醫(yī)療護(hù)理醫(yī)學(xué)培訓(xùn) 醫(yī)學(xué)數(shù)字信號(hào)處理心電圖課件

BIOMEDICALDIGITALSIGNALPROCESSING

生物醫(yī)學(xué)數(shù)字信號(hào)處理2009.03霍金教授的辦公室（劍橋大學(xué)）“我的書每增加一個(gè)公式，讀者就減少一半”——霍金教授BME在百年諾貝爾

生理與醫(yī)學(xué)獎(jiǎng)中的份額美國(guó)的保羅-勞特布爾和英國(guó)的彼得-曼斯菲爾德共同獲得了2003年諾貝爾生理學(xué)或醫(yī)學(xué)獎(jiǎng)--核磁共振成像技術(shù)--三維圖象百年總計(jì)(1901-2000)91（屆次）100%Ⅰ屬于BME范疇1618%Ⅱ與BME密切相關(guān)1314%Ⅲ不采用BME方法、技術(shù)、設(shè)備與材料就不能完成的3943%Ⅳ與BME無(wú)關(guān)的2325%教材作者：美國(guó)威斯康辛大學(xué)電氣與計(jì)算機(jī)工程系教授前IEEE生物醫(yī)學(xué)工程學(xué)會(huì)主席

WillisJ.Tompkins書名：BiomedicalDigitalSignalProcessingISBN：7560925790頁(yè)數(shù)：246Lecture2ElectrocardiologyElectrocardiogramECG

第2講心電學(xué)心臟機(jī)械收縮之前，先產(chǎn)生電激動(dòng)，心房和心室的電激動(dòng)可經(jīng)人體組織傳到體表。心電圖是利用心電圖機(jī)從體表記錄心臟每一心動(dòng)周期所產(chǎn)生電活動(dòng)變化曲線圖形。心臟的特殊傳導(dǎo)系統(tǒng)由竇房結(jié)、結(jié)間束（分為前、中、后結(jié)間束）、房間束（起自結(jié)間束，稱Bachmann束）、房間交界區(qū)（房室結(jié)、希氏束）、束支（分為左、右束支，左束支又分為前分支和后分支）以及普肯耶纖維（Pukinjefiber）構(gòu)成。心臟傳導(dǎo)系統(tǒng)與每一心動(dòng)周期順序出現(xiàn)的心電變化密切相關(guān)。正常心電活動(dòng)始于竇房結(jié)，興奮心房的同時(shí)經(jīng)結(jié)間束傳導(dǎo)至房室結(jié)（激動(dòng)傳，然后循希氏束-左、右束支-普肯耶纖維順序傳導(dǎo)，最后興奮心室。這種先后有序的電激動(dòng)的傳播，引起一系列電位改變，形成了心電圖上相應(yīng)的波段。

心電圖機(jī)是記錄心電圖的專用儀器，有單道心電圖機(jī)和多道心電圖機(jī)，多道心電圖機(jī)可以同時(shí)記錄多導(dǎo)聯(lián)的心電，最多有同時(shí)記錄12導(dǎo)聯(lián)的，而單道心電圖機(jī)只能順序記錄12個(gè)導(dǎo)聯(lián)，有手控的心電圖機(jī)，也有程控的、微電腦控制或數(shù)字式的心電圖機(jī)，在很多其它儀器中也常有心電記錄電路模塊。三道心電圖機(jī)

順序記錄１２導(dǎo)聯(lián)心電圖后重新排列在一幅紙上運(yùn)動(dòng)心電圖記錄系統(tǒng)

2.1Electrocardiologicbasis

2.1心電學(xué)基礎(chǔ)2.1.1threebasictechniques

2.1.1三種基本技術(shù)1.StandardclinicalECG（12leads）

1.標(biāo)準(zhǔn)臨床ECG（12導(dǎo)聯(lián)）

2.VCG(3orthogonalleads)

3.MonitoringECG(1or2lead(s))

2.向量心電圖(三維正交導(dǎo)聯(lián))

3.監(jiān)護(hù)ECG(1或2導(dǎo)聯(lián))

2.1.2Electrodes

2.1.2電極Figure2.3Asilver-silverchlorideECGelectrode.Manymodernelectrodeshaveelectrolytelayersthataremadeofafirmgelwhichhasadhesiveproperties.Thefirmgelminimizesthedisturbanceofthechargedoublelayer.2.1.3心電等效發(fā)生器Figure2.4Boththeelectricalandmechanicalconditionsoftheheartareinvolvedindeterminingthecharacteristicsofthespreadofelectricalactivityoverthesurfaceoftheheart．Amodelofthisactivityiscalledacardiacequivalentgenerator．2.1.3Thecardiacequivalentgenerator

