Ebook Wilcox’s surgical anatomy of the heart (4/E): Part 1

Part 1 book “Wilcox’s surgical anatomy of the heart” has contents: Surgical approaches to the heart, anatomy of the cardiac chambers, surgical anatomy of the valves of the heart, surgical anatomy of the coronary circulation, surgical anatomy of the conduction system.

of the Heart

Fourth edition

of the Heart

Fourth edition

Robert H Anderson, BSc, MD, FRCPath

Visiting Professor, Institute of Genetic Medicine, Newcastle University, Newcastle-upon-Tyne, UK;

Visiting Professor of Pediatrics, Medical University of South Carolina, Charleston, SC, USA

Diane E Spicer, BS, PA(ASCP)

Pathologists’ Assistant, University of Florida – Pediatric Cardiology, Gainesville, Florida, and

Congenital Heart Institute of Florida, St Petersburg, FL, USA

It furthers the University’s mission by disseminating knowledge in the pursuit of

education, learning, and research at the highest international levels of excellence

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Fourth edition © Robert H Anderson, Diane E Spicer, Anthony M Hlavacek, Andrew C Cook, and Carl L Backer 2013This publication is in copyright Subject to statutory exception

and to the provisions of relevant collective licensing agreements,

no reproduction of any part may take place without the written

permission of Cambridge University Press

Fourth edition first published 2013

Third edition first published 2004

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A catalogue record for this publication is available from the British Library

Library of Congress Cataloguing in Publication data

Anderson, Robert H (Robert Henry), 1942–

Wilcox’s surgical anatomy of the heart – Fourth edition / Robert H Anderson, BSc, MD, FRCPath, Diane E Spicer,

BS, Anthony M Hlavacek, MD, Andrew C Cook, BSc, PhD, Carl L Backer, MD

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Every effort has been made in preparing this book to provide accurate and

up-to-date information which is in accord with accepted standards and practice

at the time of publication Although case histories are drawn from actual cases,

every effort has been made to disguise the identities of the individuals involved

Nevertheless, the authors, editors and publishers can make no warranties that the

information contained herein is totally free from error, not least because clinical

standards are constantly changing through research and regulation The authors,

editors and publishers therefore disclaim all liability for direct or consequential

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are strongly advised to pay careful attention to information provided by the

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Preface page vii

Surgical approaches to the heart 1Anatomy of the cardiac chambers 13Surgical anatomy of the valves of the heart 51Surgical anatomy of the coronary circulation 90Surgical anatomy of the conduction system 111Analytical description of congenitally malformed hearts 128Lesions with normal segmental connections 150Lesions in hearts with abnormal segmental connections 244Abnormalities of the great vessels 321Positional anomalies of the heart 363

The books and articles devoted to

technique in cardiac surgery are legion

This is most appropriate, as the success of

cardiac surgery is greatly dependent upon

excellent operative technique But

excellence of technique can be dissipated

without a firm knowledge of the underlying

cardiac morphology This is just as true for

the normal heart as for those hearts with

complex congenital lesions It is the

feasibility of operating upon such complex

malformations that has highlighted the

need for a more detailed understanding of

the basic anatomy in itself Thus, in recent

years surgeons have come to appreciate the

necessity of avoiding damage to the

coronary vessels, often invisible when

working within the cardiac chambers, and

particularly to avoid the vital conduction

tissues, invisible at all times Although

detailed and accurate descriptions of the

conduction system have been available

since the time of their discovery, only

rarely has its position been described with

the cardiac surgeon in mind At the time

the first edition of this volume was

published, to the best of our knowledge

there had been no other books that

specifically displayed the anatomy of

normal and abnormal hearts as perceived at

the time of operation We tried to satisfy

this need in the first volume by combining

the experience of a practising cardiac

surgeon with that of a professional cardiac

anatomist We added significantly to the

illustrations in the second edition, while

seeking to retain the overall concept, as

feedback from those who had used the firstedition was very positive In the thirdedition, we sought to expand and improvestill further on the changes made in thesecond edition In the second edition, wehad added an entirely new chapter oncardiac valvar anatomy, and greatlyexpanded our treatment of coronaryvascular anatomy We retained this format

in the third edition, as we were gratifiedthat, as hoped, readers were able to find aparticular subject more easily The thirdedition also contained still more newillustrations, retaining the approach oforientating these illustrations, whereappropriate, as seen by the surgeonworking in the operating room, butreverting to anatomical orientation for most

of the pictures of specimens So as to clarifythe various orientations of each individualillustration, we continued to include a set ofaxes showing, when appropriate, thedirections of superior, inferior, anterior,posterior, left, right, apex, and base Allaccounts were based on the anatomy as it isobserved and, except in the case ofmalformations involving the aortic arch andits branches, they owe nothing to

speculative embryology

A major change was forced upon us as

we prepared this fourth edition, as ouroriginal surgical author, Benson Wilcox,died in May of 2010 It is very difficult toreplace such a pioneer and champion ofsurgical education, but we are gratified thatCarl Backer has assumed the role ofsurgical editor We are also pleased to add

