Andersons pediatric cardiology 75
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FIG.2.19 Whenconsideredasextendingfromtheatrioventriculartothe
ventriculoarterialjunctions(dashedline),theleftventriclepossessesinlet,
apicaltrabecular,andoutletcomponents.Theinletcomponentsurrounds
andsupportstheleafletsofthemitralvalve.
Thecomponentsofthevalvearebestdistinguishedintheclosedratherthan
openposition.Whenviewedwiththeleafletsadjacenttooneanother,their
solitarylineofappositionisreadilyapparent(seeFig.2.15).Intermsofvalvar
function,thiszoneofappositionrepresentsthecommissurebetweentheleaflets.
Almostalways,however,thevalveisillustratedinopenposition.Theendsof
thezoneofappositionarethereforeusuallyinterpretedasthepaired
commissures.Themural,orposterior,leafletisalengthy,albeitshallow,
structure.Itguardstwo-thirdsoftheoverallvalvarcircumference,withseveral
slitsalongitslength,whichpermitittofitsnuglyagainsttheaorticoranterior
leaflet.11Themajorfeatureofthisaorticleafletisitsfibrouscontinuityonits
ventricularaspectwithpartsoftheleftcoronaryandnonadjacentleafletsofthe
aorticvalve,henceourpreferredtitleoftheaorticleaflet.Itismuchdeeperthan
themuralleaflet,butguardsonlyone-thirdofthevalvarcircumference.The
tendinouscordsfromtheleafletsinserttothepairedpapillarymuscles,which
areseatedadjacenttooneanotherontheparietalwalloftheventricle.Theyare
locatedsuperoposteriorly,orsuperolaterally,andinferoanteriorly,or
inferomedially(Fig.2.20),althoughareusuallydescribedasbeinganterolateral
andposteromedial.Thelatterdescriptionsholdgoodonlywhentheheartis
removedfromthebodyandpositionedonitsapex.
FIG.2.20 Leftventriclephotographedfromtheleftside,withitsparietal
wallremoved.Thedissectionshowshowthepapillarymusclessupporting
theleafletsofthemitralvalvearepositionedsuperolaterallyand
inferomedially.Itisamistaketodescribethemasbeinganterolateraland
posteroseptal.Thelatterdesignationsreflectdescriptionoftheheartin
“valentine”fashion.
Complexsystemshavebeenproposedtodescribethetendinouscordsthat
supporttheleafletsoftheatrioventricularvalves.Suchcategorizationisnotvery
helpful.Inthenormalheart,cordsariseuniformlyalongthefreeleadingedgeof
allthevalvarleaflets,andextendtoinsertintothesupportingpapillarymuscles.
Eachpapillarymusclesupportstheadjacentpartsoftwoleaflets.Thecords
providinguniformsupporttothefreeedgesoftheleafletsarethenreinforcedby
theprominentstrutcordsfoundontheventricularaspectoftheaorticleaflet,and
bybasalcordsthatrunfromtheundersurfaceofthemuralleaflettoinsert
directlyintothemyocardium.Unlikethetricuspidvalve,themitralvalvehasno
cordsinsertingdirectlyintotheventricularseptum.Instead,anextensiverecess
interposesinferiorlybetweentheaorticleafletofthevalveandthesmoothseptal
surfaceoftheleftventricle(Fig.2.21).
FIG.2.21 Heartsectionedacrosstheshortaxisoftheleftventricleand
photographedfromtheapextoshowtheinferiorextensionoftheleft
ventricularoutflowtract,whichinterposesbetweenthemitralvalveandthe
inferiorpartoftheventricularseptum(arrow).
Theapicalcomponentoftheleftventricleextendsbeyondthepapillary
musclesofthemitralvalve,reachingtotherelativelythinapicalpoint.The
trabeculationsthemselvesaresignificantlyfinerthanthoseoftherightventricle,
andcrisscrossincharacteristicfashion(seeFig.2.19).Strandsoftencrossthe
cavityoftheventricle,particularlyfromthepapillarymuscles,asso-called
“telegraphwires,”orfalsetendons.Theyareofnofunctionalsignificance.The
septalsurfaceissmooth,withnoevidenceofanystructurecomparabletothe
septomarginaltrabeculationoftherightventricle.Theleftbranchofthe
atrioventricularconductionaxisdescendsfromthecrestofthemuscular
ventricularseptumandfansoutinthisarea.Theoutletcomponentis
significantlyabbreviatedincomparisontoitsrightventricularcounterpart,with
theleafletsoftheaorticvalvesupportedbymusculatureonlyarounditsanterior
quadrants(Fig.2.22).
