Ebook Wilcox’s surgical anatomy of the heart (4/E): Part 2

Part 2 book “Wilcox’s surgical anatomy of the heart” has contents: Analytical description of congenitally malformed hearts, lesions with normal segmental connections, lesions in hearts with abnormal segmental connections, abnormalities of the great vessels, positional anomalies of the heart.

6 Analytical description

of congenitally malformed hearts

Systems for describing congenital cardiac

malformations have frequently been based

upon embryological concepts and theories

As useful as these systems have been, they

have often had the effect of confusing the

clinician, rather than clarifying the basic

anatomy of a given lesion As far as the

surgeon is concerned, the essence of a

particular malformation lies not in its

presumed morphogenesis, but in the

underlying anatomy An effective system

for describing this anatomy must be based

upon the morphology as it is observed At

the same time, it must be capable of

accounting for all congenital cardiac

conditions, even those that, as yet, might

not have been encountered To be useful

clinically, the system must be not only

broad and accurate, but also clear and

consistent The terminology used,

therefore, should be unambiguous It

should be as simple as possible The

sequential segmental approach provides

emphasis is placed on its surgical

applications2 The basis of the system is, in

the first instance, to analyse individually

the architectural make-up of the atrial

chambers, the ventricular mass, and the

the nature of the junctional arrangements

(Figure 6.1) Still further attention is

devoted to the interrelationships of the

cardiac structures within each of the

individual segments This provides the

basic framework within which all otherassociated malformations can becatalogued4

ATRIAL ARRANGEMENT

The first step in analysing any malformedheart is to determine the arrangement ofthe chambers within the atrial mass Whendistinction is based on the anatomy of theappendages, which are the most constantcomponents of the atriums, and specifically

on the extent of the pectinate musclesrelative to the atrial vestibules5, atrialchambers can be of only morphologicallyright or morphologically left type Themorphologically right appendage is broadand triangular (Figure 6.2), whereas themorphologically left appendage is finger-like, and has a much narrower neck(Figure 6.3) In most instances, it ispossible to identify the appendages simply

on the basis of their shape (Figure 6.4)

Only in circumstances of uncertainty will itprove necessary to inspect the extent of thepectinate muscles (Figures 6.5, 6.6) Thisfeature, of course, is readily visible to thesurgeon once the atrial chambers have beenopened

When judged on the extent of thepectinate muscles, there are only fourtopological ways in which the appendagescan be arranged within the atrial mass(Figure 6.7) Almost always, the atrium

possessing the appendage in which thepectinate muscles extend to the crux isright-sided, while the one with a smoothinferoposterior vestibule is left-sided Thisusual arrangement is often called ‘situssolitus’ Rarely, the appendages can bedisposed in mirror-image fashion, so-called

‘situs inversus’ More common than themirror-imaged topological arrangement,but still relatively rare, is the situation inwhich the appendages of both chambers inthe atrial mass have the same morphology.This can occur in two forms, with eithermorphologically right (Figure 6.8) ormorphologically left (Figure 6.9)appendages on both sides These bilaterallysymmetrical topological patterns, orisomeric arrangements, have traditionallybeen named according to the arrangement

of the abdominal organs, particularly thespleen This is because they usuallyexist with a jumbled up abdominalarrangement, an arrangement also termedvisceral heterotaxy6 It is far moreconvenient, as well as more accurate, todesignate them in terms of their own

can be determined readily by the surgeon

in the operating room Isomerism of theright appendages is usually, but not always,found with absence of the spleen It is mostoften associated with right bronchialisomerism Isomerism of the leftappendages is typically found, but againnot always, with multiple spleens The

Ventricles

Atriums

Arterial trunks Atrioventricular

Ventriculoarterial

Fig 6.1 The cartoon shows the three segments of the heart These are the atriums, the ventricular mass, and the arterial trunks The segments are joined together at the atrioventricular and ventriculoarterial junctions.

association with left bronchial isomerism is

more constant

The anticipated topological

arrangement of the atrial appendages can

be predicted preoperatively with a high

degree of accuracy by studying therelationships of the abdominal great vessels

as determined with cross-sectional

knowledge of isomerism of the atrial

appendages is of value in two additionalways Firstly, it alerts the surgeon to

right isomerism, the sinus node, being amorphologically right atrial structure, is

Sup.

Inf.

Ant Post.

Hooked and tubular appendage

Fig 6.3 As shown in this computed tomogram, the morphologically left atrial appendage has a characteristic narrow and hooked shape (compare with Figure 6.2).

Sup.