Diane Spicer to our anatomical team Shehas contributed enormously by providingmany new and better illustrations of theanatomy as seen in the autopsied heart.These advances are complimented by thecontributions of our other new editor,Tony Hlavacek Tony has provided quiteremarkable images obtained usingcomputed tomography and magneticresonance imaging, which show that theheart can be imaged with just as muchaccuracy during life as when we hold thespecimens in our hands on the autopsybench Recognising the huge contributions

of Ben Wilcox, we are also pleased torename this fourth edition ‘Wilcox’sSurgical Anatomy of the Heart’ As withthe previous editions, it is our hope that thenew edition will continue to be of interestnot only to the surgeon, but also to thecardiologist, anaesthesiologist, and surgicalpathologist All of these practitionersideally should have some knowledge ofcardiac structures and their exquisiteintricacies, particularly those cardiologistswho increasingly treat lesions thatpreviously were the province of the surgeon.Our senior anatomist remains active, andhas been fortunate to be granted access toseveral archives of autopsied hearts held inthe United States of America subsequent tohis retirement from the Institute of ChildHealth in London We remain confidentthat, in the hands of this new team, and ifsupply demands, the book will pass throughstill further editions, hopefully continuing

to improve with each version

Robert H Anderson, Diane E Spicer,

Anthony M Hlavacek,Andrew C Cook,and Carl L Backer,London, Tampa, Charleston and Chicago

November, 2012

A good deal of the material displayed in

these pages, and the concepts espoused, are

due in no small part to the help of our

friends and collaborators As indicated in

our preface, the major change since we

produced the third edition has been the sad

passing of our founding surgical editor,

Benson R Wilcox We have renamed this

fourth edition ‘Wilcox’s Surgical Anatomy

of the Heart’ We dedicate this edition to

his eternal memory A further change has

been the retirement of Robert H Anderson

from the Institute of Child Health at

Great Ormond Street Children’s Hospital,

London Retirement, however, has

permitted him to establish new

connections, not least with the newest

additions to our team of authors This has

permitted many new hearts to be

specifically photographed for this new

edition, not only of autopsy specimens, but

also in the operating room In addition, it

has created the collaboration that permits

the inclusion of wonderful images

obtained using computed tomography andmagnetic resonance imaging We

continue, nonetheless, to owe a particulardebt to Anton Becker of the University ofAmsterdam, Bob Zuberbuhler of

Children’s Hospital of Pittsburgh,Pennsylvania, United States of America,and F Jay Fricker of University of Florida,Gainesville, Florida, United States ofAmerica, all of whom permitted us to usematerial from the extensive collections ofnormal and pathological specimens held intheir centres We also continue to

acknowledge the debt owed to Siew Yen

Ho, of the National Heart and LungInstitute, part of Imperial College inLondon Yen produced many of theoriginal drawings from which weprepared our artwork, and photographedmany of the hearts in the Bromptonarchive The initial photographs andsurgical artwork could not have beenproduced without the considerable helpgiven by the Department of Medical

Illustrations and Photography, University

of North Carolina As with the thirdedition, we owe an equal debt of gratitude

to Gemma Price, who has continued toimprove our series of cartoons For boththe third edition and this edition, she hasworked over and above the call of duty Wealso thank Vi Hue Tran, who helpedphotograph the hearts from GreatOrmond Street We are again indebted toChristine Anderson for her help duringthe preparation of the manuscript, andthank the team supporting Carl Backer atLurie Children’s of Chicago, in

particular Pat Heraty and Anne E Sarwark.Finally, it is a pleasure to acknowledge thesupport provided by Cambridge

University Press, who have ensured thatall the good parts of the previouseditions were retained In particular, wethank Nicholas Dunton and JoannaChamberlin for all their helpduring the preparation of the book forpublication

Surgical approaches

to the heart

When we describe the heart in this chapter,

and in subsequent chapters, our account

will be based on the organ as viewed in its

anatomical position1 Where appropriate,

the heart will be illustrated as it would be

viewed by the surgeon during an operative

procedure, irrespective of whether the

pictures are taken in the operating room, or

are photographs of autopsied hearts When

we show an illustration in non-surgical

orientation, this will be clearly stated

In the normal individual, the heart lies

in the mediastinum, with two-thirds of its

bulk to the left of the midline (Figure 1.1)

The surgeon can approach the heart, and

the great vessels, either laterally through

the thoracic cavity, or directly through the

mediastinum anteriorly To make such

approaches safely, knowledge is required of

the salient anatomical features of the chest

wall, and of the vessels and the nerves that

course through the mediastinum

(Figure 1.2) The approach used most

frequently is a complete median

sternotomy, although increasingly the

trend is to use more limited incisions The

incision in the soft tissues is made in the

midline between the suprasternal notch

and the xiphoid process Inferiorly, the

white line, or linea alba, is incised betweenthe two rectus sheaths, taking care to avoidentry to the peritoneal cavity, or damage to

an enlarged liver, if present Reflection ofthe origin of the rectus muscles in this areareveals the xiphoid process, which isincised to provide inferior access to theanterior mediastinum Superiorly, avertical incision is made between thesternal insertions of the

sternocleidomastoid muscles This exposesthe relatively bloodless midline raphebetween the right and left sternohyoid andsternothyroid muscles An incisionthrough this raphe gives access to thesuperior aspect of the anteriormediastinum The anterior mediastinumimmediately behind the sternum is devoid

of vital structures, so that the superior andinferior incisions into the mediastinum cansafely be joined by blunt dissection in theretrosternal space Having split thesternum, retraction will reveal thepericardial sac, lying between the pleuralcavities Superiorly, the thymus glandwraps itself over the anterior and lateralaspects of the pericardium in the area ofexit of the great arteries, the gland being aparticularly prominent structure in the

