Mayo Applied Cardiac Anatomy

This chapter reviews important topics in cardiovas-cular anatomy that pertain to the practice of clinicalcardiology. The format of the chapter is to describebriefly the anatomy followed by the clinical signifi-cance in italic type.

Mediastinum

The mediastinum contains, in addition to the heart and greatvessels, the distal portion of the trachea, right and left bronchi,esophagus, thymus, autonomic nerves (cardiac and splanch-nic, left recurrent laryngeal, and bilateral vagal and phrenic),various small arteries (such as bronchial and esophageal) andveins (such as bronchial, azygos, and hemiazygos), lymphnodes, cardiopulmonary lymphatics, and thoracic duct.

Enlargement of a cardiac chamber or great vessel may dis-place or compress an adjacent noncardiac structure. Anenlarged left atrium may displace the left bronchus superior-ly and the esophagus rightward. An aberrant retroesophagealright subclavian artery indents the esophagus posteriorly andmay cause dysphagia. Mediastinal neoplasms can compressthe atria, superior vena cava, or pulmonary veins.

Pericardium

The pericardium surrounds the heart and consists of fibrousand serous portions. The fibrous pericardium forms a toughouter sac, which envelops the heart and attaches to the greatvessels. The ascending aorta, pulmonary artery, terminal2 to 4 cm of superior vena cava, and short lengths of thepulmonary veins and inferior vena cava are intrapericardial(Fig. 1).

The fibrous pericardium is inelastic and limits the diastolicdistention of the heart during exercise. Cardiac enlarge-ment or chronic pericardial effusions, both of which developslowly, will stretch the fibrous pericardium. However, thefibrous pericardium cannot stretch acutely, and the rapidaccumulation of as little as 200 mL of fluid may producefatal cardiac tamponade. Hemopericardium results fromperforation of either the heart or the intrapericardial greatvessels.

The serous pericardium is a delicate mesothelial layerthat lines the inner aspect of the fibrous pericardium (pari-etal pericardium) and the outer surface of the heart andintrapericardial great vessels (visceral pericardium). Thevisceral pericardium, or epicardium, contains the coronaryarteries and veins, autonomic nerves, lymphatic channels,and variable amounts of adipose tissue.

927

Chapter 55

Applied Anatomy of the Heartand Great Vessels

Joseph G. Murphy, M.D.

Sections of the text in italic type are topics related to pathology.An atlas illustrating the anatomy of the heart is at the end of the chapter (Plates 1-24).Modified from Edwards WD: Applied anatomy of the heart. In Giuliani ER, Gersh BJ, McGoon MD, Hayes DL, Schaff HV (editors): Mayo Clinic Practice

of Cardiology. Third edition. Mosby, 1996, pp 422-489. By permission of Mayo Foundation.

In obese subjects, excessive epicardial depot fat mayencase the heart, but because pericardial fat is liquid atbody temperature, cardiac motion is generally unhindered.

Focal epicardial fibrosis along the anterior right ventricleor posterobasal left ventricle (so-called soldiers’ patches)may result from old pericarditis or perhaps from the traumaof an enlarged heart’s impact against the sternum or calcifieddescending thoracic aorta.

Between the great arteries (aorta and pulmonary artery)and the atria is a tunnel-like transverse sinus (Fig. 1).Posteriorly, the pericardial reflection forms an inverted U-shaped cul-de-sac known as the oblique sinus. The liga-ment of Marshall is a pericardial fold that contains theembryonic remnants of the left superior vena cava.

A sequential saphenous vein bypass graft to the left coro-nary system may be positioned posteriorly through the trans-verse sinus. A persistent left superior vena cava will occupythe expected site of the ligament of Marshall, along the junc-tion between the appendage and body of the left atrium.

Between the parietal and visceral layers of the serous peri-cardium is the pericardial cavity, which normally contains10 to 20 mL of serous fluid that allows the tissue surfacesto glide over each other with minimal friction.

Thick and roughened surfaces associated with fibri-nous pericarditis lead to an auscultatory friction rub, and

organization of such an exudate may result in fibrous adhe-sions between the epicardium and the parietal pericardium.Focal adhesions are usually unimportant, but occasionallythey may allow the accumulation of loculated fluid or, rarely,tamponade of an individual cardiac chamber, usually theright ventricle. After cardiac surgery, the opened pericardialcavity may become sealed again if the parietal pericardiumadheres to the sternum; in this setting, the raw pericardial sur-faces, which are lined by fibrovascular granulation tissue,may ooze enough blood to cause cardiac tamponade.

Densely fibrotic adhesions, with or without calcification,can hinder cardiac motion and may restrict cardiac filling.The pericardium is thickened in subjects with chronic con-striction but not necessarily so in persons with constriction thatdevelops relatively rapidly. In the setting of constrictive peri-carditis, surgical excision of only the anterior pericardium(between the phrenic nerves) is often inadequate, becausethe remaining pericardium surrounds enough of the heart tomaintain constriction.

Most postoperative pericardial adhesions are usuallyfunctionally unimportant, but they may obscure the locationof the coronary arteries at subsequent cardiac operation.

Other pericardial conditions include congenital cysts ordiverticula of the pericardium, or the parietal pericardiummay be focally deficient or absent.

928 Applied Anatomy of the Heart and Great Vessels

Fig. 1. Parietal pericardium. A, Anterior portion of the parietal pericardium has been removed to show the intrapericardial segments of the great arteries andsuperior vena cava. (Anterior view from 16-year-old boy.) B, Heart has been removed from posterior portion of parietal pericardium to show the great ves-sels, the transverse sinus (dashed line), and the oblique sinus (arrows). (Anterior view from 13-year-old boy.) (See Appendix at end of chapter for abbre-viations.) (A from Mayo Clin Proc 56:479-497, 1981. By permission of Mayo Foundation.)

Parietal pericardium

Diaphragm

SVC

RPV

LPV

AoAo

A B

RV

PA

IVC

PA

RA

SVC

● The fibrous pericardium cannot adequately stretch acutely,and the rapid accumulation of as little as 200 mL of fluidmay produce fatal cardiac tamponade.

● A sequential saphenous vein bypass graft to the left coro-nary system may be positioned posteriorly through thetransverse sinus.

Great Veins

Bilaterally, the subclavian and internal jugular veins mergeto form bilateral innominate (or brachiocephalic) veins. Thelatter then join to form the superior vena cava (or superiorcaval vein) (Fig. 2).

Superior Vena CavaThe right internal jugular vein, right innominate vein,and superior vena cava afford a relatively straightintravascular route to the right atrium and tricuspid orifice.Accordingly, this route may be used for passage of a stiffendomyocardial bioptome across the tricuspid valve andinto the right ventricular apex to obtain a cardiac biop-sy specimen. Similarly, both temporary and permanenttransvenous pacemaker leads are inserted via either thesubclavian or the internal jugular vein and are threadedinto the right ventricular apex.

Catheters and pacemakers within the innominate veinsand superior vena cava become partially coated withthrombus and may be associated with thrombotic venousobstruction, pulmonary thromboembolism, or secondaryinfection. Mediastinal neoplasms, fibrosis, and aorticaneurysms may compress the thin-walled veins and resultin the superior vena caval syndrome.

Inferior Vena CavaThe inferior vena cava receives systemic venous drainagefrom the legs and retroperitoneal viscera and, at the levelof the liver, from the intra-abdominal systemic venousdrainage (portal circulation) via the hepatic veins.

The inferior vena cava, which is retroperitoneal, maybecome trapped and compressed between the vertebralcolumn posteriorly and either an adjacent retroperitonealstructure (for example, an abdominal aortic aneurysm) oran intraperitoneal structure (for example, a neoplasm) andthereby produce the inferior vena caval syndrome.

Venous thrombi in the lower extremities may extend intothe inferior vena cava or may become dislodged andembolize to the right heart and pulmonary circulation.

Renal cell carcinomas may extend intravascularly withinthe renal veins and inferior vena cava and may even formtethered intracavitary right-sided cardiac masses.Hepatocellular carcinomas often involve the hepatic veinsand occasionally may enter the suprahepatic inferior venacava or right atrium.

The superior and inferior pulmonary veins from eachlung enter the left atrium. The proximal 1 to 3 cm of thepulmonary veins contain cardiac muscle within the mediaand may thereby function like sphincters during atrial sys-tole as well as when significant mitral valve disease exists.

The thin-walled and low-pressure pulmonary veins maybe compressed extrinsically by mediastinal neoplasms orfibrosis. Rarely, a primary neoplasm may cause luminalobstruction in the major pulmonary veins.

Applied Anatomy of the Heart and Great Vessels 929

Fig. 2. Systemic veins, excluding the portal circulation. (See Appendix atend of chapter for abbreviations.)

Congenital Abnormalities of the Venous SystemCongenital anomalies of the systemic veins include a per-sistent left superior vena cava (with or without a left innom-inate vein) joining the coronary sinus or, rarely, the leftatrium; an unroofed or absent coronary sinus; a largeright sinus venosus valve (so-called cor triatriatum dexter);azygos continuity of the inferior vena cava; and bilateralsubrenal inferior venae cavae.

Anomalous Venous ConnectionIn total anomalous pulmonary venous connection, the con-fluence of pulmonary veins does not join the left atrium butrather maintains connection to derivatives of the cardinalor umbilicovitelline veins, such as the left innominate vein,coronary sinus, or ductus venosus. An interatrial commu-nication must also be present.

In partial anomalous pulmonary venous connection, onlysome veins (usually from the right lung) lack left atrialconnections. Connection of the right pulmonary veins tothe right atrium commonly accompanies sinus venosus atrialseptal defects, whereas connection of these veins to thesuprahepatic inferior vena cava is usually part of the scimitarsyndrome.

Cor TriatriatumCor triatriatum (sinistrum) results when the junctionbetween common pulmonary vein and left atrium isstenotic. A fenestrated membranous or muscular shelfsubdivides the left atrium into a posterosuperior cham-ber, which receives the pulmonary veins, and an anteroin-ferior chamber, which contains the atrial appendage andmitral orifice.

● Mediastinal neoplasms, fibrosis, and aortic aneurysmsmay compress the thin-walled veins and result in thesuperior vena caval syndrome.

