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POCKETGUIDETO

ECGINTERPRETATION

DrArazRawshani,MD,PhDUniversityofGothenburg2017

PP

R R

Q QS S

TU

P-wave duration

PR interval

QRS duration

J pointJ 60 point

ST segment

TP intervalST-T segment


MethodologicalECGInterpretationTheECGmustalwaysbeinterpretedsystematically.FailuretoperformasystematicinterpretationoftheECGmaybedetrimental.Theinterpretationalgorithmpresentedbelowiseasytofollowanditcanbecarriedoutbyanyone.ThereaderwillgraduallynoticethatECGinterpretationismarkedlyfacilitatedbyusinganalgorithm,asitminimizestheriskofmissingimportantabnormalitiesandalsospeedsuptheinterpretation.

1.RhythmASSESSMENTS EVALUATIONAssessventricular(RRintervals)andatrial(PPintervals)rateandrhythm.♥Isventricularrhythmregular?Whatistheventricularrate(beats/min)?♥Isatrialrhythmregular?Whatistheatrialrate(beats/min)?♥P-wavesshouldprecedeeveryQRScomplexandtheP-waveshouldbepositiveinleadII.

♥Sinusrhythm(whichisthenormalrhythm)hasthefollowingcharacteristics:(1)heartrate50–100beatsperminute;(2)P-waveprecedeseveryQRScomplex;(3)theP-waveispositiveinleadIIand(4)thePRintervalisconstant.♥Causesofbradycardia:sinusbradycardia,sinoatrialblock,sinoatrialarrest/inhibition,second-degreeAVblock,third-degreeAVblock.Notethatescaperhythmsmayariseduringbradycardia.Alsonotethatbradycardiaduetodysfunctioninthesinoatrialnodeisreferredtoassinusnodedysfunction(SND).IfapersonwithECGsignsofSNDissymptomatic,theconditionisclassifiedassicksinussyndrome(SSS).♥Causesoftachycardia(tachyarrhythmia)withnarrowQRScomplexes(QRSduration<0,12s):sinustachycardia,inappropriatesinustachycardia,sinoatrialre-entrytachycardia,atrialfibrillation,atrialflutter,atrialtachycardia,multifocalatrialtachycardia,AVNRT,AVRT(pre-excitation,WPW).Notethatnarrowcomplextachyarrhythmiararelycausescirculatorycompromiseorcollapse.♥Causesoftachycardia(tachyarrhythmia)withwideQRScomplexes(QRSduration≥0,12s):ventriculartachycardiaisthemostcommoncauseanditispotentiallylife-threatening.Notethat10%ofwidecomplextachycardiasactuallyoriginatefromtheatriabuttheQRScomplexesbecomewideduetoabnormalventriculardepolarization(e.gsinustachycardiawithsimultaneousleftbundlebranchblock).

2.P-waveandPRintervalASSESSMENTS EVALUATION♥P-wavealwayspositiveinleadII(actuallyalwayspositiveinleadsII,IIIandaVF).♥P-wavedurationshouldbe<0,12s(allleads).

♥P-wavemustbepositiveinleadII,otherwisetherhythmcannotbesinusrhythm.♥P-wavemaybebiphasic(diphasic)inV1(thenegativedeflectionshouldbe<1mm).Itmayhaveaprominentsecondhumpintheinferiorlimbleads(particularlyleadII).


♥P-waveamplitudeshouldbe≤2,5mm(allleads).PRintervalmustbe0,12–0,22s(allleads).

♥Pmitrale:increasedP-waveduration,enhancedsecondhumpinleadIIandenhancednegativedeflectioninV1.♥Ppulmonale:increasedP-waveamplitudesinleadIIandV1.♥IfP-wavenotclearlyvisible:lookforretrograde(inverted)P-waves,whichcanbelocatedanywherebetweentheJpointandtheterminalpartoftheT-wave.♥PRinterval>0,22s:first-degreeAVblock.♥PRinterval<0,12s:Pre-excitation(WPWsyndrome).♥Second-degreeAV-blockMobitztypeI(Wenckebachblock):repeatedcyclesofgraduallyincreasingPRintervaluntilanatrialimpulse(P-wave)isblockedintheatrioventricularnodeandtheQRScomplexdoesnotappear.♥Second-degreeAV-blockMobitztypeII:intermittentlyblockedatrialimpulses(noQRSseenafterP)butwithconstantPRinterval.♥Third-degreeAV-block:Allatrialimpulses(P-waves)areblockedbytheatrioventricularnode.Anescaperhythmarises(cardiacarrestensuesotherwise),whichmayhavenarroworwideQRScomplexes,dependingonitsorigin.ThereisnorelationbetweenP-wavesandtheescaperhythm'sQRScomplexes,andatrialrhythmistypicallyfasterthantheescaperhythm(bothrhythmsaretypicallyregular).

