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15 March 2013 Volume 99 Issue 6

Editor’s choice The evolving epidemiology of valvular aortic stenosis. The Tromsø Study

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ReviewUnderstanding coronary artery disease using twin studies

Education in HeartCardiac anatomy: what the electrophysiologist needs to know

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ARRHYTHMIAS

Cardiac anatomy: what the electrophysiologistneeds to knowJosé Angel Cabrera,1 Damián Sánchez-Quintana2

▸ Additional references arepublished online only. To viewplease visit the journal online(http://dx.doi.org/10.1136/heartjnl-2011-301154).1Department of Cardiology,Hospital Universitario Quirón-Madrid, European University ofMadrid, Madrid, Spain2Department of Anatomy andCell Biology, University ofExtremadura, Badajoz, Spain

Correspondence toDr José Angel Cabrera,Department of Cardiology,Hospital Universitario Quirón-Madrid, European University ofMadrid, Calle de Diego deVelázquez. 28223 Pozuelo deAlarcón (Madrid), Spain;[email protected];[email protected]

Published Online First25 January 2013

To cite: Cabrera JA,Sánchez-Quintana D. Heart2013;99:417–431.

The rapid development of interventional proce-dures for the treatment of arrhythmias in humans,especially the use of catheter ablation techniques,has renewed interest in cardiac anatomy. Effectiveand safer catheter based procedures have comefrom an improved understanding of not only thegross anatomic details of the heart, but also somearchitectural and histological features of variouscardiac regions and their neighbouring landmarks.This article aims to provide the basic anatomicinformation needed to understand mapping andablative procedures for the cardiac interventionalelectrophysiologist.

SPATIAL LOCATIONS OF THE CARDIACCHAMBERS DURING ANELECTROPHYSIOLOGICAL STUDYThe correct attitudinal position and spatial relation-ships of the different cardiac structures should beunderstood. Viewed from the frontal aspect of thechest, the right ventricle (RV) is the most anteriorlysituated cardiac chamber because it is locatedimmediately behind the sternum. The cavity of theright atrium (RA) is anterior, while the left atrium(LA) is the most posteriorly situated chamber.Owing to the obliquity of the interatrial septum(IS) plane (which is at an angle of about 65° fromthe sagittal plane), and to the different levels of themitral and tricuspid valve (TV) orifices, the LA issituated more posteriorly and superiorly thanthe RA.The introduction of non-fluoroscopic electroana-

tomic mapping technologies has enabled electro-physiologists to interpret correctly the grossmorphology and attitudinal position of the cardiacchambers during the course of a mapping proced-ure.1 Intracardiac echocardiography has also beenused to visualise some endocardial structures suchas the oval fossa (OF) or terminal crest (TC) and tomonitor the effects of ablation. In spite of theserecent developments, conventional fluoroscopyremains the essential guide during an electrophysio-logical study and ablation procedure. Fluoroscopicexamination is performed using the frontal andoblique projections. Two or more fluoroscopicviews are usually needed to define the anatomicposition in the heart and to estimate more accur-ately the location of the exploring electrode. Theright anterior oblique (RAO) projection defineswhat is anterior, posterior, superior, and inferior.The left anterior oblique (LAO) defines the super-ior, inferior, anterior, and posterior locations forboth the right and left atrioventricular (AV) grooves(figures 1 and 2). The LAO is also useful to define

what is septal, permitting the differentiationbetween the complex right and left paraseptalregions. It is the preferred projection to catheterisethe coronary sinus (CS) and its continuation alongthe epicardial aspect of the postero-inferior region2

(figures 1 and 2).

RA ANATOMYThe RA has four components: the venous compo-nent, the vestibule, an appendage, and it shares theseptum with the LA.w1 The venous component islocated posterolaterally and receives the systemicvenous return from the superior caval vein (SCV),the inferior caval vein (ICV), and the coronaryvenous return from the CS. The vestibule is asmooth muscular wall around the tricuspid orifice,and supports the leaflets of the TV. The characteris-tic feature of the vestibule is that it is surroundedby the pectinate muscles of the RA. The right atrialappendage (RAA) lies over the anterosuperioraspect of the right AV groove and contains multiplepectinate muscles, which arise from the TC orcrista terminalis (figures 2 and 3).

TC AND THE REGION OF THE SINUS NODEThe TC is a significant structure in several forms ofatrial tachyarrhythmias, acting as a natural barrierto conduction in common atrial flutter. The TC is alarge muscular ridge that separates the smoothwalled venous part (venous component) from theextensive trabeculated (pectinated) RAA. Thus, theC-shaped crest extends laterally and inferiorly,turning in beneath the orifice of the inferior venacava (IVC) to ramify as a series of trabeculations inthe area between the IVC and the TV3 (figure 3).The pectinate muscles, originating from the crestand extending along the wall of the appendagetowards the vestibule of the TV, show a non-uniform trabecular pattern in most hearts. It is rele-vant the confluence between the TC at its origin inthe interatrial groove and the origin of anotherimportant muscular fascicle, the interatrialBachmann’s bundle, which extends into the LA.3

The sinus node (SN) is the source of the cardiacimpulse. It is usually localised within the TC at itsanterolateral junction with the SCV. The SN iscrescent-like in shape with an extensive longitudinalaxis. Notably, it is not insulated by a sheath offibrous tissue and varies in position and length alongthe crista terminalis. Sections through the SN alsoshow a discrete area, composed of loosely packedmyocytes, which we have termed the paranodalareaw2 (figure 4). While in 72% of the hearts thelocation of the nodal body is subepicardial, in the

Cabrera JA, et al. Heart 2013;99:417–431. doi:10.1136/heartjnl-2011-301154 417

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http://dx.doi.org/10.1136/heartjnl-2011-301154



other 28% the inner aspect of the nodal body ismore subendocardial.4 Its margin is irregular withmultiple extensions interdigitating into the neigh-bouring working atrial myocardium (figure 4). Bothinappropriate sinus tachycardia and sinus nodalre-entrant tachycardia are arrhythmias arising fromthe sino-atrial area. Box 1 shows the relevant ana-tomic determinants for SN ablation or modificationwith endocardial catheter techniques.

