Ebook Wilcox’s surgical anatomy of the heart (4th edition): Part 2

(BQ) Part 1 book Wilcox’s surgical anatomy of the heart presents the following contents: Lesions with normal segmental connections, lesions in hearts with abnormal segmental connections, abnormalities of the great vessels, positional anomalies of the heart.

7 Lesions with normal segmental

connections

SEPTAL DEFECTS

Understanding the anatomy of septal

defects is greatly facilitated if the heart

is thought of as having three distinct

septal structures: the atrial septum,

the atrioventricular septum, and the

ventricular septum (Figure 7.1) The

normal atrial septum is relatively small It is

made up, for the most part, by the floor

of the oval fossa When viewed from the

right atrial aspect, the fossa has a floor,

surrounded by rims The floor is derived

from the primary atrial septum, or septum

primum Although often considered to

represent a secondary septum, or septum

secundum, the larger parts of the rims,

specifically the superior, anterosuperior,

and posterior components, are formed by

infoldings of the adjacent right and left

atrial walls Inferoanteriorly, in contrast,

the rim of the fossa is a true muscular

septum (Figure 7.2) This part of the rim is

contiguous with the atrioventricular

septum, which is the superior component

of the fibrous membranous septum In the

normal heart, this fibrous septum is also

contiguous with the atrial wall of the

triangle of Koch (Figure 7.3) In the past,

we considered this component of the atrialwall, which overlaps the upper part of theventricular musculature between theattachments of the leaflets of the tricuspidand mitral valves, as the muscularatrioventricular septum As we discussed inChapter 2, we now know that it is betterviewed as a sandwich1 This is because,throughout the floor of the triangle ofKoch, the fibroadipose tissue of the inferioratrioventricular groove separates the layers

of atrial and ventricular myocardium(Figure 7.4) From the stance ofunderstanding septal defects, nonetheless,

it is helpful to consider the entire areacomprising the fibrous septum and themuscular sandwich as an atrioventricularseparating structure, as it is absent in thehearts we describe as having

atrioventricular septal defects

The ventricular septum is usually seen bythe surgeon only from its right ventricularaspect For this and other reasons we willdiscuss, holes between the ventricles are bestconsidered in terms of their right ventricularlandmarks Taken overall, the ventricularseptum is made up of a small fibrous

element, specifically the interventricularpart of the membranous septum, and a muchlarger muscular part The muscular part,which is significantly curved, is morecomplex geometrically than the other septalstructures, which lie almost completely inthe coronal plane At first sight, it seemspossible to divide the muscular septum intoinlet, apical trabecular, and outlet

components, each of these parts seeminglycorresponding with the components of theright ventricle, and abutting centrally on themembranous septum (Figure 7.5) Closerinspection shows that such analysis issimplistic By virtue of the deeply wedgedlocation of the subaortic outflow tract, much

of the septum delimited on the rightventricular aspect by the septal leaflet ofthe tricuspid valve separates the inlet of theright ventricle from the outlet of the left(Figure 7.6) The muscular wall forming theback of the subpulmonary infundibulum is,

at first sight, an outlet septum Only asmall part of this wall, however, interposesbetween the cavities of the right and leftventricles This is because most of thesubpulmonary infundibulum is a free-standing muscular sleeve, which forms part

de ficient in the setting of a common atrioventricular junction Note also that the superior rim of the oval fossa (arrow) is an infolding between the right and left atrial walls.

of the supraventricular crest (Figure 7.7).

The small septal component interposing

between the ventricular outlets is

inextricably linked with the more extensive

component of the crest, the

ventriculoinfundibular fold, or inner heartcurvature (Figure 7.8) It is the muscularwall separating the apical trabecularcomponents, therefore, which forms thegreater part of the muscular ventricular

septum This part extends to the apex incurvilinear fashion, reflecting theinterrelationships of the banana-shapedright ventricle and the conical left ventricle.Reinforcing the right ventricular aspect of

Sup.

Base Apex Triangle of Koch

Defect in oval fossa

Anteroinferior muscular buttress

Floor of oval fossa

Inf.

Right Left

Sup. Fig 7.2 The heart has been sectioned in the four-chamber plane,

showing that the superior rim of the oval fossa is a deep infolding (arrow) between the origin of the superior caval vein from the right atrium (red star), and the entry of the right superior pulmonary vein into the left atrium (white star) It is the floor of the oval fossa, along with the anteroinferior muscular buttress, which are the components of the atrial septum.

this part of the septum is the septomarginal

trabeculation, or septal band This muscular

strap has a body and limbs, the latter

extending to the base of the heart to clasp the

supraventricular crest A series ofseptoparietal trabeculations extend from itsanterocephalad surface and reach theparietal ventricular wall One of these, the

moderator band, is particularly prominent

It crosses from the septomarginaltrabeculation to join the anterior papillarymuscle (Figure 7.9)

Outlet component

Inlet component

Apical trabecular component

Fig 7.4 This four-chamber section of a normal heart, taken across the floor of the triangle of Koch, illustrates the differential attachments of the atrioventricular valves (arrows) Note the adipose tissue interposed between the right atrial wall and the crest of the ventricular septum, which forms the ‘meat’ in the atrioventricular muscular sandwich.

Left ventricular outlet

Right ventricular inlet

Base

Post.

Infundibular sleeve

Pulmonary trunk

Ant. Fig 7.7 The dissection of the ventricular out flow tracts, in

anatomical orientation, shows the free-standing sleeve of infundibulum that supports the lea flets of the pulmonary valve This is not a septal structure Note the extensive tissue plane that separates the infundibular sleeve from the aortic root (arrow).

Interatrial communications

There are several lesions that permit

interatrial shunting (Figure 7.10)

Although collectively termed atrial septal

defects, not all are within the confines of

the normal atrial septum1 Only theholes within the floor of the oval fossa2,and the much more rare vestibulardefects found within the muscularanteroinferior buttress3, are true

deficiencies of the septal components(Figure 7.2) The ostium primumdefect is the consequence of deficientatrioventricular septation Its cardinalfeature is the commonality of the

Ventriculoinfundibular fold Septomarginal trabeculation

Fig 7.8 The dissection, seen in anatomical orientation, shows how most of the supraventricular crest is formed by the ventriculoinfundibular fold Only a small part of crest, where it inserts between the limbs of the septomarginal trabeculation (star), can be removed so as to provide a communication with the left ventricle The area has no obvious anatomical boundaries Note that the distal part of the crest becomes continuous with the free-standing muscular infundibular sleeve.

