Discussion
In this nationwide comparative evaluation of 6,219 leadless VVI versus
10,212 transvenous VVI de novo pacemaker implants, leadless VVI
pacemakers were associated with a 32% reduction in the rate of chronic
complications and a 41% reduction in the rate of reintervention at 3
years. These results build off of the published 2-year results of the
Micra CED Study, which showed a 31% reduction in complications and a
38% reduction in reinterventions at 2 years in this
cohort.3 Lower rates of complications among leadless
pacing patients have now been observed in both clinical trials and
real-world clinical practice.4,5 This present analysis
suggests the reductions in the risk of complications and reinterventions
associated with leadless pacing, previously seen at 6 months and 2 years
of follow-up, persist and continue to accrue in the medium-to-long-term.
This analysis provides valuable new information on the expected rate of
accrual of additional complications and need for system revision over
time. At the 3-year endpoint, most complications that patients continue
to experience are related to device (device breakdown, mechanical
failure, etc.) or pocket in the transvenous VVI arm. Because the
differential benefit of leadless pacing is largest with respect to these
device-related complications, it would be reasonable to assume that the
benefits observed at 2 and now 3 years would persist over longer time
horizons.
The present analysis also provides new insight into the robustness of
the 2-year results, particularly related to device reinterventions. This
present analysis found a 29% lower rate of reinterventions requiring a
new device (device removal and replacement, and upgrades to dual-chamber
and CRT devices) among leadless VVI patients, demonstrating that the
lower rate of reintervention is not solely driven by the need for lead
revisions and lead-related reinterventions, which are less invasive and
costly than reinterventions requiring a whole new system.
As discussed in El-Chami et. al.,3 rates of device
reintervention can be influenced by both adverse events, like
pacing-induced cardiomyopathy, as well as patient selection. The
advantage that leadless pacemakers have in terms of absence of leads can
also be a limitation in that leadless pacemaker systems can be less
adaptable to modular upgrades, such as an addition of a CRT lead. The
current study shows no significant difference in all-cause mortality
after adjustment for differences in baseline patient characteristics and
a 10% lower rate of heart failure hospitalizations at 3 years. These
results are comforting and suggest the reduction in reinterventions
observed among leadless-VVI patients are not coming at the expense of
worse pacing outcomes (such as untreated pacing-induced cardiomyopathy).
In fact, these results appear to bolster previous findings suggesting
lower rates of pacing-induced cardiomyopathy among patients implanted
with a leadless pacemaker, potentially due to greater frequency of
mid-septal placement associated with leadless
implants.12 It would be valuable to explore this
hypothesis further in a randomized clinical trial.
The Micra CED Study also continues to demonstrate the benefits of
leadless pacing with regards to device infection. While the total rate
of device infection requiring full device removal in the transvenous VVI
comparator arm is low (0.7%), it is significantly higher than in the
leadless VVI arm. CMS reporting rules prevent us from displaying cell
values less than 10 in order to prevent patient identification. If we
assume that the value is actually 10, the infection rate requiring
device removal in the leadless group is only 0.16%. Prior literature
has demonstrated the serious risk of patient mortality and other adverse
clinical and economic outcomes posed by device
infection.13
To our knowledge, this is the first analysis to report on heart failure
hospitalizations among leadless pacing patients and is possible because
the large sample size and long-term follow-up of the Micra CED study
allows for the capture of an adequate number of events of interest. The
ability to capture and report on this endpoint highlights some of the
significant advantages of using real-world data to supplement
traditional clinical studies for post-market device evaluation.