Andersons pediatric cardiology 597
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FIG.23.9 Protocolsfortestingusingatreadmill.(A)Bruceprotocol
consistsof3-minutestageswithanincreaseinbothspeedandgrade.The
firsttwostagesareoftenomittedintestingoffitadults.(B)Balkeprotocol.
Thegradeisincreasedfrom0%to2%afterthefirstminuteandincreased
1%ineachsubsequentminute.Thespeedofthetreadmillisheldconstant
at3.5mph.
CycleErgometers
Cycleergometershaveseveralsignificantadvantagescomparedwithtreadmills.
Adistinctadvantageisdecreaseddistortionofelectrocardiographicandblood
pressurerecordings,particularlycrucialwhenthereareconcernsabout
arrhythmias,ischemia,orchangesinmorphologyoftheQRScomplexes.The
cyclealsoaccuratelymeasuresexternalworkperformedduringthetest.This
requiresthattherateofworkberelativelyindependentofspeedofpedaling.The
ergometershouldberegularlycalibratedandcarefullyassessedbeforeitsuse,in
lightofsignal-to-noiseratioonsomecycles,whichmaybeexcessiveatthelow
initialratesofworkusedinpediatricprotocols.Lowsignal-to-noiseratiosare
notcommonproblemsinthenewergenerationofcyclesthatusedigitalrather
thananaloguecontrollersoftherateofwork.Otheradvantagesofcycle
ergometersincludelowercost,portability,andincreasedsafety.Musculoskeletal
injuriesarealsolesslikelywithacycle.36
Disadvantages,asstatedpreviously,includeagenerallylowerachievedlevel
ofmaximalconsumptionofoxygen.Inaddition,manycommerciallyavailable
cycleergometersareunabletoaccommodatechildrenwhoarelessthan130cm
inheightbecausethecrankarmistoolarge.Thereforeergometersusedfor
testingchildrenshouldhaveanadjustablecrankarm.Severalcycleergometers
arecommerciallyavailablewithpediatricmodifications.
Protocols
Historically,themostcommonlyusedprotocolwasthatdevisedbyJames,
whichconsistsof10stages,eachlasting3minutes.40Theincrementalincreases
foreachstagevarydependinguponbodysurfacearea.TheJamesprotocolhas
beenextensivelyvalidatedforuseinchildren37,40,41andhencehaswellestablishednormativedata.Itsmajordisadvantageisthedifficultyofanalyzing
metabolicdatawithitslong3-minutestages,similartothoseencounteredwith
theBruceprotocol.Manynowusing“continuous”rampcycleprotocolshave
becomethestandardforpediatricresearchoverthepastdecadeandiscurrently
commonlyusedinmostexerciselaboratories.Inthisprotocoltherateofworkis
increasedinsmall,frequentlysingle-watt,increments,thusproducingasmooth
continuousrisethroughoutthetest.28,36,37Theseprotocolshaveseveral
advantages.First,thegradualriseinrateofworkavoidsproblemsencountered
withthelargesuddenjumpsseenwhenusing3-minuteincrements.Second,the
slopesoftherampsareseamlesslyadjustedtoaccommodateawiderangeof
sizes,ages,andlevelsofphysicalconditioning.Third,relationshipsbetween
metabolicdataandrateofworkareeasiertoappreciatewiththistypeof
protocol,facilitatingtheanalysisofcollectedgases.TheJamesandcontinuous
rampprotocolsaredepictedinFig.23.10.
FIG.23.10 Protocolsforusewithanuprightcycleergometer.(A)James
protocol.Theinitialrateofworkis200kpm/min.Therateisincreased
every3minutesbydifferentamounts,dependingonthebodysurfacearea
(BSA)ofthepatient.(B)Rampprotocol.Thepatientinitiallypedalsfor3
minuteswithunloadedcyclingtoestablishabaselinemetabolicstate.The
rateofworkisthenincreasedcontinuouslyatachosenlevelbasedonthe
physicalcondition,age,andsizeofthepatientwithanaimtoachieve
maximaleffortin8to12minutes.
ElectrocardiographicRecorders
Manyhigh-qualitycommercialelectrocardiographicrecordingsystemsare
available.Nosystemcurrentlyavailableisdesignedspecificallyforpediatric
use,butallaregenerallyacceptablewithoutmodification.Minimizationof
distortionofsignalsisaccomplishedwithcomputerdigitizationoftheanalogue
electricalsignal.31
Astandardreal-timedisplayisessentialsothattherhythm,andmorphology
oftheQRScomplexes,canbemonitoredcontinuously.Thedisplayshouldshow