Post.

Apex Base Moderator band

Supraventricular crest Septoparietal

atrioventricular junction4 It will be

considered in our next section Sinus

venosus defects, representing an

anomalous connection of a pulmonary

vein, which has retained its left atrial

connection5, are found at the mouths of

the caval veins5–8 The rare defect found

at the mouth of the coronary sinus is

the consequence of the disappearance of the

muscular walls that usually separate the

component of the coronary sinus running

through the left atrioventricular junction

from the cavity of the left atrium9

Defects within the oval fossa are often

called secundum defects Because they

represent persistence of the secondary

atrial foramen, rather than deficiencies of

the secondary atrial septum, they should

properly be called ostium secundum

defects We prefer to consider them as

defects within the oval fossa They are, by

far, the most common type of interatrial

communication They can be caused by

deficiency (Figure 7.11), perforation

(Figure 7.12), or absence (Figure 7.13) of

the floor of the fossa The floor is formed by

the flap valve of the oval foramen, itself

derived from the primary atrial septum

When the haemodynamics of the shunt

across such a defect dictate surgical closure,

the hole is rarely likely to be small enough

to permit direct suture Now, all but verylarge defects within the oval fossa are likely

to be closed by the interventionalcardiologist If attempts are made to close,directly, defects large enough to justifysurgical intervention, the results may sodistort atrial anatomy as to result indehiscence Irrespective of the size of theseptal deficiency, it is always possible tosecure a patch to the margins of the ovalfossa When placing sutures, the likeliestpotential danger relative to the rims is tothe artery supplying the sinus node(Figure 7.14) This artery can courseintramyocardially through the anteriormargin of the oval fossa, or lie deep withinthe superior interatrial fold There is also aremote chance of damaging the aorta whenplacing stitches anteriorly, as this part ofthe rim is related on its epicardial aspect tothe aortic root (Figures 7.14, 7.15) Onoccasion, deficiency of the posteroinferiorrims of the oval fossa permits holes withinthe fossa to extend into the mouth of theinferior caval vein (Figure 7.16) In thesecircumstances, care must be taken not tomistake a well-formed Eustachian valve forthe posteroinferior margin of the defect

A patch attached to the Eustachian valvewould connect the inferior caval vein to theleft atrium It is always prudent, therefore,

to ensure continuity of the inferior cavalvein and right atrium following placement

of a patch used to close a deficiency of thefloor of the oval fossa

Sinus venosus defects are more rarethan defects within the oval fossa, andpresent greater problems in repair Thedefect adjacent to the inferior caval vein(Figure 7.17) is relatively rare5 It opensinto the mouth of the inferior caval veinposterior to the confines of the oval fossa.Usually the fossa itself is intact, but it can

be deficient or probe patent The essence ofthe defect is an anomalous connection ofthe right inferior pulmonary vein to theinferior caval vein, the pulmonary veinretaining its left atrial connection5 It ismuch more frequent to find sinus venosusdefects adjacent to the mouth of thesuperior caval vein6,8 These defects, again,are due to an anomalous connection ofone or more of the right pulmonary veins tothe superior caval vein, the pulmonaryveins retaining their left atrial connection6.The defects are outside the confines of theoval fossa, and hence are interatrialcommunications rather than atrial septaldefects (Figure 7.18)1,2

When sinus venosus defects are found

in relation to the superior caval vein, theorifice of the vein usually overrides the

Atrioventricular

septal defect

Vestibular defect

Coronary sinus defect

Inferior sinus venosus defect

Oval fossa defect

Fig 7.10 The cartoon shows the various holes that permit interatrial shunting Only the holes

in the oval fossa and the rare vestibular defects are true de ficiencies of atrial septal structures.

superior rim of the oval fossa (Figures 7.19,

7.20) More rarely, such defects can be

found when the caval vein is committed

exclusively to the right atrium

(Figure 7.21)6 All the defects are

associated with anomalous connections ofthe right superior pulmonary veins, whichdrain into the superior caval vein

(Figures 7.22, 7.23), often through morethan one orifice (Figure 7.19), while

retaining their left atrial connection(Figure 7.20) The difficulty encounteredduring surgical repair reflects the need toreconstruct the anatomy so as to reroute thevenous return and, at the same time, close

Fig 7.11 The surgical view through a right atriotomy shows a

de ficiency in the flap valve of the oval fossa (star).

the interatrial communication This must

be done without obstructing venous flow

or, in the case of a superior defect,

damaging the sinus node The sinus node is

related to the anterolateral quadrant of the

cavoatrial junction It lays immediately

subepicardially within the terminal groove(Figure 7.23) Its location should beconsidered both when making theatriotomy, and when placing sutures in theatrial walls Problems arise should it benecessary either to suture in the area of the

node when rerouting the pulmonaryvenous return, or if there is need to enlargethe orifice of the caval vein The former riskcan be minimised with judicious superficialplacement of the sutures The latterproblem is much greater Because the

Post Ant.

Sup.

Artery to sinus node

Floor of oval fossa Aortic root

Inf.

Fig 7.14 The dissection, made by transecting the atrial chambers, and illustrated in anatomical orientation, shows the relationship of the artery supplying the sinus node to the anterosuperior rim of the oval fossa Note also the proximity of the rim to the aortic root The arrow shows the infolded anterior rim of the fossa.

artery to the sinus node may pass either in

front of or behind the caval vein, the entire

cavoatrial junction is a potentially

dangerous area Incisions across the

cavoatrial junction carry a high risk of

damaging the artery, or even the node

itself Should it be deemed necessary to cutacross the junction, a much better option is

to perform the Warden operation10 Thisinvolves detaching the superior caval vein,and reattaching it to the excised tip of theright atrial appendage11

Another defect that permits interatrialshunting, but which is outside the confines

of the true atrial septum, is part of aconstellation of lesions termed unroofing ofthe coronary sinus (Figure 7.24)9 In thissetting, a persistent left superior caval vein

Sup.

