Discussion
This is the first case-series reporting on the safety and feasibility of
CSP in unselected patients with a wide range of CHD subtypes. Of note,
95% of patients included in our series had moderate or complex forms of
CHD. Our results show that physiological pacing is feasible and safe in
this subset of patients with a successful implant rate of 100% when
considering both HBP and LBBAP, and 75% (15/20) when using strict
criteria for LBBP. In the remaining 5 patients LVSP pacing with
significant QRS narrowing could also be achieved. Of note, the systemic
ventricle systolic function and NYHA class significantly improved during
follow-up. Electrical parameters remained stable at last follow-up and
only 1 patient required lead revision due to acute pacing threshold rise
4 days post-implant.
In recent years, CSP has emerged as the cornerstone of physiological
pacing1-5. Several studies have demonstrated that HBP
can reduce heart failure hospitalizations and can improve
LVEF1. This potential benefit is greater for those
patients with higher percentage of ventricular pacing and those with
impaired LVEF at baseline; particularly, younger patients with a high
burden of ventricular pacing18. In a series of 238
patients with CHD, the mean age at pacemaker implantation was 26 years
IQR (13;42)19. Moreover, patients with CHD and chronic
right ventricular pacing are at particularly increased risk of
developing pacemaker induced cardiomyopathy. Recently, HBP has been
shown to improve LVEF in chronically paced patients and pacing induced
cardiomyopathy5. Our results show that CSP is feasible
in chronically paced CHD patients with longstanding AV block and thus
should be considered as a potential pacing strategy for this subset of
patients with pacing induced cardiomyopathy.
Pacemaker implantation in patients with CHD can be challenging due to
the baseline anatomical distortion and also due to the presence of
prostethic materials introduced during the surgical
corrections8-11. As a consequence, implant duration
was prolonged with higher radiation exposure. As a reference, in one of
the largest series of HBP published so far, mean implant duration was
70±34 min for single or dual chamber pacemakers thus reflecting the
complexity of the implant technique in patients with
CHD1. The use of multiple sheaths in 50% of the cases
also reflects the complex anatomy and the absence of tailored tools
available. Moore et al.12 have recently reported the
safety and feasibility of CSP in 15 patients with cc-TGA showing an
acute implant success rate of 85% with a median procedure time of 146
minutes (IQR 112– 212) and use of multiples sheaths in 27%. In
comparison, our series with unselected CHD patients including more
complex anatomies, shows that CSP is still feasible in a wide range of
CHD defects.
Localization of the proximal conduction system in our cohort poses a
challenge. Although simple defects are usually associated with minor
variations, moderate and severe defects have characteristically
significant variations in the conduction system
disposition20. Electroanatomical mapping of the
conduction system during implant in those patients with spontaneous
intrinsic rhythm should be considered, especially in patients with
complex anatomy and previous surgery. In patients with D-TGA and a prior
atrial switch operation, only the left conduction system is usually
accessible. In our 2 patients with D-TGA and a Senning correction we
unsuccessfully tried to reach the proximal left bundle within the
interventricular septum but ultimately accepted the distal portion of
the left conduction system (left anterior fascicle)(Figures 3 and 5).
Additional landmarks may be useful to localize the conduction system
such as a calcified VSD patch from a previous membranous septum VSD
closure (patient #4, cc-TGA + perimembranous VSD + dextrocardia),
(Figure 6 and Supplementary video 2).
It is of interest that LBBP could be successfully achieved in the 2
patients with a D-TGA and previous atrial switch operation. A
significant percentage of patients with an atrial switch operation are
likely to develop future systemic RV dysfunction and may also need
permanent ventricular pacing. Although biventricular pacing has been
attempted in different CHD scenarios, the CS ostium is not usually
accesible from the systemic venous atrium in these patients and thus the
only chance for CRT in this setting is the surgical implantation of an
epicardial lead in the systemic RV. Our 2 cases show that CSP can
potentially be achieved after the atrial switch operation accesing the
subpulmonic ventricle via the systemic venous atrium. In fact, this
particular anatomic disposition allows direct access to the left
conduction system as the subpulmonic ventricle is morphologically a left
ventricle. In these 2 patients, we were able to clearly record and
capture a left bundle potential (Figures 3 and 5). However, the effect
of LBBAP on systemic ventricular synchrony requires further data as it
relies on activation of the right bundle as well.
In conclusion, HBP and LBBAP are safe and feasible in patients with CHD
and a permanent pacing indication despite challenging anatomy and
advanced conduction system disease.