ekg for sts.docx

ekg for sts.docx

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ekgforsts

Electrocardiography

anterior前面的

baseline基线

bipolar双极的

coronary冠状动脉

deflection偏转

depolarization去偏极

electrocardiography心电图

electrode电极

horizontaldirection水平方向

hyperthyroidism甲状腺机能亢进

interpretation插值

intracardiac心脏内的

ischemia缺血

isoelectric等电位的

lead导联

passband通带

precordial心前区的

RRintervalR间期

STsegmentST段

transthoracic经胸廓的

unipolar单极的

vector矢量、向量

ventricular心室

Pre-reading

HaveyoueverhadanECG?

WheredoyouseeECGsinthemovies?

WhathappenswhenanECGgiveaflatline?

Reading1

Electrocardiography

History

Focus

ThepartisentitledHistroy,thusitwillprovidethebackgroundtothetopic.Itspurposeistointroduceyoutothefield,sodon'tworryabouteverydetailtoomuch.Focusonthedateofdevelopmentsandwhatwashappeningaroundthesametimeandwhatisstillinusetoday.

AlexanderMuirheadisreportedtohaveattachedwirestoafeverishpatient'swristtoobtainarecordofthepatient'sheartbeatwhilestudyingforhisDoctorofScience（inelectricity）in1872atStBartholomew'sHospital.[5]ThisactivitywasdirectlyrecordedandvisualizedusingaLippmanncapillaryelectrometerbytheBritishphysiologistJohnBurdonSanderson.[6]Thefirsttosystematicallyapproachtheheartfromanelectricalpoint-of-viewwasAugustusWaller,workinginStMary'sHospitalinPaddington,London.[7]HiselectrocardiographmachineconsistedofaLippmanncapillaryelectrometerfixedtoaprojector.Thetracefromtheheartbeatwasprojectedontoaphotographicplatewhichwasitselffixedtoatoytrain.Thisallowedaheartbeattoberecordedinrealtime.In1911hestillsawlittleclinicalapplicationforhiswork.

Einthoven'sECGdevice

AninitialbreakthroughcamewhenWillemEinthoven,workinginLeiden,Netherlands,usedthestringgalvanometerthatheinventedin1903.[8]ThisdevicewasmuchmoresensitivethanboththecapillaryelectrometerthatWallerusedandthestringgalvanometerthathadbeeninventedseparatelyin1897bytheFrenchengineerClémentAder.[9]Ratherthanusingtoday'sself-adhesiveelectrodesEinthoven'ssubjectswouldimmerseeachoftheirlimbsintocontainersofsaltsolutionsfromwhichtheECGwasrecorded.

EinthovenassignedthelettersP,Q,R,SandTtothevariousdeflections,anddescribedtheelectrocardiographicfeaturesofanumberofcardiovasculardisorders.In1924,hewasawardedtheNobelPrizeinMedicineforhisdiscovery.[10]

Thoughthebasicprinciplesofthateraarestillinusetoday,therehavebeenmanyadvancesinelectrocardiographyovertheyears.Theinstrumentation,forexample,hasevolvedfromacumbersomelaboratoryapparatustocompactelectronicsystemsthatoftenincludecomputerizedinterpretationoftheelectrocardiogram.[11]

Beforeyouproceed

Whatotherdevelopmentswerehappeningaroundthistime?

Whatdoyouthinkisstillinusetoday?

Electrocardiography

Focus

WheredidthenameElectrocardiographycomefrom?

WhywouldanEnglishdoctorwriteEKGinsteadofECG?

Electrocardiography（ECGorEKG[fromtheGermanElektrokardiogramm]）isatransthoracic（acrossthethoraxorchest）interpretationoftheelectricalactivityoftheheartoveraperiodoftime,asdetectedbyelectrodesattachedtotheoutersurfaceoftheskinandrecordedbyadeviceexternaltothebody.[1]Therecordingproducedbythisnoninvasiveprocedureistermedanelectrocardiogram（alsoECGorEKG）.

TheetymologyofthewordisderivedfromtheGreekelectro,becauseitisrelatedtoelectricalactivity,cardio,Greekforheart,andgraph,aGreekrootmeaning"towrite".InEnglishspeakingcountries,medicalprofessionalsoftenwriteEKG（theabbreviationfortheGermanwordelektrokardiogramm）inordertoavoidconfusionwithEEGinemergencysituationswherebackgroundnoiseishigh.

MostECGsareperformedfordiagnosticorresearchpurposesonhumanhearts,butmayalsobeperformedonotheranimals,usuallyforresearch.

Beforeyouproceed

WheredidthenameElectrocardiographycomefrom?

WhywouldanEnglishdoctorwriteEKGinsteadofECG?

Function

Focus

HowanECGworks.

TheECGdevicedetectsandamplifiesthetinyelectricalchangesontheskinthatarecausedwhentheheartmuscledepolarizesduringeachheartbeat.Atrest,eachheartmusclecellhasachargeacrossitsouterwall,orcellmembrane.Reducingthischargetowardszeroiscalleddepolarization,whichactivatesthemechanismsinthecellthatcauseittocontract.Duringeachheartbeatahealthyheartwillhaveanorderlyprogressionofawaveofdepolarisationthatistriggeredbythecellsinthesinoatrialnode,spreadsoutthroughtheatrium,passesthrough"intrinsicconductionpathways"andthenspreadsallovertheventricles.Thisisdetectedastinyrisesandfallsinthevoltagebetweentwoelectrodesplacedeithersideoftheheartwhichisdisplayedasawavylineeitheronascreenoronpaper.Thisdisplayindicatestheoverallrhythmoftheheartandweaknessesindifferentpartsoftheheartmuscle.

