Address for Correspondence:
George H Crossley, MD
Vanderbilt Heart and Vascular Institute
1215 21st Avenue N
Nashville, TN 37232
E-mail:
george.crossley@vanderbilt.edu
Telephone: 615-322-2318
Fax: 615-936-5064
The authors present an eloquent description of an analysis of the
durability of a cable-based lead for use in directly pacing the human
conduction system 1.
There has long been interest in pacing the conduction system to
normalize the ventricular activation sequence in patients requiring
ventricular pacing2 and clear detriment has been
demonstrated from ventricular pacing, especially when not needed3. The first forays into this were performed by pacing
the AV nodal tissues or the His bundle directly 4.
Over time, it was noted that the stimulation thresholds of His bundle
leads often rose over time. Interest was then developed in the direct
stimulation of the arborized tissues of the Left Bundle Branch. This was
initially aimed at the proximal portions of the left anterior fascicle,
but it was soon found that the early arborization of the left posterior
fascicle was much easier to approach. In this technique, a lead is
placed perpendicular to the RV septal endocardium. The lead is drilled
into the septum until it is near the LV endocardium. At this level,
there is marked arborization of the left bundle tissues. A very narrow
QRS is often obtained. The adoption of this technique spread quickly.
While this technique is medically very attractive, it presents new and
different stressors of the pacing lead used to accomplish this.
Additionally, since this technique is often used in patients with heart
block, it is imperative that the implanting physician have confidence in
the reliability of the lead.
Dr. Wilkoff eloquently expressed, in 2007, that “what has become clear
is that there are three contributing factors to lead failures. First,
lead construction is critical, including materials, design, and
manufacturing. Second is implantation technique, which continually
evolves slowly
over time. Lastly, there are patient factors, such as size, peculiar
anatomic variations, and activities such as power weightlifting, and the
potential for trauma during exercise or accidents.”5
The differences between this technique and the usual technique of RV
endocardial pacing created a great deal of concern among the community
of lead design engineers. The most common lead used for this technique
is the Medtronic 3830 lead which has several unique features: a small
diameter, a lumenless design and a very flexible central cable with a
tight weld to the tip electrode. While the durability of this lead has
been extensively studied and analyzed, it has never been studied when
used in this manner. The unique features of this implant technique
include that the lead is rotated many more times than a standard implant
and that the implantation deep into the tissue creates a fulcrum point
at the surface of the RV endothelium, near the ring electrode. Bending
at a fulcrum point, as is seen with lead implantation through the
subclavious tendon structure, has been associated with conductor
fracture. While the deleterious effect of a fulcrum point on leads has
long been recognized 6 ,the specific stressors
involved in Left Bundle pacing have never been studied that have never
been studied.
The authors used techniques that were developed during the analysis of
the Fidelis® lead failure to study the specific use conditions for a
given lead with given implantation techniques 7. Prior
to that analysis, the stressors that were induced by skeletal motor
activity on the lead in the pocket had largely been ignored and the
impact of prolapsing the lead across the valve had not been appreciated.
Using these techniques, the authors studied the Medtronic 3830 lead when
used in left bundle pacing. They demonstrated that the 10-year
durability of the lead will likely be very high. This is not only useful
in the analysis of this lead when used in this manner, but it also
demonstrates a very useful set of techniques that can help with the
conundrum of studying the long-term durability of an implanted device
that is expected to last many years without doing a 10 – 20 year
clinical study. Fortunately, this approach is becoming standard in the
cardiac rhythm management field, and we certainly hope that it will lead
to improved performance of leads in general8.
One caveat of this analysis is that it should not be extended to other
leads as other leads until they are studied in a similar manner. The
most important unique feature of this lead is that there is no central
lumen. This reduces a common mechanism of lead fracture caused by acute
bending when the lead is flexed. That make extrapolation of these
results to lumen-based leads inappropriate.
References:
1. Zou J. Clinical use conditions of lead deployment and simulated lead
fracture rate in left bundle branch area pacing. Journal of
Cardiovascular Electrophysiology. 2023;XX(NN):PP.
2. Narula OS. Longitudinal dissociation in the His bundle. Bundle branch
block due to asynchronous conduction within the His bundle in man.
Circulation. 1977;56(6):996-1006.
3. Wilkoff BL, Cook JR, Epstein AE, et al. Dual-chamber pacing or
ventricular backup pacing in patients with an implantable defibrillator:
the Dual Chamber and VVI Implantable Defibrillator (DAVID) Trial.[see
comment]. JAMA. 2002;288(24):3115-3123.
4. Deshmukh P, Casavant DA, Romanyshyn M, Anderson K. Permanent, direct
His-bundle pacing: a novel approach to cardiac pacing in patients with
normal His-Purkinje activation. Circulation. 2000;101(8):869-877.
5. Wilkoff BL. Lead failures: dealing with even less perfect. Heart
Rhythm. 2007;4(7):897-899.
6. Mond HG, Sloman JG. The Cardiac Pacemaker Clinic: Memories From a
Bygone Era. Heart, Lung & Circulation. 2021;30(2):216-224.
7. Wilkoff BL, Donnellan E, Himes A, et al. In vitro modeling accurately
predicts cardiac lead fracture at 10 years. Heart Rhythm.
2021;18(9):1605-1612.
8. Cooke DJ, Himes A, Swerdlow CD. Improved engineering standards for
transvenous cardiac leads: A progress report from the Association for
the Advancement of Medical Instrumentation Cardiac Rhythm Management
Device Committee Leads Working Group. Heart Rhythm. 2019;16(6):958-959.