● The inferior vena cava may become trapped and com-pressed between the vertebral column posteriorly andeither an adjacent retroperitoneal structure or an intraperi-toneal structure and thereby produce the inferior venacaval syndrome.

● The thin-walled low-pressure pulmonary veins may becompressed extrinsically by mediastinal neoplasms orfibrosis.

● Connection of one (usually the upper) or both right pul-monary veins to the right atrium commonly accompaniessinus venosus atrial septal defects.

Cardiac Chambers

Right AtriumThe right atrium, along with the superior vena cava, formsthe right lateral border of the frontal chest radiographic car-diac silhouette. It receives the systemic venous return fromthe superior and inferior venae cavae and receives most ofthe coronary venous return via the coronary sinus and numer-ous small thebesian veins. The ostium of the inferior venacava is bordered anteriorly by a crescentic eustachian valve,which may be large and fenestrated and form a so-calledChiari net. The coronary sinus ostium is partly shielded bya fenestrated thebesian valve. The right atrium consists ofa free wall and septum.

Its free wall has a smooth-walled posterior portion, whichreceives the caval and coronary sinus blood flow, and amuscular anterolateral portion, which contains ridge-likepectinate muscles and a large pyramid-shaped appendage.Separating the two regions is a prominent C-shaped musclebundle, the crista terminalis (or terminal crest). The rightatrial appendage abuts the right aortic sinus and overlies theproximal right coronary artery.

The thickness of the right atrial free wall varies consid-erably. The atrial wall between the pectinate muscles ispaper-thin and can be perforated by a stiff catheter.

When atrial enlargement and stasis to blood flow occur,mural thrombi may form within the recesses between thepectinate muscles, particularly in the atrial appendage.Indwelling cardiac catheters or pacemaker wires tend toinjure the endocardium at the cavoatrial junction and areoften associated with shallow linear mural thrombi. Anatrial pacing lead can be inserted into the muscle bundleswithin the appendage.

Atrial SeptumThe atrial septum has interatrial and atrioventricularcomponents (Fig. 3). The interatrial portion contains thefossa ovalis (or oval fossa), which includes an arch-shapedouter muscular rim (the limbus or limb) and a central fibrousmembrane (the valve). In contrast to the fossa ovalis, theforamen ovale (or oval foramen, which is patent throughoutfetal life) represents a potential interatrial passageway, whichcourses between the anterosuperior limbic rim and the valveof the fossa ovalis and then through the natural valvular per-foration (ostium secundum, or second ostium) into the leftatrium. In approximately two-thirds of subjects, the fora-men ovale closes anatomically during the first year of lifeas the valve of the fossa ovalis becomes permanently sealed


to the limbus. In the remaining third, this flap-valve closesfunctionally only when left atrial pressure exceeds right atri-al pressure; this constitutes a so-called valvular-competentpatent foramen ovale.

Through a patent foramen ovale, systemic venous embolimay enter the systemic arterial circulation. Such paradoxicemboli may be thrombotic (e.g., from the legs) or non-thrombotic (e.g., air emboli).

Pronounced atrial dilatation may so stretch the atrialseptum that the limbus no longer covers the ostium secun-dum in the valve of the fossa ovalis. As a result, interatrialshunting may occur across the valvular-incompetent patentforamen ovale (acquired atrial septal defect). In somesubjects, aneurysms of the valve of the fossa ovalis maydevelop and may undulate during the cardiac cycle. Atrialdilatation also stimulates the release of natriuretic peptide.

The atrioventricular component of the atrial septum,which separates the right atrium from the left ventricle, isprimarily muscular but also has a small fibrous component(the atrioventricular portion of the membranous septum).

Triangle of KochThe atrioventricular septum corresponds to the triangle ofKoch, an important anatomical landmark that contains theatrioventricular node and bundle; it is bound by the septaltricuspid annulus, the coronary sinus ostium, and the tendonof Todaro.

Tendon of TodaroThe tendon of Todaro is a subendocardial fibrous cord thatextends from the eustachian-thebesian valvular commissureto the anteroseptal tricuspid commissure (at the membra-nous septum); it very roughly corresponds to the level of themitral annulus.

The thickness of the atrial septum varies considerably.The valve of the fossa ovalis is a paper-thin translucentmembrane at birth but becomes more fibrotic with time andmay achieve a thickness of 1 to 2 mm. The limbus of thefossa ovalis ranges from 4 to 8 mm in thickness; however,lipomatous hypertrophy may produce a bulging mass morethan three times this thickness. The muscular atrioventricularseptum forms the summit of the ventricular septum andmay range from 5 to 10 mm in thickness; this may be greatlyincreased in the setting of hypertrophic cardiomyopathy orconcentric left ventricular hypertrophy. The membranousseptum generally is less than 1 mm thick.

Left AtriumThe left atrium, a posterior midline chamber, receivespulmonary venous blood and expels it across the mitral orificeand into the left ventricle. The esophagus and descending tho-racic aorta abut the left atrial wall. Thus, the left atrium, atri-al septum, and mitral valve are particularly well visualizedwith transesophageal echocardiography. The body of theleft atrium does not contribute to the frontal cardiac silhou-ette; however, the left atrial appendage, when enlarged, mayform the portion of the left cardiac border between the left ven-tricle and the pulmonary trunk. Normally the appendage,shaped like a windsock, abuts the pulmonary artery and over-lies the bifurcation of the left main coronary artery.

With chronic obstruction to left atrial emptying (forexample, rheumatic mitral stenosis), the dilated left atriummay shift the atrial septum rightward and in severe casesmay actually form the right cardiac border roentgeno-graphically. Moreover, the esophagus can be shifted right-ward, and the left bronchus may be elevated. Mural thrombioften develop within the atrial appendage or, less commonly,the atrial body, and in severe cases can virtually fill thechamber except for small channels leading from the pul-monary veins to the mitral orifice. In contrast to left atrialmural thrombi, which tend to involve the free wall, mostmyxomas arise from the left side of the atrial septum.

Comparison of AtriaThe right atrial free wall contains a crista terminalis andpectinate muscles, whereas the left atrial free wall has neither.


Fig. 3. Atrial anatomy. The atrioventricular septum lies anterior to the inter-atrial septum and posterior to the interventricular septum; note also theinfolded nature of the limbus (arrows) and the relative thinness of the valveof the fossa ovalis (open arrow). (Four-chamber view from 15-year-oldboy.) (See Appendix at end of chapter for abbreviations.)

RLPV

RA

RV

AVS

IAS

IVS

LA

LLPV

LV

The right atrial appendage is large and pyramidal, in contrastto the windsock-like left atrial appendage. Finally, the atrialseptum is characterized by the fossa ovalis on the right sideand by the ostium secundum on the left.

Owing to hemodynamic streaming within the right atriumduring intrauterine life, superior vena caval blood is directedtoward the tricuspid orifice, and inferior vena caval blood,carrying well-oxygenated placental blood, is directed bythe eustachian valve toward the foramen ovale. As a result,the most-well-oxygenated blood in the fetal circulation isdirected, via the left heart, to the coronary arteries, the upperextremities, and the brain. Even postnatally, the superiorvena cava maintains its orientation toward the tricuspidannulus, and the inferior vena cava maintains its orienta-tion toward the atrial septum (Fig. 4).

Consequently, an endomyocardial biopsy specimen ofthe right ventricular apex is much more easily obtained viaa superior vena caval approach than an inferior vena cavalapproach. In contrast, the passage of a catheter from theright atrium into the left atrium via the foramen ovale ismuch more easily performed via an inferior vena cavalapproach. In subjects in whom the foramen ovale is anatom-ically sealed, the valve of the fossa ovalis may be inten-tionally perforated (transseptal approach); however, thismembrane becomes thicker and more fibrotic with age.

Atrial Septal DefectA secundum atrial septal defect involves the fossa ovalisregion of the interatrial septum. It is the most common formof atrial septal defect and often is an isolated anomaly.

A primum atrial septal defect involves the atrioventric-ular septum and represents a malformation of the endo-cardial cushions; it is almost invariably associated withmitral and tricuspid abnormalities, particularly a cleft inthe anterior mitral leaflet.

A sinus venosus atrial septal defect involves theposterior aspect of the atrial septum and is usually asso-ciated with anomalous right atrial connection of the rightpulmonary veins. A coronary sinus atrial septal defectis usually associated with an absent (unroofed) coronarysinus and connection of the left superior vena cava to theleft atrium.

● Most myxomas arise from the left side of the atrialseptum.

● A secundum atrial septal defect involves the fossa ovalisregion of the interatrial septum.

● A coronary sinus atrial septal defect is usually associated

with an absent coronary sinus and connection of the leftsuperior vena cava to the left atrium.

Right VentricleThe right ventricle does not contribute to the borders of thefrontal cardiac silhouette roentgenographically. It is crescent-shaped in short-axis and triangular-shaped when viewed inlong-axis.

Conditions, such as pulmonary hypertension, that imposea pressure overload on the right ventricle cause straight-ening of the ventricular septum such that both ventriclesattain a D shape on cross-section. In extreme cases, suchas Ebstein’s anomaly or total anomalous pulmonary venousconnection, leftward bowing of the ventricular septum mayresult not only in a circular right ventricle and crescenticleft ventricle but also in possible obstruction of the left ven-tricular outflow tract.

The right ventricular chamber consists of three regions—inlet, trabecular, and outlet. The inlet region receives thetricuspid valve and its cordal and papillary muscle attach-ments. A complex meshwork of muscle bundles charac-terizes the anteroapical trabecular region. In contrast, theoutlet region is smoother-walled and is also known as theinfundibulum, conus, or right ventricular outflow tract.Along the outflow tract, an arch of muscle separates the tri-cuspid and pulmonary valves. The arch consists of a parietal


Fig. 4. Right atrial hemodynamic streaming. Superior vena caval blood isdirected toward the tricuspid orifice, and inferior vena caval blood is direct-ed toward the fossa ovalis. (Opened right atrium from 31-year-old man.) (SeeAppendix at end of chapter for abbreviations.) (From Edwards WD:Anatomy of the cardiovascular system. In Clinical Medicine. Vol. 6, Chap1. Spittell JA Jr [editor]. Harper & Row Publishers, 1984, p 8. By per-mission of Lippincott-Raven Publishers.)

