Discussion
Our report focuses on comparing the procedural outcomes of two current
approaches to “physiological” pacing during the initial learning curve
phase of implanting physicians at a single center. By describing this
early experience with both forms of pacing, we hope to better inform
other adopters as they consider both these options.
In this report, we observed the following: 1) His-bundle and left bundle
branch area pacing result in similarly narrow paced QRS widths ≤ 120 ms
(61.9% vs 65.9%, p = 0.62) and can be achieved with a low risk of
acute complications. 2) Significant deterioration in pacing parameters
emerged as soon as 4 weeks after implant in the HBP group and
persisted/worsened over follow up. This pattern was not seen in the
LBBAP group. 3) A significantly greater rate of adverse events (lead
revisions and premature generator change) occurred in the HBP group
(13%) compared to the LBBAP group (0%).
Immediately following implantation, the acceptable pacing endpoint (APE)
was met by 18% fewer patients in the HBP group compared to the LBBAP
group. This measure of lead safety and efficiency progressively worsened
over time. By first follow-up, 40.4% fewer patients continued to meet
the APE in the HBP group compared to LBBAP. This marked difference
persisted to the most-recent follow-up. The deterioration of pacing
parameters was driven primarily by worsening pacing thresholds,
culminating in 6 of 45 HBP patients (13.3%) requiring lead revision and
generator replacements at follow-up. R-wave amplitudes and lead
impedance remained stable with additional follow-up in both groups.
Experienced implanters place leads into the RV apex with relative ease.
Despite early procedural complications like lead dislodgement and
perforation, progressive threshold rises rarely occur and apical pacing
remains the traditional RV pacing site of choice.21 In
contrast, the 13% of patients in the HBP group who required lead
revisions in this report highlights a distinct shortcoming of choosing
the His-bundle as the site for physiological pacing as opposed to LBBAP.
The incidence of progressive rise in thresholds and lead revision rates
amongst early adopters of HBP has been variable in the
literature.22-23 Bhatt et al, Keene et al and Teigeler
et al in their respective single center reports described 8%, 7.5% and
11% rates of lead revision/intervention,
respectively.11,14,24 On the other hand, Chaumont et
al. reported a much lower incidence of lead revisions in their
multicenter experience (3.4%) and Qian et al. reported no lead
revisions.25-26 The threshold rises have been
postulated to be the result of several mechanisms: 1) a relative lack of
muscle in the underling region of the His-bundle 2) progressive fibrotic
changes that occur over time after lead fixation, and 3) progressive
degrees of micro-dislodgement.16,27 On the other hand,
while published reports of LBBAP pacing have been primarily restricted
to centers with significant technical expertise, reports of significant
threshold changes and lead revisions are distinctly uncommon
(<1%) in patients undergoing LBBAP.20,28-29
In their single center comparative study of HBP and LBBAP, Qian et al
did not report any lead revisions, while noting an increase in capture
threshold in 12.5% of patients in the HBP group.26 In
contrast, our single center comparative report describes a 13% rate of
lead revision/generator change in the HBP group. Importantly, our events
all occurred beyond the one-year of follow-up period, beyond the time
studied by Qian et al. Our study underscores how, with continued
follow-up of patients with HBP, progressive worsening of pacing
parameters over time clinically impacts the lives of our patients.
Our 13% event rate of lead revisions is higher than many of the
above-mentioned reports and may reflect differences in our implant
technique: for example, we did not consistently document His-bundle
injury during the procedure, which has been described as predictive of
lower chronic thresholds. While the early nature of our experience may
partly explain these rates, they are in stark contrast to our LBBAP
group where no patients experienced any additional procedures during
follow-up. The comparatively shorter period of follow-up of our LBBAP
group is a limitation. But at most recent follow-up, the LBBAP group has
not shown any deterioration in pacing parameters, whereas the HBP group
had already demonstrated a deterioration in APE at the same comparable
point of follow-up.
While all LBBAP implanters in this study benefited from the learning
curve of HBP, the differences in outcomes between both groups suggest
distinct advantages of placing the lead deep within the septum. In fact,
while early lead dislodgement and, rarely, lead perforations in the LV
cavity can occur in LBBAP, threshold rises have not been reported using
this technique and were not seen in our experience. Though it is likely
that inexperienced operators will fail at consistently achieving
selective or non-selective LBB capture (i.e., only left ventricular
septal capture), the necessity of actual LBB capture is unclear and the
almost obligate increases in pacing thresholds are not
seen.30 LBBAP leads to very low lead
revision/premature generator replacement rates with no incremental
procedural risk for dependent patients. These should be requisite
characteristics for the widespread adoption of any alternative to RV
apical pacing.
Study Limitations :
This report describes the experience of a select few operators at a
single institution. During this study, operators transitioned from
pursuing HBP to LBBAP in an almost sequential fashion. The initial
experience with HBP undoubtedly had a positive impact on certain
procedural aspects of LBBAP such as fluoroscopy and procedural times.
Importantly, this study did not systematically evaluate for the presence
of LBB capture in the LBBAP group.