ecg tutorial_ basic principles of ecg analysis
DESCRIPTION
ecg tutorialTRANSCRIPT
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18/1/2015 ECGtutorial:BasicprinciplesofECGanalysis
http://www.uptodate.com/contents/ecgtutorialbasicprinciplesofecganalysis?topicKey=CARD%2F2115&elapsedTimeMs=0&source=search_result&searc 1/18
OfficialreprintfromUpToDate www.uptodate.com2015UpToDate
AuthorJordanMPrutkin,MD,MHS,FHRS
SectionEditorAryLGoldberger,MD
DeputyEditorGordonMSaperia,MD,FACC
ECGtutorial:BasicprinciplesofECGanalysis
Alltopicsareupdatedasnewevidencebecomesavailableandourpeerreviewprocessiscomplete.Literaturereviewcurrentthrough:Dec2014.|Thistopiclastupdated:Oct31,2013.
INTRODUCTIONEventhoughtherecontinuestobenewtechnologiesdevelopedforthediagnosticevaluationofpatientswithcardiovasculardisease,theelectrocardiogram(ECG)retainsitscentralrole.TheECGisthemostimportanttestforinterpretationofthecardiacrhythm,conductionsystemabnormalities,andforthedetectionofmyocardialischemia.TheECGisalsoofgreatvalueintheevaluationofothertypesofcardiacabnormalitiesincludingvalvularheartdisease,cardiomyopathy,pericarditis,andhypertensivedisease.Finally,theECGcanbeusedtomonitordrugtreatment(specificallyantiarrhythmictherapy)andtodetectmetabolicdisturbances.
AsystematicapproachtointerpretationoftheECGisimportantinordertoavoidoverlookingimportantabnormalities.Patternrecognitioncanbeuseful,butonlyaftercertainsalientfeatureshavebeendetermined.ThistopicreviewprovidestheframeworkforasystematicanalysisoftheECG.
ECGGRIDTheelectrocardiogram(ECG)isaplotofvoltageontheverticalaxisagainsttimeonthehorizontalaxis.Theelectrodesareconnectedtoagalvanometerthatrecordsapotentialdifference.Theneedle(orpen)oftheECGisdeflectedagivendistancedependinguponthevoltagemeasured.
TheECGwavesarerecordedonspecialgraphpaperthatisdividedinto1mm gridlikeboxes(figure1).TheECGpaperspeedisordinarily25mm/sec.Asaresult,each1mm(small)horizontalboxcorrespondsto0.04second(40ms),withheavierlinesforminglargerboxesthatincludefivesmallboxesandhencerepresent0.20sec(200ms)intervals.Onoccasion,thepaperspeedisincreasedto50mm/sectobetterdefinewaveforms.Inthissituation,thereareonlysixleadspersheetofpaper.Eachlargeboxisthereforeonly0.10secandeachsmallboxisonly0.02sec.Inaddition,theheartrateappearstobeonehalfofwhatisrecordedat25mm/secpaperspeed,andalloftheECGintervalsaretwiceaslongasnormal.
Vertically,theECGgraphmeasurestheheight(amplitude)ofagivenwaveordeflection,as10mm(10smallboxes)equals1mVwithstandardcalibration.Onoccasion,particularlywhenthewaveformsaresmall,doublestandardisused(20mmequals1mv).Whenthewaveformsareverylarge,halfstandardmaybeused(5mmequals1mv).PaperspeedandvoltageareusuallyprintedonthebottomoftheECG.
COMPLEXESANDINTERVALSThenormalelectrocardiogram(ECG)iscomposedofseveraldifferentwaveformsthatrepresentelectricaleventsduringeachcardiaccycleinvariouspartsoftheheart(figure2).ECGwavesarelabeledalphabeticallystartingwiththePwave,followedbytheQRScomplexandtheSTTUcomplex(STsegment,Twave,andUwave).TheJpointisthejunctionbetweentheendoftheQRSandthebeginningoftheSTsegment(waveform1).
PwaveThePwaverepresentsatrialdepolarization.ThenormalsinusPwavedemonstratesrightfollowedbyleftatrialdepolarizationandisaninitiallowamplitudepositivedeflectionprecedingtheQRScomplex.Thedurationisgenerally
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18/1/2015 ECGtutorial:BasicprinciplesofECGanalysis
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thatisdirectedposteriorly.