SVC

IVC

RV

band, outlet septum, and septal band (Fig. 5), knowncollectively as the crista supraventricularis (supraventricu-lar crest).

During right ventricular endomyocardial biopsy, thebioptome is directed septally, not only to avoid injury to thecardiac conduction system and tricuspid apparatus but alsoto prevent possible perforation of the relatively thin freewall. Tissue is more often procured from the meshwork ofapical trabeculations than from the septal surface per se.When permanent transvenous pacemaker electrodes areinserted into the right ventricle, the apical trabeculationstrap the tined tip and thereby prevent dislodgment.

During vigorous cardiopulmonary resuscitation in whichribs are fractured, the jagged-edged bones may be forcedthrough the parietal pericardium, anteriorly, and may lac-erate an epicardial coronary artery or may perforate theright atrial or ventricular free wall. Furthermore, if car-diopulmonary resuscitation is exerted along the midster-num rather than the xiphoid area, the right ventricularoutflow tract may be compressed and this can result inhigh right ventricular pressure, which may produce apicalrupture.

Left VentricleThe left ventricle forms the left border of the frontal car-diac silhouette roentgenographically. It is circular in short-axis views and is approximated in three dimensions by atruncated ellipsoid.

Pressure OverloadConditions such as aortic stenosis and chronic hyperten-sion, which impose a pressure overload on the left ventricle,induce concentric left ventricular hypertrophy without appre-ciable dilatation. Although the short-axis chamber diam-eter does not increase significantly, the wall thicknessgenerally increases 25% to 75%, and the heart weight maydouble or triple.

Volume OverloadDisorders that impose a volume overload on the left ven-tricle, such as chronic aortic or mitral regurgitation ordilated cardiomyopathy, are attended not only by hyper-trophy but also by chamber dilatation. They thereby pro-duce a globoid heart with increased base-apex and short-axisdimensions. Although the heart weight may double or triple,the left ventricular wall thickness generally remains withinthe normal range because of the thinning effect of dilata-tion. Accordingly, when the left ventricle is dilated, wallthickness cannot be used as a reliable indicator of hyper-trophy (Fig. 6). The term “volume hypertrophy” is favoredin this situation. Hypertrophy, with or without chamberdilatation, decreases myocardial compliance and impairsdiastolic filling.

Like the right ventricle, the left ventricle can be dividedinto inlet, apical, and outlet regions. The inlet receives themitral valve apparatus, the apex contains fine trabecula-tions, and the outlet is angled away from the remainder of


Fig. 5. Ventricular anatomy. A, The right ventricle has a heavily trabeculated anteroapical region and exhibits muscular separation between the tricuspidand pulmonary valves. *Moderator band; arrow, papillary muscle of the conus. B, In contrast, the left ventricle (shown in long-axis) has fine apical trabeculationsand is characterized by direct continuity between the mitral and aortic valves. (See Appendix at end of chapter for abbreviations.) (A, from Schapira JN, CharuziY, Davidson RM [editors]: Two-Dimensional Echocardiography. Williams & Wilkins Company, 1982, p 131. By permission of Mayo Foundation.)

B

RAA

PV

*

PB OS

SB

TVRCA

A

AA

P

RV

A

SVC

LA

CS

PM

R Ao

the chamber. Inflow and outflow tracts are separated bythe anterior mitral leaflet, which forms an intracavitary cur-tain between the two (Fig. 5).

The anterior mitral leaflet is also in direct contact, at itsannulus, with the left and posterior aortic valve cusps. Forcomparison, the membranous septum abuts the right andposterior aortic cusps, and the outlet septum lies beneaththe right and left aortic cusps.

For practical purposes, the base-apex length of the leftventricle is divided into thirds—basal (corresponding tothe mitral leaflets and tendinous cords), midventricular(corresponding to the mitral papillary muscles), and apicallevels. Each level is then further divided into segments,thus forming the basis for regional analysis of the left ven-tricle (for example, the evaluation of regional wall motionabnormalities) (Fig. 7 and Table 1).

Hypertrophic cardiomyopathy is characterized by asym-metric (nonconcentric) left ventricular hypertrophy thatdisproportionately involves the septum. Cardiac amyloidmay mimic hypertrophic cardiomyopathy.

In the normal elderly heart, left ventricular geometry isaltered (septum is more sigmoid in shape) and in concertwith mild fibrosis and calcification of the aortic and mitralvalves may contribute to the low-grade systolic ejectionmurmurs that are so common in the elderly. With advanc-ing age, the aortic annulus dilates appreciably and tiltsrightward and less posteriorly, thereby altering the shape and

direction of the left ventricular outflow tract, which maysimulate hypertrophic cardiomyopathy.

Left ventricular trabeculae carneae are small, and per-manent apical entrapment of a tined transvenous pace-maker electrode is difficult to achieve and may necessitatethe placement of epicardial electrodes (for example, inpatients with corrected transposition of the great arteriesor with complete transposition of the great arteries and a pre-vious Mustard or Senning operation).

When left ventricular endomyocardial biopsy is per-formed, care must be taken not to injure the mitral apparatusor left bundle branch and not to perforate the apex.

In some persons, apical or anteroseptal trabeculae carneaemay form a prominent spongy meshwork that may be mis-interpreted as apical mural thrombus on imaging studies.

Comparison of VentriclesNormally, left ventricular wall thickness is three to four timesthat of the right ventricle. In short-axis, the left ventricle iscircular and the right is crescentic. Whereas the tricuspid andpulmonary valves are separated from one another, the mitraland aortic valves are in direct continuity. The right ventric-ular apex is much more heavily trabeculated than the left.

By two-dimensional echocardiography, ventricular mor-phology is best inferred by the morphology of the atrio-ventricular valves, particularly by differences in their annularlevels at the cardiac crux (Fig. 3).


Fig. 6. Compared with a normal heart (center), the heart with pressure hypertrophy (left) has a thick left ventricular wall, but the heart with volume hyper-trophy (right) has a normal wall thickness. Both hypertrophied hearts weighed more than twice normal. (Left, from 64-year-old man with aortic stenosis.Right, from 50-year-old man with idiopathic dilated cardiomyopathy.) (See Appendix at end of chapter for abbreviations.)

RV

RVRV

LVLVLV

Ventricular Septal DefectThe most common ventricular septal defect, either isolat-ed or associated with other cardiac anomalies, is the mem-branous (perimembranous) type, which involves themembranous septum. An infundibular (outlet; supracristal;subarterial) ventricular septal defect is commonly encoun-tered in tetralogy of Fallot and truncus arteriosus. Amalalignment ventricular septal defect occurs when one ofthe great arteries overrides the septum and attains biven-tricular origin, or both great arteries arise from one ven-tricle. Muscular defects involve the muscular septum andcan be solitary or multiple (so-called Swiss cheese septum).A defect of the atrioventricular septum is considered to bean atrioventricular canal defect, and straddling of an atrio-ventricular valve most commonly occurs across a defect ofthis type.

Tetralogy of FallotWithin the spectrum of cyanotic congenital heart disease isa group of anomalies that share in common a maldevelop-ment of the conotruncal septum. Tetralogy of Fallot, themost common anomaly in this group, results from dis-placement of the infundibular septum and is characterizedby a large malalignment ventricular septal defect, an over-riding aorta, and variable degrees of infundibular and valvu-lar pulmonary stenosis. When the pulmonary valve is atretic,pulmonary blood flow may come from the ductus arteriosusor systemic collateral arteries.

Transposition of the Great ArteriesComplete transposition of the great arteries is associatedwith abnormal conotruncal septation and parallel ratherthan intertwined great arteries, such that the aorta arisesfrom the right ventricle and the pulmonary artery emanates

from the left ventricle; a ventricular septal defect is presentin about one-third of cases.

Truncus ArteriosusTruncus arteriosus implies absent conotruncal septationand is characterized by a single arterial trunk from whichthe aorta, pulmonary arteries, and coronary arteries arise;the ventricular septal defect is of membranous or infundibu-lar type.

Double-Outlet Right VentricleDouble-outlet right ventricle is characterized by the originof both great arteries from the right ventricle, a malalign-ment ventricular septal defect, and infundibular septal dis-placement that differs from the type observed in tetralogy.

Myocyte Response to InjuryMyocardial cells are by volume one-half contractile elementsand one-third mitochondria. They are exquisitely sensitiveto oxygen deprivation, and ischemia represents the mostcommon form of myocardial injury. Other injurious agentsinclude viruses, chemicals, and excessive cardiac workload(volume or pressure).


Fig. 7. Regional analysis of the left ventricle. Short-axis views show the recommended 16-segment system. (See Appendix at end of chapter for abbrevi-ations.)

Basal Midventricular Apical

Table 1.—Percentage of Regional Left Ventricular(LV) Mass

% LV volume No. ofLevel per segment segments Total, %

Basal 7.2 6 43Middle 6.0 6 36Apical 5.3 4 21

The heart has only a limited response to stress or injury.Adaptive responses include hypertrophy and dilatation,whereas sublethal cellular injury is characterized by vari-ous degenerative changes. Necrosis is the histologic hall-mark of lethal cellular injury, and it elicits an inflammatoryresponse with subsequent healing by scar formation.

Hypertrophy of cardiac muscle cells is accompanied bydegenerative changes, an increase in interstitial collagen,and a decrease in ventricular compliance. In dilated hearts,hypertrophied myocytes are also stretched, but with rela-tively normal diameters. In dilated hearts, the best histologicindicators of hypertrophy are nuclear alterations.

Acute myocardial ischemia is characterized by intensesarcoplasmic staining with eosin dyes, prominent sarcoplas-mic contraction bands, and, occasionally, stretched and wavymyocardial cells. When ischemic cells are irreversibly injured,the changes of coagulative necrosis appear. Nuclei fade away(karyolysis) or fragment (karyorrhexis), and the sarcoplasmdevelops a glassy homogeneous appearance, although inmany cases the cross-striations remain intact for several days.Necrotic myocardium elicits an inflammatory infiltrate ofneutrophils and macrophages, which serves histologically todifferentiate acute infarction from acute ischemia. Becausemyocardial cells cannot replicate, healing is by organization,with scar formation.

