Andersons pediatric cardiology 1177
Bạn đang xem bản rút gọn của tài liệu. Xem và tải ngay bản đầy đủ của tài liệu tại đây (61.2 KB, 3 trang )
inthesettingofbicuspidaorticvalvediseaseissimilartothatofotherfamilial
aortopathies,suchasMarfansyndrome,withfragmentationofelastin,lossof
smoothmusclescells,andincreaseincollagen.41,42However,thegeneticbasis
forthisaorticwallpathology,anditslinktoaorticvalvemorphogenesisinthe
settingofbicuspidaorticvalvedisease,isstillnotwellunderstood.
Pathophysiology
Valvaraorticstenosisphysiologicallyresultsinincreasedwallstress,or
afterload,ontheleftventricle.Theleftventriclemustgenerateasystolic
pressuregreaterthanaorticpressuretoovercomethepressureloadimposedby
aorticstenosisduringejection.Chronicincreaseinleftventricularafterloadfrom
hemodynamicallysignificantaorticstenosis,inturn,triggerscompensatory
structuralchangescharacterizedbyconcentricremodeling(reductionofthe
chamberdiameter/wallthicknessratio)andhypertrophy(increaseinmass)ofthe
leftventricle.43–45InaccordancewithLaplace'slaw,concentricremodelingand
hypertrophyoftheleftventriclereducewallstressandmaintaincardiacoutput
despiteelevationsinleftventricularsystolicpressure.
Onacellularlevel,leftventricularhypertrophyresultsfromanincreasein
proteinsynthesisandinthesizeandorganizationofsarcomereswithin
individualmyocytes.46However,recruitmentofcontractileelementsoccursin
parallelwithfibroblastactivationandleadstopathologicincreasesincardiac
extracellularmatrixandfibrosis.47Progressivehypertrophyalsoresultsinan
imbalancebetweencoronarysupplyandmyocardialdemands,resultingin
microvascularandsubendocardialischemiathatfurthercontributetomyocardial
fibrosisandmyocardialdysfunction.48Subendocardialischemiamaybe
exacerbatedbyashortdiastoliccoronaryfillingperiodthatresultsfrom
prolongedsystolicejectionacrossastenoticaorticvalve,aswellasfromthe
tachycardiaduringperiodsofexercise.49Thesepathologicfibroticchangesof
theleftventricularmyocardiumcanbedetectedbycardiacmagneticresonance
imaginginpatientswithcongenitalaorticvalvestenosiswithevidenceof
variabledegreesoflategadoliniumenhancement.50
Overtime,ifthedegreeofaorticstenosisissevereandnotrelievedby
intervention,thesecompensatorymechanismsmayfail.Thewallthicknessdoes
notincreaseinproportiontotheleftventricularsystolicpressure.Subsequently,
wallstressandafterloadincreases,resultinginprogressiveleftventricular
chamberdilatationwithconcomitantincreaseinend-diastolicvolumeand
pressureandeventuallydecreasedcontractility.51
ClinicalFeatures
Newborn/Infancy
Thenewbornoryounginfantpresentsinoneofthreeways.Newbornswith
criticalaorticstenosispresentwithsymptomsconsistentwithcardiogenicshock
followingclosureofthearterialduct.Thesecondmodeofpresentationisseenin
neonatesoryounginfantswithleft-sidedcardiacfailurebutwithoutdependency
onthearterialducttomaintainsystemicperfusion.Inthethirdsituation,patients
maybereferredforevaluationofasystolicmurmurbutareotherwise
asymptomaticwithoutsignsofcongestivecardiacfailure.
OlderChild
Olderchildren,outsideoftheinfancyperiod,aretypicallyasymptomatic.These
patientstypicallypresentwhenamurmurisdetectedduringroutineevaluation.
Patientswithmoderateorsevereaorticstenosismaypresentwithcomplaints
suchasfatigue,exertionaldyspnea,chestpain,andsyncope.Thesesymptoms
resultfromtheinabilityoftheleftventricletoincreaseitsoutputappropriately
withexercise.Suspectedaorticstenosiswiththeseassociatedsymptoms
warrantsurgentevaluation.
PhysicalExamination
Newborn/Infancy
Newbornswhopresentwithcriticalaorticstenosisaredependentonthepatency
ofthearterialducttosustainsystemiccardiacoutput.Theydemonstratefeatures
consistentwithcardiovascularshockafterspontaneousclosureofthearterial
ductwithin1weekofage.Theseneonatesaretachypneicandtachycardic.The
physicalexaminationrevealshepatomegaly,rightventricularenlargement,and
diffuselyweakpulses.Asystolicejectionmurmurmaynotbeheardifthereis
severeleftventricularsystolicdysfunction.Agalloprhythmmaybenoted.An
ejectionclickisuncommon.Iftheyhaverightventricularhypertensionand
failure,theymayhaveasystolicmurmuroftricuspidvalvarregurgitation.
Infantswhopresentwithoutductaldependencycandemonstratephysical
examfindingsconsistentwithleft-sidedcardiacfailure.Inthissetting,the
patientsaretachypneicandhavepulsesthatareusuallylowvolume.
Hepatomegalymaybepresent.Auscultatoryfindingsmayrevealanejection
clickandatypicalharshcrescendo-decrescendosystolicejectionmurmurheard
attherightuppersternalborder.Anassociatedthrillmaybefeltinthe
suprasternalnotcheveninmildvalvarstenosis,butaparasternalthrillis
typicallyfeltonlyinsevereobstruction.
OlderChild
Physicalexamfindingsinanolderchildcanbesimilartotheasymptomatic
infantwithanejectionclickandharshcrescendo-decrescendosystolicejection
murmur.Congestivecardiacfailureisrarebecause,withtime,patientsareable
tostabilizetheirleftventricularwallstressbyincreasingmassandthus
preservingleftventricularsystolicfunction.
Thephysicalexaminationdependsontheseverityofthestenosis.The
peripheralpulsesareusuallynormalinthosepatientswithmild,andeven
moderate,stenosis.Thosewithsignificantstenosishavelowvolumeorplateau
pulses.Insomepatientstherightcarotidandbrachialpulseshavearapid
upstrokewhencomparedwiththeleft-sidedpulses.Thisisduetotransmission
oftheimpulsetowardthebrachiocephalicartery.Asystolicthrillmaybefeltin
therightinfraclavicularregion,overthecarotidarteryorsuprasternalnotch.
Thefirstheartsoundisnormalandisfrequentlyfollowedbyahigh-pitched
ejectionclick,whichisbestheardatthelowerleftsternalborderandmaybe
maximalattheapex.Thislatterfindingdifferentiatesitfromaclickproducedby
thepulmonaryvalve,whichisoftenlowerpitched,heardalongtheupperleft
sternalborderwithrespiratoryvariationinintensity(louderduringexpiration).
Clinicalcardiomegalyisuncommonintheabsenceofassociatedaortic
regurgitation.
Investigations
Electrocardiogram
Theelectrocardiogramisusuallynormalormaydemonstrateevidenceofleft
ventricularhypertrophy,dependingontheseverityofthestenosis.52These
changesincludeincreasedvoltagesintheleftprecordialleads,withorwithout
strainpatterncharacterizedbyTwaveinversionsandassociatedSTsegment