Theatrialrepolarizationsequence(atrialSTandTwavephases)occursjustbefore,simultaneously,andjustafterdepolarizationoftheventricularmyocardium.Theatrial"Twave"itselfisusuallyhiddenbytheQRScomplexandnotobservedontheroutineECG.Inaddition,theamplitudeoftheatrialTwaveisoftentoosmalltobeobservedatstandardgain.Whentheheartrateisincreased(eg,withsinustachycardia)andthereisenhancedsympathetictone,thePRintervalisshortenedatrialrepolarization(theatrialTwave)maysometimesthenbeobservedattheveryendoftheQRScomplex,alteringtheJpoint,andresultinginJpointdepressionwithrapidlyupslopingSTsegments,particularlyduringthefirst80msecaftertheQRScomplex.ThisfindingisphysiologicbutmaybeconfusedwithtrueSTdepression,generatingafalsepositivereading.Clinically,atrialrepolarization(theatrialSTphase)ismostevidentduringacutepericarditis,inwhichoneoftenseesPRsegmentelevationinleadaVRandPRsegmentininferolateralleads,reflectinganatrialcurrentofinjury.ThelowamplitudeatrialTwavemayalsobeunmaskedincertaincasesofhighdegreeAVblock,especiallywhentheatriaareenlarged.Finally,alterationsintheatrialSTsegmentandTwavemayoccurwithotherpathologies,suchasatrialinfarctionoratrialtumorinvasion.
PRintervalThePRintervalincludesthePwaveaswellasthePRsegment.ItismeasuredfromthebeginningofthePwavetothefirstpartoftheQRScomplex(whichmaybeaQwaveorRwave).Itincludestimeforatrialdepolarization(thePwave)andconductionthroughtheAVnodeandtheHisPurkinjesystem(whichconstitutethePRsegment).ThelengthofthePRintervalchangeswithheartrate,butisnormally0.12to0.20sec(threetofivesmallboxes).ThePRintervalisshorteratfasterheartratesduetosympatheticallymediatedenhancementofatrioventricular(AV)nodalconductionitislongerwhentherateisslowedasaconsequenceofslowerAVnodalconductionresultingfromwithdrawalofsympathetictoneoranincreaseinvagalinputs.
QRScomplexTheQRScomplexrepresentsthetimeforventriculardepolarization.
TheentireQRSdurationnormallylastsfor0.06to0.10seconds(1to2smallboxes)andisnotinfluencedbyheartrate.
TheRwaveshouldprogressinsizeacrosstheprecordialleadsV1V6.NormallythereisasmallRwaveinleadV1withadeepSwave.TheRwaveamplitudeshouldincreaseinsizeuntilV4V6,duetomoreleftventricularforcesbeingseen,whiletheSwavebecomeslessdeep.ThisistermedRwaveprogressionacrosstheprecordium.
STsegmentTheSTsegmentoccursafterventriculardepolarizationhasendedandbeforerepolarizationhasbegun.Itisatimeofelectrocardiographicsilence.TheinitialpartoftheSTsegment(theintersectionoftheendoftheQRScomplexandthebeginningoftheSTsegment)istermedtheJpoint(waveform1).
Iftheinitialdeflectionisnegative,itistermedaQwave.SmallQwavesareoftenseeninleadsI,aVL,andV4V6asaresultofinitialseptaldepolarizationandareconsiderednormal.
ThefirstpositivedeflectionoftheQRScomplexiscalledtheRwave.Itrepresentsdepolarizationoftheleftventricularmyocardium.Rightventriculardepolarizationisobscuredbecausetheleftventricularmyocardialmassismuchgreaterthanthatoftherightventricle.ThesmallRwaveinleadV1representsinitialseptaldepolarization.
ThenegativedeflectionfollowingtheRwaveistheSwave,whichrepresentsterminaldepolarizationofthehighlateralwall.
Ifthereisasecondpositivedeflection,itisknownasanR'.
Lowercaseletters(q,r,ors)areusedforrelativelysmallamplitudewavesoflessthan0.5mV(lessthan5mmwithstandardcalibration).
AnentirelynegativeQRScomplexiscalledaQSwave.
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TheSTsegmentisusuallyisoelectric(ie,zeropotentialasidentifiedbytheTPsegment)andhasaslightupwardconcavity.However,itmayhaveotherconfigurationsdependinguponassociateddiseasestates(eg,ischemia,acutemyocardialinfarction,orpericarditis).Inthesesituations,theSTsegmentmaybeflattened,depressed(belowtheisoelectricline)withanupsloping,horizontal,ordownslopingmorphology,orelevatedinaconcaveorconvexdirection(abovetheisoelectricline).(See"Electrocardiograminthediagnosisofmyocardialischemiaandinfarction"and"ECGtutorial:STandTwavechanges"and"Clinicalpresentationanddiagnosticevaluationofacutepericarditis",sectionon'Electrocardiogram'.)
