Medtronic’s Micra pacemakers are one-tenth the size of what was previously out there. How the medtech giant did it provides lessons for anyone looking to shrink an implantable device.It was an all-hands-on-deck effort that consumed Medtronic in the early 2010s: the in-house creation of a pacemaker small enough to go inside the heart via a catheter.
The tiny pacemaker could be a game-changer because it would do away with connecting wires to the heart — a major source of complications. To get there, though, the Medtronic development team had to solve significant challenges involving battery life and energy use. How could they create a pacemaker that was roughly one-tenth the size of a traditional pacemaker but still last at least seven years inside someone?
“It would be like taking your car and reducing the size of the tank by a factor of 10 — and now asking this same car to go the same amount of distance,” Leonardo Rapallini told Medical Design & Outsourcing in a recent interview. Now VP of R&D for Medtronic’s cardiac diagnostics and services business, Rapallini was the Micra effort’s senior program director for nearly five years.
Rapallini and his colleagues solved the challenge — and more as they boosted device longevity to 12 years for many patients. FDA initially approved the Micra in 2016. Last year, it approved the next-gen Micra AV that uses additional internal atrial sensing algorithms to provide therapies associated with dual-chamber pacing systems. During a May earnings call, CEO Geoff Martha announced that Micra has quickly grown into a $400-million-a-year business.
Here are three insights that Rapallini gained from the Micra’s creation:
1. Keep the whole system in mind
“We obviously couldn’t only think about the battery in isolation. We also had to think, ‘How do we make sure that we use the energy that we have in that battery as smartly as possible?'” Rapallini said. “It was pretty clear from the beginning that we couldn’t have a team just building the battery in isolation from the team that was building the electronics and then put them together.”
The core team that Rapallini led had representatives from all the different areas of expertise needed to put the Micra system together versus the previous approach of different groups working on various components.
Rapallini credits the setup with enabling his team to think of the whole system at once as it considered potential efficiencies. They asked about making the Micra’s electronics more efficient. They examined how they might better position the device in the heart to use the least amount of energy, and they considered battery design improvements.
Said Rapallini: “Take a system view first because the whole thing needs to work together.”
2. Be picky about what you change
The Micra’s creators needed to push the envelope to enable the device’s battery and electronics to last for years. However, they intentionally kept some things the same.
The Micra battery’s chemistry, for example, was a proven variation of a lithium-ion. “What we had is something we had a lot of knowledge of, and we knew that it was a really stable battery. We could guarantee that it would last long.”
The electrode — the part of the device that stays in contact with the heart — was a proven component from another catheter-based device.
What Rapallini and his team chose to radically change was the battery’s form factor. Instead of the battery being a wafer-shaped component that went inside the pacemaker’s “can,” the can itself became the battery’s container.
The lesson is that it’s best to quickly decide where to push the envelope — and where not to innovate, according to Rapallini. “You probably cannot change everything at the same time.”
Changing everything adds too much risk, Rapallini said. “The Micra is a combination of incredible innovations — and also portions of the system that are really proven.”
3. Understand the use condition
As the Micra moved into clinical studies, its creators gained another vital insight, that the majority of the patients only needed pacing part of the time. “That obviously saves a lot of energy,” Rapallini said.
Patients who only needed occasional pacing could see the Micra last more than 12 years — well past the original seven-year goal.
Medtronic could have added even more battery life to the Micra by making it longer. However, the Micra team still opted to make the device shorter compared with the Nanostim pacemaker that St. Jude Medical acquired, according to Rapallini. (St. Jude Medical, now part of Abbott, halted Nanostim implants in 2016 over potential battery problems.)
The decision to go shorter — even if it made the battery life challenge tougher — was based on an analysis of the range of heart sizes out there. The Micra simply had to be shorter to accommodate a broader range of heart anatomies, Rapallini and his colleagues decided.
“Try to really understand the use condition in which this device will be used.”