DISCUSSION
This prospective, randomized study assessed the feasibility of right
ventriculography in assisting deployment of MicraTMleadless pacemaker in the RV mid-septum and has several important
findings. First, this technique yielded a high accuracy (93.8%) of the
MicraTM pacemaker deployment in the target location
compared to the accuracy (48.1%) of the standard procedure without
right ventriculography. Second, with the assistance of right
ventriculography the fluoroscopy exposure time was significantly reduced
while the appropriate pacing
parameters were preserved, and no implantation-related adverse events
were observed. Finally, septal pacing, especially in the mid-septum,
provides a relatively narrow ECG QRS duration (123 ms in average).
The MicraTMCoverage with Evidence Development Study (the Micra CED) in 5746
patients implanted with MicraTM leadless pacemakers
found that the incidence of complications following implantation was
3.3% in a 6-month follow-up period, in which myocardial perforation was
the most common complication.11, 12 Other
complications included pericardial tamponade and anterior descending
artery injury.7, 11, 13 To reduce these
implantation-related complications, the right ventricular septum has
been a target location for leadless pacemakers.6, 14The presence of more myocardial trabeculae and columnae carneae in the
right ventricular septum, particularly prominent in the middle of the
septum, than in the right ventricular apex and right ventricular outflow
tract makes the RV septum an ideal location for
MicraTM leadless pacemakers with a less likely
occurrence of perforation. In the Micra CED study, 52.1% of
MicraTM leadless pacemaker locations were in the RV
septum, 39.3% in the RV apex, 1.9% in the RV outflow tract, and 6.3%
in junctions (including apex-septum and inferior
septum).11 Sharma P et al.(2020)6reported that 51.4% of leadless pacemaker implants were located in the
ventricular septum, 28.6% in the right ventricular apex, and 20% in
the RV outflow tract.
Currently, conventional fluoroscopic method is used in leadless
pacemaker implantation. In the study by Hai JJ et
al.(2019)15 in which multi-angle fluoroscopy was used
to guide leadless pacemaker implantation in the mid-septum, 90% of the
pacemaker implants were intended in the interventricular septum and 5%
were in the right ventricular outflow tract under the RAO view. However,
when left-sided fluoroscopy was performed, the actual implantation site
was observed at the anterior free wall in 17.6% of patients with
intended septal implantation. Therefore, developing an accurate and
effective method for implanting leadless pacemakers in the mid-septum
remains a challenge.
The present study observed a higher accuracy of the
MicraTM leadless pacemaker deployment at the target
location with assistance of right ventriculography than that without
right ventriculography. Furthermore, the present study demonstrated not
only the safety of the technique but also a significant reduction in
X-ray exposure dose and time. The less fluoroscopic use time in the
radiography group was likely because the operator could directly
maneuver the distal part of the delivery catheter against the mid-septum
according to the right ventriculography while in the non-radiography
group the operator used more time and fluoroscopy repositioning to
figure out the target site. The implantation site in the inferior septum
is close to the RV apex, which may have a high risk of cardiac
perforation while the implantation site in the superior site has fewer
myocardial trabecula, which can cause difficult in the leadless
pacemaker deployment. In consideration of the effects of right
ventricular anatomic variants and cardiac transposition on the leadless
pacemaker implantation process, right ventriculography provides more
detailed information on the right ventricular contours and anatomic
landmarks in the fluoroscopic LAO and RAO positions. It may also be used
to identify the septal tangent and position of the tricuspid valve.
Additionally, right ventriculography can show the specific anatomic IVC
and heart structural variants and allow easier access to the right
ventricle with guidewires and sheaths. Right ventriculography has
previously been used to identify the target site in the RV mid-septum
for the lead deployment for left bundle branch pacing and His bundle
pacing.16 Therefore, right ventriculography can be a
useful technique to facilitate the MicraTM leadless
pacemaker as well as transvenous pacing lead deployment at an intended
location.
Conventional RV apical pacing causes a significant wide ECG QRS duration
and interventricular dyssynchrony that are associated with an increased
risk of cardiac dysfunction in patients with frequent pacing. Pursuit of
more physiological pacing method is continuing. Previously, septal
pacing has been proposed as an alternative to RV apical pacing though
there has been no conclusive clinical evidence. The true location of the
pacing lead tip using fluoroscopy is often inaccurate, leading to
conflicting results of septal pacing in acute and chronic studies.
Recently, the study by Sharma et al demonstrated that a mid-septal
pacing by MicraTM leadless pacemaker resembles
physiological pacing and tends to achieve a relatively narrow paced QRS
interval.6 Our study also found that pacing by
MicraTM leadless pacemaker at the mid-septal location
generated a relatively narrow QRS duration and left ventricular
activation time, suggesting a more physiological pacing modality
(Supplemental Material Figure S2, a comparison in 12-lead ECG between RV
septal pacing vs. apical pacing). Currently, left bundle branch pacing
has been considered as a physiological pacing
modality.17-19 To achieve left bundle branch pacing
the pacing lead tip is screwed into the left side of the septum from the
right side of the RV mid-septum.20 In the future,
MicraTM leadless pacemaker with a modified long pacing
electrode and RV ventriculography for the target entry site in the RV
septum can also achieve left bundle branch pacing.
Study limitations. The study was performed in a single center
with relatively small patient numbers and in a non-blinded fashion that
might introduce potential bias. The study could not address the
potential difference in safety between the ventriculography group and
the non-ventriculography group because the operator made the effort to
place the leadless pacemaker in the RV septum in both groups. The
generalization of the technique of right ventriculography in routine
clinical practice needs further validation in a multi-center study with
a large population and diverse pacing indications. Furthermore,
long-term clinical outcomes with this approach and pacing in the
mid-septum remain unknown though the present study found a relatively
narrow QRS duration and a recent report showed a possibility of leadless
pacemaker in prevention of pacing-induced
cardiomyopathy.21 Thus, clinical studies are needed to
evaluate the long-term clinical effects of MicraTMleadless pacemaker implanted in the mid-septum in comparison with the
pacing site in the RV apical septum or apex.
Conclusion. In the present study, use of right ventriculography
yielded a high success and accuracy rate to deploy a
MicraTM leadless pacemaker in the mid-septum with
reduced time in X-ray exposure without compromising safety. Furthermore,
the study found that pacing at the mid-septum had a relatively narrow
ECG QRS duration. Septal deployment of the MicraTMleadless pacemaker has a potential to reduce complications such as
perforation, effusion and pericardial tamponade when compared to the
implantation site at the RV apex. Thus, right ventriculography to guide
MicraTM leadless pacemaker implantation in the
mid-septum can be a useful method, especially for beginners, less
experienced centres, and patients with specific cardiac anatomical
variations in a routine clinical practice.
Funding
National
Natural Science Foundation of China (Grant
number:81873487) awarded to Yaodong
Li.
Conflict of interest:
All authors report no conflict of interest.