Insomenormalcases(aswithsinustachycardia)theJpointisdepressedandtheSTsegmentisrapidlyupsloping,becomingisoelectricwithin0.08secondsaftertheendoftheQRScomplex.
TwaveTheTwaverepresentstheperiodofventricularrepolarization.Sincetherateofrepolarizationisslowerthandepolarization,theTwaveisbroad,hasaslowupstroke,andrapidlyreturnstotheisoelectriclinefollowingitspeak(ie,slowupstroke,rapiddownstroke).Thus,theTwaveisasymmetricandtheamplitudeisvariable.Inaddition,theTwaveisusuallysmoothupanddown.IfthereisanyirregularityontheTwave(bump,notch,rippled,nipple,etc)asuperimposedPwaveshouldbeconsidered.
Sincedepolarizationbeginsattheendocardialsurfaceandspreadstotheepicardium,whilerepolarizationbeginsattheepicardialsurfaceandspreadstotheendocardium,thedirectionofventriculardepolarizationisoppositetothatofventricularrepolarization.Thus,theTwavevectorontheECGnormallyisinthesamedirectionasthemajordeflectionoftheQRS.AnotherwayofsayingthisisthattheQRSandTwaveaxesaregenerallyconcordant.VariousdiseasestatescanleadtoTwavediscordance.(See"ECGtutorial:STandTwavechanges".)
QTintervalTheQTintervalconsistsoftheQRScomplex,theSTsegment,andTwave.Thus,theQTintervalisprimarilyameasureofventricularrepolarization.TheJTinterval,whichdoesnotincludetheQRScomplex,isamoreaccuratemeasureofventricularrepolarizationsinceitdoesnotincludeventriculardepolarization,butinmostclinicalsituations,theQTintervalisused.IftheQRScomplexdurationisincreased,thiswillleadtoanincreaseinQTintervalbutdoesnotreflectachangeinventricularrepolarization.AwidenedQRS,therefore,mustbeconsideredifaprolongedQTintervalisbeingevaluated.
ThetimeforventricularrepolarizationandthereforetheQT(orJT)intervalisdependentupontheheartrateitisshorteratfasterheartratesandlongerwhentherateisslower.Thus,aQTintervalthatiscorrectedforheartrate(QTc)isoftencalculatedasfollows(basedonBazett'sformula):
QTc=QTintervalsquarerootoftheRRinterval(insec)
Althoughthisapproachissimple,itisinaccurateatheartrateextremesandresultsinovercorrectingathighratesandundercorrectingatlowones[1].
AnotherapproachcorrectstheQTintervaltothecubedrootoftheRRinterval[1,2].LinearandlogarithmicregressionformulashavebeenusedtopredicttheeffectofheartrateonQTinterval[3,4].However,becauseofsubstantialvariabilityoftheQTRRrelationshipamongindividuals,noformulaforheartratecorrectioncanbeaccurateforeveryone[5,6].
ThenormalvaluefortheQTcinmenis0.44secandinwomenis0.45to0.46sec.QTcvalues,however,areonabellcurveandnormalpatientsmayhavelongerQTcvalues,whilethosewithLongQTsyndromemayhaveshorterQTvalues.(See"DiagnosisofcongenitallongQTsyndrome".)
SincetheQRSwidensinthesettingofabundlebranchblock,theQTintervalwillwiden.ThisincreaseinQTintervaldoesnotreflectanabnormalityofventricularrepolarization,sincetheincreaseisduetoanabnormalityofdepolarization.TherehavenotbeenmanydescriptionsonhowtomeasureQTintervalinthesettingofQRSwidening.OneoptionistomeasuretheJTinterval,correctedforrate:QTcQRS=JTc[7].Thisequationhassomelimitations,asitisdependentonheartrateandasnormalvalueshaventbeenderived.
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UwaveAUwavemaybeseeninsomeleads,especiallytheprecordialleadsV2toV4.Theexactcauseofthiswaveisuncertain,althoughithasbeensuggestedthatitrepresentsrepolarizationoftheHisPurkinjesystem.Alternatively,moredatasuggestitmaybeduetolaterepolarizationofthemidmyocardialMcells,duetoalongeractionpotentialdurationcomparedtotheendocardiumorepicardium,especiallyatslowheartrates[8].
