Discussion
Our adolescent patients had an upgrade at their first pacemaker
replacement after 9 to 11 years of RV pacing, exhibiting improvement of
LV function and exercise tolerance following restoration of AV synchrony
and of ventricular activation via the His-Purkinje network. CCAVB in
patients with a normal heart disrupts 2 of the 3 electrophysiological
determinants of cardiac performance: atrioventricular synchrony and
chronotropic response. Though CCAVB patients can have a normal physical
development and, occasionally, a normal life expectancy, the majority
have signs of LV dysfunction, atrial arrhythmias, or symptomatic heart
failure at long term follow-up. When a pacing indication ensues,
chronotropic response is restored at the expense of the loss of
inter-/intraventricular synchrony, with or without restoration of AV
synchrony depending on pacing mode (DDD vs VVIR).
In this perspective, key questions in CCAVB are yet unanswered owing to
the impossibility to run methodologically correct studies in this
pediatric population. The timing to consider pacing is individually
based. The choice of the pacing site and mode has been mostly debated in
literature (2, 6, 7): despite convincing evidence of superior cardiac
performance and exercise tolerance with AV-synchronous pacing, VVIR mode
seems a reasonable choice as the initial pacing strategy in small
children to minimize intravascular hardware (risk of vein thrombosis)
and lead malfunction, given the modest difference in clinical endpoints
and quality of life in pre-adolescence (8, 9).
A first pacemaker implant or replacement in adolescence is a different
setting, because key decisions are taken for long-term cardiac pacing in
a view to restore - possibly - all the 3 electrophysiologic determinants
of cardiac function. A mild LV systolic dysfunction, especially when
associated to functional mitral or tricuspid regurgitation and initial
left atrial enlargement, is a clinical hint of the RV pacing detrimental
effect, and may promote upgrading the system to restore cardiac
synchronicity. CRT is well known to improve cardiac function in RV
pacing-induced heart failure/LV dysfunction (10); recent evidence,
however, points toward a similar effect of HBP and CRT in this setting,
both in terms of LV function and clinical status improvement (11). These
results are not surprising, given the comparable efficacy reported for
HBP and CRT in heart failure patients, with a possible beneficial effect
of HBP also in non-responders to conventional CRT (12-14).
A single case of cardiac resynchronization via direct HBP in a CCAVB
patient with RV pacing-associated cardiomyopathy has been reported to
date (15), highlighting the concept of reversible LV dysfunction that
can be corrected by restoration of the normal activation pathway via the
His-Purkinje network. Our experience with milder degrees of LV
dysfunction suggests a role for the preservation of LV mechanics at long
term in CCAVB with persistent His-to-ventricle conduction, when the
first replacement in adolescence offers the opportunity to upgrade the
pacing system.
The ongoing development of dedicated tools and the improved skillfulness
in HBP implantation have now set the ground for the expansion of this
pacing modality also to CCAVB patients (14).
Limitations . The observations about these two patients need to
be confirmed in a large series of CCAVB patients. Moreover, some caveats
are to be considered, such as: persistence of conduction in the
His-Purkinje network at long term; minimization of intravascular leads
that dwell lifelong in young patients; device longevity when a
moderate-to-high HBP threshold dictates a high current drain, as the
number of replacements is a main predisposing factor to infection (16).
Technical aspects like the amount of lead slack needed to accommodate
for patients’ growth are better addressed in late rather than in early
childhood.
Conclusions . Taken the abovementioned points as a cautious
habit at innovation, we believe that HBP should be explored as the
first-choice strategy in CCAVB undergoing pacemaker implantation in late
childhood, and in CCAVB candidates to upgrading because of RV
pacing-associated LV dysfunction.
Funding : no funding supported this article
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Table . Main characteristics of the two patients.