The Journal of the Arkansas Medical Society, Vol 115, No. 9 Med Journal March 2019 Final 2 | Page 10

CASE STUDY
Leadless Pacemaker Devices
Kanishk Agnihotri, MD; Sabeeda Kadavath, MD
Anil Kumar Jonnalagadda, MD; Hakan Paydak, MD
Abstract
ince their initial introduction, im-
plantable cardiac devices have
been increasingly utilized in
medical practice. Leadless Cardiac Pacemak-
S
ers (LPMs) function as their conventional predeces-
sors, but they have the advantage of not requiring a
transvenous lead, which can minimize the various
complications associated with lead insertion. Two
LPM devices are available currently; the Nanostim
device and the Micra device. These share a similar
design and delivery methods but differ in size and
some internal characteristics. Major drawbacks of
these devices are that they can only pace through
the right ventricle and there is lack of long-term
data regarding their utilization. Limited data is avail-
able about their use, and more research is needed
to justify their incorporation into clinical practice.
Introduction
Cardiac pacemakers are extremely effective
in the management of brady-arrhythmias. Since
the first device insertion more than 50 years ago, 1
there has been a bonafide increase in their utiliza-
tion, with advancement of implantation techniques,
longevity of batteries, and the incorporation of
programmable features for better physiologic pac-
ing. More than 700,000 devices are used annually
worldwide, with 250,000 in the U.S. alone. 2 Never-
theless, they all share the same core components
with a subcutaneous pacing unit and electrical
leads implanted into the endocardium via transve-
nous route.
Since most complications were related to
the venous leads, there is increased interest in
developing smaller devices without the need for
hazardous lead insertion. Currently, there are
two devices that have shown great applicabil-
ity and promising results, even though they are
limited by a lack of long-term results and come
with certain introduction complications due to the
learning curve associated with their use. 3 To date,
only single-chamber pacing systems are available
through the right ventricle (RV), with more to be
studied and possible development of dual cham-
ber and multi-chamber pacing.
Leadless cardiac pacing systems have been
approved for use in Europe since 2013, and in April
2016 in the U.S. Currently, two leadless pacemaker
systems are commercially available, with slightly
different sizes and implantation requirements: 3
1) The Nanostim device (developed by St. Jude
Medical), measures 42 x 6 mm and requires an
18-French introducer sheath. 2) The Micra device
(developed by Medtronic), measures 26 x 7 mm
and requires a 23-French introducer sheath.
Landmark Studies
Since their introduction into practice, LPM de-
vices have been extensively studied and are still
under more research to determine their effective-
ness, reliability, outcomes, and complications. We
present some of the most important landmark
studies regarding these devices.
The LEADLESS Trial was one of the pioneer
studies to evaluate the LPM device, and enrolled
33 patients who needed RV pacing. The leadless
device was delivered via transfemoral venous ap-
proach in 32 of the 33 patients (97%). Thirty-one
patients (94%) were free from complications at 90
days. One patient suffered tamponade from RV per-
foration, which led to death. 4
The LEADLESS II Trial was a prospective,
multicenter trial and included more patients. It
enrolled 526 patients who also needed RV pacing.
Primary safety and efficacy endpoints were met in
300 patients, 5 who were followed for six months.
Among these patients, 11 had unsuccessful device
implantation. Ninety-three percent (270 of 289)
met the primary endpoint of acceptable pacing
capture threshold and sensing amplitude of rate
response. Reported device-related complications
were dislodgment (1.7%), elevated pacing thresh-
old (which required repositioning of device (1.7%),
and RV puncture and perforation leading to tam-
ponade (1.3%).
The Micra Transcatheter Pacing Study en-
rolled 725 patients who needed RV pacing. In 719
patients (99.2%), the device was introduced and
implanted successfully. Primary endpoint of free-
dom from device adverse effects at six months was
96%, and the second primary endpoint of adequate
202 • THE JOURNAL OF THE ARKANSAS MEDICAL SOCIETY
pacing capture threshold was assessed in 297
patients, among whom 292 (98.3%) reached ac-
ceptable pacing capture (at 0.24 ms pulse width). 6
Approximately 12% of patients had elevated pac-
ing thresholds at time of device implantations,
and 85% returned to normal pacing threshold at
six months post-implant. 6 Long-term performance
at 12 months showed that 96% remained free of
major device-related complications, compared to
transvenous pacemakers (HR 0.52; 95% CI 0.35-
0.77). 6
The SELECT-LV Study was a prospective,
non-randomized study of safety and efficacy of
leadless pacing for cardiac resynchronization
therapy (CRT) among patients who “failed” con-
ventional CRT. In this study, the leadless device was
successfully implanted in 34 of 35 patients 7 and bi-
ventricular pacing was achieved in 22 of the 34 pa-
tients. Nevertheless, significant complications oc-
curred in three patients (9%) at the time of implant
and eight patients (23%) within the first month.
Components and Function
The two available LPM devices share a com-
mon design, with some differences. The first device
is the Nanostim, which was developed in 2012 by
St Jude Medical group. It consists of a cylindrical
capsule that contains the power source, electrode,
and circuity. It is a single-chamber pacing device
and is delivered to the RV through an 18-French
sheath, then fixed into the myocardium by a heli-
cal screw. 3 The Nanostim device is designed to be
retrievable, which can be helpful if the pacing is
not adequate and the device needs reinsertion. It
uses a VVIR pacing system, and the rate response
is dependent on a temperature sensor. Estimated
battery life ranges from 8.4 to 12 years, depending
mainly on the burden of pacing and communication
with the St. Jude interpretation system via surface
ECG (usually 250 Hz).
As for the Micra Transcatheter Pacing System
(TCPS), it was developed in 2013 by Medtronic Inc.
in Dublin, Ireland. It also consists of a cylindrical
capsule, but it is smaller in size, with 26 mm and
6.67 mm in diameter. Similar to the Nanostim de-
vice, it is delivered through the right femoral vein
but using a 23-French sheath. The device has self-
VOLUME 115