3.QRScomplexASSESSMENTS EVALUATION♥QRSdurationmustbe<0,12s(normally0,07-0,10s).♥TheremustbeatleastonelimbleadwithR-waveamplitude>5mmandatleastonechest(precordial)leadwithR-waveamplitude>10mm;otherwisethereislowvoltage.♥Highvoltageexistsiftheamplitudesaretoohigh,i.eifthefollowingconditionissatisfied:S-waveV1orV2+R-waveV5>35mm.♥LookforpathologicalQ-waves.PathologicalQ-wavesare≥0,03sand/oramplitude≥25%ofR-waveamplitudeinsamelead,inatleast2anatomicallycontiguousleads.♥IstheR-waveprogressioninthechestleads(V1–V6)normal?

♥WideQRScomplex(QRSduration≥0.12s):Leftbundlebranchblock.Rightbundlebranchblock.Nonspecificintraventricularconductiondisturbance.Hyperkalemia.ClassIantiarrhythmicdrugs.Tricyclicantidepressants.Ventricularrhythmsandventricularextrasystoles(prematurecomplexes).Artificialpacemakerwhichstimulatesintheventricle.Aberrantconduction(abberancy).Pre-excitation(Wolff-Parkinson-Whitesyndrome).♥ShortQRSduration:noclinicalrelevance.♥Highvoltage:Hypertrophy(anylead).Leftbundlebranchblock(leadsV5,V6,I,aVL).Rightbundlebranchblock(V1–V3).Normalvariantinyounger,well-trainedandslenderindividuals.♥Lowvoltage:Normalvariant.Misplacedleads.Cardiomyopathy.Chronicobstructivepulmonarydisease.Perimyocarditis.Hypothyreosis(typicallyaccompaniedbybradycardia).Pneumothorax.Extensivemyocardialinfarction.Obesity.Pericardialeffusion.Pleuraleffusion.Amyloidosis.♥PathologicalQ-waves:Myocardialinfarction.Left-sidedpneumothorax.Dextrocadia.Perimyocarditis.Cardiomyopathy.Amyloidosis.Bundlebranchblocks.Anterior


♥Istheelectricalaxisnormal?Electricalaxisisassessedinlimbleadsandshouldbebetween–30°to90°.

fascicularblock.Pre-excitation.Ventricularhypertrophy.Acutecorpulmonale.Myxoma.♥FragmentedQRScomplexesindicatesmyocardialscarring(mostlyduetoinfarction).♥AbnormalR-waveprogression:Myocardialinfarction.Rightventricularhypertrophy(reversedR-waveprogression).Leftventricularhypertrophy(amplifiedR-waveprogression).Cardiomyopathy.Chroniccorpulmonale.Leftbundlebranchblock.Pre-excitation.♥DominantR-waveinV1/V2:Misplacedchestelectrodes.Normalvariant.Situsinversus.Posterolateralinfarction/ischemia(ifpatientexperienceschestdiscomfort).Rightventricularhypertrophy.Hypertrophiccardiomyopathy.Rightbundlebranchblock.Pre-excitation.♥Rightaxisdeviation:Normalinnewborns.Rightventricularhypertrophy.Acutecorpulmonale(pulmonaryembolism).Chroniccorpulmonale(COPD,pulmonaryhypertension,pulmonaryvalvestenosis).Lateralventricularinfarction.Pre-excitation.Switchedarmelectrodes(negativePandQRS-TinleadI).Situsinversus.Leftposteriorfascicularblockisdiagnosedwhentheaxisisbetween90°and180°withrScomplexinIandaVLaswellasqRcomplexinIIIandaVF(withQRSduration<0.12seconds),providedthatothercausesofrightaxisdeviationhavebeenexcluded.♥Leftaxisdeviation:Leftbundlebranchblock.Leftventricularhypertrophy.Inferiorinfarction.Pre-excitation.Leftanteriorfascicularblockisdiagnosediftheaxisisbetween-45°and90°withqR-complexinaVLandQRSdurationis0,12s,providedthatothercausesofleftaxisdeviationhavebeenexcluded.♥Extremeaxisdeviation:Rarelyseen.Probablymisplacedelectrodes.IftherhythmiswideQRScomplextachycardia,thenthecauseisprobablyventriculartachycardia.