Inf.

Right Left Triangular appendage

Right coronary artery Fig 6.2 The computed tomogram shows the typical triangular

shape of the morphologically right atrial appendage.

duplicated A node is found laterally in

each of the terminal grooves12 In left

isomerism, there are no terminal grooves

(Figure 6.9) In this situation, the sinus

node is a poorly formed structure, without

a constant site Usually the node is found inthe anterior interatrial groove, close to theatrioventricular junction12

The second advantage of recognisingisomeric appendages is that the

arrangements are known to be harbingers

of complex intracardiac lesions Heartswith isomerism of either type tend to havebilateral superior caval veins, an effectivelycommon atrial chamber, albeit with two

Sup Inf.

Left

Right Morphologically left appendage

Morphologically right appendage

Fig 6.4 This operative view, taken through a median sternotomy, shows the differences between the broad triangular

morphologically right atrial appendage, and the narrow finger-like morphologically left atrial appendage.

isomeric appendages, and common

atrioventricular valves Right isomerism is

always associated with a totally anomalous

pulmonary venous connection, even if the

pulmonary veins are joined to one or other

atrium It is also seen most frequently with

pulmonary stenosis or atresia, and in

association with a univentricular

atrioventricular connection, typically a

double-inlet ventricle through a common

valve Left isomerism, in the majority of

cases, is associated with interruption of the

inferior caval vein, with continuation of thevenous drainage from the abdomenthrough the azygos system of veins

THE ATRIOVENTRICULAR JUNCTIONS

Having established the arrangement of theatrial appendages, the next step insequential analysis is to determine themorphology of the atrioventricular

junctions For this, the surgeon needs toknow how the atrial chambers are, or arenot, connected to the chambers presentwithin the ventricular mass Most often,there are two such chambers, which can be

of only right or left morphology Themorphological distinction is based on thenature of the apical trabeculations In themorphologically right ventricle, thesetrabeculations are coarse, in contrast to thefine criss-crossing trabeculations thatcharacterise the morphologically left

Usual Mirror-imaged

Isomeric right Isomeric left

Fig 6.7 The cartoon shows the four possible arrangements of the atrial appendages, which cannot always be distinguished on the basis of their shape The best means of distinguishing between them is to establish the extent of the pectinate muscles These muscles extend all the way to the crux in the morphologically right atrial appendage, but are con fined around the mouth of the appendage in the morphologically left atrial appendage, leaving a smooth posterior vestibule Using this criterion, all congenitally malformed hearts have appendages fitting within one of the four groups shown in the cartoon.

ventricle (Figure 6.10) It is the

interrelationships between the two

ventricles that permit the description of

ventricular topology When analysed

according to the way that the palmar

surfaces of the hands can be placed on the

septal surface of the morphologically rightventricle such that the thumb is within theinlet component, and the fingers in theventricular outlet, the patterns reflecteither right-hand or left-hand topology(Figure 6.11) Having assessed ventricular

morphology, it is possible to determine theway in which the atrial chambers areconnected, or not connected, to theventricular mass In most instances, thereare two atrioventricular junctions, althoughone of the junctions can be absent Also

Sup Inf.

Left

Right

Right-sided morphologically left appendage

Fig 6.9 This surgical view through a median sternotomy shows a right-sided atrial appendage of morphologically left pattern The left-sided appendage is also of left morphology, so the patient has isomerism of the left atrial appendages Note the absence of any terminal groove Internal inspection con firmed the presence of smooth bilateral posterior vestibules.

Sup Inf.

Left

Right

Left-sided morphologically right appendage

Fig 6.8 This surgical view through a median sternotomy shows a left-sided atrial appendage of morphologically right pattern The right-sided appendage is also of right morphology,

so the patient has isomerism of the right atrial appendages Note the crest of the appendage in relation to the left superior caval vein and the terminal groove When examined internally, pectinate muscles encircled both atrioventricular junctions.

important is the morphology of the valves

that guard the atrioventricular junctions,

because the paired junctions can be

guarded by a common atrioventricular

valve This shows that junctional and valvar

morphology are separate and independent

features

There are five distinct and discrete ways

in which the atrial chambers may be

connected to the ventricular mass, the final

one having two subtypes, along with an

intriguing further variation Most often,the atrial chambers are connected to theirmorphologically appropriate ventricles

This pattern is called concordantatrioventricular connections When eachatrium is connected in this way to its ownventricle, there is rarely any difficulty indistinguishing the morphology of theventricles, even when the ventriclesthemselves are unusually related one to theother In the second pattern, which

represents discordant connections, eachatrium is connected with a morphologicallyinappropriate ventricle

Concordant and discordantconnections can exist with either the usual

or mirror-imaged arrangement of theatrial appendages (Figure 6.12), but notwith isomeric appendages When theappendages are isomeric, and each atrium

is connected to its own ventricle, then ofnecessity one junction will be

Fine left ventricular trabeculations

Fig 6.10 The apical part of the normal ventricular mass has been amputated, and is viewed from above It shows the marked difference between the fine apical trabeculations of the morphologically left ventricle when compared to the coarse right ventricular apical trabeculations.

