Andersons pediatric cardiology 170
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changingequipmentduringlongitudinalstudies.141
Developmentofsoftwareisunderwaytopermitanautomatedassessmentof
themyocardialvectortracesobtainedusingcolortissueDoppler,andthismay
improveperformanceofthetechnique.142
GlobalCardiacFunction
TeiIndex
Firstdescribedin1997frommeasurementsmadeinadults,143theTeiindexhas
beenusedinfetalechocardiographytodescribechangesinmyocardial
performancewithgestationalage,andinconditionsofalteredloadingsuchas
TTTS.144–146Thisindexisameasureofglobalcardiacfunctionandusespulsed
waveDopplerofthemitralinflowandaorticoutflowwaveforms.Althoughitis
technicallyeasytorecord,itsreproducibilityhasbeenquestioned,andvarious
modifications(Fig.6.15),byusingthevalvarejectionclicks,144havebeen
developed.Asforlongaxismeasurements,differentultrasoundmachines
producedifferentvalues,andresultsarenotcomparablefrommachineto
machine.Otherauthorshaveusedmyocardialtissuevelocitiestoproducea
DopplertissueTeiindex.147Thewaveformsproducedaremoredifficultto
interpretthanwithpulsedDoppler,andcautionshouldbeexercisedintheir
interpretation.
FIG.6.15 Dopplerrecordingofsimultaneousinflowintotheleftventricle
andflowthroughtheaorticvalve.TheTeiindexiscalculatedasshownin
thefigure;itincludesthevalveclickstofacilitateitsmeasurement.The
measurementaincludestheisovolumicaccelerationandrelaxationtimes.
Theratioofthesetotheejectionperiod,b,givestheTeiormyocardial
performanceindex.Thehigherthisis,theworsethemyocardial
performance.
AreductionintheTeiindexisseenwithincreasinggestationalage,duetoa
reductioninisovolumiccontractionandrelaxationtimes.Althoughithasbeen
shownineffectiveinanimalmodelstoreflectglobalmyocardialfunction,itis
sensitivetoafterloadchangesandfetalconditionscomplicatedbydifferential
loadingcanbepredictedandmonitoredusingthistechnique.145,146More
recently,developmentofsoftwarehaspermittedanautomatedassessmentofthe
Teiindex,andthisisapromisingtooltopermitmorerobuststudyofgestational
changes.148However,examinationoftherightventricleisparticularly
challenging,anddualDopplerrecordingsmaybemorereliablethanthe
automatedversion.149
MyocardialStrainandStrainRate
Definition
Strainistheincreaseordecreaseinlengthrelativetoitsrestinglengthwhena
forceisapplied,andstrainrateisitsrateofchange.Fetalmyocardialshortening
isrepresentedbynegativestrainvaluesduringsystole,whereaspositivestrain,
ormyocardiallengthening,occursduringdiastole.150
Myocardialdeformationisthreedimensionalwithbothlongitudinal,radial,
andcircumferentialcomponents,andmeasurementsoftwistandtorsionhave
beeninvestigatedinanimalmodelsandphantoms.150,151
Ventricularwallstrainmaybereportedintwoways,naturalandLagrangian.
Naturalorpointstrainisassessedbysummatingthesmallstrainvalues
calculatedbyautomatedsoftwarealongtheventricularwall,andLagrangian
strainbysummingthedistancesduringthemechanicaleventandcalculating
strainalongthewholelengthofthewall.Lagrangianstrainislikelythebetter
methodologyforthefetus,andmoresoftwarepackagesnowusethismethod.
However,bothhavebeenreportedusingthevarietyoftechnologies
available,152,153andconflictinggestationalpatternsreportedinthefetusare
likelytheresultoftechnicalfactors.154–156
Techniques
Assessmentoffetalstrainisusuallymadeofflineusingspecializedsoftware.