Apex

Base Inf.

Fig 7.16 The surgical view through a right atriotomy shows a defect within the oval fossa (large star) extending into the mouth of the inferior caval vein (arrow) Note the location of the triangle of Koch (small star).

usually drains directly to the left atrial roof

(Figure 7.25), entering the chamber between

the appendage and the left pulmonary veins

Because of the unroofing of the coronary

sinus into the cavity of the left atrium, the

mouth of the coronary sinus functions as an

interatrial communication (Figure 7.26)

Evidence is frequently seen of the walls ofthe coronary sinus and left atrium along theanticipated course of the left superior cavalvein into and through the left

atrioventricular groove (Figure 7.24)

Sometimes the mouth of the coronary sinuscan seem to open normally to the rightatrium, but in the absence of its componentusually occupying the left atrioventriculargroove, and without persistence of a leftsuperior caval vein draining to the left atrial

Sup.

Pulmonary venous orifice

Intact oval fossa Sinus venosus defect Coronary sinus

Post.

Superior caval vein

Right pulmonary veins Sinus venosus defect Oval fossa

roof In this setting, the left ventricular

coronary veins drain directly into the cavity

of the left atrium In these circumstances, the

mouth of the coronary sinus again functions

as an interatrial communication This lesion

is the extreme form of the spectrum of

fenestration of the walls of the coronarysinus, providing communications with thecavity of the left atrium (see Chapter 9)

Surgical treatment of interatrialcommunications through the mouth of thecoronary sinus is dictated by the presence,

and connections, of the left superior cavalvein If it is present, and in free

communication with the right superiorcaval vein, or if there is no left-sidedsuperior caval vein, the mouth of thecoronary sinus can simply be closed If the

Superior caval vein

Right pulmonary vein

Atrial septum

Left atrium

Fig 7.20 The computed tomogram shows how, most frequently, the mouth of the superior caval vein overrides the crest of the atrial septum in the setting of a superior sinus venosus defect Note that the right pulmonary veins drain anomalously to the superior caval vein while retaining their left atrial connection (white double- headed arrow).

Post.

Right pulmonary veins

Overriding orifice of SCV Intact oval fossa

Ant.

Sup.

Inf.

Fig 7.19 The specimen, viewed in anatomical orientation, shows

a superior sinus venosus defect with overriding of the ori fice of the superior caval vein (SCV) The probe (stars) has been passed through the fibroadipose tissue occupying the intact superior margin of the oval fossa There is anomalous drainage of the two right upper pulmonary veins, which have retained their left atrial connection.

right atrial mouth of the sinus is to be

closed, decisions must be made concerning

the treatment of the left superior caval vein

In the presence of an adequate venous

channel communicating with the

brachiocephalic vein, the left caval vein can

be ligated If, in contrast, the left-sided

channel has no anastomoses with the rightside, consideration should be given toconstruction of a left-sided cavopulmonaryanastomosis, the Glenn shunt

Alternatively, a channel can be constructedalong the posteroinferior wall of the leftatrium, connecting the left atrial opening of

the left-sided vein with the mouth of thecoronary sinus

Atrioventricular septal defects

It is becoming increasingly frequent for theanomalies variously described as

Post.

Right upper pulm veins

Sinus venosus defect

Oval fossa

Ant.

Sup.

Inf.

Fig 7.21 The specimen, viewed in anatomical orientation, shows

a superior sinus venosus defect without overriding of the ori fice

of the superior caval vein As in the specimen shown in Figure 7.18, there is anomalous drainage of the right upper pulmonary (pulm.) vein, which has retained its left atrial connection Note the distance between the defect and the oval fossa (double-headed arrow) Note also the intact rims of the oval fossa.

Sup.

Apex Sinus venosus defect

Right pulmonary vein

Intact oval fossa

Base

Inf.

Fig 7.22 This surgical view through a right atriotomy shows a superior sinus venosus defect, recognised because it is outside the con fines of the intact oval fossa.

endocardial cushion defects,

atrioventricular canal defects, or a

persistent atrioventricular canal, to be

described as atrioventricular septal

defects12 This is entirely apppropiatebecause, in anatomical terms, themalformations are due to not only theabsence of the membranous

atrioventricular septum, but also theoverlapping region of atrial and ventricularmusculatures that normally forms the floor

of the triangle of Koch The structures are

Sup.

Apex Superior caval vein

Right pulmonary vein Pericardium

Sinus node

Base Inf.

Fig 7.23 This surgical view, through a median sternotomy of the heart shown in Figure 7.20, illustrates the anomalous connection of the right superior pulmonary vein Note the site of the sinus node lying in the terminal groove.

absent because the unifying feature of the

group is the commonality of the

atrioventricular junction (Figure 7.27)4

The optimal title for the group, therefore,

would be atrioventricular septal defect with

common atrioventricular junction This is

because, on rare occasions, defects of themembranous atrioventricular septum can

be found in the setting of separate right andleft atrioventricular junctions Thesedefects, first described by Gerbode andcolleagues13, and often called Gerbode

defects, can take two forms The morefrequent variant exists when shuntingacross a ventricular septal defect enters theright atrium through a deficient tricuspidvalve (Figure 7.28) The more rare variant

is a true deficiency of the atrioventricular

Post.

Orifice of SCV

Oval fossa

Eustachian valve Interatrial communication

through mouth of coronary sinus

Ant.

Sup.

Inf.

Fig 7.26 The right atrium from the heart illustrated in Figure 7.24

is shown Because of the unroo fing of the walls of the persistent left superior caval vein (SCV), the mouth of the coronary sinus functions as an interatrial communication.

Left superior caval vein

Left atrium

Left atrial appendage

Fig 7.25 The computed tomogram shows a persistent left superior caval vein draining to the roof of the left atrium, in the absence of the walls that usually separate the course of the vein through the left atrioventricular groove to the mouth of the coronary sinus.

component of the membranous septum

(Figures 7.29–7.32)14 The key to

differentiating the true defects from those

involving passage via a deficient ventricular

septum is to demonstrate the competence

of the tricuspid valve (Figure 7.32)

Although atrioventricular septal defects

do exist in the form of the Gerbode defect

in the setting of separate right and leftatrioventricular junctions, now it is usual topresume the presence of a commonatrioventricular junction when considering

Sup.

