Miniaturized, Leadless Pacemaker Impresses With Early Safety and Performance Data

May 16, 2015

BOSTON, MA — Early evidence supporting a new transcatheter leadless pacemaker—one the size of a large vitamin implanted into the apex of the right ventricle—was presented yesterday at the Heart Rhythm Society (HRS) 2015 Scientific Sessions, with investigators reporting the device met its primary end points for safety and performance[1].

Among 140 individuals enrolled in the Micra Transcatheter Pacing System (TPS) Study (Medtronic), the device was implanted successfully in every patient, with physicians achieving a successful deployment on the first attempt in 60% of patients. The overall rate of reported serious adverse events was 5.7%, with just 1.4% of patients experiencing an adverse event requiring prolonged hospitalization.

Speaking during the late-breaking clinical-trials session, lead investigator Dr Philippe Ritter (University Hospital, Bordeaux, France) said there were no unforeseen events, no migrations, no device telemetry issues, no dislodgements, no infections, no reoperations, and no related deaths.

"We can say from the data that we got that the system is safe," said Ritter.

The overall adverse-event rate, he added, is in line with conventional right-ventricular pacing devices implanted in similar patients. Regarding the electrical performance of the leadless pacemaker at 3 months, the pacing threshold was lower than the prespecified performance objective, leading investigators to conclude the device battery should last 10 years or longer.

"I've been involved in pacing for 30 years, and I've never seen such results with conventional leads," said Ritter. "The system is able to analyze quite properly the electrical signals in order to know whether the system has to pace or not." He added the system paces with low levels of energy—0.51 V at 0.24 ms in the TPS global study—so that the energy expended by the device was quite reduced. For the rest of the time, the implant is stable, he said.

Tiny, Just a Vitamin for the Right Ventricle

The leadless, single-chamber right-ventricular pacemaker is intended as an upgrade over current pacemakers with transvenous leads. These leads can become infected or dislodge and when they do need to be explanted. The small surface area of the Micra—just 7 mm wide, 26 mm long, and weighing 2 g—is also intended to reduce the risk for bacteria and infection.

Speaking with the media, Ritter said the leadless pacemaker, which has CE Mark approval in Europe, is his preferred device in eligible patients and is also preferred by other cardiologists and patients. In fact, the investigators of Micra TPS Study hadn't expected to complete enrollment until October 2015, but there was such a demand for the device that enrollment has already finished.

In his opinion, the Micra device is likely to completely replace single-chamber pacemakers.

"You have to be trained in catheterization and you have to be trained in pacing, but the system is not that difficult to implant," Ritter told heartwire from Medscape. While he said that surgeons, radiologists, and cardiologists all could be trained in implanting the leadless pacemaker, he'd prefer to see the system implanted by cardiologists, given the need to be proficient in catheterization and as well the need to understand the heart's electrophysiology.

Asked what would happen if the device needs to come out, Ritter said they have explanted the pacemaker at 28 months in animal models with good results. As for what happens a decade from now when the battery expires, there's the possibility a second device could be added to the apex, although Ritter said it's too early to speculate on what future technologies might be available at that point.

"Who knows what we'll implant in 10 years?" said Ritter. The technology, he added, moves "so fast."

The Micra leadless pacemaker is similar in concept to the Nanostim leadless cardiac pacemaker (St Jude Medical), another device that has CE Mark approval in Europe (neither the Micra nor Nanostim are approved in the US). The two pacemakers differ slightly in terms of how they are lodged into the myocardium of the right-ventricular apex. The Micra uses tines to grab hold of the myocardium and pace the heart through an electrode at the end of the device, whereas the Nanostim, figuratively speaking, is twisted/screwed into the muscle.

Ritter reports receiving consulting fees/honoraria from the Medtronic Bakken Research Center. Disclosures for the coauthors are listed in the abstract.

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