This document discusses His bundle pacing (HBP), which aims to engage the normal conduction system through the His-Purkinje network. HBP may provide physiological stimulation compared to right ventricular pacing. The document covers anatomy and physiology of the His bundle, techniques for selective vs. nonselective HBP, indications including AV node ablation and cardiac resynchronization, long-term outcomes, and challenges such as high capture thresholds and lead revisions. While HBP shows promise, further studies are needed to validate its long-term safety, reliability and impact on arrhythmias.

1. His Bundle Pacing

2. Introduction
• Despite years of successful pacing therapy,
persistent debate regarding optimal ventricular
pacing sites.
• Initial ventricular-only pacing devices provided
adequate rate support but were not synchronized
to atrial contraction, and led to negative
hemodynamic consequences including an
increased risk of heart failure (HF) and atrial
fibrillation

3. Introduction
Even atrioventricular (AV) synchronized pacing
delivered at the right ventricular (RV) apex,
however, was noted to worsen contractile
function in many patients.
Eventually, the connection between the degree
of right ventricular apical (RVA) pacing and
cardiac dysfunction became well established.

4. • Pursuit of alternate pacing sites has included the
RV septum, the RV outflow tract, and the left
ventricle (LV).
• Although biventricular pacing has unequivocally
improved HF outcomes and reduced mortality in
patients with left bundle branch block (LBBB) and
severe LV systolic dysfunction, its role in patients
with preserved LV systolic function remains
unresolved.

5. An ideal physiological approach to ventricular
stimulation should engage the normal
conduction through the His-Purkinje
conduction system.
• In this seminar we will discuss anatomy,
physiology, and clinical role of permanent HBP.

6. Anatomy of HIS Bundle
• Anatomical continuation of the AV node.
• Provide connection for electrical signals from
the AV node to right and left ventricles
through right and left bundle branches,
respectively.

7. • There are 3 common variations of the His
bundle relative to the membranous part of
the ventricular septum.

8. Type I
• 46.7%
• The His bundle consistently coursed along the
lower border of the membranous part of the
interventricular septum, but was covered with
a thin layer of myocardial fibers spanning from
the muscular part of the septum.

10. TYPE II
• 32.4% cases
• The His bundle was apart from the lower
border of the membranous part of the
interventricular septum and ran within the
interventricular muscle

12. TYPE III
• 21% cases,
• The His bundle was immediately beneath the
endocardium and coursed onto the
membranous part of the interventricular
septum (naked AV bundle)

15. Physiological properties of HIS bundle
• The bulk of the His bundle is comprised of cells
that eventually course into the left bundle
branches (only a small number enter the right
branch).
• The cells that make up the His-Purkinje fibers are
broader and shorter than the usual working
myocardial cells with relatively few myofibrils.
• These cells are elongated and oblong in shape,
and make contact predominantly at their
terminal ends and to a lesser extent across the
lateral margins.

16. • These cells are partitioned intricately by collagen
fibers; in fact, longitudinal division of the His
bundle by collagen makes it unique from a
histological standpoint when compared with the
AV node and the working myocardium.
• The collagen may minimize or even prevent
lateral spread of the propagated impulse, while
the compartmentalized tissue with specialized
intercellular connections would facilitate rapid
longitudinal spread of the propagated impulse.

17. • An implication of these findings is that some
patients with His-Purkinje conduction disease
(HPCD) may have relatively proximal disease,
and that pacing distal to the site of block
might overcome the block and narrow the
QRS.

20. SELECTIVE HBP
During S-HBP, ventricular activation occurs directly and
completely over the HPS and is accompanied by the
following :
• The pacing stimulus to QRS (S-QRS) onset interval is
equal to the native His-QRS onset interval (H-QRS).
• However, in patients with HPCD, the S-QRS interval can
be shorter than the H-QRS intervals, as in patients with
BBB or HV block due to capture of latent fascicular
tissue.
• The local ventricular electrogram on the pacing lead
will be discrete from the pacing artifact.

21. • The paced QRS morphology is the same as the
native QRS morphology. In patients with HPCD,
the paced QRS duration may be narrower than
the native QRS with BBB or the escape rhythm.
• Usually a single capture threshold (His capture) is
observed. However in patients with HPCD, 2
distinct His capture thresholds—with and without
correction of underlying BBB—may be seen .

23. NONSELECTIVE HBP
During NS-HBP, there is culmination of both His
bundle and ventricular capture.
• The S-QRS interval is usually zero, as there is no
isoelectric interval between pacing stimulus and
QRS due to the presence of a pseudo-delta wave
(due to local myocardial capture).
• The local ventricular electrogram is directly
captured by the pacing stimulus and is not seen
as a discrete component.

24. • The paced QRS duration will usually be longer
than the native QRS duration by the H-QRS
interval, and the overall electrical axis of the paced
QRS will be concordant with the electrical axis of
the intrinsic QRS.
• In patients with HPCD, the paced QRS duration
may be narrower than the native QRS due to
correction of underlying BBB.

25. • There will usually be 2 distinct capture thresholds –
right ventricular and His capture.
• The His capture threshold may be lower or higher
than the ventricular capture threshold.
• In patients with HPCD, 3 distinct capture thresholds
may be observed in varying combination (RV capture,
His capture with correction of BBB, and His capture
without correction of BBB).

