Anatomy of cardiac structures & conducting system in

ANATOMY OF CARDIAC STRUCTURES &
CONDUCTING SYSTEM IN RELATION TO
EP STUDIES
MSN PAVAN KUMAR

 Heart has rhythmic myocardial stimulation leading to physiological
contraction of the heart.
 Anatomic & electrophysiological studies have provided strong background
on the cardiac conduction system.
 Intracardiac electrophysiologic studies (EPSs) have since been found to be
useful for a variety of cardiac arrhythmias
 The recording of intracavitary electrocardiographic signals have
experienced enormous growth during the past three decades. A better
understanding of cardiac anatomy is essential to make further progress
 Since anatomic variation of the cardiac conduction system landmarks and
associated structures is common, it is crucial to learn more about these
normal variants, especially prior to interventional procedures

 Cardiac structures
1. Right & Left atrium
2. The Atrial Septum and Interatrial Connections
3. The Atrioventricular Junctions
4. Right & left ventricles
5. The Coronary Veins
6. Pericardium
 Conducting system
 Ganglionic Plexi

Right Atrium Anatomy :
 The right atrium is best considered in
terms of three components the
appendage, the venous part, the
vestibule
 From the epicardial aspect, the right
atrium is dominated by its large,
triangular-shaped appendage that
extends anteriorly and laterally
 Usually, a fat-filled groove (sulcus
terminalis) corresponding internally to
the terminal crest (crista terminalis) can
be seen along the lateral wall
demarcating the junction between
appendage and venous components


 The division between venous and
rough zones is marked by the terminal
crest
 Arising from the terminal crest,
pectinate muscles spread throughout
the entire wall of the appendage,
reaching to the lateral and inferior
walls of the atrium
 On the endocardial aspect, the
branching and overlapping
arrangement of the pectinate muscles is
clearly visible.

Crista Terminalis:
• Superiorly it arches anterior to the
orifice of the SVC, extends to the
area of the interatrial groove, and
merges with the interatrial bundle,
commonly known as the Bachman
bundle
• This muscular bundle begins in
front of the orifice of the SVC to
descend obliquely to terminate in
number of smaller bundles that
continue toward the orifice of the
IVC , feeding into the area of the
cavo-tricuspid isthmus.

 The SVC opens into the upper and back
part of the atrium and opening has no
valve.
 The IVC opens into the lowest part of the
atrium, near the atrial septum, and
guarded by a rudimentary valve ,
Eustachian valve.
 Eustachian valve is a triangular flap of
fibrous or fibro muscular tissue that inserts
medially to the Eustachian ridge, or sinus
septum, which is the border between the
oval fossa and the coronary sinus

 The coronary sinus between the
orifice of the IVC and the AV opening
and is protected by a valve of
Thebesius
• The triangle of Koch is delineated
posteriorly by the tendon of Todaro
running in the Eustachian ridge,
anteriorly by the septal leaflet of the
tricuspid valve, and inferiorly by the
coronary sinus
• The apex of the triangle is marked by
the central fibrous body through which
the atrioventricular conduction bundle
penetrates

 The area between the inferior caval vein
and the tricuspid valve is also described
as the cavo-tricuspid isthmus.
 The posterior component is mainly
fibrous, whereas the anterior component
is the musculature of the atrial vestibule
and has a smooth endocardial surface.
 Within this area are marked three
isthmuses: paraseptal isthmus ,inferior or
central flutter isthmus ,and inferolateral
isthmus
• The inferior isthmus passes through the sinus of Keith (triangle),the
atrial wall inferior to the orifice of the coronary sinus

Right Atrium Anatomy - Importance:
 Crista Terminalis:
 Most focal ATs (83%) arise from the right atrium (RA), about two
thirds of which are distributed along the long axis of the crista
terminalis . This particular anatomical distribution of ATs may be
related to the marked anisotropy characterizing the region of
the crista terminalis. Such anisotropy, which is related to the poor
transverse cell-to-cell coupling, favors the development of
slow conduction.
 Atrial flutter is a reentrant rhythm in the right atrium constrained
anteriorly by the tricuspid annulus and posteriorly by the crista
terminalis and eustachian ridge


 The triangle of Koch :
1. The apex of the triangle is
marked by the central
fibrous body through which
the atrioventricular
conduction bundle
penetrates
2. The so-called fast pathway
corresponds to the area of
musculature close to the
apex of the triangle of Koch.