Cardiac Valves

Atrioventricular ValvesThe right (tricuspid) and left (mitral) atrioventricular valveshave five components, three of which form the valvularapparatus (annulus, leaflets, commissures) and two of whichform the tensor apparatus (chordae tendineae and papillarymuscles).

Valve AnnulusThe annulus of each atrioventricular valve is saddle-shaped.As part of the fibrous cardiac skeleton at the base of theheart, each annulus electrically insulates atrium from ven-tricle. Since the tricuspid annulus is an incomplete fibrousring, loose connective tissue maintains insulation at thepoints of fibrous discontinuity. The mitral annulus, in con-trast, constitutes a continuous ring of fibrous tissue.

Valve LeafletThe valve leaflets are delicate fibrous tissue flaps that closethe anatomical valvular orifice during ventricular systole

(Fig. 8). The leading edge of each leaflet is its free edge,and its serrated appearance results from direct cordal inser-tions into this border. The closing edge, in contrast, rep-resents a slightly thickened nodular ridge severalmillimeters above the free edge. When the valve closes,apposing leaflets contact one another along their closingedges, and interdigitation of these nodular ridges ensuresa competent seal. Each leaflet comprises two majorlayers—namely, the fibrosa, which forms the strong struc-tural backbone of the valve, and the spongiosa, which actsas a shock absorber along the atrial surface, particularlyat the closing edge (rough zone), where one leaflet coaptswith an adjacent leaflet.

Chordae TendineaeThe chordae tendineae are strong, fibrous tendinous cordsthat act as guidewires to anchor and support the leaflets.They restrict excessive valvular excursion during ventricularsystole and thereby prevent valvular prolapse into the atria.Most tendinous cords branch one or more times, so thatgenerally more than 100 cords insert into the free edge ofeach atrioventricular valve. By virtue of these numerouscordal insertions, the force of systolic ventricular blood isevenly distributed throughout the undersurface of eachleaflet.

Papillary MusclesThe papillary muscles, which may have multiple heads, areconical mounds of ventricular muscle that receive themajority of the tendinous cords. Because of their positiondirectly beneath a commissure, each papillary musclereceives cords from two adjacent leaflets. As a result, pap-illary muscle contraction tends to pull the two leaflets towardeach other and thereby facilitates valve closure.

In the elderly, mild mitral annular dilatation may occur,with or without atrial dilatation. Leaflets become thicker,with increasing nodularity of the rough zone and with mildhooding deformity of the entire leaflet. Contributing to thelatter is a decrease in ventricular base-apex length whichmakes the thickened cords appear relatively longer than nec-essary, thus simulating mitral valve prolapse.

Tricuspid ValveThe plane of the tricuspid annulus faces toward the rightventricular apex. Along the free wall, the annulus insertsinto the atrioventricular junction, whereas along the septum,it separates the atrioventricular and interventricular portionsof the septum.


In living subjects, the tricuspid annular circumferencevaries with the cardiac cycle: it is maximum duringventricular diastole (about 11 cm2) and decreases by about30% during ventricular systole. The reduction in area isdue to contraction of the underlying basal right ventricularmyocardium, since the incomplete tricuspid annulus can-not adequately constrict by itself.

The three tricuspid leaflets are not always well separatedfrom one another. The septal (medial) leaflet lies parallelto the ventricular septum, and the posterior (inferior) leafletlies parallel to the diaphragmatic aspect of the right ven-tricular free wall. In contrast, the anterior (anterosuperi-or) tricuspid leaflet forms a large sail-like intracavitarycurtain that partially separates the inflow tract from the out-flow tract.

Because of differences in leaflet size and cordal length,the excursion of the posterior and septal leaflets is less thanthat of the anterior leaflet. In the setting of annular dilatation,leaflet excursion is inadequate to effect central coaptation,and valvular incompetence results. Because the tricuspidannulus is incomplete, and because the basal right ven-tricular myocardium forms a subjacent muscular ring,dilatation of the right ventricle commonly produces annu-lar dilatation and tricuspid regurgitation. Right atrial dilata-tion alone, as in constrictive pericarditis, usually does notcause significant tricuspid insufficiency.

Valvular incompetence also may be observed in condi-tions that limit leaflet and cordal excursion, such asrheumatic disease (fibrosis and scar retraction), carcinoidendocardial plaques (thickening and retraction), and

eosinophilic endomyocardial diseases (thrombotic adher-ence to the underlying myocardium). In normal hearts,mild degrees of tricuspid regurgitation commonly exist.

Tricuspid stenosis involves commissural and cordal fusionand may occur in rheumatic or carcinoid heart disease.

Mitral Valve

Mitral AnnulusThe plane of the mitral annulus faces toward the leftventricular apex. The orifice changes shape during thecardiac cycle, from elliptical during ventricular systole tomore circular during diastole. In living subjects, the normalmitral annular circumference is maximum during ventric-ular diastole (about 7 cm2) and decreases 10% to 15%during systole.

Mitral annular calcification almost invariably involvesonly the posterior mitral leaflet and forms a C-shaped ringof annular and subannular calcium which may impede basalventricular contraction and thereby produce mitral regur-gitation. Similarly, inadequate basal ventricular contrac-tion may contribute to valvular incompetence in the settingof pronounced left ventricular dilatation; however, becauseonly part of the mitral annulus is in direct contact with thebasal ventricular myocardium, dilatation of the ventriclerarely increases annular circumference more than 25%.

Secondary left atrial dilatation may contribute to the pro-gression of preexisting mitral incompetence by displacingthe posterior leaflet and its annulus and thereby hinderingthe excursion of this taut leaflet.


Fig. 8. Components of an atrioventricular valve (from the mitral valve of an 8-year-old girl). A, Each leaflet has a large clear zone (CZ) and a smaller roughzone (RZ) between its free edge (arrow) and closing edge (dotted line). B, Each commissure (C) separates two leaflets and overlies a papillary muscle (PapM); a fan-like commissural tendinous cord (*) connects the tip of the papillary muscle to the commissure.

CZ

A B

RZ

C

Pap M

*

Mitral LeafletsThe mitral leaflets form a continuous funnel-shaped veilwith two prominent indentations, the anterolateral andposteromedial commissures. Although the two commis-sures do not extend entirely to the annulus, they effectivelyseparate the two leaflets. In contrast to the three other cardiacvalves, which each comprise three leaflets or cusps, themitral valve has only two leaflets. At midleaflet level, themitral orifice is elliptic or football-shaped, and its long axisaligns with the two commissures and their papillary muscles.

Although the anterior leaflet occupies only about 35%of the annular circumference, its leaflet area is almost iden-tical to the area of the posterior leaflet, about 5 cm2. Thetotal mitral leaflet surface area is 10 cm2, nearly twice thatnecessary to close the systolic annular orifice, 5.2 cm2.However, some folding of leaflet tissue is needed to ensurea competent seal, and the normal leaflets are not as redun-dant as they might appear.

The myxomatous (or floppy) mitral valve is character-ized by annular dilatation, stretched tendinous cords, andredundant hooded folds of leaflet tissue, which are proneto prolapse, incomplete coaptation, cordal rupture, andmitral regurgitation. In contrast, rheumatic mitral insuffi-ciency results from scar retraction of leaflets and cords. Inthe setting of infective endocarditis, virulent organisms mayperforate the leaflet tissue and produce acute mitral regur-gitation. In hypertrophic cardiomyopathy, the anteriormitral leaflet contacts the ventricular septum during systoleand contributes both to left ventricular outflow tract obstruc-tion and to mitral incompetence.

In chronic aortic insufficiency, the regurgitant streammay impact on the anterior mitral leaflet and produce notonly a fibrotic jet lesion but also the leaflet flutter and pre-mature valve closure that are so characteristic echocar-diographically.

Papillary MusclesA fan-shaped cord emanates from the tip of each of the twopapillary muscles and inserts into its overlying commissureand into both adjacent leaflets (Fig. 8B). Similarly, a small-er commissural cord inserts into each minor commissurebetween their posterior scallops. Two particularly prominentcords insert along each half of the ventricular surface of theanterior mitral leaflet, and these so-called strut cords offeradditional support for this mid-cavitary leaflet that alsoforms part of the wall of the left ventricular outflow tract.Cordal length is generally 1 to 2 cm.

Rheumatic mitral stenosis is characterized by cordal and

commissural fusion, which obliterate the secondary inter-cordal orifices and narrow the primary valve orifice. Cordalrupture may occur in a myxomatous (floppy) valve, aninfected valve, or, rarely, an apparently normal valve and leadto acute mitral regurgitation.

The mitral papillary muscles occupy the middle third ofthe left ventricular base-apex length. Two prominent musclesoriginate from the anterolateral and posteromedial (infero-medial) free wall, beneath their respective mitral commis-sures. Trabeculations not only anchor the papillary musclesbut also may form a muscle bridge between the two papil-lary groups and thereby contribute to valve closure.

The anterolateral muscle is a single structure with a mid-line groove in 70% to 85% of cases, whereas the postero-medial muscle is multiple or is bifid or trifid in 60% to 70%.The anterolateral muscle is generally larger and extendscloser to the annulus than the posteromedial muscle.Occasionally, an accessory papillary muscle is interposedbetween the two major muscles along the free wall. Nopapillary muscles or tendinous cords originate from theseptum and terminate on the mitral leaflets. However, inabout 50% of subjects, one or more cord-like structures,known as left ventricular false tendons, or pseudotendons,arise from a papillary muscle and insert either onto the septalsurface or onto the opposite papillary muscle.

Chronic postinfarction mitral regurgitation is associatedwith papillary muscle atrophy and scarring, thinning andscarring of the subjacent left ventricular free wall, and leftventricular dilatation. Acute postinfarction mitral regurgi-tation may be associated with rupture of a papillary muscle(almost invariably the posteromedial) and can involve theentire muscle or only one of its multiple heads.

Competent function of the mitral valve requires the har-monious interaction of all valvular components, includingthe left atrium and left ventricle.

● Right atrial dilatation alone usually does not cause sig-nificant tricuspid insufficiency.

● In normal hearts, mild degrees of tricuspid regurgitationcommonly exist.