infant (Figures 1.3, 1.4) It has two laterallobes, joined more or less in the midline.Sometimes this junction between the lobesmust be divided, or partially excised, toprovide adequate exposure The arterialsupply to the thymus is from the internalthoracic and inferior thyroid arteries Ifdivided, these arteries tend to retreat intothe surrounding soft tissues, and canproduce troublesome bleeding The veinsdraining the thymus are fragile, oftenemptying into the left brachiocephalic orinnominate vein via a common trunk(Figure 1.5) Undue traction on the glandcan lead to damage to this major vessel.When the pericardial sac is exposedwithin the mediastinum, the surgeonshould have no problems in gaining access

to the heart The vagus and phrenic nervestraverse the length of the pericardium, butare well lateral (Figures 1.2, 1.6) Thephrenic nerve on each side passesanteriorly, and the vagus nerve posteriorly,relative to the hilum of the lung

(Figure 1.6)

At operation, the course of the phrenicnerve is seen most readily through a lateralthoracotomy (Figure 1.7) It is when theheart is approached through a median

Obtuse margin

Long axis of heart

Long axis of body

Fig 1.1 The computed tomogram, with the cardiac cavities delimited subsequent to injection of contrast material, shows the relationships of the heart to the thoracic structures well Note the discordance between the cardiac long axis and the long axis of the body.

sternotomy, therefore, with the nerve not

immediately evident, that it is most liable to

injury Although it can sometimes be seen

through the reflected pericardium

(Figure 1.8), its proximity to the superior

caval vein (Figures 1.2, 1.9, 1.10), or to a

persistent left caval vein when that

structure is present (Figure 1.11), is not

always easily appreciated when these

vessels are dissected from the anterior

approach Near the thoracic inlet, it passes

close to the internal thoracic artery

(Figures 1.6, 1.10), exposing it to injury

either directly during takedown of that

vessel, or by avulsing the pericardiophrenic

artery with excessive traction on the chest

wall The internal thoracic arteries

themselves are most vulnerable to injury

during closure of the sternum The phrenic

nerve may be injured when removing the

pericardium to use as a cardiac patch, or

when performing a pericardiectomy

Injudicious use of cooling agents within the

pericardial cavity may also lead to phrenicparalysis or paresis

A standard lateral thoracotomy providesaccess to the heart and great vessels via thepleural space Left-sided incisions provideready access to the great arteries, leftpulmonary veins, and the chambers of theleft side of the heart Most frequently, theincision is made in the fourth intercostalspace The posterior extent is through thetriangular, and relatively bloodless, spacebetween the edges of the latissimus dorsi,trapezius, and teres major muscles(Figure 1.12) The floor of this triangle isthe sixth intercostal space Division of thelatissimus dorsi, and a portion of trapeziusposteriorly, frees the scapula so that thefourth intercostal space can be identified

Its precise identity should be confirmed bycounting down the ribs from above Theso-called muscle sparing thoracotomy isdesigned to preserve the latissimus dorsiand serratus anterior muscles In cases

requiring greater degrees of exposure, thelatissimus dorsi can be partially divided It

is rarely necessary, if ever, to divide theserratus anterior The intercostal musclesare then divided equidistant between thefourth and fifth ribs The incision is rarelycarried forward beyond the midclavicularline in a submammary position, and care istaken to avoid damage to the nipple and thetissue of the breast The intercostalneurovascular bundle is well protectedbeneath the lower margin of the fourth rib.Having divided the musculature as far asthe pleura, the pleural space is entered, andthe lung permitted to collapse away fromthe chest wall Posterior retraction of thelung reveals the middle mediastinum, inwhich the left lateral lobe of the thymus,with its associated nerves and vessels, isseen overlying the pericardial sac and theaortic arch Intrapericardial access isusually gained anterior to the phrenicnerve On occasion, the thymus gland may

Inf.

Sup.

Brachiocephalic vein Thymic veins

Pulmonary trunk

Left phrenic nerve

Fig 1.2 This view, taken at autopsy, demonstrates the anatomical relationships of the vessels and nerves within the mediastinum.

require elevation when the incision is

extended superiorly, precautions being

taken to avoid unwanted damage as

discussed earlier The lung is retracted

anteriorly to approach the aortic isthmus

and descending thoracic aorta, and theparietal pleura is divided on its mediastinalaspect This is usually done posterior to thevagus nerve In this area, the vagus nervegives off its left recurrent laryngeal branch,

which passes around the inferior border ofthe arterial ligament, or the duct if thearterial channel is still patent (Figure 1.13).The recurrent nerve then ascends towardsthe larynx on the medial aspect of the

Diaphragm

Sup.

Inf.

Left Right

Pericardial sac Thymus

Fig 1.3 This view, taken at autopsy, demonstrates the extent of the thymus as it extends over the anterior and lateral aspects of the pericardial sac at the base of the heart Note the haemorrhagic pericardial effusion.

Pericardial sac

Superior caval vein Phrenic nerve

Fig 1.4 This view, taken in the operating room through a median sternotomy in an infant, shows the extent of the thymus gland Note the right phrenic nerve adjacent to the superior caval vein.

Sup Inf.