 ISTHMUS :
1. Area between the IVC and the TV
corresponds to the isthmus of slow
conduction in the circuit of
common atrial flutter
2. Compared to the inferolateral and
paraseptal isthmuses the inferior
isthmus appears most appropriate
target to ablate
3. Paraseptal isthmus is the area often
targeted for ablation of the slow
pathway in AVNRT .
4. The depth of the sub thebesian
pouch can be a cause of procedural
difficulty.


 Right atrial appendage :
Focal atrial tachycardias (AT) can originate from various anatomic
regions in the heart . Recently , the RAA has been described as a typical
but rare site of focal AT origin , mapping and RF ablation in side the RAA
and its thin wall raises the possibility of cardiac perforation.
 Pectinate muscles :
On the endocardial aspect, the branching and overlapping
arrangement of the pectinate muscles is clearly visible. This arrangement
can play a role in initiating intra-atrial reentry.

 SVC :
The SAN is a sub epicardial, spindle shaped structure at the SVC
atrial junction . Right atrial musculature often extends a short distance
onto wall of the SVC , but muscular extension surrounding the entrance
of the inferior caval vein is less common.
 IVC :
The Eustachian valve in some cases, the valve is particular large and
muscular, posing an obstacle to passage of catheters from the IVC to the
inferior part of the RA. Occasionally, the valve is perforated, or even
takes the form of a delicate filigree sometimes described as a Chiari
network .

Left Atrium Anatomy :

 The left atrium is considered in terms of
three components the appendage, the
venous part, the vestibule
 The atrial appendage is characteristically a
small fingerlike cul-de-sac in human
hearts where thrombi can form. Owing to
its tubular shape, its junction with the left
atrium is narrow and fairly well defined
 Virtually all the pectinate muscles in the
left atrium are confined within the
appendage

 The venous component receives the
pulmonary veins and the vestibular
component leads to the mitral valve.
 There are no surface anatomical landmarks
to separate the vestibule from the
pulmonary venous component although
frequently a few pits or crevices are seen in
the inferior wall at the border zone.
 The left atrial isthmus between the left
inferior pulmonary vein and the MV
• Seemingly uniform, the left atrial walls are composed of one to three
or more overlapping layers of differently aligned myocardial fibers with
marked regional variations in thickness


 The posterior part of the left atrium
receives the pulmonary veins. The orifices
of the left pulmonary veins are more
superiorly located than those of the right
pulmonary veins
 The venous orifices are oval shaped with a
longer superoinferior diameter than
anteroposterior diameter
 Musculature of the atrial wall extends into
the veins to varying lengths, with the
longest sleeves along the upper veins

Left Atrium Anatomy - Importance:
 Pulmonary veins :
It is well established that myocardial
sleeves of the PVs in particular the superior
veins are crucial sources of triggers, which
initiate atrial fibrillation
The PV ostia are ellipsoid with a
longer supero-inferior dimension. Veins are
larger in AF patients, men, and persistent
AF pts The superior pulmonary vein ostia
are larger than the inferior pulmonary vein
ostia
It is important to report the ostial
diameters of each vein and the length to the
first order branch because these
measurements influence the selection of
circular catheter size.

 Pulmonary veins abnormalities:
Before the ablation procedure, it is useful to carry out some type
of noninvasive study for a better definition of pulmonary venous
anatomy, such as a high-resolution computed tomography or magnetic
resonance imaging study

1. It is not uncommon to see mild
narrowing of the left inferior
pulmonary vein (LIPV) at its
confluence with the left atrium. This
is most likely secondary to the
compressive effect of the pulsating
aorta and should not be mistaken for
stenosis after RFA


• Pulmonary veins abnormalities:
2. Early branching is also common and
usually is seen with right upper lobe
pulmonary vein entering near the
confluence of right superior
pulmonary vein with the left atrium.

