Anatomy of cardiac structures & conducting system in

MSN PAVAN KUMAR

ANATOMY OF CARDIAC STRUCTURES & CONDUCTING SYSTEM IN RELATION TO

EP STUDIES

Heart has rhythmic myocardial stimulation leading to physiological contraction of the heart.

Anatomic & electrophysiological studies have provided strong background on the cardiac conduction system and its electrical connection structures.

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 structures1. Right & Left atrium2. The Atrial Septum and Interatrial

Connections3. The Atrioventricular Junctions4. Right & left ventricles5. The Coronary Veins6. Pericardium

Conducting systemFat Pads and Innervations

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

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.

The venous component is characterized by smooth walls. The division between venous and rough zones is marked by the terminal crest

Right Atrium Anatomy :

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

In some cases, the valve is particular large and muscular, the valve may be perforated, or even takes the form of a delicate filigree sometimes described as a Chiari network


The coronary sinus between the orifice of the IVC and the AV opening and is protected by a valve of Thebesius

Frequently, the crescentic valve is fenestrated. Occasionally, the orifice is totally covered by a fenestrated valve, but an imperforate valve is very rare


• 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 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.

Crista Terminalis: 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

Right Atrium Anatomy - Importance:

SVC : The SAN is a subepicardial, 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 inferior caval vein to the inferior part of the right atrium. Occasionally, the valve is perforated, or even takes the form of a delicate filigree sometimes described as a Chiari network .


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.


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

Left Atrium Anatomy :

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


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.

Left Atrium Anatomy - Importance:

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

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.


• Pulmonary veins abnormalities:


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 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.

The Atrial Septum 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

Interatrial Connections Anatomy & Importance :

Multiple smaller interatrial bridges are frequently present, giving the potential for macroreentry1. Some connect the muscular sleeves of the right

pulmonary veins to the right atrium, and some connect the SVC to the LA

2. Posterior and inferior bridges joining the left atrium to the intercaval area on the right provide the potential for posterior breakthrough of sinus impulse

3. Inferiorly, further muscular bridges from the left atrial wall often overlie and run into the wall of the coronary sinus.

4. Fine bridges connecting the remnant of the vein of Marshall to the left atrium have also been demonstrated

Interatrial Connections 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.

The Atrioventricular Junctions Anatomy & Importance :

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, wthe 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 space2. 25% are within the posteroseptal space3. 13% to 21% of BTs are within the right free wall space4. 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, whereas

Left posteroseptal pathways are further into the coronary sinus and may be located at a1. Subepicardial site around the proximal coronary sinus, within

a middle cardiac vein or coronary sinus diverticulum2. 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 and may be displaced a small distance away from the mitral annulus, 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

angle2. The tricuspid annulus has a larger circumference than the

mitral annulus (12 versus 10 cm) and is not a complete fibrous ring


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, anterosuperior, and inferior or 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 Right Ventricle Anatomy & Importance :

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.


Subpulmonary muscular infundibulum that is a tubelike structure supporting the pulmonary valve .

Two of the pulmonary sinuses are adjacent to two aortic sinuses, the right and left coronary sinuses, although the planes of the aortic and pulmonary valves are at and angle to one another. Thus, the main coronary arteries can also be at risk when ablating in the septal part

Sinuses of pulmonary valve have small areas of myocardium


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 Left Ventricle Anatomy & Importance :

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.


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 .


RF catheter ablation of VT can be divided into1. Idiopathic VT, which occurs in patients with

normal hearts, 2. VT that occurs in various disease settings but

without CAD3. 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 different areas of the LV , including the 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 dilated cardiomyopathies. In these patients, ablation of the right bundle branch eliminates the tachycardia

Localization of optimal ablation sites for VT in patients with CAD and prior MI is more difficult because of the altered anatomy and electrophysiology.

Ventricle 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 Coronary Veins Anatomy & Importance :

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.

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 .

The left ventricular veins can be accessed for ablating ventricular tachycardia from a source close to the epicardium.

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.

The characteristics of the double potentials within the VOM suggest that the second potential is from the muscle bundle within the LOM

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.


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.

Pericardium Anatomy & Importance :

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 begins at the anterior margin of the sinus node and curves anteriorly around the superior vena cava to enter the anterior interatrial band, called the Bachmann bundle. This band continues to the left atrium, with the anterior internodal pathway entering the superior margin of the AV node. The Bachmann bundle is a large muscle bundle that appears to conduct the cardiac impulse preferentially from the right to the left atrium.


Internodal and Intraatrial Conduction :2.The middle internodal tract begins at the superior and

posterior margins of the sinus node, and descends in the interatrial septum to the superior margin of the AV node. (Tract Of Wenchebach)

3.The posterior internodal tract starts at the posterior margin of the sinus node and travels posteriorly around the superior vena cava and along the crista terminalis to the eustachian ridge and then into the interatrial septum above the coronary sinus, where it joins the posterior portion of the AV node.(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, only plain atrial myocardium.


Atrioventricular Junctional Area The normal AV junctional area can be divided into distinct

regions: 1. The transitional cell zone2. The compact portion, or the AV node itself3. 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, A branch of the LCX provides the AV nodal artery in the remaining hearts

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 impervious to is-chemic 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

interventricular septum under the aortic ring and then divides into several fairly discrete branches.

2. The components of the LB are the predivisional segment, the LAF, the LPF, and the LMF.

3. The LAF crosses the left ventricular outfow tract (LVOT) and terminates in the Purkinje system of the anterolateral wall of the LV.

4.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.

5. 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.


Purkinje Fibers :1.These fibers connect with the ends of the bundle

branches to form interweaving networks on the endocardial surface of both ventricles, which transmit the cardiac impulse almost simultaneously to the entire right and left ventricular 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 apparently penetrate only the inner third of the endocardium

4.Purkinje fibers appear to be more resistant to ischemia than ordinary myocardial fibers are.

5.Recently, triggers of ventricular fibrillation have been mapped to the Purkinje system in the right ventricular outflow tract and successfully ablated

The Cardiac Conduction System Anatomy & Importance :

Extracardiac nerves from the mediastinum reach the heart through the areas bounded by the serous pericardium. These sites around the great veins at the cardiac base and around the pulmonary trunk and aorta are referred to as 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, but there are also multiple connections

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

Ganglionic Plexi: Anatomy & Importance :

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