Andersons pediatric cardiology 80
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conductthesinusimpulsetowardtheatrioventricularnode.Thenode
(star),islocatedattheapexofthetriangleofKoch,withtheboundariesof
thetriangleshownbythedashedlines.
Thespecializedcardiomyocytesofthenodeanditstransitionalzonesare
situatedwithintheatrialcomponentoftheatrioventricularmuscularsandwich,
withtheatrialmyocardiumapproachingthenodefromallsides.Thefloorofthe
coronarysinusinthisarearoofstheinferiorpyramidalspace.Thisspaceis
paraseptal,situatedbetweentheatrialmusculatureandthecrestofthemuscular
ventricularseptum(seeFig.2.10).Thearterytotheatrioventricularnodecourses
anteriorlythroughthisspaceintothetriangleofKoch,havingtakenoriginfrom
thedominantcoronaryartery(seelater).FromtheapexofthetriangleofKoch,
itisbutashortdistancefortheatrioventricularconductionaxistopenetratethe
centralfibrousbodyasthebundleofHis,betterdescribedasthepenetrating
atrioventricularbundle.Havingpenetratedthroughthemembranousseptum,the
bundlereachesthecrestofthemuscularseptumbeneaththerightcoronary
leafletoftheaorticvalve,whereitbranches.Theleftbundlebranchthenruns
downthesmoothleftsurfaceoftheseptumbeforefanningoutintrifascicular
fashiontowardtheventricularapex(Fig.2.30).
FIG.2.30 DrawingtakenfromtheoriginalmonographofTawarashowing
thelocationoftheleftbundlebranchrelativetothelandmarksoftheaortic
rootandtheleftventricle.
Therightbundlebranchpassesbackthroughthemuscularventricularseptum
toemergeintherightventriclebeneaththemedialpapillarymuscle.Itthen
extendsasathininsulatedcordinthesubstanceoftheseptomarginal
trabeculationbeforeramifyingattheventricularapex.Aprominentbranch
usuallypassestotheparietalwallthroughthemoderatorband.
BloodSupplytotheHeart
CoronaryArteries
Thecoronaryarteriesarethefirstbranchesoftheaorta,usuallytakingtheir
originwithintheaorticsinusesofValsalva.Asalreadydiscussed,therearetwo
majorcoronaryarteriesandthreeaorticsinuses.Almostwithoutexception,the
arteriesarisefromoneorotherofthesinusesclosesttothepulmonarytrunk,
thesebeingtheadjacentorfacingsinuses.Inmostnormalindividuals,oneartery
arisesfromeachofthesefacingsinuses,permittingthemtobenamedtheright
coronaryandleftcoronaryaorticsinuses.Itisuseful,nonetheless,tohavea
conventionfornamingthesinusesthatworksirrespectiveoftheoriginofthe
coronaryarteriesandirrespectiveoftherelationshipoftheaortatothe
pulmonarytrunk.Thisisprovidedbyobservingtheaorticsinusesfromthepoint
ofthenonadjacentsinusandlookingtowardthepulmonarytrunk(Fig.2.31).
FIG.2.31 Essenceoftheso-calledLeidenconventionfornamingthe
coronaryarteries.Theobserverstandsinthenonadjacentsinusandlooks
towardsthepulmonarytrunk.Thesinustohisorherrightsideisthen
termedsinus1,withthesinustotheleftsidebeingsinus2.Inthenormal
heart,asshown,sinus1givesrisetotherightcoronaryartery,withsinus2
supportingthemainstemoftheleftcoronaryartery.
