12导联心电图基础.ppt

the12-leadelectrocardiogram,locationoftheheart,theheartislocatedbetweenthelungsbehindthesternumandabovethediaphragm.itissurroundedbythepericardium.itssizeisaboutthatofafist,anditsweightisabout250-300g.itscenterislocatedabout1.5cmtotheleftofthemidsagittalplane.,locationoftheheartinthethorax,anatomyoftheheart,thewallsoftheheartarecomposedofcardiacmuscle,calledmyocardium.itconsistsoffourcompartments:therightandleftatriaandventricles,theheartvalves,thetricuspidvalveregulatesbloodflowbetweentherightatriumandrightventricle.thepulmonaryvalvecontrolsbloodflowfromtherightventricleintothepulmonaryarteriesthemitralvalveletsoxygen-richbloodfromyourlungspassfromtheleftatriumintotheleftventricle.theaorticvalveletsoxygen-richbloodpassfromtheleftventricleintotheaorta,thentothebody,bloodcirculationviaheart,thebloodreturnsfromthesystemiccirculationtotherightatriumandfromtheregoesthroughthetricuspidvalvetotherightventricle.itisejectedfromtherightventriclethroughthepulmonaryvalvetothelungs.oxygenatedbloodreturnsfromthelungstotheleftatrium,andfromtherethroughthemitralvalvetotheleftventricle.finallybloodispumpedthroughtheaorticvalvetotheaortaandthesystemiccirculation.,electricalactivationoftheheart,intheheartmusclecell,ormyocyte,electricactivationtakesplacebymeansofthesamemechanismasinthenervecell,i.e.,fromtheinflowofnaionsacrossthecellmembrane.theamplitudeoftheactionpotentialisalsosimilar,being100mvforbothnerveandmuscle.,thedurationofthecardiacimpulseis,however,twoordersofmagnitudelongerthanineithernervecellorsceletalmusclecell.asinthenervecell,repolarizationisaconsequenceoftheoutflowofkions.thedurationoftheactionimpulseisabout300ms.,electrophysiologyofthecardiacmusclecell,mechanicalcontractionofcardiacmuscle,associatedwiththeelectricactivationofcardiacmusclecellisitsmechanicalcontraction,whichoccursalittlelater.animportantdistinctionbetweencardiacmuscletissueandskeletalmuscleisthatincardiacmuscle,activationcanpropagatefromonecelltoanotherinanydirection.,electricandmechanicalactivityin(a)frogsartoriusmusclecell,(b)frogcardiacmusclecell,(c)ratuteruswallsmoothmusclecell.,theconductionsystem,electricalsignalbeginsinthesinoatrial(sa)node:naturalpacemaker.causestheatriatocontract.thesignalthenpassesthroughtheatrioventricular(av)node.sendsthesignaltotheventriclesviathe“bundleofhis”causestheventriclestocontract.,theconductionsystem,conductionontheheart,thesinoatrialnodeinhumansisintheshapeofacrescentandisabout15mmlongand5mmwide.thesanodalcellsareself-excitatory,pacemakercells.theygenerateanactionpotentialattherateofabout70perminute.fromthesinusnode,activationpropagatesthroughouttheatria,butcannotpropagatedirectlyacrosstheboundarybetweenatriaandventricles.theatrioventricularnode(avnode)islocatedattheboundarybetweentheatriaandventricles;ithasanintrinsicfrequencyofabout50pulses/min.iftheavnodeistriggeredwithahigherpulsefrequency,itfollowsthishigherfrequency.inanormalheart,theavnodeprovidestheonlyconductingpathfromtheatriatotheventricles.,propagationfromtheavnodetotheventriclesisprovidedbyaspecializedconductionsystem.proximally,thissystemiscomposedofacommonbundle,calledthebundleofhis(aftergermanphysicianwilhelmhis,jr.,1863-1934).moredistally,itseparatesintotwobundlebranchespropagatingalongeachsideoftheseptum,constitutingtherightandleftbundlebranches.(theleftbundlesubsequentlydividesintoananteriorandposteriorbranch.)evenmoredistallythebundlesramifyintopurkinjefibers(namedafterjanevangelistapurkinje(czech;1787-1869)thatdivergetotheinnersidesoftheventricularwalls.propagationalongtheconductionsystemtakesplaceatarelativelyhighspeedonceitiswithintheventricularregion,butpriortothis(throughtheavnode)thevelocityisextremelyslow.,fromtheinnersideoftheventricularwall,themanyactivationsitescausetheformationofawavefrontwhichpropagatesthroughtheventricularmasstowardtheouterwall.thisprocessresultsfromcell-to-cellactivation.aftereachventricularmuscleregionhasdepolarized,repolarizationoccurs.,propagationonventricularwall,thenormalelectrocardiogram,electricaleventsintheheart,electrophysiologyoftheheartdifferentwaveformsforeachofthespecializedcells,isochronicsurfacesoftheventricularactivation,(fromdurreretal.,1970.),electricfieldoftheheartonthesurfaceofthethorax,recordedbyaugustuswaller(1887).,thecurves(a)and(b)representtherecordedpositiveandnegativeisopotentiallines,respectively.theseindicatethattheheartisadipolarsourcehavingthepositiveandnegativepolesat(a)and(b),respectively.thecurves(c)representtheassumedcurrentflowlines.,leadvector,extendingtheconceptofleadvector,unipolarlead:measuringthevoltagerelativetoaremotereference.bipolarlead:formedbyaleadpairandisthevoltagebetweenanytwopoints:,the10ecgleadsofwaller.einthovenlimbleads(standardleads)andeinthoventriangle.theeinthoventriangleisanapproximatedescriptionoftheleadvectorsassociatedwiththelimbleads.,limbleads,theeinthovenlimbleads(standardleads)aredefinedinthefollowingway:leadi:vi=l-rleadii:vii=frleadiii:viii=f-lwherevi=thevoltageofleadivii=thevoltageofleadiiviii=thevoltageofleadiiil=potentialattheleftarmr=potentialattherightarmf=potentialattheleftfootaccordingtokirchhoffslawtheseleadvoltageshavethefollowingrelationship:vi+viii=viihenceonlytwoofthesethreeleadsareindependent.,standardleadvectorsformanequilateraltriangle,leadvoltagesfromleadvectors,thegenerationoftheecgsignalintheeinthovenlimbleads-i,thegenerationoftheecgsignalintheeinthovenlimbleads-ii,thewilsoncentralterminal(ct)isformedbyconnectinga5kresistancetoeachlimbelectrodeandinterconnectingthefreewires;thectisthecommonpoint.thewilsoncentralterminalrepresentstheaverageofthelimbpotentials.becausenocurrentflowsthroughahigh-impedancevoltmeter,kirchhoffslawrequiresthatir+il+if=0.,(a)thecircuitofthewilsoncentralterminal(ct).(b)thelocationofthewilsoncentralterminalintheimagespace(ct).itislocatedinthecenteroftheeinthoventriangle.,additionallimbleads,threeadditionallimbleadsvr,vl,andvfareobtainedbymeasuringthepotentialbetweeneachlimbelectrodeandthewilsoncentralterminal.,goldbergeraugmentedleads,goldbergerobservedthatthesignalsfromtheadditionallimbleadscanbeaugmentedbyomittingthatresistancefromthewilsoncentralterminalwhichisconnectedtothemeasurementelectrode.theaforementionedthreeleadsmaybereplacedwithanewsetofleadthatarecalledaugmentedleadsbe