12導(dǎo)聯(lián)心電圖基礎(chǔ)課件

The12-LeadelectrocardiogramLocationoftheHeartTheheartislocatedbetweenthelungsbehindthesternumandabovethediaphragm.Itissurroundedbythepericardium.Itssizeisaboutthatofafist,anditsweightisabout250-300g.Itscenterislocatedabout1.5cmtotheleftofthemidsagittalplane.LocationoftheheartinthethoraxAnatomyoftheheartThewallsoftheheartarecomposedofcardiacmuscle,calledmyocardium.Itconsistsoffourcompartments:therightandleftatriaandventriclesTheHeartValvesThetricuspidvalveregulatesbloodflowbetweentherightatriumandrightventricle.ThepulmonaryvalvecontrolsbloodflowfromtherightventricleintothepulmonaryarteriesThemitral

valveletsoxygen-richbloodfromyourlungspassfromtheleftatriumintotheleftventricle.Theaorticvalveletsoxygen-richbloodpassfromtheleftventricleintotheaorta,thentothebodyBloodcirculationviaheart

Thebloodreturnsfromthesystemiccirculationto

therightatriumandfromtheregoesthroughthe

tricuspidvalvetotherightventricle.

Itisejectedfromtherightventriclethroughthe

pulmonaryvalvetothelungs.

Oxygenatedbloodreturnsfromthelungstothe

leftatrium,andfromtherethroughthemitralvalve

totheleftventricle.

Finallybloodispumpedthroughtheaorticvalvetothe

aortaandthesystemiccirculation..ElectricalactivationoftheheartIntheheartmusclecell,ormyocyte,electricactivationtakesplacebymeansofthesamemechanismasinthenervecell,i.e.,fromtheinflowofNaionsacrossthecellmembrane.Theamplitudeoftheactionpotentialisalsosimilar,being100mVforbothnerveandmuscle.Thedurationofthecardiacimpulseis,however,twoordersofmagnitudelongerthanineithernervecellorsceletalmusclecell.Asinthenervecell,repolarizationisaconsequenceoftheoutflowofKions.Thedurationoftheactionimpulseisabout300ms.ElectrophysiologyofthecardiacmusclecellMechanicalcontraction

ofCardiacMuscle

Associatedwiththeelectricactivationofcardiac

musclecellisitsmechanicalcontraction,

whichoccursalittlelater.

Animportantdistinctionbetweencardiacmuscle

tissueand

skeletalmuscleisthatincardiacmuscle,

activationcanpropagate

fromonecelltoanother

inanydirection.

Electricandmechanicalactivity

in

(A)frogsartoriusmusclecell,

(B)frogcardiacmusclecell,

(C)ratuteruswallsmooth

musclecell.

TheConductionSystemElectricalsignalbeginsinthesinoatrial(SA)node:"naturalpacemaker."causestheatriatocontract.Thesignalthenpassesthroughtheatrioventricular(AV)node.sendsthesignaltotheventriclesviathe“bundleofHis”causestheventriclestocontract.TheConductionSystemConductionontheHeart

Thesinoatrialnodeinhumansisintheshapeofacrescentand

isabout

15mmlongand5mmwide.

TheSAnodalcellsareself-excitatory,pacemakercells.

Theygenerateanactionpotentialattherateofabout70perminute.

Fromthesinusnode,activationpropagatesthroughouttheatria,but

cannotpropagatedirectlyacrosstheboundarybetweenatriaand

ventricles.

Theatrioventricularnode(AVnode)islocatedattheboundary

between

theatriaandventricles;ithasanintrinsicfrequencyof

about

50pulses/min.IftheAVnodeistriggeredwithahigherpulsefrequency,itfollowsthis

higherfrequency.Inanormalheart,theAVnodeprovides

theonly

conductingpathfromtheatriatotheventricles.

PropagationfromtheAVnodetotheventriclesisprovidedbya

specializedconductionsystem.

Proximally,thissystemiscomposedofacommonbundle,calledthebundleofHis(afterGermanphysicianWilhelmHis,Jr.,1863-1934).