TheamplitudeoftheUwaveistypicallylessthan0.2mVandisclearlyseparatefromtheTwave.Itismoreevidentinsomecircumstancessuchashypokalemiaandbradycardia.TheUwavemaymergewiththeTwavewhentheQTintervalisprolonged(aQTUwave),ormaybecomeveryobviouswhentheQTorJTintervalisshortened(eg,withdigoxinorhypercalcemia).
HEARTRATEIfthecardiacrhythmisregular,theintervalbetweensuccessiveQRScomplexesdeterminedfromtheelectrocardiogram(ECG)gridcanbeusedtodetermineheartrate.
Iftherhythmisirregular,thesimplestwaytodeterminetherateisbycountingthenumberofcomplexesontheECGandmultiplyingbysix,sincethestandardECGdisplays10secondsoftime.
Arateof60to100isconsiderednormal.Aratelessthan60isbradycardia,whilearateover100istachycardia(algorithm1AB).
AXISTheelectricalsignalrecordedontheelectrocardiogram(ECG)containsinformationrelativetodirectionandmagnitudeofthevariouscomplexes.Theaveragedirectionofanyofthecomplexescanbedetermined.
ThenormalQRSelectricalaxis,asestablishedinthefrontalplane,isbetween30and90(directeddownwardorinferiorandtotheleft)inadults[9].Anaxisbetween30and90(directedsuperiorandtotheleft)istermedleftaxisdeviation.Iftheaxisisbetween90and180(directedinferiorandtotheright),thenrightaxisdeviationispresent.Anaxisbetween90and180(directedsuperiorandtotheright)isreferredtoasextremerightorleftaxis.IftheQRSisequiphasicinallleadswithnodominantQRSdeflection,itisindeterminateaxis.TheQRSaxismovesleftwardthroughoutchildhoodandadolescence,fromanormalvalueof30to190atbirthto0to120duringages8to16years.Thereissomedisagreementamongauthorsonthedefinitions(indegrees)ofanormal,right,andleftaxis.(See"Leftanteriorfascicularblock"and"Leftposteriorfascicularblock".)
TheQRSaxiscanbedeterminedbyexaminingallofthelimbleads,buttheeasiestmethodinvolveslookingatleadsI,II,andaVFonly(figure3).
Anothermethodofaxisdeterminationistofindtheleadinwhichthecomplexismostisoelectrictheaxisisdirectedperpendiculartothislead.Asanexample,iftheQRSisisoelectricinlead3whichisdirectedat120,thentheelectricalaxisiseither30or150.
AthirdmethodistodeterminethefrontalleadinwhichtheQRSisofthegreatestpositiveamplitude.Theaxisis
Thedivisionof300bythenumberoflargeboxescalculatestheheartrate.Iftheintervalbetweentwosuccessivecomplexesisonelargebox,thentherateis300beats/min(3001=300beats/min).Iftheintervalistwolargeboxes,therateis150(3002=150beats/min).Thiscalculationmaybecarriedondownthelineforeachadditionallargebox,to100beats/min,75beats/min,60beats/min,50beats/min,etc.
Alternatively,thetimebetweenQRScomplexescanbemeasuredinseconds.Thisnumbercanbedividedinto60toderivetheheartrate.Forinstance,ifthetimebetweentwoQRScomplexesis0.75seconds,theheartrateis80beats/min(60seconds/minute0.75seconds/beat=80beats/min).
IftheQRScomplexispositive(upright)inbothleadsIandII,thentheaxisfallsbetween30and90,andtheaxisisnormal.
IftheQRScomplexispositiveinleadIbutnegativeinleadII,thentheaxisisleftward(30to90).
IfthecomplexesarenegativeinleadIandpositiveinaVF,thentheaxisisrightward(90to180).
IfthecomplexesarenegativeinbothIandaVF,thentheaxisisextreme(180to90).
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paralleltothislead.
BycombiningthequadrantdeterminedbyanalysisofleadsIandIIwiththeisoelectricleadinformation,onecanaccuratelyandrapidlydeterminetheelectricalaxis.
Thecausesofrightaxisdeviationinclude:
Causesforleftaxisdeviationinclude:
Theheartalsohasanaxisinthehorizontalplane,whichisdeterminedbyimaginingtheheartasviewedfromunderthediaphragm.Iftheaxisisrotatedinaclockwisedirection,leftventricularforcesaredirectedmoreposteriorlyandoccurlaterintheprecordialleads.ThisistermedpoorRwaveprogressionandlatetransition.Ifthereiscounterclockwiserotation,leftventricularforcesoccurearlierintherightprecordialleadsandthisistermedearlytransitioninwhichthereisatallRwaveinleadV2.
