Anatomical Basis for the Cardiac Interventional Electrophysiologist

Abstract

The establishment of radiofrequency catheter ablation techniques as the mainstay in the treatment of tachycardia has renewed new interest in cardiac anatomy. The interventional arrhythmologist has drawn attention not only to the gross anatomic details of the heart but also to architectural and histological characteristics of various cardiac regions that are relevant to the development or recurrence of tachyarrhythmias and procedural related complications of catheter ablation. In this review, therefore, we discuss some anatomic landmarks commonly used in catheter ablations including the terminal crest, sinus node region, Koch's triangle, cavotricuspid isthmus, Eustachian ridge and valve, pulmonary venous orifices, venoatrial junctions, and ventricular outflow tracts. We also discuss the anatomical features of important structures in the vicinity of the atria and pulmonary veins, such as the esophagus and phrenic nerves. This paper provides basic anatomic information to improve understanding of the mapping and ablative procedures for cardiac interventional electrophysiologists.

Figure 1

(a) The heart is viewed in attitudinally appropriate position. As can be seen, the right atrium lies anterior to its alleged left-sided counterpart. Note the arrangement of the sulcus terminalis and the atrioventricular or coronary groove (blue broken line). (b) The right atrium is shown in right anterior oblique projection. The terminal crest (yellow broken line) arches anterior to the orifice of the superior caval vein and extends toward the inferior caval vein. (b, c) Spatial relationship of the atrial structures. Right posterior (b) and superior (c) views of volume rendered CT angiographies are shown. The right atrium (RA) body (sinus venarum) is shown extending between the SCV and ICV. The right atrial appendage (RAA) is large with a wide neck compared to the left atrial appendage (LAA). Note prominent pectinate muscles of the RAA. The terminal groove (green arrows) is seen between the RAA and the venous part of the RA. The left atrium (LA) is located superior and posterior to the right atrium. (e, f) Endocardial aspects of the lateral wall of the right atrium opened. Note in (e) that the pectinate muscles have a uniform parallel alignment almost without crossovers between them. In contrast, the pectinate muscles in (f) have a nonuniform arrangement with abundant interlacing trabeculations between them. Ao = aorta, CSO = coronary sinus orifice, ICV = inferior cava vein, LA = left atrium, LAA = left atrial appendage, LI = left inferior pulmonary vein, LS = left superior pulmonary vein, OF = oval fossa, PM = pectinate muscles, PT = pulmonary trunk, RAA = right atrial appendage, RCA = right coronary artery, RI = right inferior pulmonary vein, RPA = right pulmonary artery, RS = right superior pulmonary vein, RVOT = right ventricle outflow tract, SCV = superior cava vein, TC = terminal crest, and TV = tricuspid valve.

Figure 2

(a) Axial CT angiogram shows a prominent crista terminalis (red arrows) in the right atrium. (b) Coronal CT shows a sub-Eustachian pouch (yellow arrow) in the median aspect of the right inferior cavoatrial junction. (c, d) Frontal sections through the terminal crest at the origin and ending of the pectinate muscles. Note the irregular alignment (purple arrows) of the muscular myofibrils within the pectinate muscles and between them and the circumferentially arranged myocytes in the vestibule (yellow arrows). ICV = inferior cava vein, LA = left atrium, LV = left ventricle, PM = pectinate muscles, RA = right atrium, and TC = terminal crest.

Figure 3

(a) Frontal view of the heart in a cadaver that has been dissected to show the course of the phrenic nerves relative to the atria and left ventricle. The anticipated location of the sinus node outlined with dots on yellow background. The double-headed arrow represents the sectioning plane used for making the sections through the sinus node and the terminal crest shown in the histological sections. (b, c) Histological sections with picrosirius red stain and polarized light showing variations in locations of the sinus node relative to the epicardial and endocardial surfaces and sizes of the terminal crest. Note nodal extensions (arrows) to superior caval vein, terminal crest, and epicardium. (d) With Masson's trichrome stain is recognizable a nodal extension to terminal crest by its fibrous matrix (green). (e) Histological section of the nodal body (Masson's trichrome stain). Note the contour of the node towards the neighboring myocardium (asterisks). Ao = aorta, LPN = left phrenic nerve, and LV = left ventricle. PT = pulmonary trunk, RAA = right atrial appendage, RPN = right phrenic nerve, RV = right ventricle, SCV = superior cava vein, TC = terminal crest, and TV = tricuspid valve.