27. Implantation technique
• Early studies used conventional screw-in leads
utilizing manually shaped stylets targeting the
Hisian region identified by a mapping
electrophysiology catheter.
• Subsequent studies have demonstrated the
improved success rates of HBP using a dedicated
4.1 Fr lead (SelectSecure 3830) with an exposed
screw, delivered through a steerable catheter
(SelectSite C304-L69, Medtronic), or fixed curve
sheath (Medtronic C315His).

31. Indications of HIS Bundle Pacing
• AV node block
• Infra nodal block(Intra or infra His block)
• Cardiac resynchronisation therapy
• HIS bundle pacing in RBBB and heart failure

32. HIS BUNDLE PACING FOR AV NODE
ABLATION
• ACC/AHA/HRS AF practice guidelines
recommend that AV junction ablation with
permanent ventricular pacing is a reasonable
strategy to control heart rate in AF when
pharmacological therapy is inadequate and
rhythm control cannot be achieved (Class IIa,
Level of Evidence: B)

33. AV BLOCK AND HBP
• While the feasibility of permanent HBP in
patients with AV nodal block is expected,
surprisingly high numbers of patients with
infranodal block can be corrected with HBP
• The postulated mechanisms for this recruitment
of distal His and bundle branches in patients with
intra-His block are: longitudinal dissociation in
the His bundle with pacing adjacent or distal to
the site of delay/block

35. HIS BUNDLE PACING FOR CARDIAC
RESYNCHRONIZATION THERAPY
• Despite the development of sophisticated tools to
facilitate implant and intraprocedural strategies ,rates
of nonresponse to CRT remain high—between 30% and
40%.
• In addition, rates of implant failure for CRT range
between 5% and 9%, in part due to high rates of CS
lead dislodgement (3% to 7% reported across major
trials)
• In light of this, alternative strategies to achieve
resynchronization have gained momentum, including
endocardial LV lead pacing, “wireless” LV lead
stimulation, and permanent HBP.

38. Permanent His Bundle Pacing for Cardiac
Resynchronization Therapy in Patients With Heart
Failure and RBBB

40. Long term outcome of HIS Pacing
• Compared with RVA pacing, HBP has been
associated with improved fractional shortening,
dP/dt, LVEF, and myocardial performance index
(Tei index).
• Also, improvement in interventricular
electromechanical delay, intraventricular
dyssynchrony, systolic diastolic electromechanical
delay, LV isovolumetric contraction and relaxation
times, and LV ejection time have been
demonstrated.

42. HBP: CLINICAL CHALLENGES
CAPTURE THRESHOLDS-
His capture thresholds >2 V at 1 ms may be seen in 10%
of patients at implant.
Vijayaraman et al. reported that His capture thresholds
remained relatively stable during 5-year follow-up of
75 patients (1.35 +_0.9 V at implant vs. 1.62+_ 1.00 V
at 0.5 ms; p < 0.05).
An increase in chronic pacing threshold >1 V from
baseline was noted in 9 patients in HBP compared with
6 patients in RVP (12% vs. 6%; p = 0.04)

43. LEAD REVISIONS
• Vijayaraman et al. , acute loss of capture
occurred in 2 of 100 patients with AV block
and HBP.
• Lead revisions were required in 3 additional
patients at 2 to 6 months post-implant due to
progressive increases in capture threshold for
a lead revision rate of 5%.

44. • In a long-term study of 75 patients with HBP,
lead revisions were required in 5 patients
(6.7%), 4 of whom underwent successful lead
replacement at the His bundle region even as
late as 5 years after the initial implant.

45. • Acute increase in HBP threshold or loss of
capture is most likely due to inadequate
fixation of the HBP lead.
• The mechanism for delayed increase in HBP
threshold during longer-term follow-up is less
clear.
• It is likely that due to the anatomical proximity
of the loop of the HBP lead, the tricuspid valve
motion causes slow unhinging of the lead

46. BATTERY DEPLETION
• Recent studies have demonstrated that the
majority of patients undergoing HBP do well
without need for early generator changes .
• In patients undergoing CRT with HBP, capture
thresholds required to correct underlying BBB
are often higher, and early battery depletion
can still be a major obstacle

47. DEVICE FOLLOW-UP
• During follow-up, assessment of His bundle
capture using multilead ECG (preferably 12-
lead) is recommended.
• At 3-month follow-up, the pacing output is
programmed to at least 1 V above the His
capture threshold, as confirmed with
multilead ECG rather than at twice-safety
margin, to conserve battery life.

48. FUTURE DIRECTIONS
• permanent HBP may be an attractive option
for physiological pacing in several groups of
patients, its reliability and long-term
performance are yet to be fully validated in
large prospective studies.
• Particularly relevant are patients with
infranodal, intra-Hisian AV block and BBB,
where long-term safety of HBP has not been
well studied.

49. • In such patients, should a backup RV lead be
placed with HBP?
• What happens to the His bundle when it is
traumatized by the screw on the tip of the
lead in the long term?
• Can a second His Bundle pacing lead be placed
successfully if the earlier lead fails in the long
run?

50. •Beyond implant, what are the implications of extracting
a chronic HBP lead?
•And beyond pacing hemodynamics, what is the impact
of HBP on arrhythmia?
• Does HBP reduce the risk of ventricular
tachyarrhythmias in the presence of myocardial scar?

51. CONCLUSIONS
• HBP, an attractive mode of physiological
pacing with significant promise for future
applications in patients who are traditional
candidates for RV pacing as well as CRT
• Widespread adaptation of this technique is
dependent on the improvement of tools and
further validation of its efficacy in large
randomized clinical trials.

52. Thank you