● Secondary left atrial dilatation may contribute to the pro-gression of preexisting mitral incompetence.

● In hypertrophic cardiomyopathy, the anterior mitral leafletmay contact the ventricular septum during systole andcontribute both to left ventricular outflow tract obstruc-tion and to mitral incompetence.

● Chronic postinfarction mitral incompetence is associatedwith papillary muscle atrophy and scarring.


Semilunar ValvesThe right (pulmonary) and left (aortic) semilunar valves, incontrast to the atrioventricular valves, have no tensor appa-ratus and, therefore, are structurally simpler valves. Theyconsist of annulus, cusps, and commissures. Behind eachcusp is an outpouching of the arterial root, known as a sinus(of Valsalva). There are three aortic sinuses and three pul-monary sinuses, which impart a cloverleaf shape to the arterialroots.

The annuli of the semilunar valves are part of the fibrouscardiac skeleton. They are nonplanar structures, shapedlike a triradiate crown.

The cusps are half-moon-shaped (semilunar), pocket-like flaps of delicate fibrous tissue which close the valvularorifice during ventricular diastole. The leading edge ofeach cusp is its free edge. The closing edge, in contrast,represents a slightly thickened ridge that lies a few mil-limeters below the free edge, along the ventricular surfaceof the cusp. At the center of each cusp, the closing edgemeets the free edge and forms a small fibrous mound, thenodule of Arantius. When the valve closes, apposing cuspscontact one another along the surfaces between their freeand closing edges (that is, the lunular areas), forming acompetent seal.

Like the atrioventricular valves, the semilunar valvescontain two major layers histologically. The fibrosa formsthe structural backbone of the valve and is continuouswith the annulus, whereas the spongiosa acts more as ashock absorber along the ventricular surface, especiallyat the closing edge. Cusps contain little elastic tissue and,accordingly, have no appreciable elastic recoil. Theopening and closing of the semilunar valves is a passiveprocess that entails cusp excursion and annulocuspidhinge-like motion.

In the elderly, degenerative changes in the aortic valvemay result in low-grade systolic ejection murmurs. Theclosing edges become thickened and, along the nodules ofArantius, may form whisker-like projections called Lambl’sexcrescences. Lunular fenestrations also tend to developwith increasing age.

Disease processes that tend to increase cusp rigidity,such as fibrosis or calcification, or that lead to commissur-al fusion, such as rheumatic valvulitis, tend to narrow theeffective valvular orifice and, as a consequence, producestenosis. In contrast, processes that straighten the cuspid linebetween commissures and thereby hold the commissuresopen, such as arterial root dilatation or rheumatic cuspidscar retraction, tend to produce regurgitation.

Pulmonary ValveThe plane of the pulmonary annulus faces toward the leftmidscapula with an area of about 3.5 cm2. The cusps are usu-ally similar in size, although minor variations are commonlyobserved.

Pulmonary incompetence occurs in conditions thatproduce dilatation of the pulmonary artery and annulus,such as pulmonary hypertension or heart failure. Combinedpulmonary stenosis and incompetence are features of car-cinoid heart disease, in which the annulus becomes con-stricted and stenotic and in which the cusps are also retractedand insufficient. Pure pulmonary stenosis is almost alwayscongenital in origin.

Aortic ValveThe plane of the aortic valve faces the right shoulder. Inthe living subject, the normal aortic annular area averagesabout 3 cm2.

Unoperated symptomatic aortic stenosis has a worseprognosis than many malignancies. The vast majority ofstenotic aortic valves are calcified. Most commonly, thevalve represents either degenerative (senile) calcification ora calcified congenitally bicuspid valve. Only rarely are heav-ily calcified valves the site of active infective endocarditis.

Aortic root dilatation stretches open the commissuresand thereby produces aortic insufficiency in either a tri-cuspid or a bicuspid aortic valve. Acute aortic regurgitationmay be produced by infective aortic endocarditis with cus-pid perforation or by acute aortic dissection with commis-sural prolapse. Chronic aortic regurgitation with coexistentaortic stenosis is most commonly associated withpostrheumatic cuspid retraction, which yields a fixed tri-angular orifice.

Among cases of infective endocarditis, perhaps none pre-sent so varied a clinical spectrum as those associated withaortic annular abscesses. The possible clinical presentationsdepend to a great extent on the particular cusp(s) involved.Subvalvular extension may involve the anterior mitral leaflet,left bundle branch, or ventricular septal myocardium;involvement of the ventricular septal myocardium mayproduce a large abscess cavity or result in rupture into aventricular chamber with the formation of either an aorto-right ventricular or aorto-left ventricular fistula. An aorticannular abscess may expand laterally and enter thepericardial cavity and thereby produce purulent pericardi-tis or fatal hemopericardium, or it may burrow into adjacentcardiac chambers or vessels and produce various fistulas(aorto-right atrial, aorto-left atrial, or aortopulmonary).


Fibrous Cardiac SkeletonAt the base of the heart, the fibrous cardiac skeleton encir-cles the four cardiac valves. It comprises not only the fourvalvular annuli but also their intervalvular collagenousattachments (the right and left fibrous trigones, the inter-valvular fibrosa, and the conus ligament) and the membra-nous septum and tendon of Todaro. This fibrous scaffold isfirmly anchored to the ventricles but is rather loosely attachedto the atria. Thus, the cardiac skeleton not only electricallyinsulates the atria from the ventricles but also supports thecardiac valves and provides a firm foundation against whichthe ventricles may contract.

Because of the intervalvular attachments of the fibrouscardiac skeleton, disease or surgery on one valve can affectthe size, shape, position, or relative angulation of its neigh-boring valves and also can affect the adjacent coronaryarteries or cardiac conduction system. Tricuspid annulo-plasty or replacement may be complicated by injury to theright coronary artery or atrioventricular conduction tissues,whereas mitral valve replacement may be attended by traumato the circumflex coronary artery, coronary sinus, or aorticvalve. At aortic valve replacement, the anterior mitral leaflet,left bundle branch, or coronary ostia may be injured inad-vertently.

Most congenital anomalies of the pulmonary valve areassociated with stenosis. Isolated pulmonary stenosis isalmost always due to a dome-shaped acommissural valve,with congenital fusion of all three commissures. However,forms of pulmonary stenosis which are associated with othercardiac malformations, such as tetralogy of Fallot, usuallyresult from a bicuspid or unicommissural valve (often witha hypoplastic annulus) or from a dysplastic valve with threethickened cusps.

Congenitally bicuspid aortic valves affect 1% to 2% of thegeneral population and constitute the most common form ofcongenital heart disease. Although they usually are neitherstenotic nor insufficient at birth, most bicuspid valves willbecome stenotic during adulthood as the cusps calcify, andsome will become insufficient as a result of infective endo-carditis or aortic root dilatation. In contrast, the congeni-tally unicommissural aortic valve is usually stenotic at birthand becomes progressively more obstructive as calcifica-tion develops in adulthood. Aortic atresia is associated withthe hypoplastic left heart syndrome and is usually fatalduring the first week of life. All congenital anomalies of theaortic valve are much more common in males than infemales.

In truncus arteriosus, the truncal valve most commonly

comprises three cusps and resembles a normal aortic valve.However, it may be quadricuspid, bicuspid, or, rarely,pentacuspid and may contain one or more raphes; suchnontricuspid valves are often incompetent, particularly ifthe truncal root is dilated.

● Disease processes that tend to increase cusp rigidity tendto narrow the effective valvular orifice and producestenosis.

● Processes that straighten the cuspid line between com-missures tend to produce regurgitation.

● Pulmonary incompetence occurs in conditions thatproduce dilatation of the pulmonary trunk and annulus,such as pulmonary hypertension or heart failure.

● Pure pulmonary stenosis is almost always congenital inorigin.

● An aortic annular abscess may expand laterally and enterthe pericardial cavity.

● Congenitally bicuspid aortic valves affect 1% to 2% ofthe general population.

Figure 9 shows the anatomy of the heart as seen on mag-netic resonance imaging.

Great Arteries

Pulmonary ArteriesThe pulmonary artery arises anteriorly and to the left of theascending aorta and is directed toward the left shoulder. Inadults, it is slightly greater in diameter than the ascendingaorta, although its wall thickness is roughly half that of theaorta. At the bifurcation, the right pulmonary artery travelshorizontally beneath the aortic arch and behind the superi-or vena cava, and the left pulmonary artery courses overthe left main bronchus (Fig. 10). The main and leftpulmonary arteries contribute to the left border of the frontalcardiac silhouette roentgenographically.

In pulmonary hypertension, especially in children withpliable tracheobronchial cartilage, the tense and dilatedpulmonary arteries can compress the left bronchus andthe left upper and right middle lobar bronchi and there-by contribute to recurrent bronchopneumonia in thoselobes. Furthermore, the dilated pulmonary artery maydisplace the aortic arch rightward and secondarily pro-duce tracheal indentation and, occasionally, hoarsenessas a result of compression of the left recurrent laryngealnerve.


AortaThe aorta arises at the level of the aortic valve annulusand terminates at the aortic bifurcation, approximately atthe level of the umbilicus and the fourth lumbar vertebra.The aorta has four major divisions: ascending aorta, aorticarch, descending thoracic aorta, and abdominal aorta (Fig.11).

The ascending aorta lies almost entirely within the peri-cardial sac and includes sinus and tubular portions, whichare demarcated by the aortic sinotubular junction. Theaortic valve leaflets are related to the three sinuses, and the

right and left coronary arteries arise from the right and leftaortic sinuses, respectively. The ascending aorta lies pos-terior and to the right of the pulmonary artery.

With age or with the development of atherosclerosis, theaortic sinotubular junction can become heavily calcified,particularly above the right cusp, and may produce coronaryostial stenosis. Among the causes of aortic root dilatation,perhaps aging, mucoid medial degeneration (so-called cysticmedial necrosis), and chronic hypertension are the mostcommon and may produce an ascending aortic aneurysm,aortic valvular regurgitation, or acute aortic dissection.