Fig 7.27 The section of a specimen, cut in the four-chamber orientation, shows a common atrioventricular junction (double- headed arrow) guarded by a common atrioventricular valve in a heart with de ficient atrioventricular septation The black brace shows the atrioventricular septal defect, between the leading edge

of the atrial septum and the crest of the muscular ventricular septum (stars).

Shunting through perimembranous VSD

Atrioventricular conduction axis

deficient atrioventricular septation The

presence of the common junction

fundamentally distorts the overall anatomy

when compared to the normally separate

right and left atrioventricular junctions(compare Figures 7.27 and 7.33)

Because of the lack of the membranousand muscular atrioventricular structures,

there is no septal atrioventricular junction.Instead, the leading edges of the atrialseptum and the ventricular septum, thelatter usually covered by the

Sup. Fig 7.29 The section through the heart, replicating the

echocardiographic four-chamber cut, shows how the septal lea flet

of the tricuspid valve divides the membranous septum into interventricular and atrioventricular components It is de ficiency of the atrioventricular component (white double-headed arrow) that underscores the existence of the direct Gerbode defect.

Intact interventricular membranous septum

Atrioventricular conduction axis

Shunting through deficient

atrioventricular valvar leaflets, meet at the

superior and inferior margins of the

common atrioventricular junction

(Figure 7.34) These meeting points of the

septal structures typically divide the

common junction into more-or-less equal

right and left sides An eccentric location of

the septal structures relative to the junctionproduces ventricular imbalance, or adouble-outlet atrium

It is the overall anatomy produced bythe common atrioventricular junction thatdistorts the disposition of the

atrioventricular conduction axis An

analogue of the triangle of Koch can be seenwithin the leading edge of the atrialseptum15 Because of the commonatrioventricular junction, however, theatrial septal myocardium makes contactwith the ventricular myocardium onlysuperiorly and inferiorly (Figure 7.34)

Fig 7.31 The image, taken in the operating room, shows a

de ficiency of the atrioventricular component of the membranous septum.

Sup.

Competent tricuspid valve

Shunting through deficient

atrioventricular membranous septum

Base

Apex Inf.

Fig 7.32 In the heart of the patient illustrated in Figure 7.31, insuf flations of saline in the right ventricle reveals a competent tricuspid valve, showing that the shunting from the left ventricle to right atrium is across a de ficiency of the atrioventricular part of the membranous septum; in other words, a direct Gerbode defect.

Usually the atrioventricular node is

displaced inferiorly It typically lies in a

nodal triangle, but not the triangle of Koch

When seen by the surgeon, the nodal

triangle has the coronary sinus at its base,

with the atrial septum to the left-hand side,

and the attachment of the leaflets of the

effectively common atrioventricular valve

to the right-hand side (Figures 7.35, 7.36)

The atrioventricular conduction axispenetrates the apex of the triangle It thencourses on the crest of the muscularventricular septum, covered by the inferiorbridging leaflet of the atrioventricular valve

(Figure 7.37) The proximity of thecoronary sinus to the apex of the nodaltriangle is pertinent to surgical closure ofthe septal defect Ideally, the surgeon willplace a patch so as to leave the coronarysinus draining to the systemic venousatrium The best option is to deviate the

four-Post.

Normally formed atrial septum

Atrioventricular septal defect Conjoined bridging leaflets

suture line towards the left-hand side of the

inferior bridging leaflet at its junction with

the atrial septum, using superficial surgical

bites (green line in Figure 7.35)15 An

alternative is to stay on the right-hand side,

but place the suture line within the mouth

of the coronary sinus so as to reach the edge

of the atrial septum (yellow line inFigure 7.35) The safety of this approachdepends on the margin between the

mouth of the coronary sinus and theapex of the nodal triangle (compareFigures 7.35 and 7.36) A furtheralternative is to keep the suture line to theright of the mouth of the coronary sinus,

so as to leave the coronary sinus draining to the left atrium.

Sup.

Base Apex

Leading edge of normally formed atrial septum

Conjoined bridging leaflets Atrioventricular septal defect

Inf.

Fig 7.36 In this heart, again shown as seen by the surgeon through a right atriotomy, there is less room around the coronary sinus to place a patch so as to leave the sinus draining to the right side (yellow dashed line) The site of the atrioventricular node is shown again by the white star (compare with Figure 7.35) Note that it is not within the well-formed triangle of Koch (red star) The green and blue lines show the alternate options for placement of the suture line, as indicated in Figure 7.35.

placing the sinus to the left of the atrial

patch (blue lines in Figures 7.35 and 7.36)

Occasionally, the inferior portion of the

atrial septum itself can be deficient The

coronary sinus then opens more

posteriorly and medially through the left

atrial wall The conduction axis, however,follows the course of the muscularventricular septum, with the nodeformed at the site of its union with theinferior atrioventricular junction(Figure 7.38)16

The feature that distinguishes betweenthe various forms of atrioventricular septaldefects is the morphology of the leaflets ofthe atrioventricular valve that guard thecommon atrioventricular junction,together with their relationship to the

Atrioventricular (AV) node

Branching AV bundle Analogue of triangle of Koch-

does not contain AV node

Atrial septum

Coronary sinus

Fig 7.37 The cartoon shows the usual disposition of the atrioventricular (AV) conduction axis in hearts with an atrioventricular septal defect and common atrioventricular junction The variant with a common valvar ori fice is illustrated.

Sup.

