Electrical parameters at the time of
implantation and at six months closely
approximated those seen in the investigational
study. 12
Real-world data from a worldwide registry
corroborate the findings of the investigational
study. Of 795 patients who underwent an
attempted implantation, the Micra™ was
successfully implanted in 792 (99.6%). The 30-day
major complication rate was low at 1.51%,
including six (0.75%) puncture site complications,
one (0.13%) cardiac perforation with effusion
requiring pericardiocentesis, and one (0.13%)
device dislodgement without embolisation. One
patient, a 96-year-old man with severe aortic valve
disease, died from pulmonary oedema the day
after the procedure. The device was functioning
normally at the time, had not migrated and there
was no evidence of pericardial tamponade. 12
There were four (0.50%) other cardiac perforation
events that fell outside the criteria for a major
complication, because they did not result in
death, system revision or prolonged
hospitalisation. In three cases no action was
required, and in one pericardiocentesis was
undertaken.
Figure 4
Chest X rays (A) showing
a standard single chamber
permanent pacemaker
with septal position
ventricular lead, and (B)
a Nanostim™ LCP
positioned at the right
ventricular apex.
Used with permission
of Mayo Foundation for
Medical Education and
Research, all rights reserved.
50
HHE 2018 | hospitalhealthcare.com
Nanostim™ Leadless Cardiac Pacemaker (LCP)
At 42mm in length, the Nanostim™ LCP is longer
than the Micra™, but with a smaller diameter at
5.99mm requires a smaller introducer sheath at
implantation.
The principles of the implantation procedure
are broadly the same as with the Micra™, with the
most notable difference being that the
Nanostim™ is affixed to the myocardium by
means of a screw-in helix at its tip. Figure 4 shows
two chest X rays with a transvenous single
chamber pacemaker and the Nanostim™
respectively.
The LEADLESS trial, the first study to assess
safety and efficacy of the Nanostim™, was a small
single-arm, multi-centre study involving 33
patients. Successful device implantation occurred
in 32 (97%) patients, and 31 (94%) remained free
from complications at 90 days. Of the remaining
two patients, one had a patent foramen ovale
through which the Nanostim™ had inadvertently
been passed before implantation in the left
ventricle. This was subsequently recognised and
the device successfully retrieved. The other
patient sustained cardiac perforation and
tamponade at implantation, requiring pericardial
drainage and later median sternotomy and
surgical repair of the apical perforation. He later
suffered a stroke and subsequently died. 13
The much larger LEADLESS II trial included
analysis of 526 patients, of whom successful
implantation occurred in 504 (95.8%). The rate of
freedom from complications up to six months
post-implantation was 93.3%. There were 22
device related complications in 20 patients (6.7%),
including device dislodgement (1.7%), cardiac
perforation (1.3%), vascular complications (1.3%)
and high capture thresholds requiring device
retrieval and reimplantation (1.3%). Device
migration occurred in six patients, either to the
femoral vein or pulmonary artery, and in all cases
the device was successfully retrieved
percutaneously. There were two deaths (0.4%)
adjudged to be procedure-related. Initial and
follow up electrical parameters were again found
to be very good in this larger cohort, also with
a tendency toward improvement over time
(see Table 2). 14
Despite a promising beginning, St Jude Medical
voluntarily halted further implantations of the
Nanostim™ in October 2016 due to reports of
premature battery failure leading to lost pacing
output. There were 34 such failures reported, out
of 1423 Nanostim™ implantations worldwide
(2.4%). These occurred at a mean of 2.9 ± 0.4 years
after implantation. There were no reports of any
patients having come to harm as a result. 15
Where retrieval of the device was attempted, it
was successful in 90.4% of cases. In the remaining
9.6%, the docking button proved inaccessible, and
in one case became detached and migrated to the
pulmonary artery. A total of 115 patients were
given an additional pacemaker without an
attempt at retrieving the Nanostim™, and there
were no reports of adverse interactions
subsequently between the coexistent systems. 15