Leadless Transcatheter Pacing Looks Good in the Short-term, But Long-term Questions Remain

ORLANDO, FL—The second major trial this year shows good safety and efficacy for a leadless intracardiac transcatheter pacing system in the short term, but some in the electrophysiology community worry about how long-term complications will be dealt with.

The leadless Micra transcatheter pacemaker (Medtronic) is similar in design to existing transvenous ventricular pacers, but is implanted transfemorally through a steerable catheter delivery system into the right ventricle and attaches to the myocardium with nitinol tines.

In a presentation at the American Heart Association Scientific Sessions 2015, Dwight Reynolds, MD, of the University of Oklahoma Health Sciences Center (Oklahoma City), described how his team followed 725 international patients indicated for ventricular pacing—719 (99.2%) were successfully implanted with the Micra device—for 6 months.

The study was simultaneously published in the New England Journal of Medicine.

Safe, Effective in Short-term

The device exceeded its 6-month safety performance goal of freedom from major complications (96% vs 83% in a historical control group; P < .001), and no dislodgements or systemic infections were reported. Major complications such as cardiac injury, puncture site complications, thromboembolism, and pacing issues were reported in 25 patients, including 4 of the 6 patients whose device implantation was unsuccessful. The device had to be turned off in 2 patients and retrieved in 1.

Among the 297 patients in the primary efficacy analysis, 98.3% had an adequate 6-month pacing capture threshold compared with the 80% performance goal, again based on historical controls (P < .001).

Compared with 2,667 historical controls who received transvenous pacemakers, the study patients were older and sicker. Despite this, those in the Micra group had fewer major complications than controls (HR 0.49; 95% CI 0.33-0.75). Micra-treated patients also had fewer hospitalizations and system revisions due to complications.

“The concept of transcatheter leadless pacing has been a vision for the past 35 years, and it looks as though we're finally getting it,” Reynolds said.

Highly Selected Patients

Discussing the trial, Sanjay Dixit, MD, of the University of Pennsylvania (Philadelphia, PA), cautioned that the patient population in the trial was highly selected, so the use of this new technology will not be available for everyone, at least for now. “All of these patients were typically the ones who were having single-chamber VVI pacing only, which is at the present time what this technology is capable of delivering because it is a single chamber pacemaker,” he said.

Also, despite the success of Micra compared with historical controls, Dixit noted, the 1.6% cardiac perforation rate “looks small” but seems “somewhat high” from anecdotal experience. Earlier presentations of the device had also shown that some patients develop transient complete heart block during implantation and sometimes require temporary pacing, he added, so extra precaution should be taken when treating patients with underlying left bundle branch block.

Finally, Dixit said, “in terms of the long-term performance of the device, one of the challenges is that we do not have any electrographic data that’s available from this particular platform.” Also, even though the device is rated to last for 12 years, he expressed concern over how to deal with a dead battery when the time comes.

Electrophysiologists vs Interventionalists?

Given the access route, some have speculated in the past that interventional cardiologists will be keen to move into this space. However, Suneet Mittal, MD, of Valley Hospital Health System (Ridgewood, NJ), told TCTMD that he does not think interventionalists will be “too interested in leadless pacemaker implants.”

At his institution, only electrophysiologists implant permanent pacemakers, Mittal said, and he expects the situation is similar at other hospitals.

But with regard to the observed 4% complication rate with Micra, he said it “needs to come down by at least 50%,” adding that the learning curve for managing the large introducer sheath used to implant the Micra might be at fault here.

Long-term Durability Unknown

With the combined data from this study and the LEADLESS trial published in April—which looked at the Nanostim rate-adaptive leadless cardiac pacemaker (St. Jude Medical)—leadless pacing has now been shown to be both safe and effective, and the results are “encouraging” in the short term, Mark S. Link, MD, of Tufts Medical Center (Boston, MA), writes in an accompanying editorial.

Long-term durability remains to be seen, and “there are other unanswered questions raised by these studies,” he says. For example, dealing with infection in patients could be difficult given that these devices cannot be easily removed. Also, Link says, “the rates of dislodgement of leadless devices over time are unknown and of potential concern.”

Even if long-term safety and efficacy are established, he concludes, “the current generation of leadless devices is unlikely to supplant traditional lead-containing transvenous pacemakers for most indications…. These leadless pacemakers will have limited usefulness in the treatment of the majority of pacemaker recipients, including patients with sinus-node dysfunction or heart block, and they will have no role in the treatment of patients with heart failure who need left-ventricular resynchronization to improve cardiac output.”

Sources: 
1. Reynolds D, Duray GZ, Omar R, et al. A leadless intracardiac transcatheter pacing system. N Engl J Med. 2015;Epub ahead of print.
2. Link MS. Achilles’ lead: will pacemakers break free [editorial]? N Engl J Med. 2015;Epub ahead of print.

Disclosures:

• The study was funded by Medtronic.
• Reynolds reports serving as a consultant for Medtronic.
• Mittal reports serving as a local PI in the study and receiving unrelated speaking fees from Medtronic.
• Link reports no relevant conflicts of interest.

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