Andersons pediatric cardiology 81
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Onefacingsinusisthentotherightsideoftheobserver.Thisisthesinusthat,
inthenormalheart,usuallygivesrisetotherightcoronaryartery.Theother
sinusistotheleftsideoftheobserverandusuallygivesrisetothemainstemof
theleftcoronaryartery.Byconvention,thefacingsinustotherighthandhas
becomeknownas“sinus1,”whiletheleft-facingsinusisknownas“sinus2.”
Thisconvention,knownastheLeidenConvention,18holdsgoodfornamingthe
aorticsinusesandtheoriginofthecoronaryarteries,evenwhenthearterial
trunksareabnormallydisposedincongenitallymalformedhearts.Inthenormal
heart,thecoronaryarteriesusuallyarisebeneaththesinutubularjunctions,but
canarisesignificantdistancesabovethejunction.Oftenthearteriesare
eccentricallypositionedwithinthesinus.Additionalarteriescanalsoarise
directlyfromthesinus,mostfrequentlyfromtherightsinus,whichcangiverise
separatelytotheinfundibularartery,orthearterytothesinusnode.
Havingtakenoriginfromtherightcoronaryaorticsinus,therightcoronary
arterypassesdirectlyintotherightatrioventriculargroove,lyinginthecurveof
theventriculoinfundibularfoldabovethesupraventricularcrest.Fromthisinitial
course,thearterygivesrisetoinfundibularandatrialbranchesbeforeturning
aroundtheacutemarginoftheventricularmass,whereitgivesrisetotheacute
marginalartery.Themainstemoftherightcoronaryarterythencontinuesalong
thediaphragmaticsurfaceoftherightatrioventricularjunction,givingoff
additionalatrialandventricularbranchesuntil,inaboutnine-tenthsof
individuals,itgivesrisetotheinferiorinterventricularartery.Therightcoronary
arteryusuallycontinuesbeyondthecruxtosupplyavariableportionofthe
diaphragmaticsurfaceoftheleftventricle.Thisarrangementiscalledright
coronaryarterialdominance(Fig.2.32).
FIG.2.32 Multidetector-rowcomputedtomographicdatasetfromanadult
showingthecourseandbranchesofthedominantrightcoronaryarteryas
viewedinattitudinallyappropriateorientationrelativetotheorificeofthe
tricuspidvalve,withthehingesofthevalvarleafletsreconstructedinblue.
Themainstemoftheleftcoronaryartery,havingtakenoriginfromthelefthandfacingsinus,passesintotheleftatrioventriculargroovebeneaththeorifice
oftheleftatrialappendage.Itbranchesintotheanteriorinterventricularand
circumflexarteries(Fig.2.33).
FIG.2.33 Multidetector-rowcomputedtomographicdatasetobtainedfrom
anadultshowinghowthemainstemoftheleftcoronaryarterybranchesto
giverisetotheanteriorinterventricularandcircumflexarteries.Theimage
isshownfromtheleftside.
Insomeindividualsathirdartery,theintermediateartery,suppliesdirectlythe
obtusemarginalsurfaceoftheleftventricle.Itismuchrarerforadditional
arteriestoarisewithintheleft-facingsinus,butsometimesthetwomajorarteries
haveindependentorigins.Moreusually,albeitstillrarely,thesinusnodalartery
cantakeaseparateoriginfromthissinus.Theanteriorinterventricularartery,
alsoknownastheleftanteriordescendingartery,occupiestheanterior
interventriculargroove,givingdiagonalbranchestotheadjacentsurfacesofthe
rightandleftventriclesalongwiththeperforatingarteries,whichpass
perpendicularlyintotheventricularseptum.Thefirstseptalperforatingbranchis
particularlysignificant,beinglocatedimmediatelyposteriortothefreestanding
sleeveofsubpulmonaryinfundibularmusculature(seeFig.2.33).
Theextentofthecircumflexarterydependsonwhethertherightcoronary
arteryisdominant.Whentherightcoronaryarteryisdominant,thecircumflex
arteryoftenterminatesabruptlyafterithasgivenrisetotheobtusemarginal
branchorbranches.Sometimes,inperhapsone-tenthofindividuals,the
circumflexarteryisdominant.Itthencontinuesbeyondthecruxtosupplypart