Figure 4

(a) Dissection in right anterior oblique view of the right atrium shows the borders of the triangle of Koch. In this view we have depicted the putative fast and slow pathways toward the AV node (dotted shape in yellow). (b) Example of small triangle of Koch with a bigger coronary sinus ostium size. (c, d, e) A series of histological sections in comparable orientation to the picture (a) are taken through the coronary sinus ostium and inferior extensions of the AV node, the body of the AV node, and the penetrating bundle of His. (f, g) Hearts with Ebstein's anomaly. Note in (f) the smaller size of the triangle of Koch and the fibromuscular ridge in relation to the normal insertion of the septal leaflet of the tricuspid valve and the dysplasia of the septal leaflet. In the sagittal histological section (g) note how in the specimen with Ebstein's anomaly the body of the AV node is at the level of coronary sinus ostium. (h) Sagittal section through the mouth of the coronary sinus showing the proximity of the AV nodal artery to the endocardium at the base of the triangle of Koch. Asterisk (∗) = central fibrous body, AVN artery = atrioventricular nodal artery, CSO = coronary sinus ostium, CFB = central fibrous body, ER = Eustachian ridge, ICV = inferior cava vein, MV = mitral valve, OF = oval fossa, PFO = patent foramen ovale, STV = septal leaflet of the tricuspid valve, and TT = tendon of Todaro.

Figure 5

(a) The region of the cavotricuspid isthmus in simulated right anterior oblique (RAO) view and the paraseptal, inferior, and inferolateral isthmuses are marked 1, 2, and 3, respectively. (b) Opened right atrium in simulated RAO view showing the position of the ablation catheter at the site of inferior or central isthmus (marked with number 2) of application of radiofrequency. (c) This atrial view shows the cavotricuspid isthmus with transillumination. The lines mark (1) the paraseptal isthmus, (2) the inferior isthmus, and (3) the inferolateral isthmus. Note the smooth vestibule immediately proximal to the tricuspid valve and the pectinate muscles in the posterior regions. (d, e) This series of histological sections through inferolateral (d) and inferior (e) isthmuses from a heart with dominance of right coronary artery. Note in (d) the prominent and fibromuscular Eustachian valve in the posterior sector or P, thin myocardium in middle sector or M, and thicker myocardium in the anterior sector (vestibule) or A. In (e), histologic section shows a pouch of the sub-Eustachian recess. Note the lesser transmural thickness in this area. The right coronary artery is in the epicardial fat related to the smooth vestibule. (f, g, h) These hearts show variations in morphology of the Thebesian valve guarding the coronary sinus orifice, the sub-Eustachian pouch, and Eustachian ridge. Ao = aorta, CSO = coronary sinus orifice, EV = Eustachian valve, ER = Eustachian ridge, ICV = inferior cava vein, MCV = minor coronary vein, OF = oval fossa, PT = pulmonary trunk, RAA = right atrial appendage, RCA = right coronary artery, RVOT = right ventricle outflow tract, SCV = superior cava vein, TC = terminal crest, and TV = tricuspid valve.

Figure 6

(a) Dissection through the atria with parts of the anterior walls removed and viewed from a left anterior perspective to show the interatrial septum and components of the left atrium and its relatively smooth endocardial surface. (b) This superior view of the heart showing the transverse sinus (blue broken line), the posterior interatrial groove (yellow broken line), and Bachmann's bundle crossing the interatrial grove. (c, d) Longitudinal sections through the venous component of the right atrium showing by transillumination in (c) the flap valve of the oval fossa and the muscular rim that surrounds it on the right atrial aspect. In this heart there is probe patency of the oval fossa, leaving a gap in its anterosuperior aspect. The gap can allow a catheter to be slipped between the rim and the valve (c) to enter the left atrium (d). Note in (d) by transillumination the location of the oval fossa in the left side of the septum. (e, f) Lipomatous hypertrophy of the interatrial septum. In (e) blue asterisks indicate the total volume of fat tissue and its anatomical distribution within the interatrial septum. Note in (f) that the tumor was excised of the interatrial septum and its extension is highlighted by a blue broken line. Ao = aorta, BB = Bachmann's bundle, CSO = coronary sinus orifice, ICV = inferior cava vein, LAA = left atrial appendage, LI = left inferior pulmonary vein, LS = left superior pulmonary vein, MV = mitral valve, OF = oval fossa, PM = pectinate muscles, PT = pulmonary trunk, RAA = right atrial appendage, RI = right inferior pulmonary vein, RS = right superior pulmonary vein, SCV = superior cava vein, TC = terminal crest, and TV = tricuspid valve.