3. This patient had both left veins
emptying into a common trunk
before entering the atrium and three
veins from the right lung

• Pulmonary veins abnormalities:
1. Conjoined (common) PV is very common (> 25%) and more
frequently seen on the left than the right.
2. In addition, the supernumerary veins are also visualized. The most
common is a separate right middle pulmonary vein (25%), which
drains the middle lobe of the lung
3. One or two separate middle lobe vein ostia can be seen in 26% of
patients. The ectopic focus originating from the right middle PV could
initiate AF, which is cured by catheter ablation of right middle PV.

Note the narrow fold (arrow) between the
os of the left atrial appendage and the
orifice of the left superior pulmonary vein
in this heart. It can be challenging to keep
the ablation catheter stable along this
narrow fold without dropping inadvertently
into the vein or the appendage.

Esophagus to the posterior wall of the left
atrium , the descending aorta close to the
left inferior pulmonary vein is at risk of
damage.

The Atrial Septum Anatomy & Importance :
 The true septum that
interventionalists can cross safely is
limited to the flap valve of the oval
fossa and the immediate muscular
rim that surrounds it on the right
atrial aspect
 Importantly, nearly one-fifth of
hearts have little change in contour,
and the valve is thicker making it
difficult to identify the fossa.
 The valve of the oval foramen can be
perforated or crossed without risk
of exiting the heart or damaging the
arterial supply to the sinus node.

The Atrial Septum Anatomy & Importance :
 Patent foramen ovale
1. In 25% of the normal population, there is probe patency of the oval
fossa. This is because the adhesion of the valve to the rim is incomplete,
leaving a gap usually in the anterosuperior margin corresponding to a C-
shaped mark in the left atrial side just behind the anterior atrial wall
2. A catheter lodged in this crevice will have its tip directed toward the
anterior wall of the left atrium. This part of the wall, just inferior to the
Bachmann bundle, can be very thin . Exiting the heart here leads to the
transverse pericardial sinus and, anteriorly, the aortic root.

Interatrial Connections Anatomy & Importance :

 Most important inter atrial bridge is Bachmann bundle
 Multiple smaller interatrial bridges are frequently present, giving the
potential for macroreentry
1. Some connect the muscular sleeves of the right pulmonary veins to
the right atrium, and some connect the SVC to the LA
2. Inferiorly, further muscular bridges from the left atrial wall often
overlie and run into the wall of the coronary sinus.
3. Fine bridges connecting the remnant of the vein of Marshall to the
left atrium have also been demonstrated

The Atrioventricular Junctions Anatomy & Importance :
 Anatomically, the atrioventricular junction
can be described as comprising extensive
right and left parietal junctions that meet
with a small septal component
 The right parietal junction is relatively
circular and marked by the course of the
right coronary artery in the AV groove.
 The left parietal junction surrounds the
orifice of the mitral valve and part of it is
the area of fibrous continuity between
mitral and aortic valves
 The true septal component is limited to the
area of the central fibrous body and
immediate environs.


 At the atrioventricular junctions the walls of the atriums and ventricles are
contiguous and without myocardial continuity except at the site of the
penetrating bundle of the atrioventricular conduction tissues
 The AV conduction bundle penetrates through central fibrous body
 Anomalous muscular AV connections at the AV junctions produce the
Wolff-Parkinson-White variant of ventricular preexcitation
 AV BTs connect the atria to the ventricle and can cross the AV groove
anywhere along the mitral and tricuspid annulus, except between the left
and right fbrous trigones, region of the aortomitral continuity, at which
site no LV myocardium lies below the LA.

 AV groove may be divided into quadrants consisting of the left free wall,
right free wall, posteroseptal, and anteroseptal spaces.
1. 46% to 60% of BTs are found within the left free wall space
2. 25% are within the posteroseptal space
3. 13% to 21% of BTs are within the right free wall space
4. 2% are within the right anteroseptal space


 Septal accessory pathways are classified as anteroseptal, midseptal, and
posteroseptal
 BTs with an atrial insertion in the foor of the triangle of koch,
posteroinferior to the compact AVN , have been labeled as midseptal
 Anteroseptal generally have no septal connection but are located
anteriorly along the central fibrous body or right fibrous trigone at the
right anterior free wall. Close to his bundle.
 Pathways classified as posteroseptal are located posterior to the central
fibrous body within the so-called pyramidal space, which is bounded by
the superior process of the left ventricle and infero aspects of both atria.