Right-hand topology Left-hand topology

Fig 6.11 The cartoon shows how the patterns of ventricular topology can be described, figuratively speaking, in terms of the way that the palmar surface of the hands can be placed on the septal surface of the morphologically right ventricle The fingers point up the outlet, and the thumb lies in the inlet, giving right-hand and left-hand patterns.

In the arrangements shown, the atrioventricular connections are concordant, but the ventriculoarterial connections can also

be discordant, with the aorta arising from the morphologically right ventricle (see

Figure 6.29).

concordantly connected, but the other

junction will be discordantly connected

(Figure 6.13) This will occur irrespective

of the topological pattern of the

ventricular mass (see later) Thearrangement produces a third discretepattern, namely biventricular and mixedatrioventricular connections

In the three connections describedthus far, each atrium is connected to itsown ventricle This means that theatrioventricular connections themselves

Usual arrangement Mirror-imaged pattern

Right isomerism Left isomerism

Right-hand topology Right-hand topology

Left-hand topology Left-hand topology

Fig 6.13 The cartoon demonstrates the mixed and biventricular atrioventricular connections found when there are isomeric atrial appendages, and each atrium is connected to its own ventricle In each pattern, half of the heart is concordantly connected, and the other half is discordant It is essential in these settings, therefore, to describe both the type of isomerism, and the speci fic ventricular topology.

are biventricular The essential feature in

the remaining two types of

atrioventricular connection is that the

atrial chambers, with one exception,

connect to only one ventricle In one of

these patterns, both atrial chambers

connect to the same ventricle This is a

double-inlet atrioventricular connection

(Figure 6.14) In the other variant, one of

the atrial chambers is connected to a

ventricle, but the other atrium has no

connection with the ventricular mass

This latter arrangement can be divided

into two subtypes, depending on whether

absence of the connection is right-sided

(Figure 6.15) or left-sided (Figure 6.16)

An intriguing variation is seen when one

of the atrioventricular connections isabsent, be it right-sided or left-sided,namely when the atrioventricular valveguarding the solitary connection straddlesthe septum, being attached in bothventricles The end result is a uniatrial,but biventricular, atrioventricularconnection (Figure 6.17)

There has been much controversyconcerning the description of the hearts

in which the atrial chambers connect toonly one ventricle It became conventional

to describe them in terms of singleventricle, common ventricle, oruniventricular hearts It is exceedingly rare,however, to find patients with solitaryventricles Almost always, in patients

described as having univentricular hearts,the ventricular mass contains more thanone chamber By focusing on the fact thatthe atrioventricular connection is, inreality, joined to only one ventricle, we areable to achieve a satisfactory solution forthis dilemma Thus, the hearts can logicallyand accurately be described in terms ofbeing functionally univentricular Itfollows that, in some patients withbiventricular atrioventricular connections,imbalance between the ventricles can againproduce a functionally univentricular

univentricular atrioventricularconnections, however, one of the ventriclesmust be incomplete, while the other

a double inlet to a dominant left ventricle The black braces show the segments of atrial vestibular myocardium, connected to the dominant left ventricle through separate atrioventricular valves.

ventricle is dominant The dominant

ventricle, which supports the

atrioventricular junction or junctions, can

take one of three morphologies: right, left,

or indeterminate (Figure 6.18) Most

frequently, as judged from the pattern of its

apical trabecular component, the dominantventricle will be morphologically left

There will be a complementary rightventricle, perforce incomplete because itwill lack its atrioventricular connection,and hence its inlet component Such

incomplete right ventricles are alwaysfound anterosuperiorly relative to thedominant left ventricle, irrespective ofwhether there is a double inlet, or an absentright or absent left atrioventricularconnection They can, however, be

positioned either to the right (Figure 6.19),

or to the left (Figure 6.20) relative to the

dominant ventricle

More rarely, the atrial chambers can be

connected to a dominant right ventricle

This happens most frequently in the

absence of the left atrioventricular

connection (Figure 6.21), but can be foundwith a double inlet or, rarely, with anabsence of the right atrioventricularconnection When only the right ventricle