2.1.3心電等效發(fā)生器Figure2.4Boththeelectricalandmechanicalconditionsoftheheartareinvolvedindeterminingthecharacteristicsofthespreadofelectricalactivityoverthesurfaceoftheheart．Amodelofthisactivityiscalledacardiacequivalentgenerator．2.1.3Thecardiacequivalentgenerator

Figure2.5Einthovenequilateraltriangle.RAandLAaretherightandleftarmsandLListheleftleg.Acurrentdipoleisacurrentsourceandacurrentsinkseparatedbyadistance.Sincesuchadipolehasmagnitudeanddirectionwhichchangethroughoutaheartbeatasthecellsintheheartdepolarize,thisleadstothevectorrepresentation.電流偶極子是相隔一段距離的電流源和穴(漏)。當(dāng)心肌細(xì)胞去極化(讀注：實(shí)際應(yīng)包含反極化和復(fù)極化)時(shí)，這樣一個(gè)偶極子的大小和方向在整個(gè)心搏周期都是變化的，這就導(dǎo)致了向量表示法。

P(t)=Px(t)X十Py(t)Y十Pz(t)Z(2.1)WhereP(t)isthetime-varyingcardiacvector,Pi(t)aretheorthogonalcomponentsofthevectoralsocalledscalarleads,andX,Y,Z

areunitvectorsinthex,y,zdirections.式中P(t)是時(shí)變心臟偶極子，Pi(t)

為該矢量的正交分量，也稱為標(biāo)量導(dǎo)聯(lián)，X,Y,Z是X,Y,Z方向的單位矢量。Theforwardsolutionprovidesthepotentialatanyarbitrarypointonthebodysurfaceforagivencardiacdipole.Expressedmathematically，對(duì)于給定的心電偶極子，心電正問(wèn)題的解提供了體表任意點(diǎn)的電位，數(shù)學(xué)上表示為，vn(t)=tnxPx(t)十tnyPy(t)十tnzPy(t)(2.2)Thisforwardso1utlonshowsthatthepotentialvn(t)(i．e．,theECS)atanypointnonthebodysurfaceisgivenbythelinearsumoftheproductsofasetoftransfercoefficients[tni]uniquetothatpointandtheCorrespondingorthogonaldipolevectorcomponents[Pi(t)]．

TheECSsaretime-varyingasarethedipo1ecomponents,whilethetransfercoefficientsareonlydependentonthethoracicgeometryandinhomogeneities．Thusforasetofkbodysurfacepotentials(i.e.,1eads)，thereisasetofkequationsthatcanbeexpressedinmatrixform

V=T×P(2.3)

WhereVisakxlvectorrepresentingthetime-varyingpotentials,Tisakx3matrixoftransfercoefficients,Whicharefixedforagivenindividual,andPisthe3x1time-varyingheartvector．心電信號(hào)與偶極子分量一樣是時(shí)變的，而傳遞系數(shù)則只決定于胸部的幾何形狀和非均勻性。因此，一組k體表電位(即,導(dǎo)聯(lián))，就有

kequations個(gè)方程的方程組，并可表示成矩陣形式。

Ofcourse,theheartvectorandtransfercoefficientsareunknownforagivenindividual．Howeverifwehadawaytocomputethisheartvector．Wecoulduseitintheso1utionoftheforwardproblemandobtaintheECSforanybodysurfacelocation．Theapproachtosolvingthisproblemisbasedonaphysicalmodelofthehumantorso．Themodelprovidestransfercoefficientsthatrelatethepotentialsatmanybodysurfacepointstotheheartvector.Withthisinformation，wese1ectthreeECSleadsthatsummarizetheintrinsiccharacteristicsofthedesiredabnormalECStosimulate．Thenwesolvetheinverseproblemtofindthecardiacdipolevector.自然，對(duì)于任一個(gè)體心臟向量P和傳遞系數(shù)T