 Right posteroseptal pathways insert along the tricuspid ring in the
immediate vicinity of the coronary sinus ostium
 Left posteroseptal pathways are further into the coronary sinus and may be
located at a
1. Subepicardial site around the proximal coronary sinus, within a
middle cardiac vein or coronary sinus diverticulum
2. Subendocardially along the ventricular aspect of the mitral annulus.


 Left free wall : the atrial insertion of the BT is typically discrete in size and
close to the mitral annulus, the ventricular insertion site tends to ramify
over the region of tissue toward the ventricular apex
 Right free wall : caused by the unique features of the tricuspid annulus,
one can encounter difficulty in maintaining catheter stability, mapping
difficulties and the possibility of multiple or unusual BT.
1. The mitral valve attaches to its fibrous annulus at a right angle
2. The tricuspid annulus has a larger circumference than the mitral
annulus (12 versus 10 cm) and is not a complete fibrous ring

The Right Ventricle Anatomy & Importance :

 Right ventricle: the inlet containing the atrioventricular valve, the outlet
leading to the arterial valve, and the apical trabecular component
 The right ventricle in the normal heart is the most anteriorly situated
cardiac chamber is located immediately behind the sternum.
 The right ventricular inlet extends from the hinge line (annulus) of the
tricuspid valve to the papillary muscles.
 The leaflets of the tricuspid valve can be distinguished as septal, anterior
and mural. The septal leaflet with its cords inserting directly to the
ventricular septum is characteristic of the tricuspid valve.
 Coarse muscular trabeculations crisscross the apical portion.

 The septomarginal trabeculation itself is a
y-shaped muscular band that is adherent to
the septal surface. In between its limbs lies
the infolding of the heart wall forming the
ventricular roof, an area also known as the
supraventricular crest
 The moderator band, is characteristic
of the right ventricle .This bridges the
ventricular cavity between the body of the
septomarginal trabeculation and the
parietal wall, giving rise to the anterior
papillary muscle along the way
 Within its musculature runs a major
fascicle of the right bundle branch.

RVOT:
1. The RVOT region is defned
superiorly by the pulmonic valve and
inferiorly by the supraventricular
crest
2. The lateral aspect of the RVOT region
is the RV free wall, and the medial
aspect is formed by the IVS.
3. The aortic valve cusps sit squarely
within the crescent-shaped septal
region of the RVOT and are inferior
to the pulmonic valve

RVOT:

4. The anteroseptal aspect of the RVOT
actually is located in close proximity to
the LV epicardium, adjacent to the
anterior interventricular vein and in
proximity to the left anterior
descending coronary artery.
5. The inferior aspect of the RVOT is
adjacent to the region of the right
coronary cusp, left coronary cusp.

RVOT:
 VT origins in the RVOT are anatomically classifed into 3-D
directions: anterior and posterior, right and left, and superior and
inferior
 RVOT by fluoroscopy 60 LAO position - anterior and posterior
 RVOT by fluoroscopy 30 LAO position - right and left
 RVOT relation to PV ( <, >1 CM ) - superior and inferior
 This means that the RVOT consists of eight subdivisions:
Anterior Right Superior Posterior Right Superior
Anterior Right Inferior Posterior Right Inferior
Anterior Left Superior Posterior Left Superior
Anterior Left Inferior Posterior Left Inferior

The Left Ventricle Anatomy & Importance :

 Left ventricle: the inlet containing the atrioventricular valve, the outlet
leading to the arterial valve, and the apical trabecular component
 The left ventricle approximates to a conical shape. When the heart is
viewed from the front, most of the left ventricle is behind the right
ventricle. Its outlet overlaps its inlet.
 Compared to that of the tricuspid valve, the septal hinge line of the
mitral valve is further away from the apex, and it does not have a septal
leaflet
 The larger portion of the valve is hinged to the parietal atrioventricular
junction, whereas one-third is the span of fibrous continuity with the
aortic valve
 The two leaflets of the mitral valve are disproportionate in size.

 The apical component of the left
ventricle extends from the papillary
muscles to the ventricular apex.
 The trabeculations are finer than
those found in the right ventricle.
 Occasionally, fine muscular strands or
so-called false tendons extend between
the septum and the papillary muscles
or the parietal wall. Often, they carry
the distal ramifications of the left
bundle branch. In recent years they
have been have been implicated in
idiopathic left ventricular tachycardia.