is connected to the atrial chambers, andhence dominant, it is the left ventricle that

is incomplete, lacking its atrioventricular

connection and its inlet portion Theincomplete left ventricle will always befound in a posteroinferior position Usually

it is left-sided, although rarely it can beright-sided

The third morphologicalconfiguration found with a double inlet

RA

LA

RV

LV Straddling & overriding AV valve

Absent AV connection

Fig 6.17 This cartoon illustrates the arrangement when there is an absence of the right atrioventricular (AV) connection, but with the solitary atrioventricular valve straddling the ventricular septum This produces a uniatrial but biventricular atrioventricular connection, shown here in the setting of a usual atrial arrangement with right- hand ventricular topology RA, LA, right and left atriums; RV, LV, right and left ventricles.

Usual Mirror-imaged Right isomerism Left isomerism

Dominant right with incomplete LV

Solitary and indeterminate ventricle

Dominant left with

atrioventricular connections LV, RV, left and right ventricles.

or, exceedingly rarely, with an absence of

either atrioventricular connection, is

when the atrial chambers connect to a

solitary ventricle Such solitary

ventricles have indeterminate apicaltrabecular morphology (Figure 6.22)

Incomplete second ventricles arenever found in this variant of

univentricular atrioventricularconnection, in which the only septalstructure in the ventricle is thatseparating the outflow tracts

Sup.

Inf.

Right Left Aorta

Incomplete right ventricle

Incomplete right ventricle

VSD

Fig 6.20 This anatomical specimen, again with a double-inlet left ventricle, has the incomplete right ventricle in an anterosuperior and leftward position relative to the dominant left ventricle VSD, ventricular septal defect.

VALVAR MORPHOLOGY

The atrioventricular valvar morphology is

independent of the way in which the atrial

chambers connect with the ventricles Valvar

morphology, therefore, constitutes a separate

feature of the atrioventricular junctions

When there are concordant, discordant,mixed, or double-inlet connections, thenboth atrial chambers are connected, actually

or potentially, to the ventricular mass Thetwo atrioventricular junctions can be

guarded by two separate atrioventricularvalves (Figure 6.23), or by a common valve(Figure 6.24) When there are two valves,either of them can be imperforate, blocking apotential atrioventricular connection Animperforate valve, therefore, needs to be

Right atrium

Left atrium

Dominant right ventricle Sup.

Inf.

Right Left

Incomplete left ventricle

Fig 6.21 This section through a specimen, shown in four-chamber orientation, illustrates the absence of the left atrioventricular connection (red dotted line) with the right atrium connected to a dominant right ventricle This produces one of the variants of the hypoplastic left heart syndrome.

Coarse apical trabeculations

Left AV valve

Fig 6.22 This heart, opened in clam-shell-like fashion, has a double inlet to, and double outlet from, a solitary and indeterminate ventricle, the ventricle itself having very coarse apical trabeculations AV, atrioventricular.

distinguished from absence of an

atrioventricular connection, as either can

produce atrioventricular valvar atresia

The essence of the imperforate valve is that

the atrioventricular connection has formed,but is blocked by the conjoined valvarleaflets (Figure 6.25) In the setting ofabsence of the connection, the floor of the

atrium involved is completely separatedfrom the ventricular mass by thefibroadipose tissue of the atrioventriculargroove (see Figures 6.15, 6.16)

Base

Apex

Right Left Fig 6.23 This normal heart, sectioned in

four-chamber orientation, shows the right and left atrioventricular junctions (black dotted lines with double-headed arrows) guarded by separate atrioventricular valves.

Sup.

Inf.

Right Left

Right atrium

Left atrium

Right ventricle

Left ventricle

Fig 6.24 This section, again in four-chamber orientation (compare with Figure 6.23), shows that the right and left atrioventricular junctions (black dotted line with double-headed arrow) are guarded by a common atrioventricular valve in the setting of an atrioventricular septal defect.

Either of two valves, or a common

valve, can also straddle a septum within the

ventricular mass Straddling of the tension

apparatus of a valve should be distinguished

from overriding of its supporting

atrioventricular junction Straddling exists

when the valvar tension apparatus is

attached to both sides of the ventricularseptum (Figure 6.26) Overriding is presentwhen the junction is connected to bothventricles The degree of override, whichusually coexists with straddling, determinesthe precise atrioventricular connectionpresent So as to adjudicate the connection

in the presence of overriding, the overridingvalve is assigned to the ventricle

connected to its greater part (Figure 6.27).The possible arrangements are muchmore limited when one atrioventricularconnection is absent In this situation, thesolitary valve can either be committed in its

Dominant left ventricle

Hypoplastic right ventricle

Sup.

