First-in-Human Data Shows Medtronic's Leadless Pacemaker Safe Out to 90 Days

June 19, 2014

NICE, FRANCE — The numbers are small, the follow-up is short, and results are limited to device performance only, but European investigators are reporting that a second-in-its-class leadless pacemaker can be safely implanted in patients with permanent atrial fibrillation with bradycardia[1].

Investigators, led by Dr Clemens Steinwender (Linz General Hospital, Austria), presented their first-in-human experiences with the Micra Transcatheter Pacing System (Medtronic), a self-contained, leadless, single-chamber right ventricular (RV) pacemaker implanted into the apex of the right ventricle, here at CardioStim 2014 .

Just 7 mm wide, 26 mm long, and weighing 2 g, the leadless pacemaker was inserted successfully into four patients as part of a single-arm, multicenter clinical trial that will be conducted at more than 50 global centers. As part of the company's efforts to gain European CE Mark approval for the device, approximately 60 patients will receive the Micra leadless pacemaker and will be followed for three months. For US approval, the Food and Drug Administration (FDA)–mandated study will include as many as 600 patients followed for six months. To date, approximately 80 patients have been enrolled in the studies.

The studies are designed to determine whether the device is safe and that the pacing capture threshold is low and stable. "It's hoped that the leadless pacemaker would lead to fewer problems during implantation," said Steinwender. "In the chronic phase, it would be hoped to lead to fewer infections."

Things getting smaller and smaller . . .

Micra Transcatheter Pacing System [Source: Medtronic]

Speaking with heartwire , Steinwender said the leadless single-chamber RV pacemaker is designed to reduce surface area and limit the complications that develop with the leads. Overall, he said the miniaturization process, which includes getting rid of the leads, is a very good advance in pacemaker technology because the smaller the device is, the smaller its surface.

"Surface area is a critical point for bacteria and infection," he said. "If you compare a conventional pacemaker with its large surface, and the leads, which are made of polyurethane and silicone and develop fissures as they get older and older over the years, bacteria, which are always in the blood, can find a location to spread and to grow. That's why miniaturization makes sense for all permanently implanted devices."

The Micra leadless pacemaker is similar in concept to the Nanostim leadless cardiac pacemaker (St Jude Medical), another device that is further ahead in testing. The two pacemakers differ slightly in terms of how they are lodged into the myocardium of the RV apex, however.

In 2013, the Nanostim device gained regulatory approval and is now available for use in Europe. As reported by heartwire , one-year Nanostim data from two centers in Prague, Czech Republic, and one in Amsterdam, the Netherlands, showed acceptable pacing thresholds, impedances, and battery voltages, an average implantation procedure time of 28 minutes, and a freedom-from-complications rate of 94%.

The postapproval European study evaluating the Nanostim device was recently stopped, however, after there were reports of six perforations that led to two patient deaths. After meeting with regulatory authorities and clinical investigators, which led to tightening the inclusion criteria, St Jude Medical has since restarted the study, according to various media and financial analyst reports.

Great! But What If I Need to Take It Out?

At CardioStim, Steinwender presented data on his initial experiences with the Micra device, reporting that the device was successfully implanted into four patients without complications and the average procedure time was 43 minutes. The mean R-wave amplitude at implant was 11.98 mV, the mean pacing threshold at implant was 0.41 V at 0.24 ms, and the mean impedance at implant was 712 Ω.

Speaking the during session, moderator Dr Michael Gold (Medical University of South Carolina, Charleston) asked about the battery life and what would happen when it expires, an issue that is typically the first one on the mind of those commenting on the technology. The battery life ranges between seven and 15 years—Steinwender suspects it would be more than 10 years—and while it might be possible to extract the device once the battery does expire, this could prove difficult if the pacemaker has endothelized into the tissue. Steinwender believes a second leadless pacemaker would be added into the apex if the battery expires, or the patient could undergo conventional transvenous pacemaker implantation.

For this generation of the technology, especially since it is a single-chamber device, battery expiration might not be a major issue, given that patients who receive devices are approximately 80 years old. "This is connected to the inclusion criteria," he told heartwire . "The inclusion criteria are more or less atrial fibrillation with bradycardia, which is more common in older patients. The St Jude Nanostim and the Medtronic Micra are single-chamber pacemakers. This is the simplest form of pacing. For younger patients with atrioventricular block, you have to use two-chamber pacemakers."

He said that of all eligible pacemaker patients, approximately 10% would be candidates for the single-chamber leadless device. For the remaining 90% of patients getting a dual-chamber device, the average age is younger.

The Micra Transcatheter Pacing System study, which includes the trials aiming for European and American approval, are sponsored by Medtronic. St Jude sponsors the LEADLESS study.


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