INFERIOR RIGHT ATRIAL ISTHMUS AND ITSANATOMIC DETERMINANT FOR ATRIALFLUTTER ABLATIONThe inferior right atrial cavo-tricuspid isthmus, acritical link for the macro-reentrant circuit ofisthmus dependent atrial flutter, is the target of cath-eter ablation techniques that have become the treat-ment of choice for this arrhythmia. Anatomical andimaging studies have shown a wide range of morph-ologies and architectural factors at the isthmus levelthat may influence the feasibility of obtaining a com-plete, transmural and permanent ablation line acrossthis anatomic landmark.5 w3 w4 (box 1). With theheart in an attitudinal orientation, we identified andmeasured the length of three levels of the isthmus:paraseptal (24±4 mm), inferior (19±4 mm), andinferolateral (30±3 mm).w3 The paraseptal isthmusforms the base of the triangle of Koch (figures 4–6).The inferior isthmus is also known as the ‘centralisthmus’ owing to its location between the othertwo isthmuses.6 The inferior isthmus represents theoptimal target for linear ablation because this is thesite where the orifice of the ICV is closer to the TVinsertion, the wall thickness is minimal, and there isa larger distance to the right coronary artery andthe AV node or its arterial supply6 (figure 6).

Fluoroscopically, the 6 or 7 o’clock position in theLAO view correlates with the preferred site forablation.

ARCHITECTURAL INSIGHTS OF THE TRIANGLEOF KOCH FOR CATHETER ABLATIONThe triangle of Koch contains the AV node and itsinferior extensions.7 It is bordered posteriorly by afibrous extension from the Eustachian valve and bya ridge called the tendon of Todaro. The anteriorborder is demarcated by the attachment of theseptal leaflet of the TV (figure 4). The apex of thistriangle corresponds to the central fibrous body(CFB) where the His bundle penetrates. The baseof the triangle is the orifice of the CS, and the ves-tibule of the RA immediately anterior to it. Thearea of the triangle is targeted for ablation of theslow nodal pathway. In addition, it is commonlythe seat of the atrial insertions of septal and para-septal AV accessory pathways and certain forms ofatrial tachycardia. The dimensions and spatialorientation of this right atrial region vary consider-ably, which is clinically relevant in the case of cath-eter ablation procedures largely guided by anatomiclandmarksw5 (figure 5). Energy current appliednear the compact AV node must be avoided. Theinduction of AV block during ablation of the slowpathway is more likely to occur when the triangleis small, not only because there is less space toapply energy current safely without impingingupon the area immediately overlying the inferiorextensions or compact node, but also because thereis little margin for error with regard to stability ofthe tip of the catheterw6 (box 1).The AV node consists of a compact portion and an

area of transitional cells. The compact portion lies

Figure 1 (A) Simulated (gross humanspecimens) and fluoroscopic right anterioroblique (RAO) projection showingelectrode catheters placed at the rightatrial appendage, bundle of His (His),right ventricular apex and coronary sinus(CS). (B) Simulated and fluoroscopic leftanterior oblique (LAO) projection. The CSruns on the atrial side of the mitralannulus along the inferior wall of the leftatrium towards the posterior border of theheart. Both RAO and LAO projectionsdefine what is anterior, posterior, superiorand inferior. The LAO view serves todemonstrate in an attitudinal orientationthe septal location permitting thedifferentiation between the right and leftatrioventricular grooves. AO, aorta; CSo,coronary sinus ostium; ICV, inferior cavalvein; LV, left ventricle; MCV; mid cardiacvein; P; pulmonary valve; RAA, right atrialappendage; RVA, right ventricularappendage; RVOT, right ventricularoutflow tract; TV, tricuspid valve.

418 Cabrera JA, et al. Heart 2013;99:417–431. doi:10.1136/heartjnl-2011-301154

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over the CFB at the apex of the triangle (figure 4).The compact AV node contains rightward and left-ward inferior extensions, with the right extensionclose to the tricuspid annulus.8 w7 The AV node con-tinues distally with the His bundle. During anelectrophysiological study the site of the largest Hisbundle electrogram recording does not alwayscoincide with the antero-superior vertex of the tri-angle.7 Therefore the position of the compact AVnode and its inferior extensions just proximal to theHis bundle vary within the landmarks of the triangle.

The penetrating His bundle can readily be distin-guished from the compact node at the point wherethe conduction axis itself becomes completely sur-rounded by tissues of the CFB.7 Thus the bundle ofHis is better protected than the compact node againstradiofrequency energy.

PARASEPTAL REGION AND INFERIORPYRAMIDAL SPACEThe previously called posteroseptal region is in factinferior and paraseptal, because it is inferior to thetrue atrial septum. Therefore the term ‘infero-paraseptal’ would be more anatomically correct.The complex inferior paraseptal region representsthe confluence of all four chambers (the so-calledinferior pyramidal space) and the CS.7 The pyram-idal space is an area whose superior vertex is theCFB, the lateral sides are formed by the convergenceof the left and right atria, and whose floor is themuscular ventricular septum (VS) and left ventricle(LV). The CS limits the base of this area, which has apyramidal configuration. Tissues that are continuouswith the inferior epicardial AV groove occupy thepyramidal space together with the AV nodal arteryand the proximal CS with the middle cardiac veinand posterior coronary vein (figure 7).The mid septal region corresponds to the floor

of Koch’s triangle between the His recording loca-tion and the anterior portion of the CS ostium. Inthis region, because the TV is displaced apicallyand inferiorly in relation to the mitral annulus,there is an apposition between the inferomedial RAand the posterior region of the LV (figure 7). Inaddition there is no atrial septum in the region ofthe His bundle at the apex of Koch’s triangle (for-merly anteroseptal). Thus this area is more prop-erly regarded as being supero-paraseptal (box 2).

INTERATRIAL SEPTUM AND INTERATRIALMUSCULAR CONNECTIONSThe true IS is the OF, a depression in the rightatrial aspect of the area traditionally considered tobe the IS. The antero-inferior buttress, whichanchors the flap valve of the OF into the AV junc-tions, is also a septal structure. The buttress is con-fluent with the floor of the triangle of Koch, but asmentioned above this is not a septal area. The but-tress, in contrast, forms a direct muscular boundarybetween the atrial cavities. The remaining parts ofthe ‘septal’ aspect are formed by the infolded rightatrial wall superiorly and inferiorly, and the fibro-fatty sandwich of atrial and ventricular musculatureanteriorly9 (figure 8). The muscular fold formingthe rim of the oval foramen itself is filled withfibro-fatty tissues of the epicardium and termed theinteratrial groove (or septal raphe). Superiorly andposteriorly, this is the posterior interatrial groove.On the left atrial side, the valve is usually indistin-guishable from the parietal atrial wall apart from asmall crescent-like edge that marks the site of itsfree margin, the last part of the valve to becomeadherent to the rim. Transseptal punctures to accessthe LA should be performed through the OF. Alsorelevant is the spatial relationship between the

