A Leadless Intracardiac Transcatheter Pacing System

Joseph Phan, Mercer University College of Pharmacy

It is reported that approximately one in eight patients with pacing systems have an early complication frequently related to the leads or to the subcutaneous pocket needed for current pacemakers. [1]  These complications can include hematomas, infections, pneumothoraxes, lead dislodgements, and lead/pacemaker integrity problems.

Advances in battery chemistry and component design have allowed for pacemakers that are now small enough to place within the heart.  A recently published study details the performance of a self-contained pacemaker that has been designed to avoid the need for a subcutaneous pocket and transvenous leads. [2]

Title: A Leadless Intracardiac Transcatheter Pacing System
Design Prospective, nonrandomized, single-study-group, multisite, international, clinical study
Objective To evaluate the safety and efficacy of the Micra Transcatheter Pacemaker System (Medtronic)
Study Groups Single study group; N = 725
Methods The pacemaker device will be implanted in the selected patients where appropriate indication is present.

Major complications were defined as events resulting in death, permanent loss of device function as a result of mechanical or electrical dysfunction, hospitalization, prolongation of hospitalization by at least 48 hours, or system revision.

Patients in whom the device was implanted were evaluated for adverse events and device function at hospital discharge and at follow-up assessments at 1, 3, and 6 months and every 6 months thereafter.

Duration Ongoing study with enrollment completed in May 2015
Primary Outcome Measure Freedom from system-related or procedure-related major complications, a low (≤2 V at a pulse width of 0.24 msec) and stable (increase of ≤1.5 V from the time of implantation) pacing capture threshold at the 6-month visit
Baseline Characteristics Primary indications among patients undergoing implantation: bradycardia associated with persistent or permanent atrial tachyarrhythmia (64.0%), sinus-node dysfunction (17.5%), atrioventricular block (14.8%), and other reasons (3.7%)
Results There were no radiographically visible device dislodgements, no telemetry failures, and no systemic infections. There were 28 major complications in 25 patients. 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.


Of the 297 patients who were included in the primary efficacy analysis, 292 (98.3%; 95% CI, 96.1 to 99.5) had an adequate 6-month pacing capture threshold; (p < 0.001 for the comparison with the efficacy performance goal of 80%). Among all patients who underwent implantation and for whom follow-up data were available, the pacing capture threshold tended to decrease shortly after implantation and remained stable thereafter; the mean pacing capture threshold was 0.63 V at a pulse width of 0.24 msec at implantation and 0.54 V at a pulse width of 0.24 msec at the 6-month visit.


Through 6 months of follow-up, the study patients had fewer major complications than did the patients in the historical control cohort (4.0% vs. 7.4%; hazard ratio, 0.49; 95% CI, 0.33 to 0.75; p = 0.001).

Adverse Events Common Adverse Events: N/A
Serious Adverse Events: N/A
Percentage that Discontinued due to Adverse Events: N/A
Study Author Conclusions The study concludes that the device was successfully implanted in 99.2% of patients with acceptable efficacy and safety endpoint measures at 6-month follow up. Although there were 28 major complications in 25 patients, the prespecified safety criteria were also met, and 96.0% of patients had no major complications at 6 months.

The current data on transcatheter pacing is preliminary and is limited to reports from nonrandomized studies. The author states that the delivery of the device requires a different approach as compared to transvenous leads, and although it is estimated that these newer devices will have similar longevity, it is unknown. A major limitation of the study is a lack of a comparison with a randomized control group, as is the case with previous studies. An additional limitation of this study was that follow-up data was limited to only 6 months and that the implantation experience was limited to the 94 physicians who performed the implantations. Although a placebo control group would not be ethical, additional studies with a control group having similar baseline characteristics as well as a longer duration of follow up would help to further determine the place in therapy for leadless pacemakers.


  1. Udo EO, Zuithoff NP, van Hemel NM, et al. Incidence and predictors of short- and long-term complications in pacemaker therapy: the FOLLOWPACE study. Heart Rhythm 2012;9:728-735
  1. Reynolds D, Duray GZ, Omar R, et al. A Leadless Intracardiac Transcatheter Pacing System. N Engl J Med. 2016;374(6):533-41.

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