Andersons pediatric cardiology 1119

HemodynamicsandPhysiology
Theconsequenceofobstructionattherightventricularoutflownecessitatesan
increaseinrightventricularpressuretoforcebloodthroughthestenosedvalve.
Therightventricularpressurethatdevelopsisusuallyproportionaltothedegree
ofobstructionpresent.Ifstenosisdevelopsearlyinfetalorneonatallife,right
ventricularmassincreasesbyventricularmyocytichyperplasia,andthereisalso
hyperplasiaofthesupportingapparatus,suchasthecapillariessupplyingblood
tothemyocytes,sothatthedensityofcapillariesremainsnormal.Inthiswayin
neonates,thecapacityfortherightventricletogeneratehighpressuresand
toleratemoderatestenosisishigh.Wherepulmonarystenosisdevelopslaterin
life,aftertheneonatalperiod,thecapacityforhyperplasiaislost,andany
increasesinventricularbulkareduetoahypertrophicresponse.Thereisa
compensatoryincreaseincapillarysupply,butthisdoesnotcompensateforthe
increaseinventricularmyocardialmass,andthereisareductionincapillary
density.Thusthecapacityoftheventricletosustainhighpressuresandtolerate
stenosisislessthaninthenewborn.Inthefetus,severeformsofpulmonary
stenosismayresultinacirculationthatresemblespulmonaryatresiaandright
ventriculardevelopmentmaybeimpaired,resultinginthedevelopmentofa
hypertrophicrightventriclewithahypoplasticcavity.
Whenrightventriculardilationissevere,interventricularinteractionmay
occur,suchthattheleftventricleisconstrainedwithinthepericardium,
impairingitsabilitytofillandcontributingtothecompromisedcirculation.
Centralcyanosiscanoccurinneonateswhenthereisaduct-dependent
pulmonarycirculationorwhenrightventriculardiastolicdysfunctionallows
rightatrialtoexceedleftatrialpressure,producingacyanoticshuntacrossa
defectintheatrialseptum.

NaturalHistory
Mildpulmonaryvalvestenosiswithagradientoflessthan40mmHgthatis
seenafterthefirst6monthsoflifeis,ingeneral,abenigncondition.The
severityofthediseasemayevenimproveasthechildgrows,40–44certainlywith

averylowincidenceofdeteriorationtothepointofrequiringanintervention.In
childrenwithmoderateorevenseverepulmonarystenosis,rightventricular
functionseemstobemaintained.45Whenfirstseenininfancy,however,even


mildpulmonarystenosiscanprogressanddeteriorate.46UsingDoppler
echocardiographymonitoring,25%ofinfantswithmildpulmonarystenosisin
theneonatalperiodwereshowntodevelopfurthersignificantstenosis,42andup
tohalfofthesepatientsrequireintervention.40Notallofthesecasescanbe
explainedsolelybyapostnataldropinpulmonaryvascularresistance.Thusitis
importanttomonitorinfantscarefully,especiallywhenthediagnosisismadein
theneonatalperiod,regardlessoftheirseverityofpulmonarystenosis.The
appearanceofthevalveintermsofthethicknessandmobilityoftheleafletsis
onlyweaklypredictiveoffuturedeterioration.42
Inpatientswithdeterioratingpulmonarystenosisandintactventricular
septum,rightventricularpressuremay,overtime,exceedleftventricular
pressure.Theventricularpressurewaveformchangesfromabroad-based
triangularshapewithearlypeakmaximalpressure(Fig.42.25)toatallpeaked
waveformwiththepointofmaximalpressuredelayedtoclosetotheendof
systole(Fig.42.26).Compensationforfixedseverestenosiswithright
ventricularhypertrophycanfailasthepatientgrowsandfurtherdemandsare
madeontheventricle.Atthisstage,therightventriclemaydecompensateby
dilating,andthereisheartfailure.Furthercompensatorymechanismsforlow
cardiacoutputincludeincreasedextractionofoxygen.Duringexercise,eventhis
compensatorymechanismisinsufficient,andexerciseintoleranceisnoted,often
withthepresenceofperipheralcyanosis.


FIG.42.25 Normallow-pressurerightventricularwaveformshowinga
broad-basedtriangularwaveformwithanearlypointofmaximalpressure.