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MIT OpenCourseWarehttp://ocw.mit.edu

HST.582J / 6.555J / 16.456J Biomedical Signal and Image ProcessingSpring 2007

For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms.
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Harvard-MIT Division of Health Sciences and TechnologyHST.582J: Biomedical Signal and Image Processing, Spring 2007Course Director: Dr. Julie Greenberg

Introduction to Clinical

Electrocardiography

Andrew Reisner, MD

MGH Dept. of Emergency MedicineVisiting Scientist, HST

Cite as: Andrew Reisner. Course materials for HST.582J / 6.555J / 16.456J, Biomedical Signal and Image Processing, Spring 2007. MIT OpenCourseWare(http://ocw.mit.edu), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].


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Electrocardiography

{ The heart is an electrical organ, and

its activity can be measured non-invasively

{ Wealth of information related to:z The electrical patterns proper

z The geometry of the heart tissue

z The metabolic state of the heart

{ Standard tool used in a wide-range

of medical evaluations


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Cite as: Andrew Reisner. Course materials for HST.582J / 6.555J / 16.456J, Biomedical Signal and Image Processing, Spring 2007. MIT OpenCourseWare(http://ocw.mit.edu), Massachusetts Institute of Technology . Downloaded on [DD Month YYYY].

A heart

Blood circulates, passing nearevery cell in the body, driven by this

pump

actually, two pumps

Atria = turbochargers

Myocardium = muscle

Mechanical systole

Electrical systoleCourtesy of Dr. Roger Mark. HST.542J Quantitative Physiology: Organ

Transport Systems, Spring 2004. (Massachusetts Institute of Technology:

MIT OpenCourseWare). http://ocw.mit.edu (accessed June 17, 2008).

Figure adapted from Phillips RE, Feeney MK, 1980 The Cardiac Rhythms.

Saunders, Philadelphia and from Hoffman BF, Cranefield PF 1960 Electrophysiologyof the Heart. McGraw Hill, New York.
http://ocw.mit.edu/http://ocw.mit.edu/http://ocw.mit.edu/


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To understand the ECG:

{ Electrophysiology of a single cell

{ How a wave of electrical currentpropagates through myocardium

{ Specific structures of the heartthrough which the electrical wavetravels

{ How that leads to a measurablesignal on the surface of the body


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Part I : A li ttle electrophysiology


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Once upon a time, there was a cell:

ATPaseATPase


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timetime

Intracellular

Intracellular

millivoltage

millivoltage

--9090

Resting comfortably

a myocyte


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timetime

Intracellular

Intracellularmillivo

ltage

millivo

ltage

Depolarizing trigger


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timetime

Intracellular

Intracellular

millivoltage

millivoltage

Na

channels

open,briefly


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timetime

Intracellular

Intracellular

millivoltage

millivoltage

In: Na+

Mysterycurrent


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timetime

Intracellular

Intracellular

millivoltage

millivoltage

In: Na+

Ca++ is in balance

with K+ out


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timetime

Intracellular

Intracellular

millivoltage

millivoltage

In: Na+

Excitation/Contraction Coupling:Ca++ causes the Troponin Complex

(C, I & T) to release inhibition

of Actin & Myosin


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timetime

Intracellular

Intracellular

millivoltage

millivoltage

In: Na+

Ca++ in; K+ out

More K+ out;Ca++ flow halts


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timetime

Intracellular

Intracellular

millivoltage

millivoltage

In: Na+

In: Ca++; Out: K+

Out: K+

Sodium channels reset


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timetime

Intracellular

Intracellular

millivoltage

millivoltage

In: Na+

Higher resting potential

Few sodium channels reset

Slower upstroke


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timetime

Intracellular

Intracellular

millivoltage

millivoltage

a pacemaker cell

Slow current of Na+ in;

note the resting potential

is less negativein apacemaker cell

--5555


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timetime

Intracellular

Intracellularmillivoltage

millivoltage

a pacemaker cell

Threshold voltage

--4040


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timetime

Intracellular


millivoltage

Ca++ flows in


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timetime

Intracellular


millivoltage

. . . and K+ flows out


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timetime

Intracellular


millivoltage

. . . and when it is negative

again, a few Na+

channels open


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How a wave of electrical current

propagates through myocardium

{ Typically, an impulse originating

anywhere in the myocardium willpropagate throughout the heart

{

Cells communicate electrically viagap junctions

{ Behaves as a syncytium

{ Think of the wave at a footballgame!