Inf.

Right Left

Right atrium

Left atrium

Fig 6.25 This section of a heart, cut in four-chamber orientation, shows an imperforate right atrioventricular valve connecting to

a hypoplastic right ventricle The atrioventricular connections remain concordant, even though the right valve (arrow) is imperforate.

entirety to one ventricle, or it can straddle

and override When the valve straddles and

overrides in this setting, then the

atrioventricular connection itself is

uniatrial but biventricular (Figure 6.17)

VENTRICULAR MORPHOLOGY

AND TOPOLOGY

The nature of the atrioventricular

connections is inextricably linked with the

architectural arrangement of the

ventricular mass Biventricular

atrioventricular connections, for example,

cannot be diagnosed without knowledge of

ventricular morphology Double-inlet and

absent connections can all be identified

without mention of ventricular

morphology, although in this setting it is

always necessary to give more information

concerning the arrangement of the

ventricular mass In the case of mixed and

biventricular atrioventricular connections,

it is important to describe the pattern in

which the morphologically right ventricle

is structured relative to the

morphologically left ventricle This feature

can take only one of two topological

arrangements This is because, when the

connections are mixed, the right-sided

atrium, with either a morphologically right

or left appendage, can be connected toeither a morphologically right or amorphologically left ventricle (seeFigure 6.13) When there is rightisomerism, and the right-sided atrium isconnected to a morphologically rightventricle, the ventricular mass typically isseen as in hearts with concordantatrioventricular connections and the usualatrial arrangement In contrast, when there

is right isomerism, and the right-sidedatrium is connected to a morphologicallyleft ventricle, the ventricular mass isusually found in the presence of discordantatrioventricular connections and the usualatrial arrangement

As we have discussed already, these twobasic patterns of ventricular topology canconveniently be described according to theway in which the hands, figurativelyspeaking, can be placed palm downwardsupon the septal surface of the

morphologically right ventricle The otherhand will then fit in the morphologicallyleft ventricle in similar fashion, but it is thearrangement of the morphologically rightventricle that is chosen for the purposes ofdescription (Figure 6.11) In the heartswith biventricular and mixed

atrioventricular connections, it is thisventricular topology that determines thedisposition of the atrioventricular

chambers connect to only one ventricle, themorphology of that ventricle must always

be described This is because the dominantventricle can be of left ventricular, rightventricular, or solitary and indeterminatepattern It is also necessary to describe therelationships of the dominant and

incomplete ventricles

VENTRICULAR RELATIONSHIPS

Ventricular relationships, as opposed toventricular topology, generally should bedescribed as a separate feature of the heart.Where each atrium is connected to its ownventricle, the relationships are almostalways in harmony with both theconnection and topology present Whenthe atrial chambers are in their usualposition with concordant atrioventricularconnections, the relationships described inthe setting of the heart within the chest arealmost always for the morphologically rightventricle to be right-sided, anterior, andinferior to the morphologically leftventricle In mirror-imaged atrialarrangement, with concordantatrioventricular connections, themorphologically right ventricle is almostinvariably left-sided and relatively anterior,

LV RV

LV RV

Fig 6.27 In the presence of an overriding junction, whether it is a straddling tricuspid valve as shown in Figure 6.26 or ventriculoarterial, the overriding junction (black braces) is assigned to the ventricle supporting its greater part In the situation illustrated with the straddling tricuspid valve, the atrioventricular connections are

de fined accordingly There is a spectrum between the illustrated extremes (double- headed arrow) The left-hand panel shows the situation with the junction connected primarily

to the right ventricle (large arrow), the lesser part joining the left ventricle (small arrow) Hence, the atrioventricular connections are deemed to be concordant In the right-hand panel, the larger part of the overriding junction is committed to the left ventricle, so that the connection is deemed to be a double inlet This is the essence of the 50% rule RA,

LA, right and left atriums; RV, LV, right and left ventricles.

but frequently more side-by-side relative to

its neighbour

With the atrial chambers in their usual

arrangement, and discordant atrioventricular

connections, there is almost always the

left-hand pattern of ventricular topology The

usual relationship is for the morphologically

right ventricle to be left-sided (Figure 6.28)