Figure 2 (A, B) Fluoroscopic 45° right anterior oblique projection showing theangiographic display of both the mitral valve and tricuspid valve (TV) during theinjection of radiographic contrast into the right atrium (RA) and the left ventricle (LV).(C, D) Three dimensional spatial orientation of the cardiac chambers using the NavXsystem. (E) Opened RA and left atrium (LA) in a human specimen. Note the TVdisplaced apically in relation to the mitral valve (MV) and the apposition between theinferior/medial RA and the posterior region of the LV (double white arrow in panel E).The smooth circumferential area of atrial wall surrounding the orifice of the TV and MVis described as the vestibule. The trabeculated wall of the RA anterior to the terminalcrest is the right atrial appendage (RAA) and contains multiple pectinate muscles(asterisk), which arise from the crest and extends all round the vestibule. CS, coronarysinus; ICV, inferior caval vein; LAA, left atrial appendage; LIPV, left inferior pulmonaryvein; LSPV; left superior pulmonary vein; OF, oval fossa; PA, pulmonary artery; RV, rightventricle; RVOT, right ventricular outflow tract.


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anterior atrial wall or the plane of the atrial septumand the root of the aorta (figure 8). An accidentalpuncture throughout the interatrial groove mayresult in haemopericardium in highly anticoagu-lated patients.Apart from a muscular continuity at the rim and

floor of the OF, there are multiple muscular bridgesbetween the atrial chambers.9 The anterior rightatrial wall is mainly formed by chains of cardio-myocytes aligned with their long axes in similarorientation that run parallel to the AV groove(figure 9). A prominent band of these cardiomyo-cytes is the Bachmann’s bundle that can be tracedfrom the superior cavo-atrial junction leftward to

become the superficial fibres of the LA, crossingthe anterior interatrial groove. This band is themost prominent muscular interatrial bridge.9 w8

Additionally, in some hearts the Bachmann’s bundlemay coexist with muscular bridges across theposteroinferior interatrial groove. Also connectionsbetween the muscular wall of the CS and the LAare common.9

LEFT ATRIAL ANATOMY RELEVANTTO CATHETER ABLATIONAblation techniques in patients with atrial fibrillation(AF) have evolved from rather limited initialapproaches to quite extensive left atrial intervention(box 3). From a gross anatomical viewpoint the LApossesses a venous component that receives the pul-monary veins (PVs), a vestibule, an appendage, andthe so-called IS (figure 8). In reality, both atriums alsopossess a body. This is best seen in the LA, and is thesmooth walled component between the vestibule andthe venous component. The body of the RA is muchsmaller, and represents the space between the leftvenous valve, when this structure can be recognised,and the atrial septum. The major part of the LA,including the septal component, is smooth walledexcept for the ostium of the atrial appendage and itsneighbouring structures.10 The walls of the LA can bedescribed as superior, posterior, left lateral, septal (ormedial), and anterior. The anterior wall that is imme-diately inferior to the Bachmann’s bundle, located justbehind the aorta, can be very thin and measuresapproximately 1–2 mm in thickness transmurally. Thesuperior wall, or dome, is thicker compared with theposterior and postero-inferior walls, measuring3.5–6.5 mm.11 12

PVS AND THEIR VENOATRIAL JUNCTIONSThe LA posterior wall is the anatomical location ofthe venous component and contains the venoatrialjunctions of the PVs, with the left veins located moresuperiorly than the right veins (figures 9 and 10).The superior PVs run cranially and more anteriorly,whereas the inferior veins have a more posteriorand lateral course. Usually the right superior PVpasses behind the junction between the RA and thesuperior vena cava (SVC) whereas the inferior PVspass behind the intercaval area.12 The orifices of theright PVs are directly adjacent to the plane of theatrial septum. The most common anatomic variants(30–35%) of the PVs ending in the LA include a con-joined homolateral ostia of the left PVs (25% of spe-cimens) and a supernumerary or additional right PV(figure 10). It is important to note that: (1) the PVostia are not round but ovoid; (2) the PV size variesover the cardiac cycle and respiration; and (3) thetransition from the atrial endocardium to the venousendothelial layer is smooth with an unclear anatomicborder. Thus, identification of the PV ostia may bedifficult in some patients.Atrial sleeves of non-uniform thickness, which

are made up of working atrial myocardium, extendover the veno-atrial junction into the PV walls, andare more pronounced in the superior PVs.13

Specialised cells, particularly node-like cells, were

Figure 3 (A) Opened right atrium in simulated right anterior oblique view to showthe most important landmarks and its four components. Note the oval fossa (OF) andthe terminal crest which is a thick C-shaped muscular trabecula that distally ramifies toform the pectinate muscles. The Eustachian valve (asterisks) separates the inferior venacava (IVC) from the inferior right atrial isthmus. The Thebesian valve (white arrow)guards the entry into the coronary sinus. (B) Four chamber section through the heartprofiles showing the true interatrial septum (double red arrow); the remaining parts(dotted lines) mark the superior and inferior infolding of the atrial wall and thefibro-fatty sandwich of atrial and ventricular musculature posteriorly. (C) Short axissection across the atrial chamber below the flap valve of the OF. Note theatrioventricular valves, the vestibules (dotted lines), and the different shape and size ofthe atrial appendages. Ao, aorta; LAA, left atrial appendage; MV, mitral valve; RAA,right atrial appendage; RCA, right coronary artery; RVA, right ventricular apex; RVOT,right ventricular outflow tract; SCV, superior caval vein; TC, terminal crest; TV, tricuspidvalve; VS, ventricular septum.


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not seen in our studies.11–13 Bridges of atrial myo-cardium and crossing strands have been observedconnecting the superior and inferior PV, occurringmore frequently between the left veins thanbetween the right veins.12 w9

LATERAL RIDGE AND LEFT ATRIALAPPENDAGEThe left lateral ridge between the orifices of theleft PVs and the mouth of the left atrial appendage(LAA) is the most relevant structural prominenceon the LA endocardium.14 This structure is actu-ally an infolding of the lateral atrial wall protrud-ing into the endocardial LA surface as aprominent crest or ridge (figure 10). The ridgeextends along the lateral wall of the LA from theanterosuperior to the postero-inferior region.Epicardially, this broad bundle is in continuitywith the uppermost and distal part of the intera-trial band (Bachmann’s bundle). Within the foldruns the remnant of the vein of Marshall, togetherwith abundant autonomic nerve bundles and asmall atrial artery, which in some cases is the sinusnodal artery.14

