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Lecture OutlineSee Syllabus for Detailed Objectives

1. Basis of the electrocardiogram

2. Review conductive athways

!. Standard limb leads". #$% waves& comle'es& intervals&

segments

(. )ector analysis of ventricular

deolari*ation

+. ,ugmented limb leads

-. $hest leads

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he #lectrocardiogram

,s the cardiac mass deolari*es& time varying

differences in electrical otential e'ist on the bodysurface. he electrocardiogram is a recording of these

otential differences. he electrocardiogram is

roduced by a se/uence of cardiac action otentials0 it

is not a recording of an action otential.

#lectrohysiologists sea of the interior of the cell being

negative relative to the outside& whereas electrocardiograhers

sea of the cell being ositive on the outside relative to the

inside. hile this may seem confusing& the meaning is the same.

o roduce an electrocardiogram& cardiac cell membranes

deolari*e 3transition from ositive outside to negative outside4 in

se/uence& both in time and sace& as those membranes

e'erience action otentials.

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he entire surface of a stri of resting myocardium is ositively

charged 3relative to the interior of the cells of the fiber4 so that no

otential difference e'ists between electrodes , and B. , stri chart

recording of this #$% 3right 4 records *ero otential difference and so

remains at its baseline.

+-

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he stri of myocardium deicted has been stimulated at its left side and

is now slightly more than half deolari*ed 3shaded area4. he surface of

the deolari*ed area is negatively charged 3relative to the interior of thecells of the fiber4 so that electrode B 3the ositive electrode4 is facing a

region of greater ositivity than is electrode ,. he stri chart recorder

at the right& which has been wired so that an uward deflection is written

when the ositive electrode B is more ositive than ,& thus inscribes an

ositive 3above baseline4 deflection. he deflection in this #$% reachesits ma'imum when e'actly half of the myocardial stri is deolari*ed.

- +

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he stri of myocardium is now fully deolari*ed. hen the actionotentials of all cells are in hase 2& their e'ternal surfaces are negative

relative to their interiors. Because no otential differences e'ist along the

e'ternal 3or internal4 surfaces of the cells in the stri of myocardium&

electrodes , and B both face a similar degree of negativity. he

deflection in the #$% 3right 4 thus returns to the baseline and remainsthere until reolari*ation begins.

+-

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Stri of myocardium in which reolari*ation has begun in the same

region that was first to be deolari*ed& i.e.& at the left. Because the cell

e'teriors in the reolari*ed region of the stri 3left4 have returned to

their normal& resting ositivity& ositive electrode B is facing a region of

greater negativity than is electrode ,. he #$% at the right thusinscribes a negative 3downward4 deflection.

+-

5f reolari*ation had

roceeded fromright to left& another&

identical uright

3ositive4 deflection

would have been

roduced.

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,fter the stri of myocardium has returned to its fully reolari*ed

state& the #$% 3right 4 returns to its baseline.

+-

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• , wave of deolari*ation aroaching a

ositive electrode of an #$% lead systemcauses a ositive deflection. 3Some te'ts describe this

as 6current flow7 toward the ositive electrode.4

5t then follows that8

• , wave of deolari*ation moving away from a

ositive electrode of an #$% lead system causes a

negative deflection.

• , wave of reolari*ation aroaching a ositive

electrode of an #$% lead system causes a negative

deflection.

• , wave of reolari*ation moving away from a

ositive electrode of an #$% lead system causes aositive deflection.

REMEMBER THIS!!!!!

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, ositive deflection means the tracing is above the

isoelectric 3*ero mv4 line. Such a deflection may be

ascending or descending. On the wave below& all

oints are 9OS55)#. On the descending limb& thedirection of deolari*ation is toward the ositive

electrode& just as it was on the ascending limb.

:;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;- ;;;;;;;;;;;;;;;;;;;;;;

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aves& $omle'es& Segments& and 5ntervals of the

#lectrocardiogram

ave8 Deflection that returns toward the 6baseline.7

$omle'es8 9ortion of the #$% that contains more than one wave.

Segment8 9ortion of the #$% that contains no wave.

5nterval8 9ortion of the #$% that contains at least one wave and one segment.

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aves& $omle'es& Segments& and 5ntervals of the #lectrocardiogram

<ote vertical and hori*ontal scales.

:.2 sec

:.:=

sec

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Standard #$% limb

leads. hen the

electrical a'is 3netdirection of ventricular

deolari*ation4 is

directed downward and

to the left 3i.e.& toward

the ositive electrodeof lead 554& an uward

deflection of the #$%

occurs.

<ormally the net

direction of ventricular

deolari*ation is nearly

arallel to Lead 55.

.

L L

L ,R ,

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Reflection of the vector of ventricular deolari*ation 3,4 on the

a'is of limb lead 5 3B4.

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>+: ?

9rojection of the vector of ventricular deolari*ation

3,4 on the a'es of the three limb leads

Learn to draw these a'es with correct angles and locations of theositive and negative electrodes.