When discordant atrioventricularconnections accompany mirror-imaged atrialarrangement, there is usually right-handtopology (Figure 6.29) The ventricularrelationships are thus similar to those seen inthe normal heart, although the two chambers

tend to be more side-by-side When therelationships are as anticipated, it isunnecessary to describe them Veryoccasionally, the relationships of theventricles are not as anticipated for theconnections present This disharmonybetween connections and relationships

Morph left atrium

morphologically left atrium is right-sided, but connects to a morphologically right ventricle with right-hand topology, the palmar surface of the right hand fitting on the septal surface so that the fingers are in the subaortic outlet and the thumb in the inlet component.

underscores the anomaly known as the

criss-cross heart14 With these hearts, and also

those with superoinferior ventricles,

connections and relationships must be

described separately, using as much detail as

is necessary to achieve unambiguous

categorisation The essence of the criss-cross

heart, and those with superoinferior

ventricles, is that the ventricular

relationships are not as expected for the

atrioventricular connection present Even

more rarely, the ventricular topology may be

disharmonious with the atrioventricular

described

In hearts with a univentricular

atrioventricular connection, it is the

relationship of the incomplete ventricle to

the dominant ventricle that must be

described When the left ventricle is

dominant, the incomplete right ventricle is

always anterosuperior, but can be right- or

left-sided The sidedness of the ventricle

does not affect the basic disposition of the

atrioventricular conduction tissues in these

hearts With a dominant right ventricle, the

incomplete and rudimentary left ventricle,

if present, is always posteroinferior, but

again can be right- or left-sided In this

case, the sidedness of the incomplete

ventricle will affect the disposition of the

atrioventricular conduction tissue

When considering the atrioventricular

junctions, therefore, there are four

different features to take into account

These are, firstly, the way the atrial

myocardium is connected to the ventricular

mass; secondly, the morphology of the

atrioventricular valves guarding the

junctions; thirdly, the ventricular

morphology and topology; and finally, the

ventricular relationships All are ofimportance to the surgeon because theyinfluence the disposition of the

atrioventricular conduction axis

VENTRICULOARTERIAL JUNCTIONS

Analysis of the ventriculoarterialjunctions proceeds as described for theatrioventricular junctions, with themorphology of the connections, thevalvar morphology, and the relationships

of the arterial trunks being differentfacets requiring separate description inmutually exclusive terms It is alsonecessary to take account of infundibularmorphology

Ventriculoarterial connections

There are four discrete ways in which thearterial trunks can take their origin fromthe ventricular mass; namely, inconcordant, discordant, double-outlet, andsingle-outlet fashion Concordant

ventriculoarterial connections exist whenthe arterial trunks arise from

morphologically appropriate ventricles

Discordant connections account for thetrunks being connected with

morphologically inappropriate ventricles

Double-outlet connections exist when bothgreat arteries take origin from the sameventricle, which may be of right, left, orindeterminate morphology A single-outletarrangement is seen when only one arterialtrunk is connected to the heart This may

be a common trunk, directly supplying thesystemic, pulmonary, and coronary

arteries, or it may be an aortic or pulmonarytrunk when the complementary arterialtrunk is atretic, and its connection to aknown ventricle cannot be established(Figure 6.30) Rarely, in the absence ofintrapericardial pulmonary arteries, it may

be more accurate to describe an arterialtrunk as solitary rather than common(Figure 6.30)

Arterial valvar morphology

The morphological arrangement of thearterial valves is limited because they have

no tension apparatus Furthermore, acommon valve can exist only with acommon trunk The different patterns,therefore, involve one or two arterialvalves Usually both valves are perforate,but either or both may override theventricular septum When a valvar orifice isoverriding, the valve is assigned to theventricle supporting its greater part, thusavoiding the need for intermediatecategories The other pattern of valvarmorphology is when one of the arterialvalves is imperforate As with theatrioventricular junctions, an imperforatearterial valve must be distinguished fromabsence of one ventriculoarterial

connection, as both can produce arterialvalvar atresia

Infundibular morphology

Describing the morphology at theventriculoarterial junctions also involvesthe arrangement of the musculature withinthe ventricular outflow tracts This isinfundibular morphology Although theoutlet regions are integral parts of the

trunk

Common arterial trunk

Solitary arterial trunk

Fig 6.30 This cartoon shows the patterns that identify the morphology of the arterial trunks When there is absence of the intrapericardial pulmonary arteries, there is no way of knowing if, had there been an atretic pulmonary trunk, it would have originated from the base of the heart or from the aorta This pattern, therefore, is best described as a solitary arterial trunk.

ventricular mass, it is traditional to

consider them in concert with the great

arteries The two outflow tracts together

make a complete cone of musculature,

which has parietal and septal components,along with a component adjacent to theatrioventricular junction (Figure 6.31)

The parietal components make up the

anterior free wall of the outflow tracts Theseptal component is the outlet, or

infundibular, septum This has a body,with septal and parietal insertions, best

of the ventricular out flow tracts The hinges of both arterial valves are completely surrounded by out flow musculature SMT, septomarginal trabeculation.