是未知的。然而，若我們有計(jì)算心臟矢量的方法，就可用之解正問(wèn)題并獲得任意體表位置的ECS。解此類問(wèn)題的方法建立在人體胸廓物理模型的基礎(chǔ)上。該模型提供了眾多體表點(diǎn)的電位與心臟向量的關(guān)系的傳遞系數(shù)。用該信息，則只選擇三個(gè)ECS導(dǎo)聯(lián)就能概括欲模擬的所希望的異常ECS的本質(zhì)特征。然后，就解逆問(wèn)題以求出心臟偶極向量。Ofcourse,theheartvectorandtransfercoefficientsareunknownforagivenindividual．Howeverifwehadawaytocomputethisheartvector．Wecoulduseitintheso1utionoftheforwardproblemandobtaintheECSforanybodysurfacelocation．Theapproachtosolvingthisproblemisbasedonaphysicalmodelofthehumantorso．Themodelprovidestransfercoefficientsthatrelatethepotentialsatmanybodysurfacepointstotheheartvector.Withthisinformation，wese1ectthreeECSleadsthatsummarizetheintrinsiccharacteristicsofthedesiredabnormalECStosimulate．Thenwesolvetheinverseproblemtofindthecardiacdipolevector.自然，對(duì)于任一個(gè)體心臟向量P和傳遞系數(shù)T

是未知的。然而，若我們有計(jì)算心臟矢量的方法，就可用之解正問(wèn)題并獲得任意體表位置的ECS。解此類問(wèn)題的方法建立在人體胸廓物理模型的基礎(chǔ)上。該模型提供了眾多體表點(diǎn)的電位與心臟向量的關(guān)系的傳遞系數(shù)。用該信息，則只選擇三個(gè)ECS導(dǎo)聯(lián)就能概括欲模擬的所希望的異常ECS的本質(zhì)特征。然后，就解逆問(wèn)題以求出心臟偶極向量。Thus,forthreeheartvectorcomponent,therearethreelinearequationsoftheform因此，對(duì)于

三個(gè)心臟向量的分量，有如下形式的三個(gè)線性方程Px(t)=bx1v1(t)+bx2v2(t)+…+bxkvk(t)(2.5)

P

=B×V(2．4)

WhereBisa3xkmatrixofleadcoefficientsthatisdirectlyderivedfrominvertingthetransfercoefficientsmatrixT.

IfweselectkbodysurfaceECSleads[v1(t),v2(t),…，vk(t)]forwhichtheleadcoefficients，T(orB)，areknownfromthephysicalmodelofthehumantorso,wecansolvetheinverseproblemandcomputethetime–varyingheartvector,P,usingEq.(2.4).Oncewehavethesedipolecomponents,wesolvetheforwardproblemusingEq.(2.3)tocomputetheECSforanypointonthebodysurface.如果選擇了K個(gè)體表ECS導(dǎo)聯(lián)[v1(t),v2(t),…vk(t)]，且由人體胸廓的物理模型得知了導(dǎo)聯(lián)系數(shù)T(或B），則就可由(2.4)式求解逆問(wèn)題并計(jì)算時(shí)變的心臟向量P。一旦有了這些偶極分量，則就可用方程(2.3)解正問(wèn)題以計(jì)算任意點(diǎn)的ECS.2.1.4GenesisoftheECS2.1.4心電的起源TimevaryingmotionofthecardiacvectorproducesthebodysurfaceECSforoneheartbeatwithitscharacteristicPandTwavesandQRScomplex.心臟向量的時(shí)變運(yùn)動(dòng)產(chǎn)生體表心電，每搏都有其

特征性的P、T波和QRS復(fù)合波。Figure2.7Basicconfigurationforrecordinganelectrocardiogram.Usingelectrodesattachedtothebody,theECGisrecordedwithaninstrumentationamplifier.(a)Transverse(top)viewofasliceofthebodyshowingtheheartandlungs.(b)FrontalviewshowingelectrodesconnectedinanapproximateleadIIconfiguration.

Forthepointsintimethatthevectorpointstowardtheelectrodeconnectedtothepositiveterminaloftheamplifier,theoutputECSwillbepositive-going．Ifitpointstothenegativeelectrode，theECSwillbenegative．(Thefollowingstatementisbetterandmoredetailed.“Ifthevectorpointstotheelectrodeconnectedtothenegativeterminaloftheamplifier,theECSwillbenegative”．)

在心臟矢量指向的電極連到放大器正端的那些時(shí)間點(diǎn)，輸出的ECS為正的。若心電向量指向的電極連到放大器負(fù)端，則輸出的ECS為負(fù)的。Figure2.8Electrocardiogram(ECG)foronenormalheartbeatshowingtypicalamplitudesandtimedurationfortheP,QRS,Twaves.

Figure2.9Relationshipbetweenthespreadofcardiacelectricalactivationrepresentatvarioustimeinstantsbyasummingvector(intheupperframes)andthegenesisoftheECS(inthelowerframes).