Figure 7

(a, b) Spatial relationship of the left atrial structures. Posterosuperior view of volume rendered CT angiographies is shown. The left atrium is located in superior and posterior aspect of the heart. (a) Normal arrangement of the pulmonary veins (in red) is shown. The left atrial appendage (LAA) is shown in yellow. (b) Again shown are normal pulmonary veins. A supernumerary pulmonary vein (yellow arrows) is shown arising from the superior wall of the left atrium. The supernumerary pulmonary vein usually drains a portion of the right upper lung and inserts directly into the left atrium body or at the junction of the right superior pulmonary vein (RS) and the left atrium. (c) Longitudinal section through the left atrium and left ventricle, showing the smooth endocardial aspect of the left atrium. The black arrows indicate the crescentic edge of the oval fossa valve. (d) Longitudinal section through the pulmonary venous component showing the orifices of the right pulmonary veins. Note the close relation of the right veins orifices with the atrial septum (white arrows). (e) Short-axis section across the atrial chambers to show the atrioventricular valves, the vestibule of the left atrium (dotted line), and the nonuniform thickness of the left atrial wall. (f) Endocardial visualization of the left posterolateral wall showing a prominent left lateral ridge and extra pectinate muscle trabeculations (arrows) extending inferiorly from the appendage to the vestibule of the mitral valve. Double-headed black broken line is showing the left atrial isthmus. CS = coronary sinus, ICV = inferior cava vein, LA = left atrium, LAA = left atrial appendage, LI = left inferior pulmonary vein, LS = left superior pulmonary vein, MV = mitral valve, OF = oval fossa, RPA = right pulmonary artery, RI = right inferior pulmonary vein, RS = right superior pulmonary vein, and TV = tricuspid valve.

Figure 8

(a) Short-axis view of CT angiography showing a large clot (red arrows) in the left atrium attaching to the interatrial septum in a patient with atrial fibrillation. (b) Long axis view of the left heart showing the left atrial appendage (bordered in red) containing fluid-fluid level of unmixed contrast (green arrow) due to incomplete contraction of the left atrial appendage in this patient with atrial fibrillation. Note close anatomic course of the left circumflex artery (white arrow) near the neck of the left atrial appendage. (c, d, e) Images demonstrating significant interindividual variation in left atrial appendage morphology ((c) chicken wing; (d) cauliflower; and (e) windsock). ICV = inferior cava vein, LA = left atrium, LAA = left atrial appendage, LV = left ventricle, and RA = right atrium.

Figure 9

(a) Dissection to show Bachmann's bundle, crossing the anterior interatrial groove and branching toward the left atrial appendage (white lines), and the septopulmonary bundle, which arises from the interatrial groove underneath Bachmann's bundle, fanning out to line the pulmonary veins and to pass longitudinally over the dome (yellow lines). (b) Dissection of the subendocardium showing the abrupt changes of subendocardial fiber orientation (asterisks) of the septoatrial bundle at the level of the posterior wall of the left atrium, left atrial appendage, and orifices of the pulmonary veins. (c) Cross-histological section (Masson's trichrome stain) shows Bachmann's bundle and its rightward extension toward the sinus node. (d) Cross-histological section showing a muscular bridge (arrow) across the anterior interatrial groove connecting the right atrium to the left atrium. (e) Cross-histological section showing a muscular bridge below Bachmann's bundle crossing the anterior interatrial groove (arrow). (f) Cross-histological section (Masson trichrome stain) through the CS demonstrates the coronary sinus and left atrial muscle connection (asterisk) at the distal end of the coronary sinus. Often there is continuity between musculature of the coronary sinus sleeve and left atrial wall (arrow). BB = Bachmann's bundle, ICV = inferior cava vein, LA = left atrium, LAA = left atrial appendage, LI = left inferior pulmonary vein, LS = left superior pulmonary vein, MV = mitral valve, OF = oval fossa, RA = right atrium, RI = right inferior pulmonary vein, RS = right superior pulmonary vein, SCV = superior cava vein, and SPB = septopulmonary bundle.