Ventriculoinfundibular fold

Pulmonary valve Outlet septum

Fig 6.32 The image shows the out flow tracts in a heart with tetralogy of Fallot, viewed from the apex of the right ventricle, with the aortic valve (star) overriding the crest of the muscular ventricular septum, which is reinforced by the septomarginal trabeculation, or septal band (white Y) The septal and parietal attachments of the muscular outlet septum are well seen.

seen in the setting of tetralogy of Fallot

(Figure 6.32) The component adjacent to

the atrioventricular junction is the

ventriculoinfundibular fold It separates

the leaflets of arterial from atrioventricular

valves (Figure 6.33) It is the inner heart

give arterial-atrioventricular valvar fibrouscontinuity (Figure 6.34)

The infundibular structures never

They should be distinguished fromanother structure, namely theseptomarginal trabeculation, or septal

band This latter structure is part of theventricular septum, reinforcing its rightventricular aspect It has a body thatcontinues apically as the moderator band,and two limbs (Figure 6.35) Theanterocephalad limb, in the normalheart, extends to the pulmonary valve,

Ventriculoinfundibular fold

Aortic

valve

Outlet septum

Aortic

valve

Outlet septum

Pulmonary valve

Post. Fig 6.34 This heart has the ventriculoarterial connection of a

double-outlet right ventricle, but with fibrous continuity between the lea flets of the aortic and tricuspid valves (red double-headed arrow).

overlying the outlet septum The

posterocaudal limb runs beneath the

interventricular membranous septum

This posterocaudal limb usually overlies

the branching part of the atrioventricular

bundle, with the right bundle branch

passing down to the apex of the right

ventricle within the body of the

trabeculation

Although each outflow tract is

potentially a complete muscular structure,

in most hearts it is only the outflow tract of

the right ventricle that is a complete

muscular cone This is because, within the

left ventricle, part of the

ventriculoinfundibular fold is usually

attenuated to permit fibrous continuity

between the leaflets of the arterial and

atrioventricular valves In the normal

heart, therefore, there is a muscular

subpulmonary infundibulum in the right

ventricle, and fibrous valvar continuity in

the roof of the left ventricle In

congenitally malformed hearts, three

other patterns may be found These are,

firstly, a muscular subaortic infundibulum

with pulmonary-atrioventricular

continuity; secondly, a bilaterally

muscular infundibulum; and thirdly,

bilateral deficiency of the infundibulums

In the presence of a common arterialtrunk, there may be a complete muscularsubtruncal infundibulum, but more oftenthere is truncal-atrioventricular valvarcontinuity

Arterial valvar and truncal relationships

The final feature of consideration at theventriculoarterial junctions is therelationship of the arterial valves andarterial trunks Valvar relationships areindependent of both ventriculoarterialconnections and infundibular

morphology Of the many methods ofdescription, our preference is to describethe aortic relative to the pulmonary valve

as viewed from below in right–left,anteroposterior and, when necessary,superoinferior coordinates This can bedone as precisely as required In ourexperience, eight coordinates combininglateral and anterior to posterior positionssuffice (Figure 6.36) When describing therelationship of the arterial trunks, it issufficient to account for trunks that spiralaround each other as they ascend, and todistinguish them from trunks that ascend

in parallel fashion18

POSITION OF THE HEART

The system discussed in this chapterestablishes the cardiac template

Irrespective of the internal architecture, it

is well known that the heart itself canoccupy many and varied positions (seeChapter 10), particularly when thereare complex intracardiac malformations

To describe the position of the heart inunambiguous fashion, account should

be taken separately of its site withinthe thorax, and the orientation of itsapex We describe the heart as being inthe left or right side of the chest, or inthe midline Apical orientation is described

as being to the left, to the middle, or tothe right

CATALOGUE OF MALFORMATIONS

Having described the template of the heart,and its position, finally it is necessary tocatalogue all intracardiac malformations Inmost cases, it is these lesions which willrequire surgical attention Any lesion,nonetheless, cannot be presumed to be theonly lesion present until the rest of the