Usuallymorethan2electrodesareusedandtheycanbecombinedintoanumberofpairs（Forexample:

Leftarm（LA）,rightarm（RA）andleftleg（LL）electrodesformthethreepairsLA+RA,LA+LL,andRA+LL）.Theoutputfromeachpairisknownasalead.Eachleadissaidtolookattheheartfromadifferentangle.DifferenttypesofECGscanbereferredtobythenumberofleadsthatarerecorded,forexample3-lead,5-leador12-leadECGs（sometimessimply"a12-lead"）.A12-leadECGisoneinwhich12differentelectricalsignalsarerecordedatapproximatelythesametimeandwilloftenbeusedasaone-offrecordingofanECG,traditionallyprintedoutasapapercopy.3-and5-leadECGstendtobemonitoredcontinuouslyandviewedonlyonthescreenofanappropriatemonitoringdevice,forexampleduringanoperationorwhilstbeingtransportedinanambulance.Theremayormaynotbeanypermanentrecordofa3-or5-leadECG,dependingontheequipmentused.

Beforeyouproceed

Whatisalead?

Whatarethe3basickindsofECG?

Whichoniscommonlyprintedonpaper?

ECGgraphpaper

Focus

ThelayoutofECGpaperonhowtoreadit.

OnesecondofECGgraphpaper

TheoutputofanECGrecorderisagraph（orsometimesseveralgraphs,representingeachoftheleads）withtimerepresentedonthex-axisandvoltagerepresentedonthey-axis.AdedicatedECGmachinewouldusuallyprintontographpaperwhichhasabackgroundpatternof1mmsquares（ofteninredorgreen）,withbolddivisionsevery5 mminbothverticalandhorizontaldirections.

ItispossibletochangetheoutputofmostECGdevicesbutitisstandardtorepresenteachmVontheyaxisas1 cmandeachsecondas25 mmonthex-axis（thatisapaperspeedof25 mm/s）.Fasterpaperspeedscanbeused,forexample,toresolvefinerdetailintheECG.Atapaperspeedof25 mm/s,onesmallblockofECGpapertranslatesinto40 ms.Fivesmallblocksmakeuponelargeblock,whichtranslatesinto200 ms.Hence,therearefivelargeblockspersecond.Acalibrationsignalmaybeincludedwitharecord.Astandardsignalof1 mVmustmovethestylusvertically1 cm,thatis,twolargesquaresonECGpaper.

Layout

Bydefinition,a12-leadECGwillshowashortsegmentoftherecordingofeachofthe12-leads.Thisisoftenarrangedinagridof4columnsbythreerows,thefirstcolumnsbeingthelimbleads（I,IIandIII）,thesecondcolumntheaugmentedlimbleads（aVR,aVLandaVF）andthelasttwocolumnsbeingthechestleads（V1-V6）.Itisusuallypossibletochangethislayoutsoitisvitaltocheckthelabelstoseewhichleadisrepresented.Eachcolumnwillusuallyrecordthesamemomentintimeforthethreeleadsandthentherecordingwillswitchtothenextcolumnwhichwillrecordtheheartbeatsafterthatpoint.Itispossiblefortheheartrhythmtochangebetweenthecolumnsofleads.

Eachofthesesegmentsisshort,perhaps1-3heartbeatsonly,dependingontheheartrateanditcanbedifficulttoanalyseanyheartrhythmthatshowschangesbetweenheartbeats.Tohelpwiththeanalysisitiscommontoprintoneortwo"rhythmstrips"aswell.ThiswillusuallybeleadII（whichshowstheelectricalsignalfromtheatrium,theP-wave,well）andshowstherhythmforthewholetimetheECGwasrecorded（usually5–6seconds）.SomeECGmachineswillprintasecondleadIIalongtheverybottomofthepaperinadditiontotheoutputdescribedabove.ThisprintingofLeadIIiscontinuousfromstarttofinishoftheprocess.

Theterm"rhythmstrip"mayalsorefertothewholeprintoutfromacontinuousmonitoringsystemwhichmayshowonlyoneleadandiseitherinitiatedbyaclinicianorinresponsetoanalarmorevent.

Beforeyouproceed

HowisECGgraphpaerlayedout?

Whatcanmakeithardtoread?

ReadingComprehension

WhatisthedifferencebetweenECGandEKG?

WhatdoesanECGmeasure?

Whatisalead?

WhatarethebasictypesofECG?

Whenaretheyused?

WhatdoesECGgraphpaperlooklike?

Pre-reading

Reading2

Focus

Differentusesofthewordlead.

Leads

Theterm"lead"inelectrocardiographycausesmuchconfusionbecauseitisusedtorefertotwodifferentthings.InaccordancewithcommonparlancethewordleadmaybeusedtorefertotheelectricalcableattachingtheelectrodestotheECGrecorder.Assuchitmaybeacceptabletorefertothe"leftarmlead"astheelectrode（anditscable）thatshouldbeattachedatorneartheleftarm.Thereareusuallytenoftheseelectrodesinastandard"12-lead"ECG.

Alternatively（andsomewouldsayproperly,inthecontextofelectrocardiography）thewordleadmayrefertothetracingofthevoltagedifferencebetweentwooftheelectrodesandiswhatisactuallyproducedby