Miniature Device Technologies: Creation and Design of the Micra™ Transcatheter Pacing System

Interview by Jodie Elrod
Interview by Jodie Elrod

Following Medtronic’s recent announcement of U.S. FDA 510(k) clearance, CE Mark approval and global launch of the Reveal LINQ Insertable Cardiac Monitor System, the smallest implantable cardiac monitoring device available for patients, Medtronic also announced the first U.S. implant of the world’s smallest pacemaker, the Micra Transcatheter Pacing System (TPS). This investigational device was successfully implanted at NYU Langone Medical Center in New York City as part of Medtronic’s global pivotal clinical trial. The Micra TPS is one-tenth the size of a conventional pacemaker and comparable in size to a large vitamin. In this interview we speak with Mike Hess, Vice President of Bradycardia R&D and the CRDM Division at Medtronic, about the creation of the Micra TPS seven years ago.

What were Medtronic’s primary goals in creating the Micra TPS? 

Pacing is such a mature therapy, and yet the fundamental way we deliver pacing hasn’t changed in decades despite advances in technology, so we recognized we could disrupt the market positively and give patients the same therapies they need right now, but in a less invasive way while also removing some of the known complications of these therapies. Starting with this new pacemaker made the most sense since it’s the simplest of our offerings, and it opened up the door for future and more complicated technologies down the road.

Tell us about your role in Medtronic’s “deep miniaturization” program as well as about the engineering team involved.  

I give most of the credit to our engineering team. We have a group of very talented, cross-functional engineers working on everything from the battery design to the circuits to the mechanical engineering of the device itself. They really worked with our Micra team as well as our LINQ implantable monitor team to take advantage of circuit design, low power consumption, and some of the microelectronics expertise we have to make these devices so small and yet maintain all of the functionality of devices they were replacing. It’s not a coincidence we have the Micra TPS and Reveal LINQ launching around the same time — they’re really “cousins” if you will in terms of programs that have been running together for quite a while.  

What are the components of the Micra TPS? How does it affix to the heart? 

The basic components are like other pacemakers — it has a battery, a circuit, and an electrode that attaches to the heart. However, there is also a novel fixation with tines, which are small nitinol wires which grip the heart, keeping the electrode in and hold the device in place. Normally there would be a pacing lead coming down from the chest area into the heart to do the same thing. The novelty with the Micra TPS is in the fixation in the nitinol tines that hold the device in place. 

How were the design features adjusted in order to accommodate for the smaller size and design? 

The biggest one was probably on the current drain in terms of making the circuit extremely efficient, so we could use the small battery and still have devices last ten years or more for most patients. Of course, the other feature was in recognizing this is not a lead-based device; we had to design a special fixation mechanism that would be appropriate for a capsule device as opposed to a traditional pacemaker.

Why was it important to offer an interchangeable positioning mechanism?

Currently when a pacemaker is implanted, the physician attaches the lead in the heart, and they make electrical measurements to determine if they are satisfied with that position. We know going into the procedure that the doctor will have the same potential to put the Micra TPS in place and decide they want better electrical performance so they will need to place it somewhere else. Therefore, we had to design it so you could pull the device back into the catheter, put it somewhere else in the ventricle, and try again. That is a typical flexibility you need during the implant to make sure you get the best measurement of the heart’s activity as well as low electrical thresholds.

How does the Micra TPS compare with other pacemakers currently available? 

From a functionality standpoint, the Micra TPS is essentially a fully functional replacement to our current pacemakers — it has the same cardiac ranges, the same automaticity, and the sensor to control the rate of patient activity — so all of the features currently available in a pacemaker are present in the Micra TPS.

How could the Micra TPS’s significantly smaller size impact patients as well as complication rates?

It’s premature right now to say for sure since the clinical trial is just beginning, but the concept is that we believe by having a more minimally invasive procedure, it may eliminate some of the sources of complication today. For example, regarding pocket discomfort, there should be less risk of infection with a device that doesn’t have a pocket. Also, by taking the lead out of the system – leads historically generate more complications — we’re trying to address the source of the complications. The clinical data will hopefully give us the answer we’re looking for, which is that we’ve done this successfully. 

In what ways do you think the Micra TPS will help cut costs? 

It partly relies on the elimination of complications; it’s well known that the fixing of device complications can be a very expensive procedure, very painful for the patient, as well as sometimes risky. So by eliminating the source of complications, we believe we can take those costs out of the system for a higher percentage of patients. We also think the procedure itself will be more efficient and faster, because it is inherently less invasive than what we do right now in creating a pocket and obtaining subclavian access. 

Tell us about the product development cycle for the Micra TPS. How did the timing of and collaboration on this design process compare with what might be considered a more conventional approach to product development?

There was a lot more physician interaction early on with the general concept, because the idea was so radical compared to what we do right now. There were some people who thought it was unnecessary to tackle this, since single-lead pacemakers are mature, low risk, and relatively fast procedures, so it’s really a high standard you’re trying to improve on. But as they thought more about the potential for this, especially down the road, they started getting more excited about it. We had a lot of different prototypes and concepts, different ways to attach to the heart, and different dimensions. The engineers took an in-depth systems approach to think about the procedure and how the device is implanted as well as how the device itself works. We’ve had many hands-on experiences with customers using it in a simulator or using it in a different preclinical model to give us feedback on the procedure, how the device was operating, and what functions we had to have in the device. Since it was a brand new concept, we were able to start with a clean slate and build up to what we wanted to have in the device instead of automatically starting with what was on the market and adding to that.

Do you think we’ll continue to see a trend in the miniaturization of implantable cardiac devices in the future? 

I think we will. We did it again with the Reveal LINQ monitor, which essentially is a full replacement for the insertable cardiac monitor but substantially smaller, and now we have the replacement of a traditional pacemaker with the Micra TPS. With ongoing technology advances, we have more options down the road for delivering more of these therapies with a minimally invasive approach. 

Is there anything else you’d like to add?


I think this is a good example of technology that will be beneficial for patients and customers, and will help set the course for innovation in this market.