Patrice Wendling

May 12, 2017

CHICAGO, IL — Bucking the norm, the Micra transcatheter pacing system (Medtronic) appears to be performing better in the real-world setting than in the trial that led to its approval[1].

The implant success rate in the Micra postapproval registry was 99.6% among 149 experienced operators, 86.6% of whom were new Micra implanters.

The median introducer-in to introducer-out time was a brief 25 minutes.

At 30 days, major complications were seen in 1.51% of patients compared with 2.89% using the same definition of major complications in the Micra Investigational Device Exemption (IDE) trial (adjusted odds ratio 0.59, 95% CI 0.27–1.27; P=0.18).

The data were reported at the Heart Rhythm Society (HRS) Scientific Sessions 2017 and simultaneously published in Heart Rhythm.

The leadless pacemaker was approved in April 2016, and a key issue in the minds of many cardiologists was the rate of pericardial effusion/perforation, which was cut down from 1.6% in IDE to 0.13%, possibly because more operators in the postapproval setting opted for septal placement.

"With such a delivery system and device, the risk of perforation obviously could be higher if you place it at the apex, and if you look at the Micra IDE study, 66% of pacemakers were placed at the apex vs here only 40%, so that could explain the lower rate of pericardial effusion," lead author Dr Mikhael El-Chami (Emory University, Atlanta, GA) said during a late-breaking clinical-trial session.

In all, there were five pericardial events, of which three required no intervention and only one of the two requiring pericardiocentesis met the definition of a major complication. All five patients had at least one risk factor: advanced age (>75 years), female sex, low BMI (<20 kg/m2), and chronic obstructive pulmonary disease, he said.

There was one device dislodgement and one infection treated with IV antibiotics that did not require device removal.

Of the 22 deaths that occurred within 6 months of implant, one death (pulmonary edema related to aortic-valve disease) was adjudicated as related to the Micra procedure, El-Chami said. None were related to the device itself.

Speaking to heartwire from Medscape, HRS president Dr Michael Gold (Medical University of South Carolina, Charleston) said, "I think it's exciting new technology and really again gives us more flexibility in how to treat patients and avoid leads, which is the big issue for the subcutaneous ICD and for the Micra."

He noted that development is under way combining the two technologies to have a leadless pacemaker communicating with a subcutaneous defibrillator. "In my mind that will be the future of our devices."

During a press conference on the study, Dr Matthew Reynolds (Lahey Hospital and Medical Center, Burlington, MA) pointed out that Micra was approved without a randomized controlled trial and that the postapproval registry represents a larger, more diverse population than in the IDE trial.

"There's sometimes the assumption that when new technology moves out in the community that the results won't be as good; I would certainly question that assumption, and these data actually went the other direction," he said.

Dr Thomas Deering (Piedmont Heart Institute, Atlanta, GA) told reporters the results speak to the universality of Micra's usage but also cautioned that the pacemaker is not relevant for all patients such as those at high risk of heart block over time.

"I think there are populations in whom it would be beneficial, others in whom it would not be beneficial," he added.

Of the 795 patients in the registry, 67% had atrial fibrillation. Almost one in five had a condition that precluded use of a typical transvenous pacemaker, and nearly 15% had a preexisting device that was abandoned or removed, largely due to infection.

Early Safety Results

30-d event rate
Postmarket registry, n=795 (%)
IDE trial, n=726 (%)
Odds ratio (95% CI)
Total major complications 1.51 2.89 0.59 (0.27–1.27)
Death 0.13 0.14 0.91 (0.03–14.66)
Hospitalization 0.50 1.10 0.45 (0.14–1.51)
Prolonged hospitalization 1.01 1.93 0.52 (0.22–1.24)
System revision 0.25 0.41 0.61 (0.10–3.65)
Loss of device function 0 0.28 Not estimable

"While the acute results are encouraging, it's very important to look at the longer-term results; does this safety remain when we follow these patients for a year or two or three? This is the biggest question, and this registry is designed to follow patients up to nine years after implant," El-Chami said in an interview.

El-Chami reports compensation for services to Boston Scientific and Medtronic and research grants from Medtronic. Disclosures for the coauthors are listed in the paper. Reynolds reports compensation for services to Biosense Webster, Sanofi, Medtronic, and St Jude Medical (now Abbott). Deering reports serving as a speaker for Boston Scientific; recently divesting an equity interest in CorMatrix and Zywie; research funding to his institution from CorMatrix, Spectranetics, Sorin Group, Boston Scientific, Medtronic, and St Jude Medical; and other compensation from Medtronic and Boston Scientific. Gold reports compensation for services to and research grants from Boston Scientific, Medtronic, and St Jude Medical (now Abbott).

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