ThereisnoagreementonhowtoestimatetheQRSaxisinpatientswithbundlebranchblock(BBB).AstheprolongedterminalpartoftheQRSinrightbundlebranchblockreflectsdelaysinrightventricularactivation,andaxisdeterminationisofimportanceindiagnosingfascicularblocks,onereasonableapproachistoestimatethefrontalplaneQRSaxisbasedonjustthefirst80to100msoftheQRSdeflection(primarilyreflectingactivationoftheleftventricle).Forleftbundlebranchblockandotherintraventricularconductiondelays,theentireQRScanbeusedorjusttheinitial80to100ms.
APPROACHTOECGINTERPRETATIONAsystematicapproachtointerpretinganelectrocardiogram(ECG)isessentialforcorrectdiagnosis.
Step1:RateIstheratebetween60and100?Rateslessthan60arebradycardicandgreaterthan100aretachycardic.
Step2:RhythmArePwavespresent?IsthereaPwavebeforeeveryQRScomplexandaQRScomplexaftereveryPwave?ArethePwavesandQRScomplexesregular?IsthePRintervalconstant?(See'Rhythm
Normalvariation(verticalheartwithanaxisof90)Mechanicalshifts,suchasinspirationandemphysemaRightventricularhypertrophyRightbundlebranchblockLeftposteriorfascicularblockDextrocardiaVentricularectopicrhythmsPreexcitationsyndrome(WolffParkinsonWhite)LateralwallmyocardialinfarctionSecundumatrialseptaldefect
Normalvariation(physiologic,oftenwithage)Mechanicalshifts,suchasexpiration,highdiaphragm(pregnancy,ascites,abdominaltumor)LeftventricularhypertrophyLeftbundlebranchblockLeftanteriorfascicularblockCongenitalheartdisease(primumatrialseptaldefect,endocardialcushiondefect)EmphysemaHyperkalemiaVentricularectopicrhythmsPreexcitationsyndromes(WolffParkinsonWhite)Inferiorwallmyocardialinfarction.
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analysis'below.)
Step3:AxisIsthereleftorrightaxisdeviation?(See'Axis'above.)
Step4:IntervalsWhatisthePRinterval?ShortPRintervalsaresuggestiveofWolffParkinsonWhitesyndrome.LongPRintervalsareusuallyseeninfirstdegreeAVblock,buttheremaybeothercauses.WhatistheQRSinterval?LongQRSintervalsrepresentabundlebranchblock,ventricularpreexcitation,ventricularpacing,orventriculartachycardia.WhatistheQTinterval?ShortandlongQTintervalsmaybepresent.
Step5:PwaveWhatistheshapeandaxisofthePwave?ThePwavemorphologyshouldbeexaminedtodetermineiftherhythmissinusorfromanotheratriallocation.(See'Pwave'above.)Amplitudeanddurationshouldalsobeanalyzedtodetermineleftandrightatrialenlargement.(See"Normalsinusrhythmandsinusarrhythmia".)
Step6:QRScomplexIstheQRSwide?Ifso,examinationofthemorphologycandetermineifthereisleftorrightbundlebranchblockorpreexcitationpresent.Inaddition,increasedvoltagemayindicateleftorrightventricularhypertrophy.AreQwavespresent,suggestiveofinfarction?
Step7:STsegmentTwaveIsthereSTelevationordepressioncomparedtotheTPsegment?TheTPsegment,betweentheTwaveofonebeatandthePwaveofthenextbeat,shouldbeusedasthebaseline.AretheTwavesinverted?(See"ECGtutorial:STandTwavechanges".)AbnormalitiesoftheSTsegmentorTwavemayrepresentmyocardialischemiaorinfarction,amongothercauses.
Step8:OverallinterpretationOnlyafterthepriorstepshavebeencompletedshouldanoverallinterpretationandpossiblediagnosesbedetermined.ThisensuresassimilationofallinformationintheECGandthatnodetailwillbeoverlooked.
RHYTHMANALYSISInterpretingtherhythmoftheelectrocardiogram(ECG)issometimesdifficult.However,asforECGinterpretationingeneral,asystematicapproachalongwithaknowledgeofarrhythmiasoftenleadstoacorrectdiagnosis.Calipersareextremelyhelpfulforrhythmanalysis.