Base Apex

Anterosuperior leaflet

Bridging leaflets

Right mural leaflet

Left mural leaflet

Inf. Fig 7.38 In this atrioventricular septal defect with separate right and left valvar ori fices, the atrial septum is grossly deficient The atrioventricular node is found at the point where the muscular ventricular septum joins the inferior atrioventricular junction (star).

septal structures bordering the defect17 In

any heart that lacks the separating

atrioventricular structures, the common

atrioventricular valve has five leaflets The

arrangement is seen most readily when the

valve itself has a common orifice

(Figure 7.39) Two of the leaflets extend

across the ventricular septum, with their

tension apparatus attached in both

ventricles These are the superior and

inferior bridging leaflets Two other leaflets

are contained entirely within the right

ventricle They are the anterosuperior and

inferior mural leaflets The fifth leaflet is

contained exclusively within the left

ventricle, and is also a mural leaflet

Although the two leaflets found within the

right ventricle are comparable to similar

leaflets of the tricuspid valve seen in the

normal heart, the left ventricular leaflets of

the common atrioventricular valve

(Figure 7.40) bear no resemblance to a

normal mitral valve In the normal mitral

valve, found with separate atrioventricular

junctions, the ends of the solitary zone of

apposition between the leaflets, and the

papillary muscles supporting them, are

situated inferoanteriorly and

superoposteriorly within the left ventricle

(Figure 7.41) With this arrangement, the

extensive mural leaflet guards two-thirds ofthe circumference of the valvar orifice Theleft ventricular outflow tract then

interposes between the aortic leaflet of themitral valve and the ventricular septalsurface In atrioventricular septal defectswith a common atrioventricular junction,

in contrast, the left ventricular papillarymuscles are deviated laterally, beingpositioned superiorly and inferiorly12,17.Because of this, the mural leaflet isrelatively insignificant, and guards muchless than one-third of the circumference ofthe left atrioventricular orifice The leftorifice, in effect, is guarded by a valvepossessing three leaflets, these being thesmall mural leaflet, and the more extensiveleft ventricular components of the superiorand inferior bridging leaflets (Figure 7.42)

It had originally been suggested byRastelli and colleagues18that the commonvalve possessed four rather than fiveleaflets They argued that the differingmorphology to be found in the setting of acommon valvar orifice reflected themorphology of the anterior common leaflet,which is now usually described as thesuperior bridging leaflet In thearrangement they described as Type A,they considered the anterior common

leaflet to be divided, with the twocomponents both attached to theventricular septum They considered theirType B variant again to have a dividedanterior common leaflet, but with bothparts attached to an anomalous papillarymuscle in the right ventricle In theirType C malformation, they interpreted thearrangement in terms of an undividedcommon anterior leaflet, which was free-floating and attached in the right ventricle

to an apical papillary muscle In reality, thepurported division of the anterior commonleaflet is the site of coaptation between theright ventricular part of the superiorbridging leaflet and the anterosuperiorleaflet of the right ventricle (Figure 7.43)

In the Rastelli Type A variant, the point ofcoaptation is supported by the medialpapillary muscle of the right ventricle Thevariation noted by Rastelli and his

colleagues18is then readily explained onthe basis of increased commitment of thesuperior bridging leaflet to the rightventricle, with concomitant diminution insize of the anterosuperior leaflet of the rightventricle (Figure 7.44) As the superiorbridging leaflet becomes increasinglycommitted to the right ventricle, its site ofcoaptation with the anterosuperior leaflet

Right

Anterosuperior leaflet Superior bridging leaflet

Left mural leaflet

Right mural leaflet Inferior bridging leaflet

Left Sup.

Inf.

Fig 7.39 This atrioventricular septal defect, positioned anatomically and viewed from above, and with a common valvar ori fice, has been dissected to show the arrangement of the five lea flets that guard the common atrioventricular junction The white double-headed arrow shows the zone of apposition between the two bridging lea flets.

moves towards the right ventricular apex

(Figures 7.45, 7.46)17 A further difference

between the hearts at either end of the

spectrum identified by Rastelli and

colleagues18is that, with minimal bridging,

the superior bridging leaflet is tethered by

cords to the crest of the ventricular septum

(Figure 7.43) With extreme commitment

of the supporting papillary muscle to the

right ventricle, in contrast, the superior

bridging leaflet is always free-floating The

variation noted by Rastelli and colleagues

reflected the changing morphology of the

superior bridging leaflet There is also

variation in the arrangement of the inferior

bridging leaflet This does not, however,

reflect its commitment to the two

ventricles, which is usually balanced The

leaflet is often divided along the inferior

edge of the ventricular septum, with the

attachments of the two components

providing a relatively clear zone of

separation The edges are most frequently

attached to the septal crest, but there can be

a ventricular component to the defect

through intercordal spaces Such potential

for shunting beneath the inferior bridging

leaflet is almost always found when the

superior bridging leaflet is free-floating

It is the morphology of the bridging

leaflets themselves that accounts for much

of the remaining variability inatrioventricular septal defects with acommon atrioventricular junction Theoverall valvar morphology is comparable inall hearts with this specific phenotype Thevariability depends on the relationship ofthe two bridging leaflets to each other, ortheir relationships, on the one hand, to thelower edge of the atrial septum and, on theother hand, to the crest of the muscularventricular septum If these two featuresare described separately, there is no need touse terms such as ‘complete’, ‘partial’, and

‘intermediate’ when seeking to subdividethe group It is the use of these terms that,

in the past, has created most confusion indescription From the surgical stance, if it

is possible to visualise a bare area at themidportion of the ventricular septal crest;

this would constitute a complete lesion Ifthe crest of the septum is covered by atongue of tissue that joins the bridgingleaflets together, then the lesion isconsidered either partial or intermediate

The intermediate variant is characterised

by the presence of shunting at both atrialand ventricular levels, but with separatevalvar orifices within the commonatrioventricular junction

The partial variant, with no ventricularshunting, is also well described as the

ostium primum variant The bridgingleaflets are joined to each other along thecrest of the ventricular septum by aconnecting tongue of leaflet tissue(Figure 7.47) The essence of the ostiumprimum defect, therefore, is the presence

of separate valvar orifices for the right andleft ventricles within the common

atrioventricular junction Because the heart

of necessity possesses a commonatrioventricular junction, the left valvehas three leaflets, with an extensivezone of apposition between the leftventricular components of the superiorand inferior bridging leaflets This area, inthe past, was frequently described as a cleft

It has no morphological similarity to thecleft found in the aortic leaflet of themitral valve in hearts with normalatrioventricular septation and separateright and left atrioventricular junctions19

It is necessary surgically to close part, or all,

of this zone of apposition when repairingostium primum defects (Figure 7.48) Theresulting closure, nonetheless, does notrecreate a leaflet comparable to the aorticleaflet of the normal mitral valve(Figure 7.49)

The options for haemodynamicshunting across the atrioventricular septaldefects, which largely colour the clinical

Sup.

