American Heart Association

American Heart Association

November 18, 2015
2 min read

Miniature leadless pacemaker meets safety, efficacy goals at 6 months

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ORLANDO, Fla. — A miniaturized leadless transcatheter pacing system met 6-month safety performance goals and efficacy endpoints, according to findings presented at the American Heart Association Scientific Sessions.

Researchers implanted the transcatheter intracardiac pacemaker (Micra, Medtronic) in 725 patients (mean age, 76 years; 59% men) with guideline-based indications for ventricular pacing and began the present analysis when 300 patients reached 6-month follow-up.

The aim is to reduce complications, which occur in approximately one of eight people implanted with a conventional pacemaker and are often related to the leads, Dwight Reynolds, MD, from the cardiovascular section, OU Medical Center, University of Oklahoma Health Sciences Center, Oklahoma City, said during a presentation.

“Most of the problems that we have with pacing today relate to the lead, to the device pocket and to venous access,” Reynolds said. “Transcatheter pacing systems are specifically designed to address these problems.”

The primary safety endpoint was freedom from major complications related to the system or the procedure. The primary efficacy endpoint was percentage of patients with low and stable pacing capture thresholds, defined as up to 2 V at a pulse width of 0.24 ms and an increase of up to 1.5 V from baseline. The researchers evaluated the endpoints based on historical performance goals of 83% for the safety parameters and 80% for the efficacy parameters. They also performed a post-hoc analysis comparing major complication rates to those observed in a cohort of 2,667 patients from six studies implanted with transvenous pacemakers.

According to results presented, the implantation success rate was 99.2%, with only six patients unable to receive a successfully implanted device.

The Kaplan-Meier estimate of the rate of the primary safety endpoint was 96% (95% CI, 93.9-97.3; P < .001 compared with safety performance goal), and the rate of the primary efficacy endpoint was 98.3% (95% CI, 96.1-99.5; P < .001 compared with efficacy performance goal).

Reynolds reported that 25 patients experienced 28 major complications, including one death from metabolic acidosis, but the risk was much lower than that of the transvenous pacemaker control cohort (HR = 0.49; 95% CI, 0.33-0.75). Propensity matching to a subset of the control group did not change the results (HR = 0.46; 95% CI, 0.28-0.74).

The lower risk occurred despite those receiving the leadless pacemaker being older and more likely to have hypertension, atrial fibrillation, valvular disease, diabetes, CAD and chronic obstructive pulmonary disease (COPD) than those receiving transvenous pacemakers (P = .001 for COPD; P < .001 for all others), Reynolds said.

The reduction in complications was consistent across subgroups, with trends for better results in patients without congestive HF vs. with it (P = .0828) and in patients without valvular disease vs. with it (P = .0582), he said.

Compared with controls, patients implanted with the leadless pacemaker had a 51% RR reduction for major complications, a 54% RR reduction for hospitalization and an 87% RR reduction for system revision, according to the results.

Mean pacing capture threshold for the leadless pacemaker was 0.63 V at 0.24 ms at implant and 0.54 V at 0.24 ms at 6 months, according to the researchers, who estimated median battery longevity as 12.5 years.

Mean R-wave amplitude was 11.2 mV at implant and 15.3 mV at 6 months, whereas mean pacing impedance was 724 ohm at implant and 627 ohm at 6 months.

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


Reynolds D, et al. CS.02: Cutting Edge Technologies in EP. Presented at: American Heart Association Scientific Sessions; Nov. 7-11, 2015; Orlando, Fla.

Reynolds D, et al. N Engl J Med. 2015;doi:10.1056/NEJMoa1511643.

Disclosure: The study was funded by Medtronic. Reynolds reports consulting for Medtronic. See the full study for a list of the other authors’ relevant financial disclosures.