The LAA tends to have a tubular shape with one orseveral bends resembling a little finger.w10 On theendocardial aspect, the orifice of the LAA is not per-fectly round. Instead, it is oval in shape with a meanlong diameter of 17.4±4 mm and a short diameter of10.9±4.2 mm.12 A complicated network of fine pec-tinate muscles lines the endocardial aspect.w11 Inbetween the muscle bundles the wall is paper thin. Insome specimens (28%), muscular trabeculations canbe found extending inferiorly from the appendage tothe vestibule of the mitral valve (MV) (figure 10).These extra-appendicular myocardial bands corres-pond to the small posterior set of pectinate musclesoriginating from the myocardial bundles to embracethe LAA.14 In those hearts with extra-appendicularposterior pectinate muscles, the area in between themuscular trabeculae and the atrial wall becomesexceptionally thin (0.5±0.2 mm), increasing the riskof cardiac perforation during ablation in this zone.14

The isthmus of muscle between the orifice of theinferior PV and the mitral annulus is commonlydubbed the left atrial isthmus or mitral isthmus.w12 Inthis region, the vestibule directly apposes the wall ofthe great cardiac vein and its continuation, the

Figure 4 (A) Lateral view of the right atrium (RA) showing the location of the sinus node (SN) (fusiform green colour). (B) The RA is shown inright anterior oblique projection. The terminal crest arches anterior to the orifice of the superior caval vein, and the SN is located betweenthemselves and extends toward the inferior caval vein. (C) Histological section of the SN body (Masson trichrome stain) within a dense matrix ofconnective tissue (green colour) and showing a nodal extension (arrow). (D) Endocardial view of the posterior and paraseptal walls of the RAshowing the limits of the triangle of Koch. The apex of the triangle is the central fibrous body (CFB). The atrioventricular (AV) node is illustrated inyellow. (E) Four chamber section to show the different attachment of the mitral valve and tricuspid valve. (F) Histological section corresponding tothe location of the AV node stained with Masson trichrome. Note the semi-oval shape of the compact AV node that lies over the CFB. Ao, aorta; CS,coronary sinus; Epi, epicardium; End, endocardium; ICV, inferior caval vein; IVS, interventricular septum; LIPV, left inferior pulmonary vein; LSPV, leftsuperior pulmonary vein; MV, mitral valve; PT, pulmonary trunk; RAA, right atrial appendage; RIPV, right inferior pulmonary vein; RSPV, rightsuperior pulmonary vein; SCV, superior caval vein; TC, terminal crest; TV, tricuspid valve.


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CS10 12 (figure 10). In cases where the wall at thetransition of vein to sinus is particularly muscular, itadds to the thickness of the isthmus. Frequently, thevenous/sinus musculature is continuous with the leftatrial wall. The mitral isthmus may also contain extra-appendicular posterior pectinate muscles.

CORONARY SINUSThe CS, which is the continuation of the greatcardiac vein, runs on the atrial side of the trueannulus along the postero-inferior wall of theLA.10 11 This separation from the annulus is morepronounced in the proximal 20 mm of the CS.w13

In all specimens, the venous wall of the CS is

Figure 5 A, B) Right atrial angiograms in 45° rightanterior oblique projection showing the tricuspid valve (TV)plane and the angiographic limits of the triangle of Koch.The position of the ablation catheter at the site ofapplication of radiofrequency (RF) is shown. Note thevariable dimensions of the triangle. The risk ofatrioventricular (AV) nodal injury increases when the Koch’striangle is small. (C) Injection of contrast during the slowpathway ablation. Note the exact position of the ablationcatheter close to the TV. (D) The left anterior obliqueprojection demonstrates that the ablation catheter (RF) hasa septal location in relation to the interatrial groove. LAO,left anterior oblique; RAA, right atrial appendage; RAO,right anterior oblique; RV, right ventricle; RVOT, rightventricular outflow tract; SCV, superior caval vein.

Box 1 Right-sided atrial tachycardia andatypical right atrial flutter

Inappropriate sinus tachycardia: ablation along thecrista terminalis▸ Broad location of the sinus nodal tissue▸ Potential cooling effect of the centrally located

sinus nodal artery▸ Thickness of the terminal crest▸ Non-uniform pectinate trabeculations towards

the TV▸ Risk of right phrenic nerve injury

Coronary sinus origin and near the AV node or Hisregion▸ Endocardial and close anatomic proximity of

the compact AV node▸ Variable position of the compact AV node

within the right atrial AV junction▸ Cooling effect of the CS blood flow: proximity

to the inferior AV nodal extensions▸ A better protected His bundle than the

compact AV node against radiofrequencyenergy

Atrioventricular nodal reentrant tachycardia▸ Dimensions and spatial orientation of the

triangle of Koch▸ Variable location of the His bundle recording

site within the Koch’s triangle▸ Variable position of the compact AV node and

its inferior extensions

Isthmus dependent atrial flutter▸ Length of the cavo-tricuspid isthmus: shorter

‘central isthmus’▸ Endocardial geometry of the isthmus: deeper

pouches (sub-Thebesian recess)▸ Obstacles such as a large Eustachian valve/

ridge▸ Variable content of myocardial and fibro-fatty

tissues at the ablation zone▸ Proximity of the AV nodal artery and right

coronary artery

AV, atrioventricular; CS, coronary sinus; TV, tricuspidvestibule.


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surrounded by a cuff of myocardium extending40±8 mm from the ostium.w14 Myocardial connec-tions varying in number and morphology leave thiscoronary muscle cuff and connect to the LA. Theostium of the CS abuts the superior margin of theright atrial-left ventricular sulcus and the inferior

paraseptal mitral annulus in the pyramidal space(figures 7, 9 and 11). The inferior interatrial con-nections through the CS may explain the need foradditional ablation in and on the CS to completeleft atrial ablation lines extending down to themitral annulus in this area for curing AF.w14

Figure 6 (A, B) The right inferior cavo-tricuspid isthmus is a quadrilateral area in the floor of the right atrium bounded by the inferior caval veinand the Eustachian valve posteriorly and by the septal attachment of the tricuspid valve (STV) anteriorly. Note in panel B the complex endocardialtopography of the isthmus with thicker trabeculations from the terminal crest and a deep sub-Thebesian recess (pouch). (C) Sagittal histologicalsection with Masson trichrome at the level of the central isthmus. Note the proximity of the minor coronary vein and the right coronary artery to theendocardium of the vestibule. The section shows the variable content of myocardial and fibro-fatty tissues with a thicker anterior vestibular area.(D, E) Right atrial angiograms in the right anterior oblique projections that show in panel D a large and deep pouch recess and in panel E a thickerEustachian valve and ridge, anatomic obstacles that may complicate isthmus ablation (radiofrequency). CSos, coronary sinus ostium; ICV, inferiorcaval vein; OF, oval fossa; RAA, right atrial appendage; RAO, right anterior oblique; RCA, right coronary artery; RF, ablation catheter; RV, rightventricle; TV, tricuspid valve.