InFigure2.9(a),theslowmovingdepolarizationoftheatriawhichbeginsatthesinoatrial(SA)nodeproducesthePwave.AsFigure2.9(b)shows,thesignalisdelayedintheatrioventricular(AV)noderesultinginanisoelectricregionafterthePwave,thenasthePurkinjesystemstartsdeliveringthestimulustotheventricularmuscle,theonsetoftheQwaveoccurs.InFigure2.9(c),rapiddepolarizationoftheventricularmuscleisdepictedasalarge,fast-movingvectorwhichbeginsproducingtheRwave.Figure2.9(d)illustratesthatthemaximalvectorrepresentsapointintimewhenmostofthecellsaredepolarized,givingrisetothepeakoftheRwave.InFigure2.9(e),thefinalphaseofventriculardepolarizationoccursastheexcitationspreadstowardthebaseoftheventricles(tothetopinthepicture)givingrisetotheSwave.

InFigure2.9(a),theslowmovingdepolarizationoftheatriawhichbeginsatthesinoatrial(SA)nodeproducesthePwave.AsFigure2.9(b)shows,thesignalisdelayedintheatrioventri-cular(AV)noderesultinginanisoelectricregionafterthePwave,thenasthePurkinjesystemstartsdeliveringthestimulustotheventricularmuscle,theonsetoftheQwaveoccurs.InFigure2.9(c),rapiddepolarizationoftheventricularmuscleisdepictedasalarge,fast-movingvectorwhichbeginsproducingtheRwave.Figure2.9(d)illustratesthatthemaximalvectorrepresentsapointintimewhenmostofthecellsaredepolarized,givingrisetothepeakoftheRwave.InFigure2.9(e),thefinalphaseofventriculardepolarizationoccursastheexcitationspreadstowardthebaseoftheventricles(tothetopinthepicture)givingrisetotheSwave.

圖2.9(a)中，始于竇房結(jié)的、慢運(yùn)動(dòng)的心房去極化，產(chǎn)生P波。正如圖2.9(b)所示，信號(hào)通過(guò)房室結(jié)時(shí)被延遲，產(chǎn)生P波后的等電區(qū)。然后，當(dāng)Purkinje系統(tǒng)開(kāi)始發(fā)送刺激到心室肌時(shí)，Q波開(kāi)始發(fā)生。在圖2.9(c)中，心室肌的快速去極化表現(xiàn)為大而快速運(yùn)動(dòng)的矢量，開(kāi)始產(chǎn)生R波。圖2.9(d)說(shuō)明，最大矢量代表了大多數(shù)細(xì)胞去極化的時(shí)間點(diǎn)，產(chǎn)生R波的峰。圖2.9(e)是激動(dòng)向心室的基底部(向圖的頂部)傳播時(shí)的心室去極化的終末時(shí)相，產(chǎn)生S波。2.1.5Thestandardlimbleads

2.1.5標(biāo)準(zhǔn)肢體導(dǎo)聯(lián)I+III–II=0(2.6)

Figure2.10LeadsI,IIandIIIarethepotentialsdifferencebetweenthelimbsasindicated.RAandLAaretherightandleftarmsandLListheleftleg.FromKirchhoff’svoltageslaw,thesumofthevoltagesaroundaloopequalszero.Thus2.1.6Theaugmentedlimbleads

2.1.6加壓肢體導(dǎo)聯(lián)

Figure2.11TheaugmentedlimbleadaVLismeasuredasshown.

Fromthebottomleftloop

i×R+i×R-II=0(2.8)ori×R=II/2(2.9)Fromthebottomrightloop

i×R+III+aVL=0(2.10)OraVL=i×R–III(2.11)CombiningEqs.(2.9)and(2.11)givesaVL=II/2–III=(II-2×III)/2(2.12)

Fromthetopcenterloop

II=III+I(2.13)

SubstitutinggivesaVL=(III–I-2×III)/2=(I–III)/2(2.14)2.2ECSleadsystems

2.2心電導(dǎo)聯(lián)系統(tǒng)

心電學(xué)中有三種常用的基本導(dǎo)聯(lián)系統(tǒng)。最通用的是12導(dǎo)聯(lián)方法，該法定義了12種電位差的集合，構(gòu)成標(biāo)準(zhǔn)臨床ECG。第二種導(dǎo)聯(lián)系統(tǒng)規(guī)定了記錄VCG的電極位置。典型的監(jiān)護(hù)系統(tǒng)只分析1或2個(gè)導(dǎo)聯(lián)。

Therearethreebasicleadsystemsusedincardiology.Themostpopularisthe12-leadapproach,whichdefinesthesetof12potentialdifferencesthatmakeupthestandardclinicalECG.AsecondleadsystemdesignatesthelocationofelectrodesforrecordingVCG.Monitoringsystemstypicallyanalyzeoneortwoleads.