Th di l fi ld d t t fl i di l ll t th


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The dipole field due to current flow in a myocardial cell at the

advancing front of depolarization.

Vm is the transmembrane potential.

Courtesy of Dr. Roger Mark.HST.542J Quantitative Physiology: Organ Transport Systems, Spring 2004. (Massachusetts

Institute of Technology: MIT OpenCourseWare).http://ocw.mit.edu (accessed June 17, 2008).


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Cardiac Electrical Activity

Figure by MIT OpenCourseWare.

Q S

T

R

P

SA node

(Pacemaker)

AV node

(delay)

AV bundle

& branches

(Insulated)

Purkinje fibers (Activation)

Fibro-fatty atrioventricular

groove (Separates atrial and

ventricular tissue)

Contractile

Conductive

Nonconductive

Important specific structures


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Important specific structures

{ Sino-atrial node = pacemaker

(usually){ Atria{ After electrical excitation:

contraction{ Atrioventricular node (a tactical

pause){ Ventricular conducting fibers

(freeways)

{ Ventricular myocardium (surfaceroads)

After electrical excitation: contraction{

The Idealized Spherical Torso with the


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The Idealized Spherical Torso with the

Centrally Located Cardiac Source (Simple

dipole model)

Courtesy of Dr. Roger Mark. HST.542J Quantitative Physiology : Organ Transport Systems, Spring 2004. (Massachusetts

Institute of Technology: MIT OpenCourseWare).http://ocw.mit.edu (accessed June 17, 2008).

Excitation of the Heart


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Figure by MIT OpenCourseWare. After F. Netter.



E it ti f th H t


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Figure by MIT OpenCourseWare. After F. Netter.


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-1200

-1500

aVR

aVF

aVL

I

IIIII

-900

-800

-300

+300

+600

+900+120

0

+1500

1800

00


The temporal pattern of the heart vector


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combined with the geometry of the standard

frontal plane limb leads.


I

IIIII


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Cardiac Electrical Activity


Courtesy of Dr. Roger Mark. HST.542J QuantitativePhysiology: OrganTransport Systems, Spring 2004.(Massachusetts Institute of Technology:MIT OpenCourseWare).http://ocw.mit.edu (accessed June 17, 2008).Figure adaptedfrom Phillips RE, Feeney MK, 1980 The Cardiac Rhythms.

Saunders, Philadelphia and from Hoffman BF, Cranefiel

PF 1960 Electrophysiologyof the Heart. McGraw Hill, New York.

Q S

T

R

P

SA node

(Pacemaker)

AV node

(delay)

AV bundle

& branches

(Insulated)

Purkinje fibers (Activation)

Fibro-fatty atrioventricular

groove (Separates atrial and

ventricular tissue)

Contractile

Conductive

Nonconductive

Normal features of the electrocardiogram.
http://ocw.mit.edu/http://ocw.mit.edu/


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Figure by MIT OpenCourseWare. After p. 50 in Netter, Frank H. A Compilation of Paintings on the Normal and Pathologic

Anatomy and Physiology, Embryology, and Diseases of the Heart, edited by Fredrick F. Yonkman. Vol. 5 of The Ciba

Collection of Medical Illustrations. Summit, N.J.: Ciba Pharmaceutical Company, 1969.


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Normal sinus rhythm

Figure 15 - Normal Sinus RhythmRate 85



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What has changed?

Figure 16 - Sinus TachycardiaRate 122



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Sinus bradycardia

Figure 17 - Sinus BradycardiaRate 48

V1



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timetime

Intracellula

r

Intracellula

rmillivoltag

e

millivoltag

e

Neurohumeral factors

Vagal stimulation makes

the resting potential

MORE NEGATIVE. . .


