Andersons pediatric cardiology 77
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commissures,ratherthanmerelytheirperipheralattachments.
Thepulmonarytrunkrunsonlyashortcoursebeforebifurcatingintotheright
andleftpulmonaryarteries,whichthenextendtotherespectivelunghilums.The
aortacontinuesthroughitsascendingcomponentabovethesinutubularjunction,
havingintrapericardialandextrapericardialcomponents,andcontinuing
extrapericardiallyasthetransversearch,whichgivesrisetothebrachiocephalic,
leftcommoncarotid,andleftsubclavianarteries(Fig.2.25).
FIG.2.25 Dissectionshowingthecourseoftheextrapericardialarterial
trunks.Theaorticarchgivesrisetothebrachiocephalic(BCA),left
commoncarotid(LCA),andleftsubclavian(LSCA)arteries.Theisthmus
(arrow)isthesegmentofthearchbetweentheoriginoftheleftsubclavian
arteryandtheunionofthearterialductwiththedescendingaorta.
Thezonebetweentheoriginsoftheleftsubclavianarteryandthearterial
ligament,orthejunctionwiththearterialductpriortoclosureofthisstructure,is
knownastheisthmus.Beyondthispoint,thearchbecomesthedescending
thoracicaorta.Thearterialduct,orligamentafteritsclosure,runsfromthe
undersideofthearchtotheuppersurfaceoftheleftpulmonaryartery.Theleft
recurrentlaryngealnerveturnsbackintothemediastinumaroundtheductorits
ligamentousremnant.
ValvesoftheHeart
Wehavealreadydiscussedsomeofthemorphologicfeaturesofthe
atrioventricularandarterialvalves.Thesearesuchsignificantstructuresin
normalandabnormalfunctionoftheheartthatitisworthwhilereviewingagain
thecomponentpartsofeachsetofvalves,andthetermsweusetodescribe
them.
AtrioventricularValves
Theatrioventricularvalvesguardtheinletstotheventricularmass.Assuch,they
mustwithstandthefullforceofventricularcontractionwhenintheirclosed
position.Forthisreason,itisbettertoexaminethevalvesintheirclosed
position,takingcare,ofcourse,alsototakenoteoftheirfeatureswhenopen.
Consideredoverall,thevalvarcomplexismadeupoftheannulus,theleaflets,
thetensionapparatus,andthepapillarymuscles.Theannulusisamuchfirmer
structureinthemitralthaninthetricuspidvalve.Eveninthemitralvalve,itis
unusualtofindacompletecollagenousstructuresupportingtheentire
circumferenceoftheleaflets.Inthetricuspidvalve,itistheruleforthevalvar
leafletstobesuspendedfromtheendocardialsurfaceoftheatrioventricular
junction,withthefibrofattytissueoftheatrioventriculargrooveservingto
insulateelectricallytheatrialfromtheventricularmusculature.Thezonesof
appositionarethekeystructuresindefiningtheextentofthevalvarleaflets.
Focusingonthezonesofappositionproducesasystemthatworksforboth
arterialandatrioventricularvalves.Itisasusefulforthevalvesseenin
congenitallymalformedasinotherwisenormalhearts.Thetendinouscordscan
bedividedintothoseoriginatingfromthefreeedgesoftheleafletsandthose
comingfromtheventricularaspects,thelatterbeingdividedintostrutandbasal
cords.Inthenormalheart,theentireleadingedgesoftheleafletsareuniformly
supportedbytendinouscords,withtheedgesofadjacentleafletsatthe
peripheralendsofthezonesofappositionbeingtetheredtothesamepapillary
muscle.Attheendsofthezonesofapposition,thereisacurtainofvalvartissue
separatingthevalvarorificefromtheannulus(Fig.2.26).
FIG.2.26 Mitralvalvephotographedfromabove,withthevalvarleafletsin
closedposition.Notethatthesolitaryzoneofappositionbetweenthe
leafletsdoesnotextendtothevalvarannulus(stars).Instead,thereis
leaflettissueextendingtotheannulus(brackets).Notealsotheslitsinthe
muralleafletthatpermitthetwoleafletstoclosesnuglytogether.
Intermsofthepapillarymusclessupportingthetendinouscords,thetricuspid
valveissupportedbyasmallmedialmusclethatarisesfromtheposteriorlimb
oftheseptomarginaltrabeculation,aprominentanteriormuscle;andaninferior
muscle,thelatteroftenduplicatedortriplicated.Theseptalleafletofthevalveis
characterizedbyitsmultipledirectcordalattachmentstotheseptum.Themitral
valve,incontrast,haspairedpapillarymuscleslocatedinferomediallyand
superolaterallywithintheventricularcavity,albeittheheadsofbothmusclesare
frequentlymultiple.
ArterialValves
Thearterialvalves,supportedwithinthearterialroots,aremadeupofthe
leaflets,thesinuses,andtheinterleaflettriangles,withtherootsbeinglimited
distallybythesinutubularjunctions.Thepresenceofan“annulus”withinthe
arterialvalvarcomplexesremainscontroversial.13Theentirevalvarcomplexis
ring-likeintermsofbeingshapedtofitonthefinger.Unliketheatrioventricular
valves,however,thereisnocord-likecollagenouscirclewithinthevalvar