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5f @RS is isoelectric in any lead& the direction of ventricular

deolari*ation will be erendicular to that a'is.

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Standard Limb Leads& ,ugmented Limb Leads& and Standard $hest Leads

Right

,rm

Right

,rm

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,'es of the Standard and ,ugmented Limb LeadsLearn to draw these a'es with correct angles and locations of the

ositive and negative electrodes. <ote that the augmented limb leadsbisect the angles of the standard limb leads.

>!: ?

, f th St d d d , t d Li b L d

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> 5

; a)R

> 55

> a)A> 555

;

a)L

; 5

>a)R

; 55;a)A

; 555

> a)L

,'es of the Standard and ,ugmented Limb Leads.

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9 di l $h t L d

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9recordial or $hest Leads

6$urrent flow7 e/uals 6direction of deolari*ation.7

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Standard $hest Leads

Why does the ECG change from V1 to V6?

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Lecture OutlineSee Syllabus for Detailed Objectives

1. ,bnormal waves and durations

2. ,ltered ventricular deolari*ation

!. Deolari*ation during diastole current of injury

". ,bnormal rates

(. $onduction blocs

+. #arly and abnormal e'citation ectoic beats and

reentry

-. Alutter and fibrillation

Many slides are from Textbook of Medical

Physiology by Guyton

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,lterations in the @RS )oltage

• Cyertrohy increases voltage.

• Loss of myocardium decreases voltage.

• #'cessive fluid around the heart decreases voltage.

• #'cessive air in the lunges decreases voltage.

Guyton, Textbook of Medical Physiology, 7 ed

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Duration of the @RS $omle'

<ormal8 :.:+: ; :.1:: sec

Duration increases with

• Cyertrohy

• Bundle Branch Bloc

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,'es of the three biolar and three uniolar leads.

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Right ,'is DeviationR) Cyertrohy Due to 9ulmonary Stenosis

Guyton, Textbook of Medical Physiology, 7 ed

L ft , i D i ti D t S t i

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Left ,'is Deviation Due to Systemic

Cyertension

%uyton& e'tboo of edical 9hysiology& - ed

L ft , i D i ti

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Left ,'is DeviationLeft Bundle Branch Bloc

Guyton, Tetboo! of Medical "hysiology, # ed

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Dislacement of the S Segment

$urrent of 5njury

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$urrent of 5njury

he resence of deolari*ed myocardium during diastole shifts

the #$% away from the isoelectric line during diastole.

Cowever& by convention& we reference systolic ortions of the

#$% to the diastolic segment. hus& ischemic injury aears to

roduce S segment elevation or deression. $linically

seaing& S segment dislacement is an indication ofm ocardial ischemia.

During the S segment&

all of the ventricular

myocardium is

deolari*ed& so the

#$% is on the : m)&

isoelectric line. his is

true whether or notinjured tissue is

resent.

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Rhythms and ,rrhythmias

• Sinus 3S, nodal4 ; 5s the rate normalE

• #ctoic ; here is the abnormal acemaerE

• ,tria ; Suraventricular

• ,) <ode ; Suraventricular

• )entricle

• Reentry ; hereE

• $onduction Blocs ; hereE $onstant or

5ntermittentE

• 9ree'citation Syndromes ; #lectrical $onduction

Shortcut

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Sinus achycardiaCeart Rate #'ceeding 1:: BeatsFinute


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Sinus BradycardiaCeart Rate Less than +: BeatsFinute


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Sinus ,rrhythmia

Ceart Rate 5ncreases During 5nsiration andDecreases During #'iration


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S, <odal Bloc


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Airst Degree ,) Bloc9rolonged 9R 5nterval

3greater than :.2: sec4


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Second Degree ,) BlocOccasional Droed )entricular Beat


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hird Degree ; $omlete ; ,) Bloc


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9remature ,trial $ontraction39,$4


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,) <odal 9remature $ontraction


<ote normal @RS comle'.

9remature )entricular $ontraction

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9remature )entricular $ontraction

39)$4

<ote characteristics of a 9)$ that does not originate high in the

ventricular conduction system8

1. %reater duration& 24 Gnusual shae& !4 Aollowed by altered wave.


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)entricular 9aro'ysmal achycardia


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Reentry

Ree'citation of cardiac tissue through whiche'citation had reviously assed. here is no

new acemaer discharge.

, necessary condition for reentry is a region

with one;way conduction of e'citation& i.e.&

unidirectional bloc.

he refractory eriod of the reentered region

must be shorter than the roagation timearound the loo.

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Gnidirectional

Bloc

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$onditions hat Aavor Reentry

• Slow conduction velocity

• Long athways

• Short Refractory eriods

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,trial Alutter


<ote irregular ventricular rhythm.

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,trial Aibrillation


<ote irregular ventricular rhythm.

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)entricular Aibrillation


ecg 1 and 2 2012

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