• Micra complications were half that of standard pacemakers
  • Device is approved in Europe, under consideration in the U.S.

Medtronic Plc’s Micra, a pacemaker that is inserted inside the heart rather than attached to it with wires, was safely implanted and functioned successfully in a study of 725 patients, a finding that may help the device win U.S. regulatory approval.

Micra is designed to reduce complications from the wires, called leads, on a traditional pacemaker that can break, become infected or impede blood flow inside the 3 million people worldwide living with the devices that keep their hearts beating steadily. The company-funded study, presented at the American Heart Association’s annual meeting, found that device complications and resulting hospitalizations were more than 50 percent lower in Micra patients.

“What happens over time with traditional pacemaker systems is the body says these leads don’t belong here,” said Dwight Reynolds, the trial’s lead investigator and the cardiovascular chief at the University of Oklahoma Health Sciences Center. “The elimination of the leads goes a long way toward fixing some of the problems we have today. I have no doubt what we are seeing will translate into considerable health-care savings.”

The results are comparable to previous work with St. Jude Medical Inc.’s Nanostim, said Mark Link, of Tufts Medical Center’s cardiac arrhythmia service in Boston, in an editorial that accompanied the published article in the New England Journal of Medicine. Trials of the devices show that pacing without the wire leads is feasible and relatively safe in the short-term, though questions still remain, he wrote.

The Micra is a 10th the size of a conventional pacemaker and is inserted into the right ventricle of the heart via a catheter in the femoral vein. The ideal patient is one who had problems with pacemaker wires or infections that can develop around a traditional device that’s implanted in the chest, Reynolds said. About a third of the market is for devices like the Micra that pace just one of the heart’s four chambers.

The device was successfully implanted in 719 patients in the six-month study. The results were compared to 2,667 patients given a traditional device in six previous studies. Major complications including heart perforation, pacing problems and repeat procedures occurred in 25 patients, or 4 percent, about half the number seen with traditional pacemakers.

Promising Findings

There were no infections or dislodgements of the Micra during the study -- two of the most promising findings, Reynolds said. While most complications occur during the first months after a pacemaker is implanted, Micra patients may do even better long-term. There are no wires in the body to become infected or carry microbes to the heart from the blood stream, or that rest on top of the tricuspid valve where they can do damage.

The Micra won European clearance in April, and Minneapolis-based Medtronic submitted the study results to the U.S. Food and Drug Administration for approval this fall. In the study, the device paced 98 percent of patients appropriately, suggesting a battery life of more than a dozen years.

While infections in both studies were rare, they will eventually occur, Link said. It’s not clear how easy it will be to remove the devices at that point, and there is also continued risk of dislodgement and questions about battery life, he said.

“In spite of these concerns, these two studies have encouraging short-term results that show the promise of leadless pacing,” Link wrote. “They are likely to generate substantial interest in leadless pacing and defibrillation technology” and suggest the potential for the next generation of devices, he said.

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