Moredistally,itseparatesintotwobundlebranchespropagating

alongeachsideoftheseptum,constitutingtherightandleftbundle

branches.(Theleftbundlesubsequentlydividesintoananteriorand

posteriorbranch.)

EvenmoredistallythebundlesramifyintoPurkinjefibers(namedafterJanEvangelistaPurkinje(Czech;1787-1869))thatdivergetotheinnersidesoftheventricularwalls.

Propagation

alongtheconductionsystemtakesplaceatarelativelyhighspeedonceitiswithintheventricularregion,butpriortothis(throughthe

AVnode)thevelocityisextremelyslow.

Fromtheinnersideoftheventricularwall,themany

activationsitescausetheformationofawavefront

whichpropagatesthroughtheventricularmasstoward

theouterwall.

Thisprocessresultsfromcell-to-cellactivation.

Aftereachventricularmuscleregionhasdepolarized,

repolarizationoccurs.PropagationonventricularwallThenormalelectrocardiogramElectricaleventsintheheartElectrophysiologyoftheheart

Different

waveformsforeachofthespecializedcellsIsochronicsurfacesoftheventricularactivation(FromDurreretal.,1970.)Electricfieldoftheheartonthesurfaceofthethorax,recordedbyAugustusWaller(1887).

Thecurves(a)and(b)representtherecordedpositiveandnegativeisopotentiallines,respectively.Theseindicatethattheheartisadipolarsourcehavingthepositiveandnegativepolesat(A)and(B),respectively.Thecurves(c)representtheassumedcurrentflowlines..

LeadVectorThepotentialΦatpointPduetoanydipolepcanbewrittenas

Thevectorcistheleadvector.Notethatthevalueoftheleadvectorisapropertyoftheleadandvolumeconductoranddoesnotdependonthemagnitudeanddirectionofthedipolep.Extendingtheconcept

ofleadvectorUnipolarlead:measuringthevoltagerelativetoaremotereference.Bipolarlead:formedbyaleadpairandisthevoltagebetweenanytwopoints:

The10ECGleadsofWaller.

Einthovenlimbleads(standardleads)andEinthoventriangle.

TheEinthoventriangleisanapproximatedescriptionoftheleadvectorsassociatedwiththelimbleads.

LimbleadsTheEinthovenlimbleads(standardleads)aredefinedinthefollowingway:

LeadI:

VI

=ΦL-ΦR

LeadII:

VII

=ΦF–ΦR

LeadIII:

VIII

=ΦF-ΦL

where

VI

=thevoltageofLeadI

VII

=thevoltageofLeadII

VIII

=thevoltageofLeadIII

ΦL

=potentialattheleftarm

ΦR

=potentialattherightarm

ΦF

=potentialattheleftfootAccordingtoKirchhoff'slawtheseleadvoltageshavethefollowingrelationship:

VI+VIII=VII

henceonlytwoofthesethreeleadsareindependent.StandardleadvectorsformanequilateraltriangleLeadvoltagesfromleadvectors

ThegenerationoftheECGsignalintheEinthovenlimbleads-IThegenerationoftheECGsignalintheEinthovenlimbleads-IITheWilsoncentralterminal(CT)isformedbyconnectinga5kresistancetoeachlimbelectrodeandinterconnectingthefreewires;theCTisthecommonpoint.

TheWilsoncentralterminalrepresentstheaverageofthelimbpotentials.Becausenocurrentflowsthroughahigh-impedancevoltmeter,Kirchhoff'slawrequiresthat

IR+IL+IF=0.(A)

ThecircuitoftheWilsoncentralterminal(CT).

(B)ThelocationoftheWilsoncentralterminalintheimagespace(CT').ItislocatedinthecenteroftheEinthoventriangle.AdditionallimbleadsThreeadditionallimbleadsVR,VL,andVFareobtainedbymeasuringthepotentialbetweeneachlimbelectrodeandtheWilsoncentralterminal.GoldbergerAugmentedleadsGoldbergerobservedthatthesignalsfromtheadditionallimbleadscanbeaugmentedbyomittingthatresistancefromtheWilsoncentralterminalwhichisconnectedtothemeasurementelectrode.Theaforementionedthreelea