 The left ventricular outlet is bordered by the muscular ventricular septum
anterosuperiorly and the aortic (anterior) leaflet of the mitral valve
posteroinferiorly .
 In the outlet, two leaflets of the aortic valve have muscular support,
these being the ones adjacent to, or facing, the pulmonary valve. The
third sinus, the noncoronary sinus, does not have muscular support.
 Like the pulmonary valves, these two sinuses contain small segments of
ventricular myocardium within, a source of repetitive monomorphic
ventricular tachycardia.
 LVOT are not divided into subdivisions like RVOT


 Owing to the spatial relationship of the
subpulmonary infundibulum and the left
ventricular outlet , the foci can be ablated
from within the part of the right ventricular
outlet that overlies the adjacent aortic
sinuses.
 The noncoronary aortic sinus, being
immediately adjacent to the paraseptal region
of the left and right atriums and close to the
superior atrioventricular junction, can be
used to map and ablate focal atrial tachycardia
that have earliest activation in the vicinity of
the His bundle area .

Ventricle Anatomy & Importance :

 RF catheter ablation of VT can be divided into
1. Idiopathic VT, which occurs in patients with normal hearts,
2. VT that occurs in various disease settings but without CAD
3. VT in patients with CAD and usually prior MI .

Ventricle Anatomy & Importance :

 Idiopathic VT:
1. Right ventricular tachycardias most commonly originate in the
outflow tract less often, VTs arise in the inflow tract or free wall.
2. Most LV VTs are septal in origin , less commonly arise from
LVOT and aortic sinuses of Valsalva
 VTs in abnormal hearts without CAD can be the result of bundle
branch reentry , most typically observed in patients with DCM. In
these patients, ablation of the RBB eliminates the tachycardia
 Localization of ablation sites for VT in patients with CAD and prior MI
is more difficult because of the altered anatomy and electrophysiology.

The Coronary Veins Anatomy & Importance :

 The venous return from the
myocardium is channelled either by
means of small thebesian veins that
open directly into the cardiac
chambers or, more significantly, is
collected by the greater coronary
venous system that drains 85 percent
of the venous flow.
 The main coronary veins in the
greater system are the great, middle,
and small cardiac veins.

 The great veins run alongside the
anterior descending drain into the
coronary sinus
 As the great cardiac vein ascends into
the left atrioventricular groove, it
passes close to the first division of the
left coronary artery and under the
cover of the left atrial appendage.
 Approaching the coronary sinus, the
great vein is joined by tributaries from
the left ventricular obtuse margin and
the inferior wall, as well as veins from
the left atrium

 The distribution, courses, and calibres of the left ventricular veins
vary from individual to individual.
 The left ventricular veins can be accessed for ablating ventricular
tachycardia from a source close to the epicardium.
 When using them for pacing lead implants it is worth noting that the
left phrenic nerve running in the pericardium can pass across the
obtuse marginal vein .
 Although coronary veins are usually superficial to arteries, crossovers
between arteries and veins are not uncommon.
 Furthermore, when deploying catheters or wires in superficial veins,
care should be taken because venous wall is thin and unprotected by
muscle on the epicardial side.


 The entrance of the vein of Marshall, or
oblique left atrial vein, marks the venous
end of the tube-shaped coronary sinus.
 The vein is a fibrous ligament in most
individuals.
 The Marshall bundle may serve as the
origin of focal AF in some patients.
 If adequately wide, this channel can be
used for ablating the left atrial wall

 In the absence of the vein of Marshall, or its remnant, the Vieussens
valve is taken as th e anatomic landmark for the junction between the
coronary sinus and the great cardiac vein
 Found in 80 to 90 percent of hearts, this very flimsy valve has one to
three leaflets that can provide some resistance to the catheter.
 Once past the Vieussens valve, a sharp bend in the great cardiac vein
can cause further obstruction in 20 percent of cases
 Another marker for the junction between vein and coronary sinus is the
end of the muscular sleeve around the sinus.
 But, in some cases, the sleeve can extend to 1 cm or more over the
vein. Bundles from the sleeve sometimes run into the left atrial wall and
also cover the outer walls of adjacent coronary arteries

 The middle cardiac vein drains into the
coronary sinus just within the sinus os.
 Occasionally the middle vein enters the RA
directly and opens adjacent to the os of the
CS, providing the coronary sinus catheter
with an alternative, but undesired, portal.
 The middle vein passes just superficial to the
right coronary artery at the cardiac crux.
 It is a useful portal for ablating accessory
atrioventricular pathways located in the
inferior pyramidal space.
• Very rarely, the entrance of the middle vein is dilated and surrounded
by a cuff of muscle giving the potential for accessory atrioventricular
connections.