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The CS musculature may form extensions overthe proximal portion of the middle cardiac veinand posterior cardiac vein. The oblique vein ofMarshall (diameter 0.4–1.8 mm), located betweenthe LAA and the left upper and lower PVs, runsinferiorly along the postero-inferior atrial wall tojoin the CS. In most hearts (70%), the oblique veinis <3 mm from the endocardium of the LA and hasmuscular connections to the left PVs.14

RIGHT AND LEFT VENTRICLESIn contrast to the conical morphology of the LV,the RV is more triangular in shape when viewed

Figure 7 (A) Left atrial angiography throughout atransseptal puncture in the left anterior obliqueprojection (LAO). The LAO projection makes it possible todefine the anatomic relation between the right and leftparaseptal regions and the fluoroscopic limits of theinferior pyramidal space. Note the variable relation of thecoronary sinus (CS) catheter and the atrial side of themitral annulus. (B) Heart specimen in simulated LAOprojections showing the right and left atrioventricular(AV) groove. The convergence of the left and right atriaforms the lateral side of the inferior pyramidal space; thesuperior vertex is the central fibrous body and the CSlimits the base of this space. Note the AV nodal arteryoriginates from the apex of the U-turn of the distal rightcoronary artery and penetrates into the base of theinferior paraseptal region (inferior pyramidal space) atthe level of the crux of the heart. (C, D) Right anterioroblique (RAO) projection. Ablation of an inferiorparaseptal accessory pathway within the mid cardiac vein(MCV) using the CS myocardial sleeve as connectionbetween the atria and ventricle. The MCV end ups in theproximal CS and runs an inferior course before bendinganteriorly along the epicardial surface of the muscularinterventricular septum. LV, left ventricle; MV, mitralvalve; P, pulmonary trunk; RCA, right coronary artery; RF,ablation catheter; RV, right ventricle; TV, tricuspid valve.

Box 2 Accessory atrioventricularconnections

Left free-wall accessory pathways▸ Fibrous tissue around the MA interposed

between the atrial and ventricular myocardium▸ Basal cords of ventricular myocardium on the

ventricular side of MA▸ Aortic–mitral valve continuity (anterior limit of

the left free wall)▸ The CS as guidance for MA: variable

separation of the CS from the annulus

Right free-wall accessory pathways▸ The TA is displaced apically in relation to the

MA▸ Less developed fibrous tissue and frequently

discontinuous TA▸ Acute angulation of the tricuspid leaflets

towards the ventricle

Inferior paraseptal accessory pathways(‘posteroseptal’)▸ Complex relation between the right and left

inferior paraseptal region▸ Musculature over the coronary venous system:

coronary sinus diverticulum▸ The AV nodal artery towards the compact AV

node along the inferior paraseptal area▸ The inferior extension of the compact AV node

Supero-paraseptal accessory pathways(‘anteroseptal’)▸ Proximity to normal conduction system▸ Variable extension of the central fibrous body:

the region of the His penetrating bundle▸ Discontinuous fibrous tissue around the

tricuspid annulus (superior limit)

Mid septal accessory pathways▸ Area between the His recording location and

the anterior portion of the CS ostium▸ Apposition between the inferior/medial RA and

posterior region of the left ventricle▸ Similar anatomic determinants to the slow

pathway ablation

CS, coronary sinus; MA, mitral annulus; RA, right atrium;TA, tricuspid annulus.


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from the front and it curves over the LV.15 Thegeometry of the RV is also influenced by theconvexity of the VS toward the RV in both systoleand diastole under normal loading conditions. Boththe RV and the LV have been described as havingthree components: the inlet (inflow tract), apicaltrabecular, and outlet portions (outflow tract)(figure 11). Morphologically, the RV is distin-guished from the LV by having coarser trabeculae,a moderator band, and a lack of fibrous continuitybetween its inlet and outflow valves. The musculartrabeculations in the apical part of the RV arecoarser than those in the LV.15 16 The apical trabe-culations of the LV are fine and display a criss-crosspattern. The inlets also differ notably in the normalventricles, as do the outlets. Thus, the TV, posses-sing inferior, septal and antero-superior leaflets, hasextensive chordal attachments to the VS, and issupported by notably eccentric papillary muscles.The MV possesses two leaflets, located anteriorlyand posteriorly but positioned obliquely within theLV, and closing along a solitary zone of apposition.The anterior leaflet of the MV is separated fromthe septum by the subaortic vestibule, having

fibrous continuity with two of the leaflets of theaortic valve.

ANATOMY OF THE OUTFLOW TRACTS:IMPLICATION FOR ABLATION OF VENTRICULARTACHYCARDIASPremature ventricular contractions, ventriculartachycardias (VTs) and initiating beats for ventricu-lar fibrillation have all been localised at the level ofthe right and left ventricular outflow tracts (RVOTand LVOT).w15 w16 Absence of structural heartdisease is the rule with these arrhythmias.17

The majority of RVOT tachycardias originate inthe superior, septal and anterior aspects of theinfundibulum just underneath the pulmonary valve(box 3). The RVOT (outlet portion of the RVor theinfundibulum) is a muscular structure of variablelength (range 13–24 mm) that supports the semi-lunar leaflets of the pulmonary valve.15 Its posteriorand inferior part consists of a prominent muscularcrest, called the supraventricular crest (SC), thatseparates the inflow and outflow components of theRV (figure 11). The SC is in contact with the poster-ior part of the LVOT, as it inserts into the

Figure 8 (A) Dissection of the posterior wall of the left atrium (LA) close to the posterior interatrial groove. The smooth walled venous componentof the LA is the most extensive. The septal aspect of the LA shows the crescentic line of the free edge of the flap valve (green dotted line) againstthe rim of the oval fossa (OF). The orifices of the right superior and inferior pulmonary veins (RSPV and RIPV) are adjacent to the plane of the septalaspect of the LA. (B) Longitudinal sections showing the orifices of the right pulmonary veins. Note the relation of the superior vena cava to theRSPV and right pulmonary artery. (C) The dome or roof of the LA has been removed and the left atrial side of the septum can be seen bytransillumination of the OF. In the case of patent foramen oval, the LA can be accessed from the right atrium (RA) through a crevice (blue dottedline) that is the last part of the valve to be sealed to the rim. (D) Short axis through the interatrial septum (green arrow). Note by transilluminationthe so-called left atrial ridge that is a fold in the LA wall between the left atrial appendage and the left pulmonary veins. (E) Histological sectionwith Masson trichrome taken through the short axis of the heart to show the thin flap valve and the muscular rim of the fossa. Note thenon-uniform thickness of the left atrial wall and the close relationship of the anterior wall of the RA with the transverse sinus and aorta (Ao). ER,Eustachian ridge; LAA, left atrial appendage; LIPV, left inferior pulmonary vein; LSPV, left superior pulmonary vein; MV, mitral valve; PT, pulmonarytrunk, RAA, right atrial appendage; RI, right inferior pulmonary vein; RPA, right pulmonary artery; RS, right superior pulmonary vein; SCV, superiorcaval vein; TV, tricuspid valve.


