Six months after implantation with an investigational leadless intracardiac transcatheter pacing system from Medtronic, 96 percent of patients did not have system-related or procedure-related major complications, according to a prespecified interim analysis of a prospective, multicenter study presented on Nov. 9 at the American Heart Association (AHA) Scientific Sessions and simultaneously published online in the New England Journal of Medicine.

Further, 98.3 percent of the patients had a low and stable pacing capture threshold, and the device was successfully implanted in 99.2 percent of patients.

Each of the 725 patients was implanted with the Micra Transcatheter Pacemaker System, a single-chamber ventricular pacemaker that is not yet FDA-approved. Medtronic, the device’s manufacturer, expects to hear about an FDA approval during fiscal year 2017, which begins in May 2016. The Micra received a CE mark in Europe in April.

Medtronic funded the study, which is ongoing. Researchers will follow all of the patients for a year. Medtronic also plans on conducting long-term trials.

“We really feel as though the Micra answered the call both in its safety profile and its efficacy profile,” lead researcher Dwight Reynolds, MD, of Oklahoma University Medical Center, told Cardiovascular Business. “We’ve been talking about leadless devices, transcatheter deliverable devices, for 35 years. This has been a vision. We just haven’t had the technology to make it happen. Now we have the technology to make it happen. We’re all delighted with how Micra has answered this call.”

Each year, 350,000 patients in the U.S. are implanted with pacemakers, which have been around for more than 50 years.

The researchers enrolled patients at 56 centers in 19 countries who met class I or II guideline-based indications for pacing and were suitable candidates for single-chamber ventricular demand pacing. Patients were excluded if they had a pacemaker or implantable cardioverter-defibrillator.

Of the patients, 64 percent had bradycardia associated with persistent or permanent atrial tachyarrhythmia, 17.5 percent had sinus-node dysfunction and 14.8 percent had atrioventricular block.

Reynolds noted there were 28 major complications in 25 patients, including four of the patients who had unsuccessful implantation. The major complications included 11 cardiac injuries, five complications at the groin puncture site, two cases of thromboembolism, two pacing issues and eight other complications. There was one death.

The researchers also mentioned there were no radiographically visible device dislodgements, no telemetry failures and no systemic infections.

In a post hoc analysis, they compared the 725 patients in this study with 2,667 patients who received transvenous pacemakers in six previous trials. The patients who received the Micra transcatheter pacemaker were older and had more coexisting conditions compared with the transvenous pacemaker group.

After six months of follow-up, 4 percent of patients in the Micra transcatheter pacemaker group and 7.4 percent of patients in the transvenous pacemaker group had major complications. In addition, 2.3 percent and 3.9 percent of patients, respectively, were hospitalized and 0.4 percent and 3.5 percent, respectively, had system revisions due to complications.

Mark S. Link, MD, of Tufts Medical Center in Boston, wrote an accompanying editorial comparing the Micra transcatheter pacemaker with the Nanostim leadless pacemaker (St. Jude Medical), which is also not yet FDA-approved.

Link noted that major device-related complications occurred in 6.5 percent of patients who received the Nanostim device and 4 percent of patients who received the Micra device, while 1.6 percent and 1.5 percent of patients, respectively, had cardiac perforation or pericardial effusion.

“These two studies demonstrate that leadless pacing is feasible and relatively safe, at least in the short-term,” Link wrote. “Whether the long-term results will show that these devices remain safe and effective over time and that these leadless devices are as durable as transvenous pacemakers remains to be seen.”

Link also mentioned that removing an infected leadless device may be challenging and that it is uncertain if the battery will last more than 10 years. He added that the leadless pacemakers can currently only be used for single-chamber ventricular pacing and are not applicable for the majority of pacemaker recipients.

“In spite of these concerns, these two studies have encouraging short-term results that show the promise of leadless pacing; they are likely to generate substantial interest in leadless pacing and defibrillation technology,” Link wrote. “Importantly, the results of these studies suggest the potential value of the next generation of leadless devices, which will include atrial-based systems and left-ventricular resynchronization systems that are more widely applicable.”