Step1:LocatethePwaveThemostimportantandfirststepinrhythminterpretationistheidentificationofPwavesandananalysisoftheirmorphology.Thereareseveralquestionsthatshouldbeaddressed:
Step2:EstablishtherelationshipbetweenPwavesandtheQRScomplexThenextstepistodeterminetherelationshipbetweenthePwavesandtheQRScomplexes,addressingthefollowingquestions:
ArePwavesvisible?EachleadneedstobeexaminedforPwaves,astheymaynotbeobviousinsomeleads.Onoccasion,PwavesmaybelocatedonorattheendofTwavesandnotobvious.TheywillthereforecausetheTwaveupslopeordownstroketonolongerbesmooth.ItisalsoimportanttolookforPwavesduringanypauseintherhythm.AbsenceofPwavesmayoccursecondarytoatrialfibrillation.Alternatively,PwavesmaybepresentbutnotvisibleiftheyaresimultaneouswithandburiedwithintheQRScomplexasinajunctionalrhythmoratrioventricular(AV)nodalreentranttachycardia.Inaddition,theymaybelocatedwithintheSTsegmentaswithanAVreciprocatingtachycardiaorventriculartachycardia.IfaPwaveishalfwaybetweentwoQRScomplexes,asecondPwaveisoftenburiedwithintheQRScomplex.
WhatistherateofthePwaves(ie,thePPinterval)?Iftherateislessthan60,thenabradycardiaispresent.IftheatrialorPwaverateisover100,thenatachycardiaispresent.Ingeneral,sinustachycardiaoccursatratesof100to180atrialtachycardia,AVnodalreentranttachycardia,orAVreciprocatingtachycardiaoccuratratesof140to220atrialratesof260to320areseenwithatrialflutter.
WhatisthemorphologyandaxisofthePwaves?ThenormalsinusPwaveisgenerallyuprightinleadsI,II,aVF,andV4V6.ItwillbenegativeinleadaVR.ItmaybenegativeorbiphasicinleadsIIIandV1.AnegativePwaveintheinferiorleadsorleadIsuggestsanectopicrhythm(lowatrialorleftatrialrespectively).Similarly,acompletelypositivePwaveinV1suggestsaleftatriallocation.
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Often,establishingtherelationshipbetweenthePwaveandtheQRScomplexisthemostimportantdiagnosticstepinrhythminterpretation.(See'Overallapproachtorhythmanalysis'below.)(See"ApproachtothediagnosisandtreatmentofwideQRScomplextachycardias".)
Step3:AnalyzetheQRSmorphologyIftheQRScomplexesareofnormalduration(0.12sec),thentherhythmiseithersupraventricularwithaberrantconduction,preexcitation,orventricularpacing,oritisofventricularorigin.ItmaybepossibletodifferentiatethembycarefulinspectionoftheQRSmorphology,especiallyiftheQRSmorphologyappearssimilartothebaselineQRS.(See"ApproachtothediagnosisandtreatmentofwideQRScomplextachycardias"and"Basicapproachtodelayedintraventricularconduction".)
Step4:SearchforothercluesOftenthediagnosisofarhythmdisturbancecanbemadebycluesprovidedbybreaksintherhythmorotherirregularitiesinanotherwiseregularrhythm.Asanexample,anincreaseinthedegreeofAVblockasoccurswithcarotidsinusmassagemayunmasktheflutterwavesofatrialflutter.
Capturebeatsandfusionbeatsmaybethecluesthathelpestablishthediagnosisofventriculartachycardia.
TheregularityoftheQRScomplexesshouldbeestablishedbyaskingthefollowingquestions:
Step5:InterprettherhythmintheclinicalsettingOften,theclinicalhistory,includingdrugsbeingtaken,canbehelpfulinestablishingadiagnosis.Asanexample,aregularwidecomplexrhythminanolderpatientwithahistoryofischemiccardiomyopathyismostlikelyventriculartachycardia.(See"ApproachtothediagnosisandtreatmentofwideQRScomplextachycardias".)Similarly,anarrowcomplextachycardiaofsuddenonsetinayoungpersonwithnomedicalhistoryislikelyAVnodalreentrantorAVreciprocatingtachycardia.(See"Clinicalmanifestations,diagnosis,andevaluationofnarrowQRScomplextachycardias".)