Left

Right

Aorta in pericardium

Right lobe of

thymus

Thymic veins Brachiocephalic vein

Fig 1.5 This operative view, again taken through a median sternotomy, shows the delicate veins that drain from the thymus gland to the left brachiocephalic veins.

Left phrenic nerve

Left pericardiophrenic

artery and vein

Left vagus & recurrent laryngeal nerve

Left internal thoracic artery

Right phrenic nerve

Right vagus & recurrent laryngeal nerve Right pericardiophrenicartery and vein

Fig 1.6 As shown in this cartoon of a median sternotomy, the pericardium can be opened in the midline so that the phrenic and vagus nerves stay well clear of the operating field.

posterior wall of the aorta, running adjacent

to the oesophagus Excessive traction of the

vagus nerve as it courses into the thorax

along the left subclavian artery can cause

injury to the recurrent laryngeal nerve just

as readily as can direct trauma to the nerve

in the environs of the ligament The

superior intercostal vein is seen crossing

the aorta, then insinuating itself between

the phrenic and vagus nerves (Figures 1.11,1.14, 1.15) This structure, however, israrely of surgical significance, but isfrequently divided to provide surgicalaccess to the aorta The thoracic duct(Figure 1.16) ascends through this area,draining into the junction of the leftsubclavian and internal jugular veins

Accessory lymph channels draining into

the duct, which is usually posteriorlylocated and runs along the vertebralcolumn, can be troublesome whendissecting the origin of the left subclavianartery

A right thoracotomy, in either thefourth or fifth interspace, is made through

an incision similar to that for a left one Thefifth interspace is used when approaching

Ant.

Post.

Inf Sup.

Left pericardiophrenic artery

Left pericardiophrenic vein

Left phrenic nerve

Fig 1.7 This operative view, taken through a left lateral thoracotomy, shows the course of the left phrenic nerve over the pericardium.

Right phrenic nerve

Fig 1.8 This operative view, taken through a median sternotomy, shows the right phrenic nerve as seen through the re flected pericardium.

Sup Inf.

Left

Right

Cut edge of

pericardium Right phrenicnerve

Right pulmonary veins

Fig 1.9 This operative view, taken through a median sternotomy having pulled back the edge of the pericardial sac, shows the right phrenic nerve in relation to the right pulmonary veins.

Superior caval vein

Ant.

Post.

Inf Sup.

Right internal thoracic artery

Right phrenic nerve

a right thoracotomy, shows the relationship of the right phrenic nerve to the right internal thoracic artery and the superior caval vein.

Persistent left

superior caval vein

Fig 1.11 This operative view, taken through a left thoracotomy, shows the relationship of the left phrenic nerve to a persistent left superior caval vein Note also the course of the superior intercostal vein.

Fig 1.13 This operative view, taken through a left lateral thoracotomy in an adult, shows the left recurrent laryngeal nerve passing around the arterial duct.

Left vagus nerve

Fig 1.15 This operative view, taken through a left lateral thoracotomy, shows the course of the left superior intercostal vein (Compare with Figure 1.14.)

thoracotomy, the thoracic duct is seen coursing below the left subclavian artery to its termination in the brachiocephalic vein.

Azygos vein Intercostal veins

Fig 1.17 This anatomical image, taken at autopsy, shows the normal location of the azygos vein as it extends along the spine, receives the intercostal veins, and crosses over the root of the right lung to empty into the superior caval vein.

Fig 1.18 This operative view, taken through

a median sternotomy, shows the course of the right recurrent laryngeal nerve relative to the right subclavian artery.

the heart, while the fourth permits access to

the right-sided great vessels Access to the

pericardium is gained by incising anterior

to the phrenic nerve, this approach often

necessitating retraction of the right lobe of

the thymus To reach the right pulmonary

artery, and its adjacent mediastinal

structures, it is sometimes useful to divide

the azygos vein near its junction with the

superior caval vein (Figure 1.17)

Extension of this incision superiorly

exposes the origin of the right subclavian

branch of the brachiocephalic trunk

Laterally, this artery is crossed by the right

vagus nerve, the right recurrent laryngealnerve taking origin from the vagus andcurling around the posteroinferior wall ofthe artery before ascending into the neck(Figure 1.18) Also encircling thesubclavian origin on this right side is thesubclavian sympathetic loop, the so-calledansa subclavia, a branch of the sympathetictrunk that runs up into the neck Damage

to this structure can produce Horner’ssyndrome

An anterior right or left thoracotomy isoccasionally used in treating congenitalmalformations Once the chest is opened,

the same basic anatomical rules apply asdescribed previously Thus far, ouraccount has presumed the presence ofnormal anatomy In many instances, thedisposition of the thoracic structures will

be altered by a congenital malformation.These alterations will be described in theappropriate sections

Reference

1 Cook AC, Anderson RH Attitudinallycorrect nomenclature Heart 2002; 87:503–506

Anatomy of the cardiac chambers

Regardless of the surgical approach, once

having entered the mediastinum, the

surgeon will be confronted by the heart

enclosed in its pericardial sac In the strict

anatomical sense, this sac has two layers,

one fibrous and the other serous From a

practical point of view, the pericardium is

essentially the tough fibrous layer; the

serous component forms the lining of the

fibrous sac, and is reflected back onto the

surface of the heart as the epicardium It is

the fibrous sac, therefore, which encloses

the mass of the heart By virtue of its own

attachments to the diaphragm, it helps

support the heart within the mediastinum

Free-standing around the atrial chambersand the ventricles, the sac becomesadherent to the adventitial coverings ofthe great arteries and veins at theirentrances to and exits from it, theseattachments closing the pericardial cavity