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interventricular septum. On the septal aspect, thiscrest inserts between the limbs of the septomarginaltrabeculation (SMT), or septal band.15 This muscu-lar strap reinforces the septal surface of the RV,breaking up at the apex to form the moderator bandand the anterior papillary muscle. The moderatorband incorporates the right bundle branch, as con-duction tissue fibres move towards the apex of theventricle before entering the anterior papillarymuscle.16 The septo-parietal trabeculations taketheir origin from the anterior margin of the SMTand run round the parietal ventricular wall of theinfundibulum.15 These trabeculations show a vari-able extension (between five and 22 trabeculations)and thickness (range 2–10 mm) along the right andleft septo-parietal wall of the RVOT.All these structures are absent from the LV, where

the outlet (LVOT) is much more reduced in sizebecause of the fibrous continuity between two ofthe leaflets of the aortic valve and the aortic leafletof the MV. Therefore, in the LV there is no muscu-lar separation between inflow and outflow tracts.16

Although the two ventricular outlets haveimportant differences in their structure, they alsohave one feature in common, namely the semilunar

attachment of their leaflets. Because of the semi-lunar shape of the pulmonary leaflets this valvedoes not have a ring-like annulus.15 16 The semi-lunar hinges of the arterial valve leaflets extendproximally beyond the anatomic ventriculo-arterialjunction, such that crescents of myocardium areincorporated into the bases of all three valvarsinuses of the pulmonary valve, and into two of thethree aortic sinuses of Valsalva (figure 11). Weobserved in histological sections the existence ofmyocardial extensions or myocardial remnants onthe epicardial aspect above the sinotubular junctionin 20% of human specimens, showing continuitywith the myocardium of the RVOT (figure 11).These extensions could justify the existence of idio-pathic supravalvular tachycardia.

PERICARDIAL SPACE AND NEIGHBOURINGSTRUCTURES OF THE HEARTThe heart and its adjoining great vessels areenclosed in a sac, the parietal (fibrous) pericar-dium.w17 Superiorly, the fibrous pericardium is con-tinuous with the adventitia of the great vessels.Within the fibrous pericardium there is a delicatedouble layered membrane known as the serous

Figure 9 (A–C) In these specimens the epicardium has been removed to show the arrangement of the myocardial strands in the superficial partsof the walls. In panel A an interatrial muscle bundle or Bachmann bundle is present in this heart. Panel B is a view of the roof and posterior wall ofthe left atrium (LA) showing the myocardial strands (septopulmonary bundle) in the region between the left and right pulmonary veins (PVs). PanelC is a view of the posterior wall of the LA with transillumination to demonstrate the non-uniform myocardial thickness of the LA wall. (D) Crosshistological section stained with elastic van Gieson of the LA, PVs and the superior vena cava. Also note the variable myocardial content of thewalls of the LA and the epicardial location of vegetative nerves and ganglia. (E) Cross histological section of the left PVs stained with Massontrichrome. Note the inter-PV myocardial connections (arrow) between the superior and inferior veins. Ao, aorta; Epi, epicardium; ICV, inferior cavalvein; LAA, left atrial appendage; LIPV, left inferior pulmonary vein; LPA, left pulmonary artery; LSPV, left superior pulmonary vein; LV, left ventricle;RAA, right atrial appendage; RIPV, right inferior pulmonary vein; RSPV, right superior pulmonary vein; SCV, superior caval vein.


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pericardium. One layer of the serous pericardium isfused to the fibrous pericardium while the otherlayer lines the outer surface of the heart and con-tinues over the surfaces of the vessels as the visceralpericardium. Over the great vessels, the junctionsbetween the two layers are the pericardial reflec-tions. The pericardial cavity is the space betweenthe layers of the serous pericardium.There is a small area behind the lower left half

of the body of the sternum and the sternal ends ofthe left fourth and fifth costal cartilages where thefibrous pericardium is in direct contact with the

Figure 10 (A) Three dimensional reconstruction of theleft atrium (LA) and pulmonary veins using the NavXsystem from data obtained with a 32 slice multidetectorCT scanner to show conjoined ostia, a common variantseen in up to 25% of cases, on the left side, and aseparate right middle pulmonary vein (PV), which drainsthe middle lobe of the lung. (B) Human necropsyspecimen showing the superior and posterior walls of theLA were anchored by the entrance of one PV at each ofthe four corners. (C, D) Endocardial left atrial wall in twopostmortem heart specimens showing prominent leftlateral ridges, extending in panel C (transillumination) tothe inferior margin of the left inferior pulmonary veinand in panel D (asterisk) to the inferior margin of the leftsuperior pulmonary vein. Note in panels C and D theextra-appendicular posterior pectinate muscles extendinginferiorly from the left appendage toward the vestibule ofthe mitral valve (red arrows), and note the thinnestmuscular wall in between the muscular trabeculae. CS,coronary sinus; LAA, left atrial appendage; LIPV, leftinferior pulmonary vein; LSPV, left superior pulmonaryvein; RIPV, right inferior pulmonary vein; RSPV, rightsuperior pulmonary vein.