Figure 10

(a–d) Transverse section of four heart specimens with the roof of the left atrium removed and viewed from above to show the entrance of the pulmonary veins. Note, in (a), the arrangement of four individualized endings of the pulmonary veins into the left atrium. In (b), a separate right middle pulmonary vein (arrow) can be seen, which drains the middle lobe of the lung. (c) showed a conjoined ostia (arrow), a common variant seen in up to 25% of cases, on the left side. In (d) a single left pulmonary vein can be seen. (e) Cross-histological section of the left PVs stained with elastic van Gieson. Note the interpulmonary myocardial connections (double-headed black broken line) between the left superior and inferior veins. Also note a nonuniform in circumferential thickness of the myocardial sleeves in left pulmonary veins. (f) Longitudinal histological section stained with elastic van Gieson showing the thicker atrial wall becoming thinner at the entrance of the left inferior pulmonary vein to form the muscular sleeve, which tapers toward the lung. Note the presence of gaps of connective tissue bridges between the myocytes (arrow). LA = left atrium, LAA = left atrial appendage, LI = left inferior pulmonary vein, LPV = left pulmonary vein, LS = left superior pulmonary vein, RAA = right atrial appendage, RI = right inferior pulmonary vein, RS = right superior pulmonary vein, and SCV = superior cava vein.

Figure 11

(a) Specimen viewed from a left posterolateral perspective to show the course of the esophagus and descending aorta relative to the left atrium. (b) This dissection of a cadaver viewed from the front shows the course of the right and left phrenic nerves. (c) Dissection of the left vagus nerve and its branch the left recurrent laryngeal which descends onto the roof of the left atrium. (d) Histological sections (Masson's trichrome stain) through the right superior pulmonary vein and superior cava vein. The right phrenic nerve is adherent to the fibrous pericardium. Note the short distance between the endocardium of these veins and the right phrenic nerve. (e) This dissection of a cadaver viewed from the front shows the transverse (double-headed yellow broken line) and oblique sinuses following removal of the heart. Note that we have opened a window on the oblique sinus to show the close anatomic relationship of the esophagus with the posterior left atrial wall. (f, g) Transillumination of the roof of the left atrium and posterior interatrial groove showing the acetylcholinesterase stained epicardial ganglionated nerves (blue arrows) extending to the superior surface of the left venoatrial junctions in (f) and intercaval region in (g). Ao = aorta, LB = left bronchus, DA = descending aorta, ESO = esophagus, ICV = inferior cava vein, LI = left inferior pulmonary vein, LRLN = left recurrent laryngeal nerve, LS = left superior pulmonary vein, LV = left ventricle, PT = pulmonary trunk, RAA = right atrial appendage, RI = right inferior pulmonary vein, RS = right superior pulmonary vein, and SCV = superior cava vein.

Figure 12

Right anterior views of volume rendered CT angiographies. (a) Right ventricle and (b) left ventricle. (c) The right ventricle is crescent-shaped in cross section. (d) This is a right lateral view showing the three components of the right ventricle and the characteristic muscle bundles as septomarginal trabeculation and supraventricular crest or ventriculoinfundibular fold. Ao = aorta, APM = anterior papillary muscle, AV = aortic valve, CSO = coronary sinus ostium, ICV = inferior cava vein, LAA = left atrial appendage, LV = left ventricle, LVOT = Left ventricle outflow tract, OF = oval fossa, PT = pulmonary trunk, RAA = right atrial appendage, RV = right ventricle, RVOT = right ventricle outflow tract, SC = supraventricular crest, SCV = superior cava vein, SMT = septomarginal trabeculation, and TV = tricuspid valve.

Figure 13

(a) The right side of the heart is opened to show the hinge of the tricuspid valve and the location of the right papillary muscles and leaflets of the tricuspid valve. (b) The right ventricle is opened from the front to show the septal papillary muscle, moderator band, and septoparietal trabeculations. (c) Window dissection of the right heart to show the AV node and right bundle branch crossing the central fibrous body (∗). (d) Histological section of the septal papillary muscle (double-headed black broken line). Note the close relationship with right bundle branch of His. Ao = aorta, APM = anterior papillary muscle, CSO = coronary sinus ostium, IPM = inferior papillary muscle, OF = oval fossa, RVOT = right ventricle outflow tract, SC = supraventricular crest, SCV = superior cava vein, SMT = septomarginal trabeculation, and SPM = septal papillary muscle.