Apex

Superior bridging leaflet

Zone of apposition

Left mural leaflet

Inferior bridging leaflet

Base Inf.

Fig 7.40 This operative view through a right atriotomy shows the typical trifoliate formation of the left atrioventricular valve in a heart with a de ficient atrioventricular septation and common atrioventricular junction It bears no resemblance to the formation

of the lea flets as seen in the normal mitral valve Note the extensive zone of apposition between the two lea flets that bridge the ventricular septum (dashed white double-headed arrow).

Mitral valve Aorta

Left Sup.

Inf.

Fig 7.41 This view of the left ventricle, taken from the apex with the ventricular mass sectioned in its short axis, shows the

interrelationship of the normal mitral valve and the out flow tract

to the aorta Note the oblique position of the papillary muscles supporting the solitary zone of apposition between the lea flets of the mitral valve, along with the extensive space between the aortic lea flet of the mitral valve and the septal surface of the left ventricle (star).

Right Zone of apposition

Inferior bridging leaflet Left mural leaflet

Superior bridging leaflet

Left Sup.

Inf.

Fig 7.42 This view of the left atrioventricular valve and the out flow tract in a heart with an atrioventricular septal defect is taken in comparable fashion to the normal heart seen in Figure 7.41, showing the short axis of the left ventricle Note that the left valve in the heart with de ficient atrioventricular septation has three lea flets, with papillary muscles positioned directly superiorly and inferiorly, rather than being obliquely positioned as

in the normal heart There is an extensive zone of apposition between the bridging lea flets (dashed white double-headed arrow) Note also the way that the out flow tract is squeezed between the superior bridging lea flet and the superior margin of the left ventricle (star).

features, depend upon the relationship of

the bridging leaflets to the septal

structures4 When there is a common

valvar orifice, it is extremely rare for the

leaflets to be attached directly to the crest ofthe ventricular septum, although the extent

of their tethering by tendinous cords canvary markedly When the bridging leaflets

lack direct attachments to the septalstructures, the potential exists for shunting

at both atrial and ventricular levels, themagnitude of the shunts depending on the

Post.

Inferior bridging leaflet

Superior bridging leaflet

arrangement to represent a divided common anterior lea flet.

Medial papillary muscle Anterior papillary muscle

Anomalous apical muscle

of bridging of the superior lea flet in hearts with

an atrioventricular septal defect and common ori fice that underlies the classification introduced

by Rastelli and his colleagues 18 As the superior bridging lea flet (pink) extends further into the right ventricle, there is concomitant diminution in size of the anterosuperior lea flet (pink, cross- hatched), and fusion of the anterior and medial papillary muscles of the right ventricle, which increasingly are attached towards the right ventricular apex.

prevailing haemodynamic conditions,

together with the extent of the tethering If

the leaflets are firmly attached to the

ventricular septum, shunting will be

confined at atrial level This is thearrangement found most frequently in thetypical ostium primum defect, withseparate right and left valvar orifices within

the common junction, but with bothbridging leaflets firmly fused to the crest ofthe ventricular septum (Figure 7.50)

Much less frequently, the bridging leaflets

Post.

Superior bridging leaflet Anterosuperior leaflet

Inferior leaflet Anomalous apical PM

can be firmly attached to the underside of

the atrial septum (Figure 7.51) This

arrangement will confine the potential for

shunting at the ventricular level It

produces the true ventricular septal defect

of atrioventricular canal variety, as thevalve guarding the common

atrioventricular junction will have the

characteristics of a commonatrioventricular valve, rather than tricuspidand mitral valves (Figures 7.51–7.55) Thepotential also exists, nonetheless, for the

Right Inferior bridging leaflet Right mural leaflet

Left mural leaflet

Superior bridging leaflet Anterosuperior leaflet

Sup.

Apex

Left mural leaflet

Superior bridging leaflet Inferior bridging leaflet

Base Inf.

Fig 7.48 This view, taken through a right atriotomy, shows the trifoliate con figuration of the left atrioventricular valve

subsequent to repair of the zone of apposition between the left ventricular components of the bridging lea flets (dashed black double-headed arrow) Even after the surgical repair, the valve has

no similarity to the normal mitral valve (see Figure 7.49).

leaflets to be free-floating even in the

presence of separate valvar orifices

(Figure 7.56) Most would consider the

lesion shown in Figure 7.56 as an

intermediate defect If the variability interms of attachment of the bridging leaflets

is described, along with informationconcerning the presence of a common

valvar orifice or separate right and leftorifices, there is no need to introduce theconcept of intermediate or transitionalvariants We recognise, nonetheless, the

Right Mural leaflet

Aortic leaflet

Left Sup.

Inf.

Fig 7.49 This view through a right atriotomy shows a normal mitral valve The structure bears no comparison to the trifoliate valve shown in Figure 7.48.

Right Superior bridging leaflet

Inferior bridging leaflet Left mural leaflet

Left Sup.

Inf.

