4.2. Technical Considerations
Fluoroscopy is inaccurate for localizing lead positions compared with
other imaging methods, such as cardiac computed tomography (CT). Indeed,
in a series of 59 heart failure patients undergoing CRT, the agreement
for the left ventricular lead position was observed in 35% and for the
right ventricular lead position in only 22% of the patients with
fluoroscopy, respectively.12 The agreement within and
between observers was much better and more accurate for cardiac CT
(kappa 0.87 and 0.85 for both left and right ventricular lead position,
respectively). Further, another technical limitation is the implantation
tools for HBP. Although several companies in the pharmaceutical industry
have created pacing leads for His Bundle, the most commonly used HBP
lead is the 69 cm Select Secure™ 3830 (Medtronic), a non-stylet-driven
active fixation lead.13 This lead can be delivered to
the His bundle region using either the specially-designed
non-deflectable His delivery sheath (C315 43 cm; Medtronic) or a
deflectable sheath (C304 69 cm; Medtronic). A characteristic of this 4.1
Fr (French gauge) bipolar lead is that the 1.8 mm exposed-helical-screw
design forms part of the tip electrode, with 9 mm tip to ring spacing,
allowing easier detection and thus pacing of His Bundle fibers. It has
unipolar mapping capabilities and minuscule size, reducing flow stresses
and valvular motion effects, thus giving maximum stability in that
demanding area.14 This lead has the best features
after 50 years of trying pacing His Bundle using primarily fluoroscopic
guidance and afterward electrical mapping for its placement.
As a technique, it does not have any critical complications for the
patient, apart from those related to the vein puncture, as with
conventional pacemakers implantation. However, there are two main
troubles: the possibility of an increase in pacing threshold, which is
observed at about 10% of the patients, leading to shorter battery-life
duration, as well as the higher rate of lead revisions in an actual
percentage ranging from 6.7 - 8.9 %, due to loss of capture or
increased threshold. In order to avoid the above two concerns, a
’backup’ right ventricular lead can be used. The use of a ’backup’ lead
is recommended in HBP in cases of the inexperience of the implanter,
acceptable threshold achieved at the upper limit, at about 2V/1ms,
possible schedule of an AV node ablation shortly, but also in cases of
high-degree or infranodal block, especially in entirely
pacemaker-dependent patients.1 Undoubtedly, an extra
third lead for pacing has the advantage of safety, especially in cases
of loss of capture, and it has better sensing compared with the HBP
lead. However, more transvenous hardware for pacing (three versus two
leads) increases the procedure’s cost, along with the risk of
complications, both during implantation (ventricular perforation or vein
thrombosis) and after, such as lead damage or risk of endocarditis. From
all the anatomical and technical limitations mentioned, which may lead
to a possible increase in pacing threshold and the need for lead
revisions, arises the third consideration, which is also restrictive of
HBP widespread application.