 The small cardiac vein receives tributaries from the right atrium and the
inferior wall of the right ventricle before coursing in the right
atrioventricular junction to open to the right margin of the coronary
sinus orifice, or into the middle cardiac vein.
 When joined by the acute marginal vein, or vein of Galen, the small
vein becomes larger.
 Several other veins, from the anterior surface of the right ventricle and
from the acute margin, drain directly into the right atrium.
 In some hearts, the anterior veins merge into a venous lake in the right
atrial wall. Again, these can be surrounded by a cuff of myocardium
that gives the potential for accessory atrioventricular connection as the
vein passes through the atrioventricular groove.


 CARDIAC RESYNCHRONISATION THERAPY :
1. Perhaps the single most important factor affecting the outcome of CRT is
the placement of the left ventricular lead.
2. The main challenges of the implant procedure are coronary venous
access, stability of the guide catheter, and variation in the anatomy of the
coronary sinus.
3. It is not always possible to achieve a favorable posterolateral position that
is stable, with a good threshold, and avoids diaphragmatic pacing.
4. In up to 10% of cases, transvenous placement of the left ventricular lead
is not possible. The default option at present is surgical positioning of
this lead.

Pericardium Anatomy & Importance :
 The heart itself is enclosed in a fibrous sac,
the pericardium, which separates the surface
of the heart from adjacent structures.
 The pericardial cavity is the space between
the layers of the serous pericardium.
 Two recesses are found within the pericardial
cavity.
1. One is the transverse sinus lying
between the back of the arterial trunks
and the front of the atrial chambers.
2. Another is the oblique sinus lying behind the left atrium and is
limited by the right pulmonary veins and the inferior caval vein to
the right side and by the left pulmonary veins to the left side.

The Cardiac Conduction SystemAnatomy & Importance :

 Sinus node :
1. The sinus node is crescent like in shape with a mean length of 13.5 mm in
the adult present at the superior vena cava–atrial junction
2. In most cases the head is subepicardial, whereas the tail penetrates
inferiorly into the myocardium of the terminal crest to lie closer to the
subendocardium.
3. Although the specialized myocytes of the nodal cells are set in a fibrous
matrix, the node is not encased in a fibrous sheath, with frequent
interdigitations between nodal and ordinary atrial myocytes
4. The node is richly supplied with nerves from both the sympathetic chains
and the vagus nerve.
5. The artery supplying the sinus node branches from the RCA (55 to 60
percent) or the LCX (40 to 45 percent)

 Internodal and Intraatrial Conduction :
1. The anterior internodal pathway
Bachmanns bundle
2. Middle internodal pathway
Wenkhebach bundle
3. Posterior internodal pathway
Tract Of Thorel
4. These groups of internodal tissue are
best referred to as internodal atrial
myocardium, not tracts, because they do
not appear to be histologically discrete
specialized tracts.

Interatrial Connections Anatomy & Importance :
 Bachmann bundle.
1. The most prominent interatrial bridge is the Bachmann bundle
2. This is a broad muscular band that runs in the subepicardium
connecting the anterior right atrial wall of the SVC RA junction with
the anterior wall of the LA.
3. The SAN artery and its branches are the principal vascular supply of BB
4. BB is less visible in patients with severe coronary artery disease, atrial
fibrillation, and interatrial conduction block
5. Changes in the musculature of BB could block or prolong interatrial
conduction resulting in abnormal atrial excitability, atrial dysfunction,
AF, and other arrhythmias

 Atrioventricular Junctional Area
 The normal AV junctional area can be divided into distinct regions:
1. The transitional cell zone
2. The compact portion, or the AV node itself
3. The penetrating part of the AV bundle (His bundle)
 The transitional cells differ histologically from atrial myocardium and
connect the latter with the compact portion of the AV node.
 The compact portion of the AV node is a superficial structure lying just
beneath the right atrial endocardium at the apex of triangle of Koch ,
5 mm long and wide.
 In triangle of Koch, the tendon of Todaro, which forms one side of the
triangle of Koch, is absent in about two thirds of hearts.

