The document summarizes the anatomy and electrophysiology of the human atrioventricular (AV) node. It describes the AV node's location near the triangle of Koch. Immunohistochemistry reveals the AV node is divided into the lower nodal bundle and compact node based on differences in connexin 43 expression. The dual pathway electrophysiology of the AV node involves faster conduction through the connexin 43-negative compact node and slower conduction through the connexin 43-positive lower nodal bundle and extensions. Understanding the molecular compartmentalization of the AV node provides insight into its roles in cardiac conduction and as a potential arrhythmia substrate.

2. ANATOMYAND
ELECTROPHYSIOLOGY OF
THE HUMAN AV NODE
GUIDE- Dr A UDYAVAR
BY- Dr SUMEDH

3. INTRODUCTION
AV NODE, aka Tawara’s node, described by
Sunao Tawara in 1906
compact spindle shaped cells in ‘knoten’ (node)
Das Reizleitungssytem des Saugetierherzens
(The Stimulus Conducting System of
Mammalian Hearts): provides description of AV
node, His bundle , surrounding atrial
myocardium.

4. AV Node is located near the apex of the triangle
of Koch.
In adults, AV Node is 5 mm long and wide.
Blood Supply- from AV Nodal Artery,
which arises from RCA in 80 %
LCX in 10 % and
both in 10 %

5. TRIANGLE OF KOCH
location: at base of Rt atrium.
coronary sinus ostium (cs) : INFERIORLY
tendon of Todaro (tT) : POSTERIORLY
septal leaflet of the tricuspid valve (TV) : ANTERIORLY
septal leaflet of TVtendon of
Todaro
coronoray sinus ostium

7. using central fibrous body (CFB) as demarcation
between His bundle and AV node, as Tawara
suggested,
AV node divided into----------
Lower Nodal Bundle (LNB)
and Compact Node (CN)

8. LNB:
cells are longer and arranged more parallel to
one another
CN:
cells are small and spindle shaped with no clear
orientation.

9. extending proximally from LNB towards CS is
“inferior nodal extension/ rightward nodal
extension”
“second nodal extension/ leftward nodal
extension” , only in humans, extends from CN
towards the CS, is usually shorter than right
one.

10. Our current understanding
of the 3 D structure of the
AVJ based on expression
patterns of CX43 which
delineate 2 discreate
structures.
Green denotes the His Bundle
Yellow denotes the LNB and RE ( a CX43 +
region)
Blue denotes the CN and LE (a CX43 – region )

11. Immunofluoroscence
identified differences in the
expression of CX43
between the 2 extensions
and their corresponding
counterparts in the AV
node.
CN/ Leftward Extension: CX43 NEGATIVE
LNB/ Rightward Extension: CX43 POSITIVE

12. STRUCURAL OVERVIEW
Immunohistochemistry reveals that gap junction proteins
involved in cell to cell signaling and cardiac conduction.
Connexin 43 (Cx43), major cardiac gap protein.
fig (b-d) : Histological sections
fig (e-g) : Corresponding immunostained sections for CX43.

13. AVJ plays important role in :
1. in coordinating and maintaining
appropriate AV conduction
2. protecting the ventricles from atrial
tachyarrhytmia
3. functioning as a backup pacemaker in the
setting of SA node dysfunction.

14. Functional overview
1 Independent Pacemaker
2 Filter for impulses between atria &
ventricles
3 Potential arrhythmogenic substrate
molecular compartmentalization i.e, CX 43
expression provides basis for unique properties
in AV node –arrhythmia formation and
pacemaker function.

15. INE inferior nodal extension/Rightward
extension – considered as leading pacemaker
location in the absence of SA nodal impulses
in rabbit hearts.
This same location in another study was found to
have high levels of HCN4- which is the major
cardiac pacemaker current responsible for If.
In other study in human hearts, leading
pacemaker was found to be located in CN area

16. Functional longitudinal dissociation
between fast and slow pathway
A spontaneous reentrant beat originates in CN
area, similar to where the intrinsic junctional
rhythm originates, progresses in retrograde
fashion through the fast compartment, returns
anterogradely through the slow pathway.
This displays functional compartmentalization
within AVJ between Cx43(+) & Cx43(-)
regions.

17. AV nodal dual pathway
A standard S1-S2 protocol was applied to
unmask dual pathway electrophysiology.
During a routine S1 train @ 1000ms, conduction
consistently occurred through fast pathway
Then, decreased to S2 of 600 ms, conduction
block occurred in fast pathway d/t long
refractory period

18. Correlating Structure and Function
Anatomically, 2 pathways- RE/LNB and LE/CN.
Functionally, 2 pathways- slow and fast .
SLOW PATHWAY FAST PATHWAY
RE/LNB LE/ CN
CX43 POSITIVE CX43 NEGATIVE

19. Substrate for the slow pathway involves
structures in isthmus of myocardium located
along tricuspid annulus below coronary sinus.
Evidence exists- RE is the anatomical substrate
of slow pathway.

20. Fast pathway is less well defined.
The probable anatomical substrate of this is
transitional cell layers located around the CN
at the interface between CN and transiional
cells, which expresses Cx43 at levels similar to
the interatrial septum.

21. Cx43(-)- >as the fast pathway compartment
Cx43(+)->as the slow pathway compartment
We dont believe that Cx43 expression is directly
responsible for slow pathway conduction, nor
the absence of it responsible for fast pathway
conduction.
However, Cx43 expression provides a starting
point for characterizing the region from a
molecular standpoint.

22. Clinical Implications
AVJ pacemaker located within region of slow
pathway opens the possibility of genetic &
cellular manipulation , results in modification
of existing native AVJ pacemaker function.
Proteins/ encoding genes involved in modulating
the pacemaker (HCN4, calcium handling etc)
and conduction could be delivered.

23. Role of ANS in regulating the AVJ
Bianchi, et al implanted the atrial lead in the
postero septal right atrium (slow pathway) in
pt with AF receiving defibrillators, with help
of high frequency stimulation at this particular
pacing, they were able to induce conduction
block at level of AVJ.
This may be used in rate control of rapid
ventricular response in atrial fibrillation.

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