The cavity of the pericardium is limited

by the two layers of serous pericardium,which are folded on one another toproduce a double-layered arrangement

The outer or parietal layer is denselyadherent to the fibrous pericardium, whilethe inner layer is firmly attached to the

myocardium, and is the epicardium(Figure 2.1) The pericardial cavity,therefore, is the space between the innerparietal serous lining of the fibrouspericardium and the surface of the heart(Figure 2.2) There are two recesseswithin the cavity that are lined by serouspericardium The first is the transversesinus, which occupies the inner curvature

of the heart (Figure 2.3) Anteriorly, it isbounded by the posterior surface of thegreat arteries Posteriorly, it is limited bythe right pulmonary artery and the roof ofthe left atrium There is a further recess

Pericardial cavity

Transverse sinus Aorta

Right pulmonary artery

Left atrium

Oblique sinus

Fibrous pericardium

Visceral Parietal Serous pericardiumApex

Base Ant.

Post.

Fig 2.1 The cartoon shows the arrangement of the pericardial cavity as seen in a parasternal long axis view.

Right appendage

Right ventricle Aorta

Right Left appendage

Fig 2.2 The operative view through a median sternotomy shows the anterior surface

of the heart following a pericardial incision The white asterisks show the extent of the pericardial cavity.

from the transverse sinus that extends

between the superior caval and the right

upper pulmonary veins, with its right

lateral border being a pericardial fold

between these vessels (Figure 2.4) When

exposing the mitral valve through a left

atriotomy, incisions through this fold,

along with mobilisation of the superior

caval vein, provide excellent access to thesuperior aspect of the left atrium and theright pulmonary artery This fold is alsoincised when a snare is placed around thesuperior caval vein Laterally, on eachside, the ends of the transverse sinus are infree communication with the remainder ofthe pericardial cavity

The second pericardial recess is theoblique sinus This is a blind-ending cavitybehind the left atrium (Figure 2.5), with itsupper boundary formed by the reflection ofserous pericardium between the upperpulmonary veins The right border is thereflection of pericardium around the rightpulmonary veins and the inferior caval

Right

Clamp in transverse sinus

Pulmonary trunk

Fig 2.3 Operative view through a median sternotomy The clamp has been passed through the transverse sinus.

Superior caval vein

Sup.

Left

Inf.

Right

Clamp tenting pericardial fold

Fig 2.4 Operative view through a median sternotomy showing the posterior recess of the transverse sinus limited by a pericardial fold around the superior caval vein In this picture, the fold is being tented by a right-angled clamp passed behind the superior caval vein.

vein, while the left border is the reflection

of pericardium around the left pulmonary

veins (Figure 2.6)

With the usual surgical approach

through a median sternotomy, the fibrous

pericardium is opened more-or-less in the

midline and retracted laterally, exposingthe anterior sternocostal surface of the heartand great vessels The pulmonary trunk andaorta are seen leaving the base of the heartand extending in a superior direction, withthe aortic root in the posterior and

rightward position (Figure 2.2) Shouldthe aortic root not be in this expectedrelationship, the ventriculoarterialconnections will almost always be abnormal(see Chapter 8) The atrial appendages areusually seen one to either side of the

Left atrial

appendage

Left pulmonary veins

Fig 2.5 Anatomical view showing the oblique sinus of the pericardial cavity, which lies behind the left atrium Note the oblique ligament, which occupies the site during development of the left superior caval vein.

Oblique sinus

Sup.

Inf.

Right Left Right atrium

Coronary sinus

Left pulmonary veins

Right pulmonary veins Inferior caval vein Fig 2.6 The heart has been re flected superiorly from its

pericardial cradle to show the location of the oblique sinus.

prominent arterial pedicle The

morphologically right appendage is more

prominent It has a blunt triangular shape,

and possesses a broad junction with the

atrial cavity (Figure 2.7) The

morphologically left appendage may not be

seen immediately When found at the left

border of the pulmonary trunk, it is a

tubular structure, having a narrow junction

with the rest of the atrium (Figure 2.8) The

presence of the two appendages on the same

side of the arterial pedicle is an anomaly initself, which is called juxtaposition Thisarrangement is most often associated withadditional malformations within the heart(see Chapter 8) Inspection of the left border

of the heart should always include a searchfor persistence of the left superior cavalvein When present, the venous channelwill be found by following the course of theleft pulmonary artery The vein crossesanterior to the pulmonary artery and is seen

superiorly within the pericardial cavity,with the left atrial appendage locatedanteriorly and laterally (Figure 2.9)

Within the pericardial cavity, it extendsdown the posterior aspect of the left atrium,passing through the inferior left

atrioventricular groove to reach the rightatrial orifice of the coronary sinus(Figure 2.10)

The ventricular mass extends from theatrioventricular grooves to the apex, and

Fig 2.8 Operative view through a median sternotomy showing the tubular morphologically left atrial appendage.

usually extends into the left hemithorax.