4.STsegmentASSESSMENTS EVALUATION♥TheST-segmentshouldbeflatandisoelectric(inlevelwiththebaseline).ItmaybeslightlyupslopingatthetransitionwiththeT-wave.

• ♥STsegmentdeviation(elevationanddepression)ismeasuredintheJpoint.

♥BenignSTsegmentelevationisverycommoninthepopulation,particularlyintheprecordialleads(V2–V6).Upto90%(insomeage-ranges)ofhealthymenandwomendisplayconcaveST-segmentelevationsinV2–V6(thisiscalledmale/femalepattern).ST-segmentelevationswhicharenotbenignnorduetoischemiaarerathercommon(listedbelow).

• ♥ST-segmentdepressionisuncommonamonghealthyindividuals.ST-segmentdepressionisparticularlysuspiciousinthechestleads.Guidelinesrecommendthat<0.5mmST-segmentdepressionbeacceptedinallleads.


• ♥CausesofST-segmentelevation:Ischemia.STsegmentelevationmyocardialinfarction(STEMI/STE-AKS).Prinzmetal'sangina(coronaryvasospasm).Male/femalepattern.Earlyrepolarization.Perimyocarditis.Leftbundlebranchblock.Nonspecificintraventricularconductiondisturbance.Leftventricularhypertrophy.Brugadasyndrome.Takotsubocardiomyopathy.Hyperkalemia.Postcardioversion.Pulmonaryembolism.Pre-excitation.Aorticdissectionengagingthecoronaryarteries.Leftventricularaneurysm.

• ♥CausesofST-segmentdepression:Ischemia.Non-STsegmentelevationmyocadialinfarction(NSTEMI/NSTE-AKS).PhysiologicalST-segmentdepression.Hyperventilation.Hypokalemia.Highsympathethictone.Digoxin.Leftbundlebranchblock.Rightbundlebranchblock.Pre-excitation.Leftventricularhypertrophy.Rightventricularhypertrophy.Heartfailure.Tachycardia.

• ♥Causesofwaves/deflectionsintheJpoint(Jwavesyndromes):Brugadasyndrome.Earlyrepolarization.

5.T-waveASSESSMENTS EVALUATION

• ♥ShouldbeconcordantwiththeQRScomplex.Shouldbepositiveinmostleads.

• ♥T-waveprogressionshouldbenormalinchestleads.

• ♥InlimbleadstheamplitudeishighestinleadII,andinthechestleadstheamplitudeishighestinV2–V3.

♥Normalvariants:Anisolated(single)T-waveinversionisacceptedinleadV1andleadIII.InsomeinstancestheT-waveinversionsfromchildhoodmaypersistinV1–V3(V4),whichiscalledpersistentjuvenileT-wavepattern.Rarely,allT-wavesremaininverted,whichiscalledglobalidiopathicT-waveinversion(V1–V6).

• ♥T-waveinversionwithoutsimultaneousST-segmentdeviation:Thisisnotasignofongoingischemia,butmaybepost-ischemic.Onetypeofpost-ischemicT-waveinversionisespeciallyacute,namelyWellen'ssyndrome(characterizedbydeepT-waveinversionsinV1–V6inpatientwithrecentepisodesofchestpain).Cerebrovascularinsult(bleeding).Pulmonaryembolism.Perimyocarditis(afternormalizationoftheST-segmentelevation,T-wavesbecomeinvertedinperimyocarditis).Cardiomyopathy.

• ♥T-waveinversionwithsimultaneousST-segmentdeviation:acute(ongoing)myocardialischaemia.

• ♥HighT-waves:Normalvariant.Earlyrepolarization.Hyperkalemia.Leftventricularhypertrophy.Leftbundlebranchblock.Occasionallyperimyocarditis.High(hyperacute)T-wavesmaybeseenintheveryearlyphaseofSTEMI.


