ecg tutorial_ basic principles of ecg analysis

18/1/2015 ECGtutorial:BasicprinciplesofECGanalysis

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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



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.



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.)

http://www.uptodate.com/contents/ecg-tutorial-atrial-and-atrioventricular-nodal-supraventricular-arrhythmias?source=see_linkhttp://www.uptodate.com/contents/ecg-tutorial-basic-principles-of-ecg-analysis/abstract/3http://www.uptodate.com/contents/ecg-tutorial-basic-principles-of-ecg-analysis/abstract/4http://www.uptodate.com/contents/ecg-tutorial-ventricular-arrhythmias?source=see_linkhttp://www.uptodate.com/contents/image?imageKey=CARD%2F77276%7ECARD%2F52259&topicKey=CARD%2F2115&rank=1%7E150&source=see_linkhttp://www.uptodate.com/contents/image?imageKey=CARD%2F85685%7ECARD%2F85684&topicKey=CARD%2F2115&rank=1%7E150&source=see_linkhttp://www.uptodate.com/contents/ecg-tutorial-basic-principles-of-ecg-analysis/abstract/1http://www.uptodate.com/contents/licensehttp://www.uptodate.com/contents/ecg-tutorial-basic-principles-of-ecg-analysis/abstract/7http://www.uptodate.com/contents/ecg-tutorial-basic-principles-of-ecg-analysis/abstract/2http://www.uptodate.com/contents/ecg-tutorial-basic-principles-of-ecg-analysis/abstract/5http://www.uptodate.com/contents/ecg-tutorial-rhythms-and-arrhythmias-of-the-sinus-node?source=see_linkhttp://www.uptodate.com/contents/ecg-tutorial-basic-principles-of-ecg-analysis/abstract/6



8. HopenfeldB,AshikagaH.OriginoftheelectrocardiographicUwave:effectsofMcellsanddynamicgapjunctioncoupling.AnnBiomedEng201038:1060.

9. SurawiczB,ChildersR,DealBJ,etal.AHA/ACCF/HRSrecommendationsforthestandardizationandinterpretationoftheelectrocardiogram:partIII:intraventricularconductiondisturbances:ascientificstatementfromtheAmericanHeartAssociationElectrocardiographyandArrhythmiasCommittee,CouncilonClinicalCardiologytheAmericanCollegeofCardiologyFoundationandtheHeartRhythmSociety.EndorsedbytheInternationalSocietyforComputerizedElectrocardiology.JAmCollCardiol200953:976.

Topic2115Version14.0

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http://www.uptodate.com/contents/ecgtutorialbasicprinciplesofecganalysis?topicKey=CARD%2F2115&elapsedTimeMs=0&source=search_result&sear 10/18

GRAPHICS

GridlinesandstandardizationoftheECG

Theelectrocardiogamisrecordedonpaperthathaslargeboxes(heavylines)of0.5cmsides.Onthehorizontalaxis,eachlargebox,whichrepresents0.2secondsatatypicalpaperspeedof25mm/sec,isdividedintofivesmallerboxes,eachonerepresenting0.04seconds.Ontheverticalaxis,thelargeboxalsohasfivesubdivisions,each1mminheight10mmequals1mVwithstandardcalibration.

Graphic62799Version1.0



ECGcomplexesandintervals

ECGwavesarelabeledalphabeticallystartingwiththePwave,followedbytheQRScomplex,andtheSTTcomplex(STsegmentandTwave).TheJpointisthejunctionbetweentheendoftheQRSandthebeginningoftheSTsegment.ThePRintervalismeasuredfromthebeginningofthePwavetothefirstpartoftheQRScomplex.TheQTintervalconsistsoftheQRScomplexwhichrepresentsonlyabriefpartoftheinterval,andtheSTsegmentandTwavewhichareoflongerduration.




Jpoint

TheJpointisthejunctionbetweentheendoftheQRSandthebeginningoftheSTsegment.




Approachtobradycardia




Approachtotachycardia




Calculationoffrontalplaneaxis

IftheQRScomplexispositiveinleadsIandII,itfallsbetween30and90andisnormal,asindicatedbytheyellowarea.IftheQRScomplexisnegativeinIandpositiveinaVF,thereisrightaxisdeviation.IftheQRScomplexispositiveinIandnegativeinII,thereisleftaxisdeviation.IftheQRScomplexisnegativeinIandaVF,thereisextremeaxisdeviation.




PwavebeforeeachQRScomplexwithconstantPRrelationship




PwaveinfrontofeachQRScomplex:PwaveandQRSrelated

*PwavemorphologyandPRintervalvariable.




Disclosures:JordanMPrutkin,MD,MHS,FHRSGrant/Research/ClinicalTrialSupport:BostonScientificSt.JudeMedical[Electrophysiology(ICDsandpacemakers)].AryLGoldberger,MDNothingtodisclose.GordonMSaperia,MD,FACCEmployeeofUpToDate,Inc.Contributordisclosuresarereviewedforconflictsofinterestbytheeditorialgroup.Whenfound,theseareaddressedbyvettingthroughamultilevelreviewprocess,andthroughrequirementsforreferencestobeprovidedtosupportthecontent.AppropriatelyreferencedcontentisrequiredofallauthorsandmustconformtoUpToDatestandardsofevidence.Conflictofinterestpolicy

Disclosures

http://www.uptodate.com/home/conflict-interest-policy

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