Figure 14

(a, b) These two halves of a heart are bisected longitudinally to show the three aortic sinuses and the papillary muscles of the mitral valve. Note that the muscular subpulmonary infundibulum of the right ventricular outflow tract abuts the right and left coronary sinuses. (c) The kidney-shaped vestibule of the mitral valve is shown from the atrial side. The commissure between the leaflets of the mitral valve and the fibrous continuity between the aortic leaflet of the mitral valve and left coronary and noncoronary of the aortic sinuses are shown. There is no muscular infundibulum in the left ventricle. Note the coronary sinus (blue broken line) next to the left atrioventricular groove surrounding the mitral valve from behind. (d) The aortic root has been opened through the left coronary aortic sinus showing the musculature in the depth of the sinus and the area of fibrous continuity between the leaflets of the aortic and mitral valves. It is photographed by transillumination from behind to show the three sinuses showing the left aortic sinus (L), the right aortic sinus (R), and the posterior or noncoronary aortic sinus (N). Two of the three interleaflet fibrous triangles are shown (∗). Note that the right fibrous trigone is continuous with the membranous septum, the two fibrous structures together forming the so-called central fibrous body (the brightest area by transillumination, black broken line). The specialized atrioventricular conduction axis penetrates through this fibrous area and left bundle branch. (e) Short-axis view from atria side, after removal of the epicardium and coronary vessels, shows the relationship of the aortic valve and the right (blue asterisk) and left (red asterisk) fibrous trigones. Pulmonary sinuses are named according to their relationship to the heart (nonattitudinal), including anterior (A), left posterior (LP), and right posterior (RP) pulmonary sinus. (f) Cross-histological section stained with Masson's trichrome through the left and the right atria. Note the anatomic relation of the right ventricular outflow tract with the subaortic outflow. Note that while all of the leaflets of the pulmonary valve are supported by infundibular musculature, only two of the leaflets of the aortic valve have muscular support. Ao = aorta, CS = coronary sinus, MV = mitral valve, LVOT = left ventricle outflow tract, PT = pulmonary trunk, RVOT = right ventricle outflow tract, and TV = tricuspid valve.

Figure 15

(a) This bovine heart shows the left bundle branch and Purkinje network after Indian ink injection. (b) Histological section stained with Masson's trichrome in a human heart showing Purkinje fibers at the level of the subendocardium of the left ventricle. (c) Histological section of a false tendon in a human heart which presents within Purkinje fibers, myocytes, and connective tissue in green colour. (d) Histological section of the pulmonary valve shows how the hinge of the valvar leaflet is attached to the ventricular myocardium well proximal to the anatomic ventriculoarterial junction. (e, f) Histologic sagittal sections of the right ventricular infundibulum, pulmonary valve root, left ventricle outflow tract, and aortic root. Note the differences in length of the right ventricular outflow tract infundibulum and in the contact area between both outflow tracts (red dotted lines) depending on the level of the section: at the right posterior pulmonary leaflet (e) or left posterior pulmonary leaflet (f). The subendocardial fibers in the infundibulum run longitudinally. At subendocardial levels of the left ventricular outflow tract, the orientation is mainly spiral and circumferential. Note that there are connections (asterisks) between myocytes in the contact area between both outflow tracts. (g) Histologic cross section of infundibulum of pulmonary valve stained with Masson's trichrome. In right ventricle, fibers orientation is different in infundibulum and at subendocardial (∗) and subepicardial (arrow) levels of pulmonary valve. (h) Histologic sagittal section of the aortic valve root at the level of right coronary leaflet. Note the relationship of the aortic valve with the conduction tissue and right atrium. (i) Endocardial view of right ventricular outflow tract (RVOT) is shown (d). Note that endocardial infundibular sleeve consists of septoparietal trabeculations (∗) arising from septomarginal trabeculation (SMT). Note crossing architecture pattern of myocardial strands between septomarginal trabeculation with septoparietal trabeculations and supraventricular crest below pulmonary valve. (j) Histological section of the pulmonary valve stained with Masson's trichrome shows the attachment of the pulmonary leaflet. Note the myocardial extension above the sinotubular junction (arrow). L = the left aortic sinus, LCA = left coronary artery, M = myocyte, MV = mitral valve, N = noncoronary aortic sinus, LP = left posterior pulmonary sinus, PF = Purkinje fiber, PT = pulmonary trunk, R = right aortic sinus, RA = right atrium, RCA = right coronary artery, RP = right posterior pulmonary sinus, RVOT = right ventricle outflow tract, SC = supraventricular crest, SCV = superior cava vein, SMT = septomarginal trabeculation, and SPM = septal papillary muscle.