6.QTcintervalandU-waveASSESSMENTS EVALUATION♥QTcdurationmen≤0,45s.♥QTcdurationwomen≤0,46s.♥ProlongedQTcdurationmaycausemalignantarrhythmias(torsadedepointes,whichisatypeofventriculartachycardia).♥ShortenedQTcduration(≤0.32s)israre,butmayalsocausemalignantventriculararrhythmias.♥TheU-waveisseenoccasionally,especiallyinwell-trainedindividuals,andduringlowheartrate.ItislargestinV3–V4.AmplitudeisonefourthofT-waveamplitude.

♥AcquiredQTprolongation:antiarrhythmicdrugs(procainamide,disopyramide,amiodarone,sotalol),psychiatricmedications(tricyclicantidepressants,SSRI,lithiumetc);antibiotics(macrolides,kinolones,atovaquone,klorokine,amantadin,foscarnet,atazanavir);hypokalemia,hypocalcemia,hypomagnesemia;cerebrovascularinsult(bleeding);myocardialischemia;cardiomyopathy;bradycardia;hypothyroidism;hypothermia.AcompletelistofdrugscausingQTprolongationcanbefoundhere.

• ♥CongenitalQTprolongation:geneticdiseaseofwhichthereareapproximately15variants.

• ♥ShortQTcsyndrome(≤0,32s):causedbyhyperkalcemiaanddigoxintreatment.Maycausemalignantventriculararrhythmia.

• ♥NegativeU-wave:highspecificityforheartdisease(includingischemia).

•

7.ComparewithearlierECGtracingsItisfundamentaltocomparethecurrentECGwithpreviousrecordings.Allchangesareofinterestandmayindicatepathology.

8.ClinicalcontextECGchangesshouldbeputintoaclinicalcontext.Forexample,ST-segmentelevationsarecommoninthepopulationandshouldnotraisesuspicionofmyocardialischemiaifthepatientdonothavesymptomssuggestiveofischemia.

Theguidecontinuesonthenextpage.


Thecardiacconductionsystem

Waves,intervalsanddurationsontheECG


Thewallsoftheleftventricleandtheleadsthatviewthesewalls

TheECGleads


P-wavechanges


STsegmentdepressions


STsegmentelevations


T-wavechanges


Electricalaxisoftheheart

Asevidentfromthefigureabove,thenormalheartaxisisbetween–30°and90°.Iftheaxisismorepositivethan90°itisreferredtoasrightaxisdeviation.Iftheaxisismorenegativethan–30°itisreferredtoasleftaxisdeviation.Theaxisiscalculated(tothenearestdegree)bytheECGmachine.TheaxiscanalsobeapproximatedmanuallybyjudgingthenetdirectionoftheQRScomplexinleadsIandII.Thefollowingrulesapply:

• Normalaxis:NetpositiveQRScomplexinleadsIandII.• Rightaxisdeviation:NetnegativeQRScomplexinleadIbutpositiveinleadII.• Leftaxisdeviation:NetpositiveQRScomplexinleadIbutnegativeinleadII.• Extremeaxisdeviation(–90°to180°):NetnegativeQRScomplexinleadsIandII.


Pro-arrhythmicECGchangesduringsinusrhythm


AssessmentofRPintervalfortachyarrhythmias


DiagnosisandmanagementoftachyarrhythmiaswithnarrowQRScomplex


DiagnosisandmanagementoftachyarrhythmiaswithwideQRScomplex


Intraventricularconductiondefects


Hypertrophyanddilatation


Classificationofacutecoronarysyndromes(ACS)


Criteriaforacutemyocardialinfarction(AMI)

STE-ACS(STEMI)–STelevationacutemyocardialinfarction

CriteriaforSTEMINewSTsegmentelevationsinatleasttwoanatomicallycontiguousleads:

• Menage≥40years:≥2mminV2-V3and≥1mminallotherleads.

• Menage<40years:≥2,5mminV2-V3and≥1mminallotherleads.

• Women(anyage):≥1,5mminV2-V3and≥1mminallotherleads.

• Men&womenV4RandV3R:≥0,5mm,exceptfrommen<30yearsinwhomthecriteriais≥1mm.

• Men&womenV7-V9:≥0,5mm.

NSTE-ACS(NSTE-ACS)–NonSTelevationacutemyocardialinfarction:NSTEMIandunstableangina

• NewhorizontalordownslopingSTsegmentdepressions≥0,5mminatleasttwoanatomicallycontiguousleads.

• Twaveinversion≥1mminatleasttwoanatomicallycontiguousleads.TheseleadsmusthaveevidentR-waves,orR-waveslargerthanS-waves.

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