Box 3 Atrial fibrillation and left atrialflutter. Ventricular tachycardias

Dimensions and non-uniform myocardial thicknessof the LA▸ Variant anatomy of the PVs: length of the

common pulmonary trunk▸ Inter-PVs myocardial connections (some

epicardially located)▸ Endocardial ridges: the left atrial ridge and the

interpulmonary isthmus (PV carina)▸ Extra-appendicular pectinate muscles (mitral

isthmus and vestibule)▸ Cooling effect by the intramyocardial atrial

arteries▸ Autonomic nervous system on the epicardial

surface of the LA wall▸ Fibrous tissue around the mitral annulus▸ Proximity with phrenic nerves, oesophagus,

vagus nerve and left circumflex artery▸ The true atrial septum: transseptal punctures to

access the LA– Spatial orientation of the interatrial groove

and plane of the atrial septum– Thickness of the flap valve: fibrous/muscular

rim (septum primun)– Patent foramen oval/aneurysmal oval fossa– Relation with the aortic root and transverse

pericardial sinus

Ventricular outflow tract tachycardias▸ Myocardial extension above the anatomic

ventriculo-arterial junctions▸ Proximity of the AV conduction: aortic–mitral

valve continuity (LVOT)▸ Extension of the supraventricular crest (RVOT)▸ Variable septo-marginal and septo-parietal

trabeculations (RVOT)

Epicardial ablation▸ Overlying epicardial fat: varying presence of

epicardial adipose tissue▸ Proximity to epicardial coronary vessels,

pericardiophrenic vessels and phrenic nerve▸ Local variation of pericardial reflections

AV, atrioventricular; LA, left atrium; LVOT, left ventricularoutflow tract; PV, pulmonary vein; RVOT, right ventricularoutflow tract.


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thoracic wall. This area allows the pericardial spaceto be accessed.w18 The pericardial cavity has twomain sinuses and several recesses.18 These are notcomplete compartments but represent extensions ofthe cavity. The transverse sinus is delineated anteri-orly by the posterior surface of the ascending aortaand pulmonary trunk bifurcation and posteriorlyby the anterior surface of the atria (figure 12). The

oblique sinus, a large cul-de-sac behind the LA, isformed by the continuity between the reflectionsalong the PVs and caval veins.18 The right and leftpulmonary venous recesses are at the back of theLA between the superior and inferior PVs on eachside, indenting the side walls of the oblique sinus toa greater or lesser extent. The pericardial reflec-tions at the veins, particularly the PVs, are varied

Figure 11 (A) Window dissection of aheart prepared by removing the anteriorsuperior wall of the right ventricle (RV).The three components of the RV arerevealed: the inlet (tricuspid valve (TV)),apical trabecular, and right ventricularoutflow tract (RVOT) or infundibulum.Note the location of the supraventricularcrest and septomarginal trabeculation(SMT). The body of the SMT continues asan important muscular strand, themoderator band, to the anterior papillarymuscle and the parietal wall of the RV.(B) Sagittal section through the parietalwall of the left ventricle that shows thesubaortic outflow tract and how thepapillary muscles of the mitral valveclosely face each other. (C) The anteriorwall of the RV is opened to show theleaflets of the pulmonary trunk mainlysupported by the RVOT; however, at thelevel of their commissures the leaflets areattached to the pulmonary artery trunk.The SMT (septal band) consists of a bodyand two limbs anterior and posterior. Theanterior limb extends along theinfundibulum (blue dotted arrow) and theposterior limb runs toward the TV (yellowdotted arrow). The septo-parietaltrabeculations take their origin from theanterior margin of the SMT and extendalong the parietal ventricular wall of theinfundibulum. (D) Left ventricularendocardial view to show themembranous septum by transillumination.This is the point of emergence of the leftbundle of His. The yellow arrows show themitro-aortic continuity. (E) Crosshistological section stained with Massontrichrome through the left and the rightatria. Note the anatomic relation of theRVOT with the subaortic outflow. Alsonote the close proximity to the epicardialcoronary vessel, the left phrenic nerve andthe left atrial appendage, relevant duringthe epicardial approach for arrhythmiaablation. (F) Histological section of thepulmonary valve stained with Massontrichrome shows the attachment of thepulmonary leaflet. Note the myocardialextension above the sinotubular junction.Ao, aorta; CS, coronary sinus; DA,descending artery; L, left coronary sinus;LA, left atrium; LCx, left circumflex artery;LV, left ventricle; MV, mitral valve; NC,non-coronary sinus; PA, pulmonary artery;PT, pulmonary trunk; R, right coronarysinus; SC, supraventricular crest; SCV,superior caval vein.


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Figure 12 (A) Schematic drawing showing the superior, transverse and oblique sinuses. The fibrous pericardium is coloured in orange and theparietal layer of the serous pericardium in blue. The white area represents the reflections where the serous pericardium is continuous with thefibrous pericardium. (B) This dissection of a cadaver viewed from the front shows the transverse and oblique sinuses following removal of the heart.(C–E) Cross sections in three different specimens to show the close anatomic relationship of the oesophagus with the posterior left atrial wall (D)and the right and left veno-atrial junction (D and E). (F) The course of the right phrenic nerve is closely related to the superior cavo-atrial junctionand the orifice of the right superior pulmonary vein. (G) The left phrenic nerve in its course has a close anatomic relationship with the left atrialappendage and the lateral wall of the left ventricle to penetrate into the left part of the diaphragm close to the apex of the ventricle. Ao, aorta; Es,oesophagus; ICV, inferior caval vein; LA, left atrium; LAA, left atrial appendage; LIPV, left inferior pulmonary vein; LSPV, left superior pulmonaryvein; LV, left ventricle; PT, pulmonary trunk; RB, right bronchus; RIPV, right inferior pulmonary vein; RPA, right pulmonary artery; RSPV, right superiorpulmonary vein; SCV, superior caval vein.


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and they can restrict access around the veins.18 Theinferior and superior aortic recesses are extensionsfrom the transverse sinus. The superior recess liesbetween the ascending aorta and the RA, whereasthe inferior recess between the aorta and the LAextends to the level of the aortic valve.The close anatomic vicinity of the cardiac cham-

bers to important structures and the regional distri-bution of the autonomic nervous system elementsthat may be affected by interventional manoeuvresshould also be understood by the electrophysiolo-gist (figures 11 and 12). Preganglionic parasympa-thetic and postganglionic sympathetic fibres cometogether into the fat pads of fatty tissues, and gan-glionated plexuses populate the subepicardium.Abundant nerves and ganglions of the autonomicnervous system are present at the junction betweenthe PVs and the LA with differential patterns ofinnervation.w19 w20

The oesophagus descends in virtual contact withthe posterior wall of the LA (figure 12). Behind theposterior left atrial wall is a layer of fibrous pericar-dium and fibro-fatty tissue of irregular thickness thatcontains oesophageal arteries and the vagus nerveplexus.19 Understanding the course of the oesopha-gus is essential to reduce the risk of atrio-oesophageal

fistula during the left atrial ablation procedure.Thermal injury during endocardial LA may alsoinvolve the peri-oesophageal nerves,w21 resulting inan acute pyloric spasm and gastric hypomotility as anextracardiac adverse effect of AF ablation.The right phrenic nerve has a close anatomic

relationship with the SVC and the right PVs20

(figure 12). Consequently, catheter ablation techni-ques aimed at modifying the SN function at thelateral RA, and AF ablation at the orifice and adja-cent area of the right superior PV, carry a certainrisk of injuring the right phrenic nerve.20 Ourstudy on cadavers also revealed that the course ofthe left phrenic nerve and its accompanying peri-cardiophrenic vessels in the fibrous pericardiumwere overlying the atrial appendage in the majorityof cases20 w22 (figures 11 and 12).