Tricuspid valve

Pulmonary valve Supraventricular crest

of the trabeculation The star shows the moderator band, one of the series of septoparietal trabeculations that take origin from the anterior surface of the marginal trabeculation.

heart has been established as normal It is

these associated lesions that will be

emphasised in subsequent chapters, taking

particular note, as before, of the features of

surgical significance

References cited

1 Shinebourne EA, Macartney FJ, Anderson

RH Sequential chamber localization:

the logical approach to diagnosis in

congenital heart disease Br Heart J 1976; 38:

327–340

2 Anderson RH, Wilcox BR Understanding

cardiac anatomy: the prerequisite for optimal

cardiac surgery Ann Thorac Surg 1995; 59:

1366–1375

3 Van Praagh R The segmental approach to

diagnosis in congenital heart disease In:

Bergsma D (ed) Birth defects original article

series, Vol VIII, No 5 The Fourth

Conference on the Clinical Delineation of Birth

Defects Part XV The Cardiovascular System

The National Foundation March of Dimes

Baltimore, MD: Williams and Wilkins, 1972;

pp 4–23

4 Anderson RH, Ho SY Continuing Medical

Education Sequential segmental analysis –

description and categorization for the

millennium Cardiol Young 1997; 7:

98–116

5 Uemura H, Ho SY, Devine WA, Kilpatrick

LL, Anderson RH Atrial appendages and

venoatrial connections in hearts withpatients with visceral heterotaxy AnnThorac Surg 1995; 60: 561–569

6 Van Mierop LHS, Gessner IH, Schiebler

GL Asplenia and polysplenia syndromes

In: Bergsma D (ed) Birth Defects: OriginalArticle Series, Vol VIII, No 5 The FourthConference on the Clinical Delineation ofBirth Defects Part XV The CardiovascularSystem The National Foundation March ofDimes Baltimore, MD: Williams andWilkins, 1972: 36–44

7 Ivemark BI Implications of agenesis ofthe spleen on the pathogenesis ofconotruncus anomalies in childhood Ananalysis of the heart; malformations inthe splenic agenesis syndrome, with 14new cases Acta Paediatr Suppl 1955; 44:

7–110

8 Macartney FJ, Zuberbuhler JR, Anderson

RH Morphological considerationspertaining to recognition of atrialisomerism Consequences for sequentialchamber localisation Br Heart J 1980; 44:

657–667

9 Sharma S, Devine W, Anderson RH,Zuberbuhler JR The determination ofatrial arrangement by examination ofappendage morphology in 1842 heartspecimens Br Heart J 1988; 60: 227–231

10 Huhta JC, Smallhorn JF, Macartney FJ

Two dimensional echocardiographicdiagnosis of situs Br Heart J 1982; 48:

97–108

11 Smith A, Ho SY, Anderson RH, et al Thediverse cardiac morphology seen in heartswith isomerism of the atrial appendageswith reference to the disposition of thespecialized conduction system CardiolYoung 2006; 16: 437–454

12 Ho SY, Seo J-W, Brown NA, et al

Morphology of the sinus node in humanand mouse hearts with isomerism of theatrial appendages Br Heart J 1995; 74:437–442

13 Jacobs ML, Anderson RH Nomenclature

of the functionally univentricular heart.Cardiol Young 2006; 16(Suppl 1): 3–8

14 Anderson RH Criss-cross hearts revisited.Pediatr Cardiol 1982; 3: 305–313

15 Anderson RH, Smith A, Wilkinson JL.Disharmony between atrioventricularconnections and segmental combinations –unusual variants of “criss-cross” hearts

J Am Coll Cardiol 1987; 10: 1274–1277

16 Anderson RH, Becker AE, Van MieropLHS What should we call the “crista”? BrHeart J 1977; 39: 856–859

17 Hosseinpour A-R, Jones TJ, Barron DJ,Brawn WJ, Anderson RH An appreciation

of the structural variability in thecomponents of the ventricular outlets incongenitally malformed hearts Eur JCardiothorac Surg 2007; 31: 888–893

18 Cavalle-Garrido T, Bernasconi A, Perrin

D, Anderson RH Hearts with concordantventriculoarterial connections but parallelarterial trunks Heart 2007; 93: 100–106

posterior

left posterior

left side-by-side

left anterior

anterior right

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 better

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.

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

and the much more rare vestibulardefects found within the muscular

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

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

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

Sup.

Artery to sinus node

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

involves 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

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

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 and

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

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 atrial

atrioventricular 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.