Andersons pediatric cardiology 1078

arterialduct.Therightdorsalaortaisstillpresentbutisnowsignificantly
smallerthattheleftcomponent,whichwillbecomethedescendingaortaas
therightsidecontinuestoregress.(CourtesyDr.SimonBamforth,
NewcastleUniversity,UnitedKingdom.)

Whenthedevelopingdistalpartoftheoutflowtractisdividedtoformthe
intrapericardialcomponentsoftheaortaandpulmonarytrunk,thesixtharches,
originatingfromthecaudalpartoftheaorticsac,areplacedincontinuitywith
thepulmonarychannel.Asignificanteventintheappropriateconnectionofthe
pulmonaryarterieswiththeintrapericardialpulmonarytrunkistheobliteration
anddisappearanceoftherightsixtharch.Ontheleftside,thearteryofthesixth
archpersistsasthearterialduct,withthepulmonaryarteriesleftincontinuity
withthechannelfromthepulmonarytrunktotheleftsixtharch(seeFig.41.2,
right).
Alldevelopmentalanomaliesoftheaorticarch,includingthoseassociated
withanabnormallysituatedduct,arewellexplainedonthebasisofthe
hypotheticaldoublearchsystemdevisedbyEdwards,18irrespectiveofwhether
theductitselfispatentorrepresentedbythearterialligament.Thevarious
possibilitiesarediscussedinChapter47,includingthoseinwhichthereis
persistenceofbothsixtharches,producingbilateralarterialducts.Such
circumstancesarerareandarealwaysassociatedwithintracardiacanomalies.
Typically,bilaterallypersistentlypatentarterialductssupplydiscontinuous
pulmonaryarteriesinthesettingoftetralogyofFallotwithpulmonaryatresia,
albeitthatsuchbilateralductscanalsobefoundinassociationwithisolationofa
subclavianartery.20
However,thearterialductdoesnotalwayspersistononeorotherside.Its
absencewasfirstdescribedasapostmortemfindingin1671,beingseenina
grosslymalformedinfantwithanextrathoracicheartandtetralogyofFallot
describedbyNicolasSteno.21Absenceoftheductisatypicalfindinginthe
syndromeoftetralogyofFallotwithso-calledabsentpulmonaryvalveand
dilatedpulmonaryarteries.22Itwasthoughtthattheabsenceoftheduct,and

henceabsenceofany“overflow,”explainedthedilatedpulmonaryarteries,but
thepulmonaryarteriescanbedilatedevenwhentheductispresentandpatent.
Theductisalsoabsentinthemajorityofpatientshavingacommonarterial
trunk.Absenceofsignificantflowthroughtheductinthepresenceofalarger
aortopulmonaryconnectionpermitstheducttodisappearearlyinfetallife.
However,inmorecomplexvarietiesofcommonarterialtrunk,suchasthose
withso-calledabsenceofonepulmonaryarteryorthosepatientswithan


associatedinterruptionoratresiaoftheaorticarch,patencyoftheductis
essentialtomaintainboththesystemicandpulmonarycirculations(seeChapters
43,45,69).
Anumberofteratogensareknowntoinfluencethedevelopmentoftheduct,
includingrubella,alcohol,amphetamines,theanticonvulsanthydantoin,and
topiramate,23withtheductbeingmostsensitivefrom18to60daysof
gestation.24Absenceoftheducthasbeeninducedexperimentallyinchick
embryosbytheadministrationofagonistsofβ-adrenoceptors,leadingtothe
suggestionthattheteratogenesisismediatedbycyclicadenosine
monophosphate.25


Anatomy
ArterialDuctandItsNormalClosure
Patencyismaintainedbytherelativelylowfetaloxygentension26and
cyclooxygenase-mediatedproductsofarachidonicacidmetabolism,primarily
prostaglandinandprostacyclin,27whoselevelsarehighbecauseofproductionby
theplacentaanddecreasedmetabolisminthefetallungs.Producedbothlocally,
inductaltissue,andcirculating,thesemediatorscausevasodilationthrough
interactionwithprostanoidreceptors.
Inthefetus,andintheneonatepriortoitsclosure,thearterialductisashort

andwidevesselofvariablelength.Itconnectsthepulmonaryarteriestothe
lessercurveofthearchoftheaorta,terminatingatthepointoftransitionfrom
theisthmustothedescendingaorta,distaltotheoriginoftheleftsubclavian
artery(Fig.41.3).