EE 5340/7340, SMU Electrical Engineering Department, © 2005 1

Electrocardiogram (ECG)

Generated in the heart amplitude range: 0.5 - 4 mV frequency range: 0.01-250 Hz measurement: surface electrodes

2 EE 5340/7340, SMU Electrical Engineering Department, © 2005 2

Structure of Heart heart chambers

r. atrium, l. atrium r. ventricle, l. ventricle

heart valves tricuspid (RA:RV) Mitral (LA:LV) semilunar (RV:pulm. art.) aortic (LV:aorta)

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Structure of Heart (cont.)

RA

RV

sup. vena cava

pulmonary art.

LA

LV

lungs

pulmonary v.

aorta

coronary arteries

coronary sinus

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Conductive Tissues in Heart

sino-atrial (SA) node internodal tracts AV node Bundle of His Purkinje fibers

} atria

} ventricles

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Cardiac Cycle

venous blood enters LA, passes through TC valve to RV RV contracts, TC valve closes. pulm. valve opens, blood goes to lungs via pulm. art. blood enters LA through pulm. vein, passes through open

mitral valve to LV LA contracts, mitral valve closes, aortic valve opens,

blood goes to aorta. 2 atria contract nearly simultaneously (RA contracts a bit

earlier) 2 ventricles contract simultaneously.

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Cardiac Output and Chamber Pressures

typically 5 l/min 70-80% total blood volume in veins 20% in arteries remainder in capillaries systolic (max) pressure: 95-140 mm Hg (120 average) diastolic (min) pressure: 60-90 mm Hg (80 average) LV: 130/5 mm Hg (sys/dias) LA: 9/5 mm Hg RV 20/5 mm Hg RA: 3/0 mm Hg

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Electrocardiogram Features

P

Q

R

S

T

0.6s

P: atrial depolarization QRS: ventricular depolarization T: ventricular repolarization

typical heart rate: 72 BPM

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Lead Configurations for ECG Measurement

Bipolar Leads Augmented Leads Chest (V) Leads

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Bipolar Leads: lead I

+ _

vo

+

_

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Bipolar Leads: lead II

+ _

vo

+

_

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Bipolar Leads: lead III

+ _

vo

+

_

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Augmented Leads: aVR

+ _

vo

+

_

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Augmented Leads: aVL

+ _

vo

+

_

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Augmented Leads: aVF

+ _

vo

+

_

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Unipolar Chest Leads

v1 v2

v3

v4

v5 v6

v1: fourth intercostal space, at right sternal margin. v2: fourth intercostal space, at left sternal margin. v3: midway between v3 and v4. v4: fifth intercostal space, at mid clavicular line. v5: same level as v4, on anterior axillary line. v6: same level as v4, on mid axillary line.

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Unipolar Chest Leads (cont.)

+ _ +

_

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ECG Lead Color Codes

C (brown)

LA (black)

LL (red)RL (green)

RA (white)

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Surface Cardiac Potentials

taken at t = to suggests an equivalent dipole located within the heart

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Eindhoven’s Triangle

-very crude solution to inverse problem using bipolar limb leads:

RA LA

LL

_

_

+

_

++

lead II

lead I

lead III

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Abnormal ECG Rhythms

Complete Heart Block (AV Block): -atria and ventricles contract independently

P P P P

+

=

RT T TRR

P

R

T P

RT P

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Abnormal ECG Rhythms (cont.)

First Degree AV Block: increased AV node delay, get increased P-R intervals.

Second Degree Block: get one QRS complext for every two P waves.

heart block can be treated with drugs, artificial pacemakers.

P PP

R

T

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Ectopic Focus PVC’s

Ectopic Focus: region of ischemic cardiac tissue that becomes injured, depolarizes spontaneously, may cause an entire ventricular contraction:

PVC

also called extrasystole

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Tachycardia (Rapid Heart Rate)

ectopic focus can also discharge repeatedly producing ventricular (paroxysmal) tachycardia:

all QRS complexes

if etopic focus is located in atrium, can get atrial flutter:

P P P P P

R R

P P P P

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Tachycardia (Rapid Heart Rate)

ectopic focus can also discharge repeatedly producing ventricular (paroxysmal) tachycardia:

all QRS complexes

if etopic focus is located in atrium, can get atrial flutter:

P P P P P

R R

P P P P