Discussion
This study is the first to compare LBBAP using lumen-less pacing leads
with fixed helix design to standard stylet driven leads with extendable
helix design. The main findings of this study are that LBBAP with
stylet-driven leads yields comparable implant success and similar pacing
characteristics at implant and short-term follow up without affecting
procedural safety.
LBBAP is a novel pacing technique aiming to capture the conduction
system of the heart at the left side of the interventricular
septum.4 Compared to HBP, LBBAP aims to pace the
conduction system more distally on the left bundle branch. Although no
direct comparisons between HBP and LBBAP have been published, current
evidence shows promising effects of LBBAP in terms of maintaining
physiologic ventricular activation, hemodynamic benefits and the
potential for cardiac resynchronization in patients with LBBB and heart
failure.3, 5, 13, 17 Moreover, LBBAP is associated
with lower pacing thresholds, and higher sensing values compared to HBP.
As such, LBBAP might overcome the limitations of HBP, as HBP has been
associated with high pacing thresholds, especially in the setting of
bundle branch block or infranodal disease, and is associated with two to
three times more lead revision compared to RVP.8, 9,
18
Until now, LBBAP has been exclusively performed with a 4.1Fr thin
lumen-less lead with a fixed helix (SelectSecure 3830 lead, MDT)
delivered though a fixed curved delivery sheath (C315HIS,
Medtronic).4, 6, 7, 10, 11 This approach has been
shown to yield high implant success and is associated with excellent
pacing threshold both in patients with narrow QRS, atrioventricular
block and bundle branch blocks. The main advantage of this type of lead
is the isodiametric shape between the lead tip and the lead body which
facilitates screwing the lead into the ventricular septum. Stylet-driven
leads with extendable screws however lack the isodiametric shape at the
location where the helix exits the helix case, which might limit lead
penetration into the septum. Recently, the first two cases of LBBAP with
an SDL delivered through a new preshaped sheath (Selectra 3D sheath)
have been reported by Zanon et al.15 In these two
cases, HBP with the SDL failed and the same lead was implanted
successfully at the area of the left bundle branch. In our experience,
the combination of a standard stylet-driven lead (Solia S60) delivered
through the Selectra 3D sheath performed excellent to achieve LBBAP with
similar success rates as compared to thin lumens-less leads. Neither the
larger lead diameter (5.6 Fr), nor the non-isodiametric lead design
limit the screwing of the lead towards the left side of the septum. On
the contrary, the larger outer diameter of the SDL allows more grip on
the lead body when applying manual rotations. The screwing of an SDL
into the septum was further facilitated by the extra support of the
stylet and the wider (8,7 Fr) and sturdier Selectra 3D sheath. As
described by Zanon et al15, we tend to extend the
helix and routinely add additional tension on the inner coil of the lead
before screwing into the septum. This approach avoids unwinding of the
inner coil and partial retraction of the helix when manual rotation on
the outer lead body is applied and allows the applied torque to be
transferred predictably to the lead tip.
In our experience, LBBAP with LLL and SDL reveals comparable procedural
characteristics and safety. Despite the larger lead diameter, the use of
an inner stylet and a wider delivery sheath, LBBAP with SDL did not
result in more septal perforations. However, we detected an asymptomatic
septal coronary artery fistula on echocardiography in one patient who
underwent LBBAP with SDL. Although perforation of septal coronary artery
branches could occur with any transseptal lead, the risk might be
considered higher with larger pacing lead diameters. This complication
highlights the importance of routine echocardiographic screening to
assure integrity of the interventricular septum after LBBAP.
Our study shows that both types of leads tend to have comparable LBBAP
thresholds immediately post implant and at short term follow up. Both
leads have an electrical active pacing helix and use steroids at the
helix, although the steroid location differs. The LLL helix is
steroid-coated, whereas the SDL leads contain steroids within a capsule
at the distal lead tip. A recent study showed that with HBP, SDL leads
with steroid containing capsules presented with higher acute HBP
thresholds compared to LLL with steroid coated helices. Although no such
difference in acute pacing thresholds was detected in our patients with
LBBAP, further studies are needed to assess whether differences in lead
design and steroid location could affect long-term LBBAP pacing
thresholds.