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timetime

Intracellula

r

Intracellula

rmillivoltag

e

millivoltag

e

Neurohumeral factors

. . . and the pacemaker

current SLOWER. . .


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timetime

Intracellula

r

Intracellula

rmillivoltag

e

millivoltag

e

. . . and raise the

THRESHOLD


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timetime

Intracellula

r

Intracellula

rmillivoltag

e

millivoltag

e

Catecholamines make

the resting potential

MORE EXCITED. . .


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timetime

Intracellula

r

Intracellula

rmillivoltag

e

millivoltag

e

. . . and speed the

PACEMAKER

CURRENT. . .


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timetime

Intracellula

r

Intracellula

rmillivoltag

e

millivoltag

e

. . . and lower the

THRESHOLD FOR

DISCHARGE. . .


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timetime

Intracellular

Intra

cellularmillivoltage

millivoltage

Ricardo Montelban EffectVagal Stimulation:

Image removed due tocopyright restrictions.

Photo of actor RicardoMontelban.


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timetime

Intrac

ellular

Intrac

ellularmillivoltage

millivoltage

Adrenergic Stim. =


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timetime

Intrac

ellular

Intrac

ellularmillivoltage

millivoltage

Adrenergic Stim. =

Potsy Effect

Image removed due tocopyright restrictions.

Photo of characters from TV

show Happy Days, includingPotsy.


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Sinus arrhythmia

Figure 18 - Sinus Arrhythmia


Atrial premature contractions


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Cite as: Andrew Reisner. Course materials for HST.582J / 6.555J / 16.456J, Biomedical Signal and Image Processing, Spring 2007. MIT OpenCourseWarehttp://ocw.mit.edu), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].(

Atrial premature contractions

(see arrowheads)


Figure 25 - Atrial Premature Contractions


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{ Usually just a spark; rarely sufficientfor an explosion

{Leakiness leads to pacemaker-likecurrent

{ Early after-depolarization

{ Late after-depolarization


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Whats going on here?


Figure 36 - Ventricular Premature Contractions

Wave-front Trajectory in a Ventricular


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j y

Premature Contraction.


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Is this the same thing?


Figure 24 - Ventricular Escape Beat


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Whats going on here?

Figure 50 - Complete A-V Block with Junctional Escape Rhythm



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Whats going on here?Figure 35 - Atrial Fibrillation (2 examples)


Non-sustained ventricular tachycardia


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(3 episodes)


Figure 43 - Short Bursts of Ventricular Tachycardia


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Slow Refractory

Quick Refractory

KeyWords:Heterogeneous, Circus, Self-Perpetuating

Side A Side B


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No Longer

Refractory


Side A Side B


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Side A Side B


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Side A Side B


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Side A Side B


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INCREASED

Refractory

Side A Side B


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INCREASED

Refractory

Side A Side B


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INCREASED

Refractory

Side A Side B


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INCREASED

Refractory

Side A Side B


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INCREASED

Refractory

Side A Side B


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INCREASED

Refractory

Side A Side B

Ventricular Fibrillation


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Ventricular Fibrillation

Figure 45 - Three Examples of Ventricular Fibrillation



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Heart attack


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Heart attack


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-1200

-1500

aVR

aVF

aVL

I

II

III

-900

-800

-300

+300

+600

+900+120

0

+1500

1800

00


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Hyperkalemia


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See ECG Wave-Maven (http://ecg.bidmc.harvard.edu/maven/mavenmain.asp) formany other examples of how metabolic conditions can affect the ECG.

Courtesy of Ary Goldberger, M.D. Used with permission.

Source: Nathanson L A, McClennen S, Safran C, Goldberger AL. ECG Wave-Maven: Self-Assessment Program for Students andClinicians.http://ecg.bidmc.harvard.edu. Case #164.
http://ecg.bidmc.harvard.edu/maven/mavenmain.asphttp://ecg.bidmc.harvard.edu/http://ecg.bidmc.harvard.edu/http://ecg.bidmc.harvard.edu/http://ecg.bidmc.harvard.edu/http://ecg.bidmc.harvard.edu/maven/mavenmain.asp


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