Fig. 9. Transverse (A through D), sagittal (E through H), and coronal (I through L) planes of the heart shown in analogous magnetic resonance images (atleft) and anatomic sections (at right). aAo, ascending aorta; Ao, aortic arch; AoR, aortic root; AV, aortic valve; AzV, azygos vein; CS, coronary sinus; dAo,descending thoracic aorta; IA, innominate artery; LA, left atrium; LAA, left atrial appendage; LAD, left anterior descending coronary artery; LB, leftbronchus; LCC, left coronary cusp; LCCA, left common carotid artery; LCX, left circumflex coronary artery; LCX-OM, left circumflex coronary artery, obtusemarginal branch; LIV, left innominate vein; LLPV, left lower pulmonary vein; LMA, left main coronary artery; LPA, left pulmonary artery; LPV, left pul-monary vein; LSA, left subclavian artery; LSV, left subclavian vein; LUPV, left upper pulmonary vein; LV, left ventricle; MPA, main pulmonary artery;MV, mitral valve; PS, pericardial sac; PV, pulmonary valve; RA, right atrium; RAA, right atrial appendage; RCA, right coronary artery; RCCA, right com-mon carotid artery; RIV, right innominate vein; RJV, right internal jugular vein; RPA, right pulmonary artery; RSV, right subclavian vein; RV, right ven-tricle; RVOT, right ventricular outflow tract; SVC, superior vena cava; T, trachea; TV, tricuspid valve; VS, ventricular septum. (From Mayo Clin Proc62:573-583, 1987. By permission of Mayo Foundation.)

A B

CC D


The aortic arch travels over the right pulmonary arteryand the left bronchus. From its superior aspect emanate theinnominate (or brachiocephalic), left common carotid, andleft subclavian arteries, in that order. In 11% of subjects,the innominate and left common carotid arteries form acommon ostium, and in 5%, the left vertebral artery arisesdirectly from the aortic arch, between the left commoncarotid and left subclavian arteries. The ligamentum arte-riosum represents the obstructed fibrotic or fibrocalcific

remnant of the fetal ductus arteriosus (ductal artery), whichjoins the proximal left pulmonary artery to the undersur-face of the aortic arch. The aortic arch contributes to theleft superior border of the frontal cardiac silhouette andforms the roentgenographic aortic knob.

Aortic DissectionWhen aortic dissections do not involve the ascending aorta(type III or type B), the intimal tear is commonly near the

E F

G HFig. 9 continued

ligamentum arteriosum or the ostium of the left subclavianartery. By virtue of severe torsional and shear stresses placedon the heart and great vessels during nonpenetrating decel-erative chest trauma, as can occur in motor vehicle acci-dents, the aorta may be transected at the junction betweenthe aortic arch and the descending thoracic aorta. Whenthe tear is incomplete, a posttraumatic pseudoaneurysm candevelop with time. Aneurysms of the aortic arch may beassociated with hypertension, atherosclerosis, or aortitis, orthey may be idiopathic.

Descending Thoracic AortaThe descending thoracic aorta abuts the left anterior surfaceof the vertebral column and lies adjacent to the esophagusand the left atrium. Its posterolateral branches are the bilateralintercostal arteries, and its anterior branches include thebronchial, esophageal, mediastinal, pericardial, and superiorphrenic arteries. The bronchial arteries, most commonlytwo left and one right, nourish the bronchial walls and thepulmonary arterial and venous walls. Uncommonly,bronchial arteries may arise from intercostal or subclavian


Fig. 9 continued

I J

K L

arteries or, rarely, from a coronary artery. The bronchialveins drain not only into the azygos and hemiazygos veinsbut also into the pulmonary veins.

If the bronchial circulation is adequate, pulmonary emboliusually do not cause pulmonary infarction. In several formsof pulmonary hypertension, the bronchial arteries becomequite enlarged and tortuous.

Aneurysms of the descending thoracic aorta may beassociated with aortic dissection, aortitis, atherosclerosis,hypertension, or trauma. They may or may not extendbelow the diaphragm.

Abdominal AortaThe abdominal aorta travels along the left anterior surfaceof the vertebral column and lies adjacent to the inferior venacava. The major lateral (retroperitoneal) branches includethe renal, adrenal, right and left lumbar, and inferior phrenicarteries. The gonadal arteries arise somewhat more anteri-orly but remain retroperitoneal. The intraperitoneal branchesarise anteriorly and include the celiac artery (with its leftgastric, splenic, and hepatic branches) and the superior andinferior mesenteric arteries. The distal aortic branchesinclude the right and left common iliac arteries and a smallmiddle sacral artery.

Atherosclerotic abdominal aortic aneurysms are mostcommonly infrarenal. They tend to bulge anteriorly andthereby stretch and compress the gonadal and inferiormesenteric arteries. Such aneurysms are generally filledwith laminated thrombus and so their residual lumens often

appear normal or even narrowed rather than dilated.Rupture of an atherosclerotic abdominal aortic aneurysmmay be associated with extensive retroperitoneal hemor-rhage, with or without intraperitoneal hemorrhage.

Aortopulmonary WindowAn aortopulmonary septal defect represents a large open-ing between the ascending aorta and the pulmonary trunkand hemodynamically resembles a patent ductus arteriosus.Rarely, one pulmonary artery may originate from the ascend-ing aorta or ductus arteriosus, while the other arisesnormally from the pulmonary trunk. Congenital stenosisof the pulmonary arteries is usually associated with maternalrubella during the first trimester. In pulmonary atresia withventricular septal defect, the pulmonary arteries may bederived from the right or left ductus arteriosus and from


Fig. 10. Pulmonary and bronchial arteries. The right and left pulmonary arter-ies do not exhibit mirror-image symmetry. (See Appendix at end of chap-ter for abbreviations.)

Fig. 11. Systemic arteries. The aorta may be divided into ascending, arch,descending thoracic, and abdominal regions. (See Appendix at end of chap-ter for abbreviations.)

R Ext. iliac

Asc

end

ing

ao

rta

Ao

rtic

arc

h

Ab

do

min

al a

ort

a

R Subclavian

Innominate

Tubular aorta

Sinotubular jct.

Aortic sinus

Coronary art.

R Common carotid

CeliacHepatic

Middle sacral

R Gonadal

R Renal

Sup. mes. art.R Adrenal

L Common carotid

L Subclavian

Bronchial

Intercostal

Esophageal

Diaphragm

L GastricSplenic

L AdrenalL Renal

L Gonadal

Inf. mes. art

L Common iliac

L Ext. iliac

R Int. iliac L Int. iliac

Ligamentum arteriosum D

escend

ing

tho

racic aorta

Trachea

RUL

RML

RLL

RPA

PT

LPALUL

LLL

Lingula

bronchial or other systemic collateral arteries (analogousto total anomalous pulmonary venous connection).

Aortic Arch Congenital AbnormalitiesVarious anomalies result from faulty development of theaortic arches. A right aortic arch results from persistenceof the right fourth aortic arch and disappearance of its leftcounterpart; it most commonly accompanies tetralogy ofFallot, pulmonary atresia with ventricular septal defect,and truncus arteriosus. A double aortic arch results frompersistence of both fourth aortic arches. An aberrant retro-esophageal right subclavian artery is a relatively commonanomaly, which may cause dysphagia; it probably resultsfrom persistence of the right dorsal aorta and resorption ofthe right fourth aortic arch.

Ductus ArteriosusThe patent ductus arteriosus may be isolated or may accom-pany other cardiac malformations. A left ductus arteriosusjoins the proximal left pulmonary artery to the aortic arch,whereas a right ductus arteriosus joins the proximal rightpulmonary artery to the right subclavian artery; in cases ofright aortic arch with mirror-image brachiocephalic branch-ing, the opposite pertains.

Coarctation of the AortaCoarctation of the aorta represents an obstructive infoldedridge just distal to the left subclavian artery and opposite theductus arteriosus; it is associated with a congenitally bicus-pid aortic valve in at least half of the cases.

● Acute aortic dissection is commonly associated with anintimal tear above the right aortic cusp and with eventualrupture into the pericardial sac.

● When aortic dissections do not involve the ascendingaorta (type III or type B), the intimal tear is commonlynear the ligamentum arteriosum or the ostium of the leftsubclavian artery.

Coronary Circulation

Right Coronary ArteryThe right coronary artery arises nearly perpendicularly fromthe right aortic sinus. In 50% of subjects, one or more conusarteries also originate from the right aortic sinus, anterior tothe right coronary ostium. Rarely, the descending septal arteryor the sinus nodal artery may originate directly from the aorta.

The left coronary artery arises from the left aortic sinusand tends to arise at an acute angle and to travel parallel tothe aortic sinus wall. When the left main artery isexceptionally short, its ostium may assume a double-barrelappearance.

Among the various causes of coronary ostial stenosis,perhaps the most common is degenerative calcification ofthe aortic sinotubular junction, which often affects the rightaortic sinus. Stenosis of the right coronary ostium occurssix to eight times more often than that of the left. Aortitisassociated with syphilis or ankylosing spondylitis also maybe complicated by coronary ostial obstruction. Iatrogenicostial injury may complicate coronary arteriography, intra-operative coronary perfusion, or aortic valve replacement.

The right coronary artery travels within the right atrio-ventricular sulcus (or groove) (Fig. 12). In 50% of subjects,the first anterior branch is the conus artery, which nourishesthe right ventricular outflow tract; in the remainder, thisartery arises independently from the right aortic sinus. Thedescending septal artery, which arises from the proximalright coronary artery or, rarely, from the conus artery orright aortic sinus, supplies the infundibular septum and, insome individuals, the distal atrioventricular (His) bundle.Along the acute cardiac margin, from base to apex, coursesa prominent acute marginal branch, and between this ves-sel and the conus artery, several smaller marginal branchesarise and travel parallel to the acute margin; these vesselsnourish the lateral two-thirds of the anterior right entricularfree wall.

Beyond the acute margin, along the inferior surface ofthe heart, the length of the right coronary artery variesinversely with that of the circumflex coronary artery.However, in 90% of human hearts, the right coronary arterygives rise not only to the posterior descending artery, whichtravels in the inferior interventricular sulcus, but also tobranches that supply the inferior left ventricular free wall.Accordingly, these arteries nourish the inferior third of theventricular septum (the inlet septum), including the rightbundle branch and the posterior portion of the left bundlebranch, and the inferior left ventricular free wall, includingthe posteromedial mitral papillary muscle.