Fig 7.50 This heart with a common atrioventricular junction and separate right and left valvar ori fices is shown from the left side in anatomical orientation The bridging lea flets are firmly fused to the crest of the ventricular septum (red dotted line), con fining shunting through the atrioventricular septal defect at the atrial level The white double-headed arrow shows the zone of apposition between the left ventricular components of the bridging lea flets This is the essence of the ostium primum defect.

value of the shorthand terms of partial,

intermediate, and complete variants,

providing that all working on the same

team understand the definitions used for

the different types

Thus, in many patients with so-calledpartial defects, with separate right and leftvalvar orifices within the common junction,echo Doppler interrogation reveals thepotential for interventricular shunting

beneath the tongue that joins together thebridging leaflets, or otherwise throughintercordal spaces tethering the bridgingleaflets themselves Such patients arewell described as having separate valvar

Right atrium Left atrium

Inferior bridging leaflet

Inferior bridging leaflet

Superior bridging leaflet Ventricular septal defect

orifices, with predominantly atrial

shunting, but with the potential for

minimal ventricular shunting The basic

morphology of the deficient ventricular

septum, therefore, is comparable in all

patients having atrioventricular septal

defects with a common atrioventricularjunction12 As already emphasised, it isthis disposition that determines thecourse of the ventricular conductionpathways (Figure 7.34)13,20 Although thehallmark of the malformation is the

common atrioventricular junction,coupled with the absence of theatrioventricular muscular and membranousseparating structures, there is also

hypoplasia of the muscular ventricularseptum to a greater or lesser extent This

Inferior bridging leaflet

Superior bridging leaflet

Ventricular septal defect

Inferior bridging leaflet Superior bridging leaflet

Intact atrial septum

Apex

Base Sup Inf.

Fig 7.54 This picture, taken in the operating room, shows the right atrial aspect of an atrioventricular septal defect with a common atrioventricular junction, in which shunting is con fined at the ventricular level because the bridging lea flets are firmly attached to the underside of the atrial septum In this image, the septal defect itself is not obvious.

involves disproportion between the inlet

and outlet dimensions of the ventricular

septum when compared to the normal heart

(compare Figures 7.57 and 7.58) The

degree of septal hypoplasia also varies with

regard to the extent of scooping of theseptum (Figure 7.58) The scooping isgreater in hearts with a common valvarorifice than in those with separate right andleft orifices Although the scooping is

greater in hearts with a common valvarorifice, thus increasing the likelihood ofthere being a ventricular component to thedefect, variability is still found among thesehearts When there is minimal scooping, it

Inferior bridging leaflet Superior bridging leaflet

Intact atrial septum

Apex

Base Sup Inf.

Ventricular

septal defect

Fig 7.55 This image shows how, when the surgeon separated the right ventricular components of the bridging lea flets of the heart shown in Figure 7.54, the common atrioventricular junction is seen, with shunting at the ventricular level across the

atrioventricular septal defect.

is certainly possible to close the ventricular

component of the septal defect by attaching

the bridging leaflets directly to the right

ventricular aspect of the ventricular

septum21 This manoeuvre, in fact, is

feasible in all patients with a common

valvar orifice22,23, although not all are

convinced of its utility Thus, the use of themodified single patch approach remainscontroversial Some consider that thetechnique creates potential narrowing ofthe left ventricular outflow tract Theremay be subtle technical differences thatproduce the different results

If the technique is used, care must betaken not to damage the exposedconduction tissues along the septal crest.The non-branching bundle runs down thecrest of the scooped-out septum, and iscovered by the inferior bridging leaflet.The inferior leaflet itself is often divided by

of the ventricular mass.

a midline raphe immediately above the

vulnerable non-branching bundle The

branching component of the conduction

axis is found astride the midportion of

the septal crest This is usually covered

by the connecting tongue and leaflet

tissue in hearts with separate right and left

valvar orifices It is exposed in thepresence of a common orifice and free-floating leaflets The right bundle branchthen runs towards the medial papillarymuscle Anterior to this point, the septum

is devoid of conduction tissue(Figures 7.59, 7.60)15

Although not readily evident to thesurgeon during operation, the left ventricularoutflow tract in atrioventricular septal defects

is intrinsically narrow24 It is much longer inhearts with separate orifices This is because

of the attachment of the superior bridgingleaflet to the ventricular septal crest (compare

Atrioventricular septal defect

Atrioventricular node Atrioventricular conduction axis

Right bundle branch

Atrioventricular septal defect

Figures 7.61 and 7.62) The area is

prone to postoperative obstruction, and

surgical enlargement may be necessary

Obstruction may be due to naturally

occurring lesions25, or to injudicious

placement of a prosthesis used to replace the

left atrioventricular valve If a prosthesis

must be employed, the anatomy dictates

insertion of a model with low profile,otherwise resection of the shelf that existsbetween the hingepoint of the superiorbridging leaflet and the attachment of theaortic valve24 The superior bridging leafletcan also be liberated from the septal crest,inserting a gusset to enlarge the outflow tract(Figures 7.63 and 7.64)

Further variability is found in thecommitment of the commonatrioventricular junction to theventricular mass Usually it is sharedequally, giving a balanced arrangement(Figure 7.27) Should the commonjunction favour one or other ventricle,producing so-called right or left ventricular

Atrioventricular septal defect

Sup.

Inf.

Ant Post.

Atrioventricular septal defect

Superior bridging leaflet

Fig 7.62 In this heart, again shown in anatomical orientation from the left side (compare with Figure 7.61), the out flow tract (black double-headed arrow) is much shorter in the presence of a common atrioventricular valvar ori fice The star shows the zone of apposition between the bridging lea flets.

dominance, the other ventricle is often

severely hypoplastic This can have a major

influence on the outcome of surgery, and

should always be assessed preoperatively

In the setting of right ventriculardominance, there is usually alignmentbetween the atrial and ventricular septalstructures at the crux The essence of left

ventricular dominance, in contrast, ismalalignment between the atrial septumand the muscular ventricular septum(Figure 7.65) This produces an

Trifoliate left AV valve

Disattached superior bridging leaflet

arrangement analogous to straddling of the

tricuspid valve26 As with straddling the

tricuspid valve, this has major consequence

for the disposition of the atrioventricular

conduction axis27 Because of the septal

malalignment, the connecting

atrioventricular node is no longer to be

found at the crux It continues to be formed

at the point where the malaligned muscularventricular septum meets the

atrioventricular junction (Figure 7.66)

This particular arrangement must beidentified preoperatively, as it can beexceedingly difficult to recognise duringsurgery If unrecognised, it is likely that astandard repair will damage the conduction

axis Septal malalignment, therefore,should be excluded in all cases ofatrioventricular septal defect with leftventricular dominance This arrangementshould also be distinguished from thosehearts in which the atrial septum is absent,and the coronary sinus terminates in theleft atrium16

Cut-back coronary sinus

Plane of

atrial septum

Superior bridging leaflet

Bifid inferior bridging leaflet

Left ventricle

an anomalous node (star) in the inferior aspect of the right atrioventricular junction, rather than at the crux of the heart.