Acknowledgements The authors thank Drs Gonzalo Pizarro andMargarita Murillo for their contribution to the preparation of thisarticle.

Contributors Hospital Universitario Quirón-Madrid, Universidad deExtremadura.

Competing interests In compliance with EBAC/EACCMEguidelines, all authors participating in Education in Heart havedisclosed potential conflicts of interest that might cause a bias inthe article. The authors have no competing interests.

Patient consent Obtained.

Ethics approval Bioethics and Biosafety Committee of theUniversity of Extremadura (Badajoz, Spain).

Provenance and peer review Commissioned; externally peerreviewed.

REFERENCES1 Cosío FG, Anderson RH, Kúck KH, et al. Living anatomy of the

atrioventricular junctions. A guide to electrophysiologic mapping.A consensus statement from the Cardiac Nomenclature StudyGroup, Working Group of Arrhythmias, European Society ofCardiology, and the Task Force on Cardiac Nomenclature fromNASPE. Circulation 1999;100:e31–7.

2 Farré J, Anderson RH, Cabrera JA, et al. Cardiac anatomy forcatheter mapping and ablation of arrhythmias. In: Huang SK,Wood MA. Catheter ablation of cardiac arrhythmias. 2nd edn.Philadelphia: Elsevier Inc, 2011:74–102.

▸ A good review about fluoroscopic and angiographic heartanatomy for catheter ablation mapping and ablation ofarrhythmias.

3 Sánchez-Quintana D, Anderson RH, Cabrera JA, et al. Theterminal crest: morphological features relevant toelectrophysiology. Heart 2002;88:406–11.

4 Sánchez-Quintana D, Cabrera JA, Farré J, et al. Sinus noderevisited in the era of electroanatomical mapping and catheterablation. Heart 2005;91:189–94.

▸ This article shows the architecture of the human sinus node tofacilitate understanding of mapping and ablative procedures in itsvicinity.

5 Cabrera JA, Sánchez-Quintana D, Ho SY, et al. Angiographicanatomy of the inferior right atrial isthmus in patients with andwithout history of common atrial flutter. Circulation1999;99:3017–23.

6 Cabrera JA, Sánchez-Quintana D, Farré J, et al. The inferior rightatrial isthmus: further architectural insights for current and comingablation technologies. J Cardiovasc Electrophysiol 2005;16:402–8.

▸ This study provides important morphological details for a betterunderstanding of the structure of the right atrial cavo-tricuspidisthmus.

7 Sánchez-Quintana D, Ho SY, Cabrera JA, et al. Topographicanatomy of the inferior pyramidal space: relevance toradiofrequency catheter ablation. J Cardiovasc Electrophysiol2001;12:210–17.

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8 Inoue S, Becker AE. Posterior extensions of the human compactatrioventricular node: a neglected anatomic feature of potentialclinical significance. Circulation 1998;97:188–93.

9 Ho SY, Anderson RH, Sánchez-Quintana D. Atrial structure andfibres: morphologic bases of atrial conduction. Cardiovasc Res2002;54:325–36.

▸ This is an interesting study about the gross arrangement of theprincipal muscular bundles of the atria to provide a morphologicbasis for atrial conduction and potential substrates of arrhythmias.

10 Cabrera JA, Farré J, Ho SY, et al. Anatomy of the left atriumrelevant to atrial fibrillation ablation. In: Aliot E, Haïssaguerre M,Jackman WM. Catheter ablation of atrial fibrillation. Oxford:Blackwell Futura, 2008:3–31.

11 Ho SY, Sánchez-Quintana D, Cabrera JA, et al. Anatomy of theleft atrium: implications for radiofrequency ablation of atrialfibrillation. J Cardiovasc Electrophysiol 1999;10:1525–33.

▸ This article re-examines the anatomy of the left atrium from theviewpoint of an electrophysiologist.

12 Ho SY, Cabrera JA, Sánchez-Quintana D. Left atrial anatomyrevisited. Circ Arrhythm Electrophysiol 2012;5:220–8.

13 Ho SY, Cabrera JA, Tran VH, et al. Architecture of the pulmonaryveins: relevance to radiofrequency ablation. Heart 2001;86:265–70.

▸ This study reveals the characteristics of normal pulmonary veins soas to provide more information relevant to radiofrequency ablation.

14 Cabrera JA, Ho SY, Climent V, et al. The architecture of the leftlateral atrial wall: a particular anatomic region with implicationsfor ablation of atrial fibrillation. Eur Heart J 2008;29:356–62.

▸ This study aims to provide an insight into the structure of the leftlateral atrial ridge and associated structures in this region such asthe oblique vein of Marshall and vegetative nerves.

15 Ho SY, Nihoyannopoulos P. Anatomy, echocardiography, and normalright ventricular dimensions. Heart 2006;92(Suppl 1):i2–13.

16 Partridge JB, Anderson RH. Left ventricular anatomy: itsnomenclature, segmentation, and planes of imaging. Clin Anat2009;22:77–84.

17 Natale A, Raviele A, Al-Ahmad A, et al. Venice ChartInternational Consensus document on ventricular tachycardia/ventricular fibrillation ablation. J Cardiovasc Electrophysiol2010;21:339–79.

18 D’Avila A, Scanavacca M, Sosa E, et al. Pericardial anatomy forthe interventional electrophysiologist. J Cardiovasc Electrophysiol2003;14:422–30.

▸ This review explores the anatomy of the pericardial space and theanatomic variants that may be encountered in this approach tothe heart.

19 Sánchez-Quintana D, Cabrera JA, Climent V, et al. Anatomicrelations between the esophagus and left atrium and relevance forablation of atrial fibrillation. Circulation 2005;112:1400–5.

▸ This study reveals the characteristics of the non-uniform thicknessof the posterior left atrial wall and the variable fibro-fatty layerbetween the wall and the oesophagus which are risk factors thatmust be considered during the ablation procedure.

20 Sánchez-Quintana D, Cabrera JA, Climent V, et al. How closeare the phrenic nerves to cardiac structures? Implications forcardiac interventionalists. J Cardiovasc Electrophysiol2005;16:309–13.

▸ This study clarifies the spatial relationships between thephrenic nerves and important cardiac structures which is essentialto reduce risks during epicardial and endocardial catheterablation.


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