more focus on the procedures and the physiology of this novel technology, compared to our incrementally developed products, which have been proven for a long time. How do you test something like this? How do you deliver and place it? Those questions led us to do a lot of additional work in the animal models.

As for the device itself, the mechanical and electrical engineering, the materials science, and the integrated circuit design were performed by people that were essentially pulled from projects in other areas. The big difference was that they were all concentrated in one very small project team.

It was a good example of collaboration across different facilities and different organizations. Several facilities in Europe and several in the United States, with different responsibilities and different parts of the puzzle, were all working together. It was more complicated, in that respect, than a traditional pacemaker project.

MDO: Were there any other discernible changes in the overall approach of the design process?

Hess: The biggest area of additional emphasis was the extra focus on animal models and the additional procedures. We had to develop some new models because we were not satisfied that what we had used in the past was going to work well for this product.

We had hundreds of physicians come in to do hands-on testing, , try procedures, and then give us feedback. Those were the same physicians that have given us feedback on traditional pacemakers for a long time. That was a key question for us: “Will our existing customers accept and embrace this new product and approach?”

MDO: Did Medtronic’s growing global footprint play a role in the product development plan?

Hess: It did not affect the development too much, but it definitely affected the clinical and regulatory strategy. This was probably the most global pre-market study we had ever done. We had centers in the United States and Western Europe, as we almost always do. We also had centers in Canada, China, India, Malaysia, Australia, and Japan.

We often don’t involve some of those countries in the early phase regulatory work. We usually bring them the clinical results from the U.S. and Western Europe, but we felt — this being a different procedure and a different project — those countries would want some local evidence as part of the global evidence story.

It was a very broad approach to the clinical study, driven by a desire to see this eventually get accepted in all these markets around the world.

MDO: What were the engineering challenges related to this device?

Hess: The two biggest challenges were electrical current drain and fixation. On the current drain side, to make that small battery last as long as possible, the team took on some very advanced microelectronic designs and reduced the drain of the integrated circuit to one-tenth that of a traditional device, which helped with the battery longevity goal.  

The electrode is a novel design in that you have an atraumatic contact with the tip of the electrode of the Micra and the heart. The fixation is somewhat distanced from that, so we don’t traumatize the tissue around the electrode. Minimum tissue trauma improves the interface. That led to extremely low power use thresholds, giving the device longevity of over 12 years for most patients. That was probably one of the largest challenges, making sure the device used as little energy as possible, yet still successfully paced the heart.

Next, we know how pacing leads attach to the heart, but they are also attached to a pacemaker, so they are not going to go anywhere if they dislodge. We didn’t feel that the fixation approach of pacing leads was appropriate for this kind of device. We envisioned a novel approach, where the device could extend small tines to hold the device securely to the heart, but not have a risk that the device could turn or unscrew, for example, and lose that fixation mechanism.  We also wanted the implant procedure to be as simple as possible, requiring less manipulation by the implanter.

On the material side, we brought nitinol (nickel-titanium alloy) into the pacemaker product line for the first time.  We were able to apply the nitinol expertise and usage experience from Medtronic’s other cardiac business units — particularly its shape memory and temperature-controlled properties — to the tines we designed that hold the Micra in place.

It is, to my knowledge, the first cardio rhythm device that uses this kind of fixation, and we have been very satisfied with the clinical performance of the fixation so far. There have been no dislodgements.

MDO: What were some of the technological leaps with the electronic components, compared to those on the conventional-size pacemaker?

Hess: It was a very challenging circuit design, reducing both the electrical current drain and the physical size. The engineers had to find many new components that were smaller and more efficient than what we use in regular devices.

We were developing the Reveal LINQ Insertable Cardiac Monitoring System at the same time as Micra, so there was some co-development going on.  We were looking at parts that could be used across our whole miniaturization portfolio. That collaboration gave us a resource advantage.

But, there are no substantial differences in the basic types of materials we are using inside this device, compared to what we would use in a regular device.

MDO: What are the short- and long-term plans to integrate this platform to maximize its functionality with connected health?

Hess: In the short term, Micra Patients can be monitored through the CareLink network, like any other pacemaker user. Micra uses the same telemetry, the same communication protocols to our programmers and monitors. We are moving more into the smart technology and app space, with things like MyCareLink Smart, where we are trying to create an interface that allows the patient to better interact with the device and to share information over time.  

Longer-term, I think that is a broader discussion. The design cycle, for anything that the patient is going to interact with, needs to be dramatically different. We have to benchmark ourselves against the consumer world. Rather than predicating devices on the more controlled healthcare environment that doctors and nurses interact with, we must ask, what challenges will patients and their devices deal with, in their own environment, in the future?

MDO: Where do you see the next breakthrough in miniaturized implantables?

Hess: I think, in the cardiac rhythm space, the biggest question we get when people see Micra is, “When can we have a version that treats more patients?” I think a dual-chamber pacemaker is likely going to be the next area of focus.

It’s a substantial technology challenge. How can you provide a system like this that would be a first-line option not only for a subgroup of the patients, but for any pacemaker patient? That will reset the expectations for what a pacemaker can do, decreasing complications while improving patient cosmetics and quality of life. That will be pretty dramatic.

MDO: Do you see that as a long-term development?

Hess: I think it’s going to be a journey. I don’t think it is going to be a situation where you flip a switch and suddenly you have a solution for everyone. We are going to step into it over time, and we will be able to address more patients with each step. I think it is a long-term transition to a new paradigm, and Micra is the first major step in that direction.