Left Main Coronary ArteryThe left main coronary artery travels between the pulmonaryartery and the left atrium and is covered in part by the leftatrial appendage. In two-thirds of subjects, it bifurcates intoleft anterior descending and circumflex branches, and in theremaining one-third, it trifurcates into the aforementioned


branches and an intermediate artery (ramus intermedius),which follows a course similar to that of either the first diag-onal or first marginal branch.

Left Anterior Descending Coronary ArteryThe left anterior descending coronary artery travels withinthe anterior interventricular sulcus (or groove) and, afterwrapping around the apex, may ascend a variable distancealong the inferior interventricular sulcus. Septal perforatingbranches nourish not only the anterosuperior two-thirds andentire apical one-third of the ventricular septum but also theatrioventricular (His) bundle and the right and anterior leftbundle branches. The proximal septal perforators anasto-mose with the descending septal artery. Epicardial branches,called diagonals, nourish the anterior left ventricular freewall and the medial third of the anterior right ventricularfree wall. Myocardial bridges may be demonstratedangiographically in 12% of subjects and almost invariablyinvolve the anterior descending artery; they produce criticalsystolic luminal narrowing in only 1% to 2% of hearts andprobably have a benign prognosis in most cases.

Left Circumflex Coronary ArteryThe (left) circumflex coronary artery travels within the leftatrioventricular sulcus (or groove) and often terminates justbeyond the obtuse marginal branch. The circumflex arterynourishes the lateral left ventricular free wall; however, inthe 10% of subjects in whom the circumflex artery givesrise to the posterior descending branch, it also supplies theinferior left ventricular free wall and the inferior third of theventricular septum. The circumflex and anterior descendingarteries nourish the anterolateral mitral papillary muscles, andthe circumflex and right coronary arteries supply the

posteromedial mitral papillary muscles.The four major epicardial coronary arteries occupy only

two planes of the heart. The right and circumflex arteriesdelineate the plane of the atrioventricular sulcus (cardiacbase), and the left main artery and anterior and posteriordescending arteries delineate the plane of the ventricularseptum.

The origin of the posterior descending artery determinesthe blood supply to the inferior portion of the left ventricleand thereby defines coronary dominance. In 70% of hearts,the right coronary artery crosses the crux and gives rise tothis branch, and right coronary dominance pertains. In 10%,the circumflex coronary artery terminates as the posteriordescending branch and thereby establishes left coronarydominance. Both the right and circumflex arteries supplythe cardiac crux in the remaining 20% and constitute so-called shared coronary dominance. The dominant coronaryartery, however, does not supply most of the left ventricularmyocardium. In subjects with right coronary dominance,for example, the anterior descending artery supplies about45% of the left ventricle and the circumflex and right coro-nary arteries nourish about 20% and 35%, respectively.

Blood Supply of the Cardiac Conduction SystemThe sinus nodal artery arises from the right coronary arteryin 60% of subjects and from the circumflex artery in 40%,but its artery of origin does not depend on patterns of coro-nary arterial dominance. The atrioventricular nodal arteryoriginates from the dominant artery and, accordingly, arisesfrom the right coronary in 90% and the circumflex in 10%.The atrioventricular nodal artery and the first septal perfo-rator of the anterior descending artery offer dual blood supplyto the atrioventricular (His) bundle. Other septal perforating


Fig. 12. Coronary arteries. A, Base of heart. B, Superior and inferior views of the heart. (See Appendix at end of chapter for abbreviations.)A B

branches of the anterior descending artery supply the ante-rior aspect of the left bundle branch, and septal perforatorsof the posterior descending branch, an extension of the dom-inant artery, supply the posteroinferior portion of the leftbundle branch. The right bundle branch receives a dualblood supply from the septal perforators of the anterior andposterior descending arteries.

Coronary Collateral CirculationIn the human heart, the major epicardial coronary arteriescommunicate with one another by means of anastomoticchannels 50 to 200 µm in diameter. Normally, these smallcollateral arteries afford very little blood flow. However,if arterial obstruction induces a pressure gradient acrosssuch a channel, then with time the collateral vessel maydilate and provide an avenue for significant blood flowbeyond the stenotic lesion. Such functional collaterals maydevelop between the terminal branches of two coronaryarteries, between the side branches of two arteries, betweenbranches of the same artery, or within the same branch (viathe vasa vasorum). They are most numerous in theventricular septum (between septal perforators of anterior andposterior descending arteries), in the ventricular apex(between anterior descending septal perforators), in theanterior right ventricular free wall (between anteriordescending and right or conus arteries), in the anterolateralleft ventricular free wall (between anterior descendingdiagonals and circumflex marginals), at the cardiac crux(between the right and circumflex arteries), and along theatria (Kugel’s artery between right and circumflex arteries).Smaller subendocardial anastomoses also exist.

The most common sites for high-grade atheroscleroticlesions are the proximal one-half of the anterior descend-ing and circumflex arteries and the origin and entire lengthof the right coronary artery. The distribution and severityof atherosclerotic plaques do not differ significantly amongpatients with angina pectoris, acute myocardial infarction,end-stage ischemic heart disease, or sudden death.

Congenital malformations of the coronary arteries includeanomalous ostial origin, anomalous arterial branchingpatterns, and anomalous arterial anastomoses.

Coronary VeinsThe venous circulation of the heart comprises a coronarysinus system, an anterior cardiac venous system, and thethebesian venous system (Fig. 13). Small thebesian veinsdrain directly into a cardiac chamber, particularly the rightatrium or right ventricle; the ostia of these veins are easily

recognized along the relatively smooth atrial walls but aredifficult to identify in the trabeculated ventricles.

During cardiac electrophysiologic studies among patientswith Wolff-Parkinson-White syndrome and left-sided bypasstracts, a catheter electrode may be positioned within thecoronary sinus and great cardiac vein, adjacent to the mitralannulus, to localize the aberrant conduction pathways.

Cardiac LymphaticsMyocardial lymphatics drain toward the epicardial surface,where they are joined by lymphatic channels from theconduction system, atria, and valves. Larger epicardial lym-phatics then travel in a retrograde manner with the coronaryarteries back to the aortic root, where a confluence of rightand left cardiac lymphatics drains into a pretracheal lymphnode and eventually empties into the right lymphatic duct.

The coronary veins and cardiac lymphatics work in con-cert to remove excess fluid from the myocardial interstitiumand pericardial sac. Accordingly, obstruction of eithersystem or of both systems may result in myocardial edemaand pericardial effusion.

Cardiac Conduction System

Sinus NodeThe sinus node is the primary pacemaker of the heart. It isan epicardial structure that measures approximately 15 by5 by 2 mm and is located in the sulcus terminalis (inter-cavarum) near the superior cavoatrial junction (Fig. 14).Through its center passes a relatively large sinus nodal artery.Sinus nodal function is greatly influenced by numeroussympathetic and parasympathetic nerves that terminatewithin its boundaries.

Histologically, the sinus node consists of specializedcardiac muscle cells embedded within a prominent collage-nous stroma. Its myocardial cells are smaller than ventric-ular muscle cells and contain only scant contractile elements.Ultrastructurally, the sinus node comprises transitional cellsand variable numbers of P cells centrally and atrial myocar-dial cells peripherally. The P cells are thought to be thesource of normal cardiac impulse formation.

Because the sinus node occupies an epicardial position,its function may be affected by pericarditis or metastaticneoplasms. In the setting of cardiac amyloidosis, the sinusnode may be involved by extensive fibrosis or amyloid depo-sition. Although the sinus node is rarely infarcted, its func-tion can be altered by adjacent atrial infarction.


Internodal TractsThere are no morphologically distinct conduction pathwaysbetween the sinus and the atrioventricular nodes by lightmicroscopy, but electrophysiologic studies support the con-cept of three functional preferential conduction pathways.By ultrastructural studies, some investigators have observedspecialized cardiac muscle cells in these internodal tracts.

Lipomatous hypertrophy of the atrial septum may inter-fere with internodal conduction and induce various atrialarrhythmias. Because the functional preferential pathwaystravel only in the limbus and not in the valve of the fossaovalis, internodal conduction disturbances do not occurwith intentional septal perforation at cardiac catheterization(transseptal approach), with the Rashkind balloon atrialseptostomy, or with the Blalock-Hanlon partial (posterior)atrial septectomy. With the Mustard operation for completetransposition of the great arteries, in which the entire atrialseptum is resected and in which the surgical atriotomy maydisrupt the crista terminalis, severe disturbances of inter-nodal conduction may result.

Atrioventricular NodeThe atrioventricular node is a subendocardial right atrialstructure that measures approximately 6 by 4 by 1.5 mm.It is located within the triangle of Koch (bordered by thetendon of Todaro, septal tricuspid annulus, and coronarysinus ostium) and abuts the right fibrous trigone (centralfibrous body). The atrioventricular nodal artery courses

near the node but not necessarily through it. Sympatheticand parasympathetic nerves enter the atrioventricular nodeand greatly influence its function.

Like the sinus node, the atrioventricular node histolog-ically consists of a complex interwoven pattern of smallspecialized cardiac muscle cells within a fibrous stroma.With advanced age, the atrioventricular node acquires pro-gressively more fibrous tissue, although not as extensivelyas the sinus node.

The so-called mesothelioma of the atrioventricular nodeis a small and rare primary neoplasm which, by virtue ofits position, produces various arrhythmias and may causesudden death. Metastatic neoplasms may rarely infiltratethe atrioventricular node but do not necessarily alter itsfunction. Sarcoid granulomas tend to involve the basalventricular myocardium and may destroy the atrioventric-ular conduction system. Because of its subendocardial posi-tion, the atrioventricular node may be ablated nonsurgicallyat the time of electrophysiologic study.

Atrioventricular BundleThe atrioventricular (His) bundle arises from the distalportion of the atrioventricular node and courses through thecentral fibrous body to the summit of the muscular ven-tricular septum, adjacent to the membranous septum. Itaffords the only normal physiologic avenue for electricalconduction between ventricles. By virtue of its positionwithin the central fibrous body (right fibrous trigone), the


Fig. 13. Coronary veins. Superior and inferior views of the heart. (See Appendix at end of chapter for abbreviations.)

atrioventricular bundle is closely related to the annuli of theaortic, mitral, and tricuspid valves. The atrioventricularbundle has a dual blood supply—from the atrioventricularnodal artery and the first septal perforating branch of theanterior descending artery. In some subjects, a septal branchof the proximal right coronary artery also nourishes theatrioventricular bundle.