 The arterial supply to the AV node is a branch from the RCA in 85 to 90
percent of human hearts, LCX in 10 to 15%.
 Fibers in the lower part of the AV node may exhibit automatic impulse
formation
 The compact portion of the AV node is divided from and becomes the
penetrating portion of the his bundle at the point where it enters the
central fibrous body

 Bundle of His :
1. This structure connects with the distal part of the compact AV node,
perforates the central fibrous body, and continues through the annulus
fibrosis, where it is called the nonbranching portion as it penetrates the
membranous septum
2. Proximal cells of the penetrating portion are heterogeneous and resemble
those of the compact AV node; distal cells are similar to cells in the
proximal bundle branches.
3. Branches from the anterior and posterior descending coronary arteries
supply the upper muscular interventricular septum with blood, which
makes the conduction system at this site more resistant to ischemic damage
unless the ischemia is extensive.

 Characteristics of the Right Bundle.
1. The RB is a long, thin, discrete, and vulnerable structure that
consists of fast response Purkinje fbers.
2. The RB courses down the right side of interventricular septum near
the endocardium in its upper third, deeper in the muscular portion of
the septum in the middle third, and then again near the endocardium
in its lower third.
3. The RB does not divide
throughout most of its course, and
begins to ramify as it approaches
the base of the right anterior
papillary muscle, with fascicles
going to the septal and free walls
of the RV.

 Characteristics of the Left Bundle and Its Fascicles.
1. The main LB penetrates the membranous portion of the IVS under the
aortic ring and then divides into several fairly discrete branches.
2. The LAF crosses the LVOT and terminates in the Purkinje system of the
anterolateral wall of the LV.
3. The LPF appears as an extension of the main LB and is large in its initial
course. It then fans out extensively posteriorly toward the papillary
muscle and inferoposteriorly to the free wall of the LV.
4. An estimated 65% of individuals have a, the left median fascicle
(LMF).The LMF runs to the interventricular septum, and it arises in most
cases from the LPF, or LAF or from both, or independent origin from the
central part of the main LB at the site of its bifurcation.

The Cardiac Conduction System Anatomy &
Importance :

 Purkinje Fibers :
1. These fibers connect ends of the BBs to ventricles muscle, which transmit
the cardiac impulse almost simultaneously to the entire RV and LV
endocardium.
2. Purkinje fibers tend to be less concentrated at the base of the ventricle and
at the papillary muscle tips.
3. In humans, they penetrate only the inner 1/3rd of the endocardium
4. PFs appear to be more resistant to ischemia than ordinary cardiac muscle
5. Recently, triggers of VF have been mapped to the Purkinje system in the
right ventricular outflow tract and successfully ablated

Ganglionic Plexi: Anatomy & Importance :

 Extracardiac nerves from the mediastinum reach the heart and form
plexus around the hilum of the heart.
 Nerves from the venous part of the hilum extend mainly to the atria,
whereas those from the arterial pole predominantly reach the ventricles
 Six to ten collections of ganglia, ganglionated subplexuses of the
epicardiac neural plexus, have been described in the human heart.One-
half are located on the atria and the other half on the ventricles .
 The ganglionated subplexuses are generally associated with islands of
adipose tissue referred to as fat pads that serve as visual landmarks to
cardiac surgeons.

Ganglionic Plexi: Anatomy & Importance :

 The atrial fat pads are located in the
interatrial groove, at the cavo-atrial
junctions and on the left atrial wall in
the vicinity of the venoatrial junctions
 Vagal stimulation shortens the atrial
effective refractory period that
facilitates the initiation and
maintenance of AF. By adding the LA
ganglion plexus to other ablation
targets, may improve ablation success
in patients undergoing circumferential
PV ablation for paroxysmal AF

Better understanding of detailed anatomy is relevant to
clinical electrophysiologists not only to avoid or minimize
complications during interventional procedures but also to
provide the anatomical background for some of the substrates
of certain arrhythmias.

Anatomy of cardiac structures & conducting system in

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