However,theclinicalpresentationandassociatedhemodynamicfindingsdonotnecessarilycorrelatewiththeetiologyofanabnormalrhythm.Thepresenceofhemodynamicstabilityduringatachycardia,forexample,doesnotimplyasupraventricularetiology,nordoesinstabilitymeanthatthediagnosisisventriculartachycardia.Hemodynamicchangesarerelatedtotherateofthearrhythmiaandthepresenceandextentofunderlyingheart
ArethePwavesassociatedwithQRScomplexesina1:1fashion?Ifnot,aretheremoreorlessPwavesthanQRScomplexesandwhataretheatrialandventricularrates?IftherearemorePwavesthanQRScomplexes,thensomeformofAVblockispresent,whichmaybephysiologicifthereisaconcomitantatrialtachycardiaorflutter.IftherearemoreQRScomplexesthanPwaves,thentherhythmisanacceleratedventricularorjunctionalrhythm.
DothePwavesprecedeeachQRScomplexasisthecasewithmostnormalrhythms?WhatisthePRinterval,andisthisintervalfixed?
DoPwavesoccuraftereachQRScomplex(ie,retrogradePwaves)asoccursinjunctionalorventricularrhythmswithretrogradeVAconduction,orinAVnodalreentrantorAVreciprocatingtachycardias?TheRPintervalshouldbenotedanditshouldbeestablishedifitisfixedorvariable.
DotheQRScomplexesoccurwithregularintervalsoraretheyirregular?
Ifthecomplexesareirregular,isthereapatterntotheirregularity?Istherhythmregularlyirregular(ie,thereisarepeatingpatternofirregularity)oristherhythmirregularlyirregularwithoutanypatternofirregularity?Atleastfivesupraventricularrhythmsareirregularlyirregular:sinusarrhythmia(inwhichthereisonlyonePwavemorphologyandastablePRinterval)sinusrhythmwithprematureatrialcontractionssinusorotherrhythmwithvariableAVblockmultifocalatrialrhythm(wanderingatrialpacemaker)whentherateis100(inwhichthereare3differentPwavemorphologiesandPRintervals)oratrialfibrillation(inwhichthereisnoorganizedelectricalactivity).
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disease.
OVERALLAPPROACHTORHYTHMANALYSISApproachingeachnewrhythmwithamethodicalstandard,asshowninthefollowingalgorithms,permitthecorrectdiagnosistobeestablishedinmostcircumstances.Anapproachtothediagnosisoftachycardiaandbradycardiaisshown(algorithm2ABandalgorithm1AB).Thisissueisdiscussedinotherelectrocardiogram(ECG)tutorials.(See"ECGtutorial:Ventriculararrhythmias"and"ECGtutorial:Atrialandatrioventricularnodal(supraventricular)arrhythmias"and"ECGtutorial:Rhythmsandarrhythmiasofthesinusnode".)
SUMMARYTheelectrocardiogram(ECG)isagraphicalrepresentation(timeversusamplitudeofelectricalvectorprojection)oftheelectricalactivityoftheheart.Whileimperfectasadiagnosticorprognostictool,itcontainsawealthofinformationnecessaryforthepropercareofthepatientwithpotentialcardiovasculardisease.
TheelectricalactivityofeachnormalcardiaccycleisrepresentedinsequencebythePwave,thePRinterval,theQRScomplex,theSTsegment,theTwave,and(sometimes)theUwave.Thefollowingpiecesofinformationshouldbeevaluatedforeachofthese.
AsystematicapproachtointerpretationoftheECGiscriticallyimportant.(See'ApproachtoECGinterpretation'above.)
UseofUpToDateissubjecttotheSubscriptionandLicenseAgreement.
REFERENCES
1. FunckBrentanoC,JaillonP.RatecorrectedQTinterval:techniquesandlimitations.AmJCardiol199372:17B.
2. FridericiaL.DiesystolendauerimElektrokardiogrammbeinormalenmenschenundbeiherzkranken.ActaMedScand192053:469.
3. MossAJ.MeasurementoftheQTintervalandtheriskassociatedwithQTcintervalprolongation:areview.AmJCardiol199372:23B.
4. SagieA,LarsonMG,GoldbergRJ,etal.AnimprovedmethodforadjustingtheQTintervalforheartrate(theFraminghamHeartStudy).AmJCardiol199270:797.
5. MalikM,FrbomP,BatchvarovV,etal.RelationbetweenQTandRRintervalsishighlyindividualamonghealthysubjects:implicationsforheartratecorrectionoftheQTinterval.Heart200287:220.