2.2.112leadECS

2.2.112導(dǎo)聯(lián)心電

Figure2.16

Standard12-leadclinicalelectrocardiogram.(a)LeadI.(b)LeadII.(c)LeadIII.Notetheamplifierpolarityforeachoftheselimbleads.(d)aVR.(e)VL.(f)aVF.Theseaug-mentedleadsrequireresistornetworkswhichaveragetwolimbpotentialswhilerecordingthethird.(g)ThesixVleadsarerecordedreferencedtoWilson’scentralterminalwhichistheaverageofallthreelimbpotentials.EachofthesixleadslabeledV1-V6arerecordedfromadifferentanatomicalsiteonthechest.中心電端C相連。所有單極導(dǎo)聯(lián)皆參考此點(diǎn)電壓。所有輸入端皆采用高輸入阻抗電路。12個(gè)標(biāo)準(zhǔn)心電圖導(dǎo)聯(lián)雙極肢體導(dǎo)聯(lián)：I、II、III單極加壓肢體導(dǎo)聯(lián)：aVL、aVR、aVF胸導(dǎo)聯(lián)：V1、V2、V3、V4、V5、V6電極安放的位置：肢體導(dǎo)聯(lián)監(jiān)護(hù)導(dǎo)聯(lián)Figure2.17The12-leadECGofanormalpatient.Calibrationpulsesontheleftsidedesignate1mV.Therecordingspeedis25mm/s.EachminordivisionisImm,sothemajordivisionare5mm.ThusinleadI,theR-waveamplitudeisabout1.1mVandthetimebetweenbeatsisalmost1S(i.e.,heartrateisabout60bpm).ThenotesareID0042804,S=26,L=×2,C=×1,I,II,III,aVR,aVL,aVF,V1,V2,V3,V4,V5,V6,PatientNO:4307400respectively.

2.2.2VCSleadsystem2.2.2向量心電導(dǎo)聯(lián)系統(tǒng)Figure2.18TheelectrodeplacementfortheFrankvectorECSsystem.Figure2.19Theresistornetworkforcombiningbodysurfacepotentialstoproducethethreetime-varyingscalarleadsoftheFrankVCSleadsystem.

Figure2.20Thevectorcardiogramofanormalmalepatient.Thethreetime-varyingscalarleadsforoneheartbeatareshownontheleftandarethex,yandzleadsfromtoptobottom.Inthetopcenteristhefrontalviewofthetipofthevectorasitmovesthroughoutonecomputedheartbeat.Inbottomcenterisatransverseviewofthevectorlooplookingdownfromabovethepatient.Onthefarrightisaleftsagittalviewlookingtowardtheleftsideofthepatient.

2.2.3MonitoringECS

leadsystem2.2.3監(jiān)護(hù)心電導(dǎo)聯(lián)系統(tǒng)Monitoringapplicationdonotusestandardelectrodepositionsbuttypicallyusetwoleads.Sincetheprincipalgoalofthesesystemsistoreliablyrecognizeeachheartbeatandperformrhythmanalysis,electrodesareplacedsothattheprimaryECShasalargeR-waveamplitude.Thisensuresahighsignal-to-noiseratioforbeatdetection.SinceLeadIIhasalargepeakamplitudeformanypatients,thisleadisfrequentlyrecommendedasthefirstchoiceofaprimaryleadbymanymanufacturers.Asecondaryleadwithdifferentelectrodeplacementsservesasabackupincasetheprimaryleaddevelopsproblemssuchaslossofelectrodecontact.

監(jiān)護(hù)應(yīng)用不采用標(biāo)準(zhǔn)電極位置，典型使用兩個(gè)導(dǎo)聯(lián)。因該系統(tǒng)的主要目標(biāo)是可靠識(shí)別每一心搏，完成節(jié)律分析，所以電極的放置以能獲得最大R波幅度為準(zhǔn)，這樣就能保證檢測(cè)心搏時(shí)有高的信噪比。因II導(dǎo)聯(lián)對(duì)很多病人都有大的峰值，故該導(dǎo)聯(lián)常被很多