The atrioventricular bundle is made up of numerous

parallel bundles of specialized cardiac muscle cells, whichare separated by delicate fibrous septa. The entire atrio-ventricular bundle is insulated by a collagenous sheath.With increasing age, the fibrous septa become thicker, andthe functional elements may be partially replaced by adi-pose tissue. Ultrastructurally, the atrioventricular bundlecontains Purkinje cells and ventricular myocardial cells inparallel arrangement.


A

BFig. 14. Cardiac conduction system. A, Right heart. The sinus and AV nodes are both right atrial structures. B, Left heart. The left bundle branch forms abroad sheet that does not divide into distinct anterior and posterior fascicles. (From Edwards WD: Anatomy of the cardiovascular system. In ClinicalMedicine. Vol. 6, Chap 1. Spittell JA Jr [editor]. Harper & Row Publishers, 1984, p 8. By permission of Lippincott-Raven Publishers.)

Superior vena cava

Sinus node

Crista terminalis

Fossa ovalis

Right atrium

Inferior vena cava

AortaPulmonary valve

Atrioventricular node

AV (His) bundle

RIght bundle branch

Septal band

Moderator band

Right ventricle

Anterior papillary muscle

Ventricular septumTricuspid valve annulus

Pulmonary artery

Left bundle branch

Left ventricle

Papillary muscles

Ventricular septum

Mitral valve annulus

Left atrium

Aorta

In some subjects, alternate conduction pathways existbetween the atria and the ventricles, either within the exist-ing atrioventricular conduction system or elsewhere alongthe fibrous cardiac skeleton, and may produce variousarrhythmias. Atrionodal bypass tracts (of James) connectthe atria to the distal atrioventricular node, and atriofas-cicular tracts (of Breckenmacher) connect the atria to theatrioventricular bundle. Nodoventricular and fascic-uloventricular bypass fibers (of Mahaim) connect the atrio-ventricular node and atrioventricular bundle, respectively,to the underlying ventricular septal summit. These bypassfibers are quite commonly observed histologically and areapparently nonfunctional in most persons, although theymay produce ventricular preexcitation in some instances.

Ventricular preexcitation is usually associated with aber-rant atrioventricular bypass tracts that bridge the tricuspidor mitral annuli. These tracts often travel within the adi-pose tissue of the atrioventricular sulcus rather than througha defect in the valvular annuli. Such bypass tracts can besingle or multiple and may be identified by electrophysio-logic mapping.

Acquired complete heart block may involve the atrio-ventricular node and bundle or both bundle branches. Thatoccurring with acute myocardial infarction is usually transientand more commonly complicates inferoseptal than anterosep-tal infarction. Usually the atrioventricular node and atrio-ventricular bundle are edematous, or the bundle branchesare focally infarcted. Acute heart block also can complicateaortic infective endocarditis. Chronic heart block may beassociated with ischemic heart disease or with fibrocalcificdisorders of the aortic or mitral valves, but it is mostcommonly due to idiopathic fibrosis of the atrioventricularbundle and bilateral bundle branches. Heart block may alsocomplicate aortic or mitral valve replacement.

Congenital complete heart block presents as persistentbradycardia in utero and can represent an isolated anomalyor may accompany other cardiac malformations. It resultsfrom interruption of atrioventricular conduction pathways,either at the junction between atrial muscle and theatrioventricular node or at the junction between the atrio-ventricular node and the atrioventricular bundle. Thedifferent embryologic origins of these three regions accountfor the specific sites of disrupted conduction tissue.

Bundle BranchesAs an extension of the atrioventricular bundle, the rightbundle branch forms a cordlike structure, approximately 50mm in length and 1 mm in diameter, which courses along

the septal and moderator bands to the level of the anteriortricuspid papillary muscle. The left bundle branch forms abroad fenestrated sheet of conduction fibers which spreadsalong the septal subendocardium of the left ventricle andseparates incompletely and variably into two or three indis-tinct fascicles. The fascicles travel toward the left ventricularapex and both mitral papillary muscle groups. The bundlebranches are nourished by septal perforators arising fromthe anterior and posterior descending coronary arteries.Histologically, the bundle branches consist of parallel tractsof specialized cardiac muscle cells which are insulated by adelicate fibrous sheath. Ultrastructurally, Purkinje cells andventricular myocardial cells form the bundle branches.

Right bundle branch block may be idiopathic or be asso-ciated with ischemic heart disease, chronic systemic hyper-tension, or pulmonary hypertension. Right ventriculotomyusually produces the electrocardiographic features of rightbundle branch block, even though the bundle may not havebeen transected.

Chronic left bundle branch block may be associated withfibrocalcific degeneration of the ventricular septal summitas a result of chronic ischemia, left ventricular hyperten-sion, calcification of the aortic or mitral valves, or any formof cardiomyopathy.

● The sinus node comprises transitional cells and variablenumbers of P cells centrally and atrial myocardial cellsperipherally.

● With the Mustard operation for complete transpositionof the great arteries, in which the entire atrial septum isresected, severe disturbances of internodal conductionmay result.

● The atrioventricular bundle has a dual blood supply—from the atrioventricular nodal artery and the first sep-tal perforating branch of the anterior descending artery.

● Acute heart block may complicate aortic infective endo-carditis.

Cardiac InnervationBecause the embryonic heart tube first forms in the futureneck region, its autonomic innervation also arises from thislevel. From the cervical ganglia originate three pairs of cer-vical sympathetic cardiac nerves, which intermingle as theyjoin the cardiac plexus, between the great arteries and thetracheal bifurcation. Several thoracic sympathetic cardiacnerves arise from the upper thoracic ganglia and also join thecardiac plexus. From the parasympathetic vagus nervesemanate the superior and inferior cervical vagal cardiac



nerves and the thoracic vagal cardiac nerves, which like-wise interweave within the cardiac plexus. The varioussympathetic and parasympathetic nerves then descend fromthis plexus onto the heart and thereby innervate the coro-nary arteries, cardiac conduction system, and myocardium.Furthermore, afferent nerves concerned with pain and variousreflexes ascend from the heart toward the cardiac plexus.

The transplanted human heart is completely denervatedand responds only to circulating (humoral) substances and notto autonomic impulses. Similarly, afferent pathways are alsolost, including pain tracts and various reflexes. Consequently,if chronic cardiac transplant rejection produces diffuse coro-nary arterial obstruction, subsequent myocardial ischemia

and infarction will be asymptomatic.The asplenia syndrome is characterized by bilateral right-

sided symmetry and is generally associated with right atrialisomerism, right pulmonary isomerism, abdominal situsambiguus, and, in some instances, bilateral sinus nodes. Incontrast, the sinus node may be congenitally absent or mal-positioned in cases of polysplenia with left atrial isomerism.

● The transplanted heart is completely denervated andresponds only to circulating (humoral) substances andnot to autonomic impulses.

● Congenital complete heart block may present as persis-tent bradycardia in utero.

A AnteriorAo AortaArt. ArteryAL AnterolateralAS AnteroseptalAV AtrioventricularAVS AV septumCS Coronary sinusDesc DescendingExt ExternalI InferiorIAS Interatrial septumIL InferolateralInf InferiorInt InternalIS Inferoseptal (Fig. 7 only)IVC Inferior vena cavaIVS Interventricular septumL LeftLA Left atriumLAD Left anterior descending coronary arteryLCX Left circumflex coronary arteryLLL Left lower lobeLLPV Left lower pulmonary veinLMA Left main coronary arteryLPA Left pulmonary arteryLPV Left pulmonary veinLUL Left upper lobeLV Left ventricleLVOT Left ventricular outflow tract

Mes MesentericMV Mitral valveOS Outlet septumP PosteriorPA Pulmonary arteryPB Parietal bandPL PosterolateralPM PosteromedialPost. PosteriorPS PosteroseptalPT Pulmonary trunkPV Pulmonary valveR RightRA Right atriumRAA Right atrial appendageRCA Right coronary arteryRLL Right lower lobeRLPV Right lower pulmonary veinRML Right middle lobeRPA Right pulmonary arteryRPD Right posterior descending coronary arteryRPV Right pulmonary veinRUL Right upper lobeRV Right ventricleS SeptalSB Septal bandSup SuperiorSVC Superior vena cavaTV Tricuspid valve


Appendix

Abbreviations Used in Figures


Plate 1. Calcification of aortic valve in degenerative aortic stenosis.

Plate 2. Normal aortic valve, opened (left) and closed (right).


Plate 4. Thin valve of foramen ovale (transilluminated).

Plate 6. Tricuspid and mitral valves in profile on four-chamber view of theheart. Note that the normal tricuspid valve takes origin below that of themitral valve, allowing the possibility of a right atrial-to-left ventricular shunt.

Plate 7. Pulmonary valve.

Plate 5. Normal atria.

Plate 3. Four valves at base of heart.


Plate 8. Right ventricle, showing marked trabeculation and tricuspid valve. Plate 9. Mitral valve leaflets and annulus (short-axis).

Plate 11. Mitral valve leaflets and chords (short-axis).Plate 10. Mitral valve papillary muscles (short-axis).

Plate 12. Mitral valve commissural cords. Plate 13. Left ventricle with membranous septum (transilluminated).


Plate 14. Left ventricle (free wall and septum) with mitral valve on free wall.

Plate 15. Position of atrioventricular node (triangle of Koch).


Plate 16. Right atrium, showing hemodynamic streaming (superior venacava to tricuspid valve to inferior vena cava to foramen ovale).

Plate 17. Myocardial bridge, left anterior descending coronary artery.

Plate 18. Myocardial arteriole.


Plate 19. Septal perforators (coronary cast).

Plate 20. Left anterior descending coronary artery with septal perforators.


Plate 21. Coronary ostia (conus, right, and left).

Plate 22. Normal aortic valve, closed (left) and opened (right).


Plate 23. Aortic valve (from below).

Plate 24. Valve fibrosis in rheumatic mitral stenosis.

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