Medical device maker Medtronic, which commercialized the world's first battery-powered pacemakers more than 60 years ago, just won approval for a new minimally invasive pacer that can tell whether the heart's upper chamber is beating without touching it.
The Micra AV, approved by the U.S. Food and Drug Administration on Jan. 21, is an innovation wrapped in an innovation. The original version of the device approved several years ago was so small it could be delivered through the blood vessels and attached to the heart without lead wires, eliminating the sources of most complications in traditional devices that maintain a regular heartbeat.
The newly approved Micra AV looks exactly the same on the outside: like a metal vitamin pill with four small hooks on one end. But the new device comes with a sensitive instrument called an accelerometer and a special algorithm designed to allow the device to sense whether the upper heart chamber is beating, even though the device is implanted in the lower chamber.
As a result, the Micra AV is applicable to a much wider pool of patients than the original, spurring hope among the device's proponents that the tiny device will finally make its mark on the pacemaker market, though questions linger in the medical community about who is the ideal patient to get one of these capsule-sized pacemakers.
Medtronic continues to look for ways to improve the Micra, while major competitors including Boston Scientific, Abbott Laboratories and Biotronik have all confirmed working on similar "leadless" pacemakers that don't use wires to touch the heart.
Medtronic declined to release pricing information on the Micra, the only leadless pacer approved in the U.S. Worldwide, Medtronic and its competitors sold about $6 billion worth of implantable pacemakers in 2017, according to research from Coherent Market Insights.
"We're just at the beginning of the development of leadless technology, and I think this is the future of cardiac pacing," said New York City electrophysiologist Dr. Larry Chinitz, co-principal investigator for the Medtronic study that led to the Micra AV's U.S. approval, and a consultant to Medtronic and other device makers. "But it is still a little bit early in the development. Micra AV is a really phenomenal start."
About 200,000 Americans have permanent pacemakers implanted every year to monitor their hearts and deliver mild electric pulses to speed up a slow heart beat. All such implants run on non-rechargeable batteries that last for about 10 to 15 years, depending on how they are programmed.
A traditional pacemaker includes a silver-dollar-sized pulse generator implanted in a "pocket" of tissue near the shoulder, and one or more insulated wires called leads that are strung through the blood vessels and attached permanently to the inner surface of the heart.
Though the devices are considered safe, about 1 in 8 patients experiences a problem related to the pocket or leads, like dislodgment or infection, according to a January report in the Journal of the American College of Cardiology.
Leadless pacemakers like the Micra are designed to avoid such complications. Such devices attach directly to the heart, avoiding the need for lead wires and pocket, and they are implanted using a thin catheter inserted through blood vessels, avoiding a chest incision. Micra implants are typically performed in an outpatient procedure.
Florida resident Stephen Combs, 43, said he had his Micra implanted in 2015 in a same-day procedure after blacking out from poor blood circulation. Compared to other people he knows with traditional pacemakers, Combs said he doesn't have any limitations on daily activities: "I had the device put in on a Thursday, and by Tuesday I was back in the gym running on a treadmill," he said. "It has completely cut out the blackouts and dizzy spells."
A 2018 study in Heart Rhythm examined 1,817 implants of the original Micra device outside of clinical trials and found that patients had a 99% implant-success rate and a 2.7% complication rate after 12 months. That's a 63% reduction in complications compared to traditional devices, the study reported.
"So why hasn't Micra taken over the entire pacing population?" said Minneapolis electrophysiologist Dr. William Katsiyiannis, chairman of cardiology at the Minneapolis Heart Institute. The biggest challenge to the original Micra was that it only worked for people who needed pacing in a single heart chamber, right ventricle. "That serves a minority of the patients that need pacemakers," he said.
As a "single-chamber" device, the original Micra only worked for about 15% of pacemaker patients. The Micra AV is applicable to at least 55% of pacemaker patients because it can sense the pumping activity of the upper chamber, allowing it to accurately synchronize the beating of the lower ventricle and optimize blood flow.
Dr. Rob Kowal, chief medical officer for Medtronic's heart-rhythm division, explained that the Micra AV senses activity in the atrium without touching it by analyzing subtleties in how the device moves in space. Motion is recorded on a three-axis accelerometer similar to those in smartphones and exercise trackers, and analyzed by an algorithm that filters out the "noise" to figure out when the atrium is contracting.
Inferring atrial activity from accelerometer readings conserves battery life, compared to proposals to put a second sensor in the atrium, Kowal said.
That's an important consideration since Micra devices won't be easy to remove after their decade or so of expected battery life. Chinitz said techniques for clean extractions are still under development, but physicians also have the option of implanting a second Micra next to the first one. The average patient who got a single-chamber Micra in Medtronic's analysis of real-world use was 76 years old.
A second consideration is that even with the Micra AV, patients didn't have perfect synchronization of atrial and ventricular contractions. The trial that led to Micra AV's approval found that 95% of the 40 patients with impaired communication between their atria and ventricles achieved "AV synchronous pacing" at least 70% of the time during testing.
"I think the [medical] community is going to say that's really remarkable," the Heart Institute's Katsiyiannis said. "It's an advancement. But it's still going to be an issue until that's 100%."
Joe Carlson • 612-673-4779