Malaligned muscular ventricular septum

Anomalous inferolateral node

Atrial septum comes to crux Fig 7.66 The cartoon shows how, when there is malalignment

between the atrial septum and the muscular ventricular septum, with left ventricular dominance, the atrioventricular node is formed at the point where the ventricular septum meets the inferior atrioventricular junction.

Ventricular septal defects

When asked to close a clinically significant

hole between the ventricles, the primary

concern of the surgeon is to ensure that the

task can be achieved in a safe and secure

fashion The important anatomical

considerations reflect the location of the

defect relative to the landmarks of the right

ventricle These features determine the

proximity of the defect to the

atrioventricular conduction axis, and to the

leaflets of the atrioventricular and arterial

valves One categorisation of the defects28

was designed specifically to focus the

attention of the surgeon on these pertinent

features The essence of the system was

that, according to the anatomical features of

the margins of the defects as seen from the

morphologically right ventricle, all the

holes fitted into one of three groups

The first group included all those holes

that, when viewed from the right ventricle,

had exclusively muscular borders

(Figure 7.67) The phenotypical feature of

the second group was that part of the right

ventricular border was composed of fibrous

continuity between the leaflets of an

atrioventricular valve and an arterial valve

(Figure 7.68) The patients falling in the

third group were unified because part oftheir right ventricular borders was made up

of fibrous continuity between the leaflets ofthe aortic and pulmonary valves

(Figure 7.69), with holes of this third typeshowing additional variability depending

on whether the fibrous continuity extended

to include the leaflet of an atrioventricularvalve The defects in the patients making

up the third group, of necessity openbetween the outflow tracts of the ventricles

Defects within the other groups, however,need further description depending onwhether they open primarily to the inlet, tothe apical, or to the outlet components ofthe right ventricle There is thus anadditional feature that always requiresdescription, if present, namelymalalignment between the septalcomponents

There are, of course, othercategorisations available for distinguishingbetween types of holes between theventricles One time-honoured systemidentified four variants, and grouped them

in numerical fashion29 Another popularsystem used developmental

considerations so as to distinguish betweenthe different holes30 We prefer the systemdesigned specifically to emphasise the

surgical considerations (Figure 7.70).When using this system, nonetheless, theborders of the holes between the

ventricles must be assessed as seen by thesurgeon working through the

morphologically right ventricle(Figures 7.67–7.69)

The essence of the largest group ofdefects requiring surgical closure is thatpart of the central fibrous body, specificallythe area of fibrous continuity between theleaflets of the mitral, aortic, and tricuspidvalves, that forms a direct part of the rim ofthe defect as seen from the right ventricle(Figure 7.68) This fibrous area

incorporates the atrioventricularcomponent of the membranous septum,which retains its integrity when ventricularseptation is incomplete, being an integralpart of the central fibrous body Thedefects, therefore, surround themembranous part of the septum, and aredescribed, justifiably, as being

perimembranous In many instances, theinterventricular component of themembranous septum is found as a fold offibrous tissue in the posteroinferior margin

of the defect (Figure 7.71)

The defects themselves represent theunclosed embryonic interventricular

communication (Figure 7.72) They

presumably result from a deficiency of the

muscular ventricular septum forming the

apical and cranial rims of the persisting

hole Defects requiring surgical closure will

always be considerably larger than the areaoccupied by the interventricular

membranous septum of the normal heart

The degree of septal deficiency hasimportant consequences for the disposition

of the axis of atrioventricular conductiontissue31 In the normally formed heart, theaxis penetrates the atrioventricularmembranous septum to reach the crest ofthe muscular septum Having penetrated, it

Coronary sinus

Ventricular septal defect Fibrous continuity

is sandwiched between the muscular

septum and the interventricular

component of the membranous septum

(Figure 7.73) In perimembranous defects,

when the atrioventricular connections are

concordant, so as to reach the crest of the

muscular ventricular septum, the axispenetrates the area of continuity betweenthe leaflets of the aortic and tricuspid valves(Figure 7.74) When a remnant of theinterventricular membranous septum ispresent, it lies immediately on top of the

atrioventricular bundle (Figure 7.74) Ifsuch a remnant is seen at operation(Figure 7.71), and is substantial, it maysafely be used for anchorage of suturesplaced superficially to anchor a surgicalpatch

Septomarginal trabeculation

Triangle of Koch and atrioventricular node Sinus node

Central fibrous body

Outlet

Trabecular

Fig 7.70 The cartoon, shown in surgical orientation, illustrates the categorisation used for differentiating the phenotypical variations for holes between the ventricles It combines the phenotypical features shown in

Figures 7.67 to 7.69 with the location of the hole relative to the components of the right ventricle.

Septal leaflet of tricuspid valve

Remnant of membranous ventricular septum

Apex

Base

Sup Inf. Fig 7.71 In this heart, viewed through a right atriotomy and

through the ori fice of the tricuspid valve, a remnant of the interventricular membranous septum is present in the posteroinferior margin of the perimembranous defect.

The location of the medial papillary

muscle, together with the apex of the

triangle of Koch, provides the guide for

predicting the location of the conduction

axis in almost all holes that are

perimembranous, in other words the holesbordered posteroinferiorly by fibrouscontinuity between the leaflets of the aorticand tricuspid valves (Figure 7.75) Theonly exceptions to this rule are the defects

associated with straddling and overriding

of the tricuspid valve27 The proximity ofthe conduction tissues to the leaflets of theaortic and atrioventricular valves, however,varies depending upon the precise area of

Developing aortic valve

Developing tricuspid valve

re flect failure to close this embryonic interventricular communication.

Right

atrium

Left atrium

Right ventricle

Left ventricle

Aortic root

Atrioventricular membranous septum

Septal leaflet

of tricuspid valve

Sup.

Inf.

Right Left Fig 7.73 This four-chamber section, shown in anatomical

orientation, reveals the position of the penetrating atrioventricular bundle (star) in the normal heart It is sandwiched between the central fibrous body and the crest of the muscular ventricular septum.