Andersons pediatric cardiology 169

cardiacoutputcalculatedinthiswayisapproximately550mL/minperkgbody
weight.However,therangeconsideredtobenormalissowideastomakeits
interpretationdifficult,exceptinserialassessment.123Variousinvestigationsin
humans,supportedbyanimaldata,haveshownrightcardiacoutputtobegreater
thanleftbyatleasttwo-fifths.51,52Themajorsourceoferrorinthecalculationof
cardiacoutputresultsfrommeasurementerrorofthediameterofthevessel,
particularlyforclinicalstudies,andfailuretoaccountforpulsatilityofthevessel
intheequation.Inonestudy,theupper95%confidencelimitsforintraobserver
variationwerereducedto0.04and0.09mmfordiametersof0.6and6mm,
respectively,bymakingsixrepeatedmeasurementsofthevessel.124


FunctionalAnalysisoftheFetalHeart
Thepreviouslydiscussedlimitedmethodsusedtoassessfunctionofthefetal
ventricleshavebeenreplacedinmoststudiesbymeasurementoflongaxis
functionofthefetalheartusingamplitudeofdisplacementoftheatrioventricular
ring,andDopplertissuevelocitiesusingspectralorcolormethods.These
methodshavebeenincorporatedintoroutineclinicalpractice,whereasmore
research-basedtoolsincludeofflineassessmentofstrain,strain-rate,and
ventriculartwistandtorsion.

LongAxisFunction
M-ModeMeasuresofDisplacementofthe
AtrioventricularRing
Thepatternofarrangementofmyocytesdiffersintherightandleftventricles,
withtherightventriclelackingmyocytesaggregatedincircularfashion.125The
myocytesaggregatedinlongitudinalfashionliepredominantlyintheventricular
subendocardiumandareaffectedfirstbyischemia.Thusreduceddisplacement
oftheatrioventricularringmayindicateearlymyocardialischemia.Thereare
additionalbenefitsbecausethegeometryoftherightventriclemakesitdifficult
toassessrightventricularfunctionintheminoraxisbecauseofpoordetectionof

theendocardialborders.Studiesinadultswithheartfailurehavereportedthat
assessmentoftheamplitudeinthelongaxispredictsexercisetoleranceand
survival.126,127DisplacementoftheatrioventricularringisassessedusingMmodetechniquesandreflectsshorteningofthemyocytesaggregatedin
longitudinalfashiontowardtheapexoftheventricleinsystoleandtheiractive
lengtheningindiastole.114Themethodologyissimpleandreliable,andoffline
assessmentusinganatomicM-modeprovidescomparablevalueswhenfetallieis
transverse.Normalreferencerangeshavebeendescribedinthefetusand
adult.128–130
AcomparisonwithpostprocessingM-modemeasurementsofdisplacement
derivedfrom3Dvolumeshasshowngoodcorrelation.131Nomogramsshowagerelatedincreasesinamplitudeofdisplacementinthefetus,confirmingright
ventriculardominanceastherightventricularfreewallshowsincreased


displacementcomparedwiththeleftortheventricularseptum.130,131

DopplerTissueImaging
Dopplertissueimagingcanbeperformedusingtwomodalities,spectraland
colorDopplerimaging.Spectralimagingproduceshighervaluesthanthose
obtainedwithcolor.Technologicdifferencesmayexplainsomeofthereported
differencesinvalues.132,133
ColorDopplerimagingproducesinformationfromthewholeimagingfield
andnotjustthetissueselectedbyplacingaDopplersamplevolume.Thisallows
assessmentofmultiplesamplingpointsinthesamecardiaccycle.Furthermore,
itproducesvelocityvectorsthathavethepotentialtobemanipulatedby
automatedprograms.SpectralDopplerallowstheplacementofasample
volume,butthesamplingusuallyproducesaspectrumofvelocities,depending
onthegainsettingsandthiscaninfluencethepeaksystolicvelocity
measured.134
Ventricularlong-axisshorteningvelocitiesandamplitudecorrelatewith
overallventricularfunctionasassessedbyejectionfraction,andearlyandlate

diastoliclengtheningvelocitiescorrelatewithventricularfillingvelocities
assessedbyDoppler.Maturationalchangeshavebeencharacterizedinthe
normalfetusandgestationallyrelatedvaluesshowsimilar
increases.129,133,135–138
Long-axisfetalcardiacfunctionhasbeenstudiedusingM-modeandtissue
Dopplerinpregnanciescomplicatedbymaternaldisease,suchasdiabetes
mellitusandfetalgrowthrestrictionandalteredfunctionhasbeen
described.139,140
Theinconsistenciesinreportedresultsaredueinparttothetechnical
limitationsinapplyingthesemeasurements,developedinadulthearts,tothe
smallerfetalheart.Thereisalackofelectronicgating,andsmallertissue
volumesappeartobethemostimportant.Inaddition,allDopplermodalities
requirehighframerates,with200Hzbeingideal(althoughvelocitiesnearerto
100Hzaremoreusualusingultrasoundmachineswithobstetricplatforms)and
mustbecloselyalignedparalleltothemuralmotion,ideallylessthan20
degrees.Accuracyofmeasurementrequiresthatthesamplevolumeissmall,and
velocitylimitsreducedtooptimizethetrace.Thetechnicaldifferencesinthese
methodsandinrecordingsmadeondifferentequipmentleadtodifferentresults,
andthismustberecognizedasalimitationwhencomparingdifferentstudiesor