6. ManionCV,WhitsettTL,WilsonMF.ApplicabilityofcorrectingtheQTintervalforheartrate.AmHeartJ198099:678.
7. RautaharjuPM,ZhangZM,PrineasR,HeissG.AssessmentofprolongedQTandJTintervalsinventricularconductiondefects.AmJCardiol200493:1017.
RateIstheratebetween60and100?(See'Step1:Rate'above.)
RhythmIsitnormalsinusorother?(See'Step2:Rhythm'above.)
AxisIsthereaxisdeviation?(See'Step3:Axis'above.)
IntervalsAreallintervalsnormal?(See'Step4:Intervals'above.)
PwaveWhatisitsheight,width,andaxis?(See'Step5:Pwave'above.)
QRScomplexAretherepathologicQwaves,bundlebranchblock,orchamberhypertrophy?(See'Step6:QRScomplex'above.)
STTwavesIsitisoelectric,elevated,ordepressedrelativetotheTPsegment?(See'Step7:STsegmentTwave'above.)
OverallinterpretationWhatisthediagnosis?(See'Step8:Overallinterpretation'above.)
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8. HopenfeldB,AshikagaH.OriginoftheelectrocardiographicUwave:effectsofMcellsanddynamicgapjunctioncoupling.AnnBiomedEng201038:1060.
9. SurawiczB,ChildersR,DealBJ,etal.AHA/ACCF/HRSrecommendationsforthestandardizationandinterpretationoftheelectrocardiogram:partIII:intraventricularconductiondisturbances:ascientificstatementfromtheAmericanHeartAssociationElectrocardiographyandArrhythmiasCommittee,CouncilonClinicalCardiologytheAmericanCollegeofCardiologyFoundationandtheHeartRhythmSociety.EndorsedbytheInternationalSocietyforComputerizedElectrocardiology.JAmCollCardiol200953:976.
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GRAPHICS
GridlinesandstandardizationoftheECG
Theelectrocardiogamisrecordedonpaperthathaslargeboxes(heavylines)of0.5cmsides.Onthehorizontalaxis,eachlargebox,whichrepresents0.2secondsatatypicalpaperspeedof25mm/sec,isdividedintofivesmallerboxes,eachonerepresenting0.04seconds.Ontheverticalaxis,thelargeboxalsohasfivesubdivisions,each1mminheight10mmequals1mVwithstandardcalibration.
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ECGcomplexesandintervals
ECGwavesarelabeledalphabeticallystartingwiththePwave,followedbytheQRScomplex,andtheSTTcomplex(STsegmentandTwave).TheJpointisthejunctionbetweentheendoftheQRSandthebeginningoftheSTsegment.ThePRintervalismeasuredfromthebeginningofthePwavetothefirstpartoftheQRScomplex.TheQTintervalconsistsoftheQRScomplexwhichrepresentsonlyabriefpartoftheinterval,andtheSTsegmentandTwavewhichareoflongerduration.
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Jpoint
TheJpointisthejunctionbetweentheendoftheQRSandthebeginningoftheSTsegment.
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Approachtobradycardia
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Approachtotachycardia
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Calculationoffrontalplaneaxis
IftheQRScomplexispositiveinleadsIandII,itfallsbetween30and90andisnormal,asindicatedbytheyellowarea.IftheQRScomplexisnegativeinIandpositiveinaVF,thereisrightaxisdeviation.IftheQRScomplexispositiveinIandnegativeinII,thereisleftaxisdeviation.IftheQRScomplexisnegativeinIandaVF,thereisextremeaxisdeviation.
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PwavebeforeeachQRScomplexwithconstantPRrelationship
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PwaveinfrontofeachQRScomplex:PwaveandQRSrelated
*PwavemorphologyandPRintervalvariable.
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Disclosures:JordanMPrutkin,MD,MHS,FHRSGrant/Research/ClinicalTrialSupport:BostonScientificSt.JudeMedical[Electrophysiology(ICDsandpacemakers)].AryLGoldberger,MDNothingtodisclose.GordonMSaperia,MD,FACCEmployeeofUpToDate,Inc.Contributordisclosuresarereviewedforconflictsofinterestbytheeditorialgroup.Whenfound,theseareaddressedbyvettingthroughamultilevelreviewprocess,andthroughrequirementsforreferencestobeprovidedtosupportthecontent.AppropriatelyreferencedcontentisrequiredofallauthorsandmustconformtoUpToDatestandardsofevidence.Conflictofinterestpolicy
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