An anomalous position of the ventricular

mass, or its apex, is again highly suggestive

of the presence of congenital cardiac

malformations (see Chapter 10) In shape,the ventricular mass is a three-sidedpyramid, having inferior diaphragmatic,anterior sternocostal, and posterior

pulmonary surfaces (Figure 2.11) Themargin between the first two surfaces issharp Because of this, it is described as theacute margin The angulations of the

Pulmonary trunk

Sup Inf.

Left

Right

Left atrial appendage

Fig 2.9 The operative view through a median sternotomy shows the location of a persistent left superior caval vein, snared by the surgeon in this image.

Fig 2.10 The base of the heart has been dissected by removing the atrial walls The dissection shows the course of a persistent left superior caval vein as it passes through the left atrioventricular groove (red dotted lines), emptying into the right atrium through the enlarged ori fice of the coronary sinus.

margins between the pulmonary and the

sternocostal surfaces anteriorly, and the

pulmonary and diaphragmatic surfaces

posteriorly, are much more obtuse The

surgeon encounters these obtuse marginal

areas when the apex of the heart is tipped

out of the pericardium They are supplied

by the obtuse marginal branches of the

circumflex coronary artery The greater

part of the anterior surface of the

ventricular mass is occupied by the

morphologically right ventricle, with its left

border marked by the anterior

interventricular or descending branch of

the left coronary artery This artery curves

onto the ventricular surface between the

left atrial appendage and the basal origin of

the pulmonary trunk The right border of

the morphologically right ventricle is

marked by the right coronary artery, which

runs obliquely in the atrioventricular

groove Unusually prominent coronary

arteries coursing on the ventricular surface

should always raise the suspicion of

significant cardiac malformations

The surface anatomy of the heart is

helpful in determining the most appropriate

site for an incision to gain access to a given

cardiac chamber For example, the relatively

bloodless outlet portion of the right ventricle

just beneath the origin of the pulmonary

trunk affords ready access to the cavity of

the subpulmonary infundibulum

(Figure 2.8) The important landmark for

the right atrium is the terminal groove, orsulcus terminalis This marks the junctionbetween the appendage and the systemicvenous component of the right atrium(Figure 2.12) The sinus node is locatedwithin this groove, usually laterally andinferiorly relative to the superior cavoatrialjunction (Figures 2.13, 2.14), but

occasionally extending over the crest of theappendage (Figure 2.15) The clinicallysignificant artery to the sinus node can also

be seen on occasion, either as it crosses thecrest of the right appendage, or as it coursesbehind the superior caval vein to enter theterminal groove between the orifices of thecaval veins Posterior to, and parallel with,the terminal groove is a second, deepergroove, which interposes between the cavity

of the right atrium and the right pulmonaryveins The surgeon can use this interatrialgroove, known as Waterston’s or

Sondergaard’s groove, to gain access to theleft atrium (Figure 2.16), either by making

an incision in the floor of the groove, orthrough the left atrial roof The latter area isseen behind the aorta, to the left of thesuperior cavoatrial junction (Figure 2.12)

MORPHOLOGICALLY RIGHT ATRIUM

The right atrium has three basic parts, theappendage, the venous componentreceiving the systemic venous return, and

the vestibule of the tricuspid valve It alsohas a small body, but the boundaries of thispart usually cannot be distinguished fromthe venous sinus It is separated from theleft atrium by the septum The junction ofthe appendage and the systemic venoussinus is identified externally by theprominent terminal groove (Figure 2.12).Internally, the groove corresponds with theterminal crest, which gives origin to thepectinate muscles of the appendage(Figure 2.17) In shape, the appendage isblunt and triangular, having a widejunction to the venous sinus across theterminal groove The venous sinus is muchsmaller when viewed externally, with onlythat part extending between the terminaland Waterston’s grooves being visible tothe surgeon It receives the superior andinferior caval veins at its extremities.Superiorly and anteriorly, the appendagehas a particularly important relation withthe superior caval vein Here, theappendage terminates in a prominent crest(Figure 2.13) This forms the summit ofthe terminal groove, and is continuous inthe transverse sinus behind the aorta withthe interatrial groove (Figure 2.14)

Absence of such a right-sided crest shouldalert the surgeon to the presence ofisomerism of the left atrial appendages (seeChapter 6) As already discussed, the sinusnode almost always lies immediatelysubepicardially within the terminal groove

Cigar-shaped, it usually lies to the right of

the crest as seen by the surgeon; in other

words, lateral and inferior to the superior

cavoatrial junction (Figure 2.13) In about

one-tenth of cases, the node extends acrossthe crest into the interatrial groove It isthen draped across the cavoatrial junction

in horseshoe fashion (Figures 2.14, 2.15)1

Also of significance is the course ofthe artery to the sinus node (Figure 2.18).This artery is a branch of the right coronaryartery in about 55% of individuals, and a

‘Horseshoe’ node

Fig 2.13 The cartoon shows the usual site of the sinus node within the terminal groove (upper panel) The lower panel shows the horseshoe arrangement found in about one-tenth of cases SCV, superior caval vein; ICV, inferior caval vein.

Right atrial appendage

Sup.

Inf.

Left Right Superior caval vein

Systemic venous sinus

branch of the circumflex artery in the

remainder2 Irrespective of its origin, it

usually courses through the anterior

interatrial groove towards the superior

cavoatrial junction (Figure 2.19),

frequently running within the atrial

myocardium The artery usually takes its

origin from the proximal segment of its

parent coronary artery (Figure 2.20) A

significant variant is found when the artery

originates from either coronary artery somedistance from the aorta If taking originfrom the right coronary artery, it coursesover the lateral surface of the appendage toreach the terminal groove (Figure 2.21) Iforiginating from the circumflex artery, itcrosses the roof of the left atrium(Figure 2.22) Such lateral origin is rare innormal hearts3,4, but more frequent inassociation with congenital malformations5

Irrespective of its origin, as it enters thesinus node, the artery may cross the crest ofthe appendage, course retrocavally(Figure 2.23), or even divide to form anarterial circle around the junction(Figure 2.24) All these variations should

be taken into account when planning thesafest right atrial incision, particularlywhen the nodal artery crosses the lateralmargin of the right appendage, or courses

Roof of left atrium Sup Inf.

Left

Right

Sinus nodal artery

Crest of right atrial appendage

Fig 2.15 Operative view through a median sternotomy showing

a sinus node arranged in horseshoe fashion across the crest of the right atrial appendage, with one limb in the terminal groove and the other extending towards the interatrial groove The nodal location is again highlighted by the white cross-hatched area Note the course of the artery to the node.

over the roof of the left atrium Although it

might seem obvious, care should be taken

to ensure that the incision cuts across

neither the terminal crest nor the right

coronary artery (Figure 2.25)

Opening the atrium through the most

appropriate incision shows that the

terminal groove is the external counterpart

of a prominent internal muscle bundle, the

terminal crest This separates the pectinate

muscles of the appendage from the smoothwalls of the systemic venous sinus

(Figure 2.17) The cardiomyocytes arealigned along the long axis of the crest,which is one of the major routes forconduction from the sinus node towardsthe atrioventricular node Anteriorly, thecrest curves in front of the orifice of thesuperior caval vein, with its medialextension forming the border between the

appendage and the superior rim of the ovalfossa The crest continues through thesuperior interatrial groove as Bachmann’sbundle, the major route for conduction intothe left atrium On first sight, wheninspecting the right atrium through thisincision, there appears to be an extensiveseptal surface between the openings of thecaval veins and the orifice of the tricuspidvalve (Figure 2.26) The apparent extent of

Superior caval vein

this septum is spurious6,7 The true

septum7,8is confined to the floor and the

anteroinferior margin of the oval fossa

(Figures 2.27 and 2.28) The extensive

superior rim of the fossa is produced by the

folds of the interatrial groove, which

separate the mouth of the superior cavalvein and the entrance of the pulmonaryveins to the left atrium (Figures 2.28) Theposteroinferior rim is another fold, thistime formed by reflection of themusculature forming the mouth of the

coronary sinus and the orifice of theinferior caval vein (Figure 2.29) Thesemuscular structures continue anteriorlywithin the atrium as the Eustachian ridge.This is seen to advantage when the floor ofthe oval fossa is itself deficient

Origin from right coronary artery

Distal origin from right coronary artery

Origin from circumflex artery

Distal origin from circumflex artery

Aorta

Sup Inf.

Left

Right Artery to sinus node

Roof of left atrium

Fig 2.19 Operative view through a median sternotomy showing the artery to the sinus node, which in this case originates from the circum flex coronary artery and extends across the dome of the left atrium.

Right Fig 2.20 Operative view through a median sternotomy showing

the artery to the sinus node originating proximally from the right coronary artery.

Sup Inf.

Left

Right

Artery to sinus node

Fig 2.21 Operative view through a median sternotomy showing the artery to the sinus node originating distally from the right coronary artery and coursing over the lateral surface of the right atrial appendage The site of the sinus node is shown by the white cross-hatched area.

(Figure 2.30) Because of the limited extent

of these septal components, it is an easy

matter for the surgeon to pass outside the

heart when attempting to gain access to the

left atrium through a right atrial approach

In addition to the position of the sinus

node, and the extent of the atrial septum,

the other major area of surgical significance

within the right atrium is the site of theatrioventricular node This is containedwithin the triangle of Koch9 Thisimportant landmark is bounded by thetendon of Todaro, the attachment of theseptal leaflet of the tricuspid valve, and theorifice of the coronary sinus (Figure 2.31)

The tendon of Todaro9is a fibrous

structure formed by the junction of theEustachian valve, the valve of the inferiorcaval vein, and the Thebesian valve, thevalve of the coronary sinus The fibrouscontinuation of these two valvar structuresburies itself in the anterior continuation ofthe Eustachian ridge It then runs medially

as the tendon of Todaro before inserting

Dome of left atrium

Superior caval vein

Retrocaval course Sup.

Sup Inf.

Left

Right Retrocaval nodal artery

Crest of appendage

Fig 2.23 Operative view through a median sternotomy showing

a retrocaval course of the artery to the sinus node, the site of the node itself being emphasised by the white cross-hatched area.

into the atrioventricular part of the

membranous septum (Figure 2.32) The

entire atrial component of the axis of

atrioventricular conduction tissues is

contained within the confines of the

triangle of Koch If, in hearts with normal

segmental connections, this area is

scrupulously avoided during surgicalprocedures, the atrioventricularconduction tissues will not be damaged

Should the node need to be identified moreprecisely, it should be remembered that theattachment of the tricuspid valve is someway down the surface of the septum relative

to that of the mitral valve (Figure 2.33).The relationship between the atrial andventricular muscular walls within thetriangle of Koch is complex At first sight,because of the off-setting of the

attachments of the mitral and tricuspidvalves, the entire muscular area seems to

Sup Inf.

Left

Right

Retrocaval branch Artery to sinus node

Anterocaval branch Fig 2.24 Operative view through a median sternotomy showing

the artery to the sinus node dividing to form an arterial circle around the cavoatrial junction.

interpose between the cavities of the right

atrium and the left ventricle Indeed, in

earliest editions of the book, we described

this area as representing an atrioventricular

muscular septum In the floor of thetriangle, however, the atrial musculature isseparated from the underlying ventricularmyocardium by an extension of the inferior

atrioventricular groove, with the fibrofattytissue in this area insulating the atrialfrom the ventricular muscular layers10.The extent of this insulating layer can be

Sup.

Inf.

Post Ant.

Oval fossa

Coronary sinus Fig 2.26 In this specimen, viewed in the anatomical position, the

white dotted circle shows the apparently extensive ‘septal surface’ within the right atrium.

Inf.

Post Ant.

Infolded posterior rim

Infolded anterior rim

demonstrated by dissecting away the

superficial atrial musculature, at the same

time revealing the location of the artery

supplying the atrioventricular node

(Figure 2.34) The larger part of Koch’s

triangle as seen by the surgeon, therefore, is

formed by the atrial layer of anatrioventricular muscular sandwich, ratherthan a true muscular atrioventricularseptum

Much was written in the latter part ofthe twentieth century concerning the role

of allegedly specialised pathways ofmyocardium in conducting the sinusimpulse to the atrioventricular node11,12.Molecular biologists are currently showingthat, during development, it is possible torecognise areas of the atrial myocardium on

Infolded superior rim

Fig 2.28 This heart has been sectioned in the four-chamber plane, showing that the superior rim of the oval fossa is a deep infolding producing the interatrial groove between the systemic venous sinus of the right atrium and the entry of the pulmonary veins into the left atrium.

the basis of their genetic lineage.

Subsequent to birth, however, all of the

atrial myocardium, apart from the nodal

components, has achieved a working

phenotype There is no anatomical

evidence, therefore, to support suggestions

that surgical operations should be speciallymodified to avoid presumed specialisedinternodal tracts13 The anatomicalparadigm of tracts of myocardium modifiedfor conduction in the heart is provided bythe ventricular conduction system, which is

additionally insulated from the adjacentworking ventricular myocardium14 Thereare no such insulated and isolated tractswithin the atrial walls15,16 The majormuscle bundles of the atrial chambers,nonetheless, serve as preferential pathways

Sup. Inf.

Left

Right Septal leaflet

Eustachian ridge

Coronary sinus

Fig 2.30 The heart has been opened through an atriotomy, and the interior surface of the right atrium is shown in surgical orientation Note the Eustachian ridge separating the mouth of the coronary sinus from the ori fice of the inferior caval vein The floor

of the oval fossa is de ficient, producing an atrial septal defect.

Hinge of tricuspid valve

Sup.

Inf.

Left

Right

Site of membranous septum

Site of tendon of Todaro Coronary sinus Fig 2.31 This operative view through a right atriotomy shows the

location of the triangle of Koch.

of conduction, with the location of these

preferential pathways dictated by the

overall geometry of the chambers

(Figure 2.35) Ideally, therefore, prominent

muscle bundles, such as the terminal crest,

the superior rim of the oval fossa, the

myocardium of the Eustachian ridge, andthe superior interatrial fold, should bepreserved during atrial surgery Even ifthey cannot be preserved, the surgeon canrest assured that internodal conduction willcontinue as long as some strand of viable

atrial myocardium interposes between thenodes, providing that the arterial supply tothe nodes, or the nodes themselves, are nottraumatised The key to avoiding

postoperative atrial arrhythmias, therefore,

is the fastidious preservation of the sinus

Thebesian valve

Hinge of tricuspid valve Tendon of Todaro

Floor of oval fossa

Mitral valvar attachment

Anteroinferior rim of oval fossa

Adipose tissue

Ventricular septum Tricuspid valvar attachment

Fig 2.33 The heart has been sectioned in the four-chamber plane

to show the off-setting of the hinges of the tricuspid and mitral valves Note the adipose tissue separating the atrial and ventricular musculatures in the area of off-setting.

and atrioventricular nodes and their

arteries, rather than concern about

non-existent tracts of purportedly specialised

atrial myocardium

Much is also written about the fibrousskeleton of the heart The strongest part ofthis skeleton is the central fibrous body

This area of fibrous tissue touches on three

of the four cardiac chambers, but is seenmost clearly by the surgeon when workingfrom the right atrium (Figure 2.36) Ratherthan being considered as a specific body, it

Left atrium

Right atrium

Artery to AV node

Membranous septum

Circumflex coronary artery

Fig 2.34 This dissection, in anatomical orientation having removed the non-coronary sinus of the aortic valve, shows the fibrofatty tissue (star) interposed between the atrial and ventricular muscular layers (yellow and blue dashed lines) of the atrioventricular muscular sandwich Note the artery to the atrioventricular (AV) node.

Inferior caval vein Coronary sinus

Fig 2.35 The right atrium, seen in anatomical orientation, has been opened through a window in the appendage The muscular walls surround several ori fices, producing

preferential routes of conduction (arrows).