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EKG Basics # 2
That Squigglely Line What Does It Really Mean ?
Part # 2
David Arnall, Ph.D., P.T. (2000)
The V Leads
 The
Precordial Chest Leads
Record The Heart’s Electrical
Activity In The Transverse
Or Horizontal Plane.
http://www.publicsafetynet.net/12lead_dx.htm#electrode
 To
Create The Six Precordial
Chest Leads, Each Chest Lead
Is Made Positive & The Whole
Body Is Considered Negative.
Lead Positioning
 V1
Is Placed In The Fourth
Intercostal Space To The Right
Of The Sternum.
 V2 Is Placed In The Fourth
Intercostal Space To The Left
Of The Sternum.
 V3
Is Placed In Between V2
And V4.
 V4 Is Placed In The Fifth
Intercostal Space In The
Midclavicular Line Near The
Nipple.
 V5
Is Placed In Between V4
And V6.
 V6 Is Placed In The Fifth
Intercostal Space In The
Midaxillary Line.
http://endeavor.med.nyu.edu/courses/physiology/courseware/ekg
_pt1/EKGprecordial.html
 When
placing the precordial
chest leads across the thorax,
the clinician places the
electrodes under the pectoralis
major & not over the breasts.
 In
The Chest Cavity, The Heart
Is Positioned With The Right
Ventricle Lying Anteriorly &
Medially While The Left
Ventricle Lies Anterolaterally
& Posteriorly
 Therefore,
Leads V1 & V2 Lie
Directly Over The Right
Ventricle. Their Line Of Sight
Is To View The Electrical
Activity Coming From The
Right Ventricle.
 Leads
V3 & V4 Lie Directly
Over The Interventricular
Septum. Their Line Of Sight Is
To View The Electrical Activity
Of The Interventricular Septum.
http://endeavor.med.nyu.edu/courses/physiology/courseware/ekg
_pt1/EKGprecolead.html
 Leads
V5 & V6 Lie Over The
Left Ventricle. Therefore,
These Leads View The
Electrical Activity Of The Left
Ventricle.
 The
Precordial Chest Leads
Can Be Divided Up Into Areas
Of The Heart They View.
 Leads
V1, V2, V3, & V4 Are
The Anterior Leads.
 Leads
V5 & V6 Look At The
Left Lateral Wall.
In Review
Anterior Chest Leads
V1, V2, V3 & V4
Left Lateral Wall Leads
aVL, Lead I , V5 & V6
Inferior Chest Leads
Lead II, Lead III, & Lead aVF
No Man’s Land
aVR
A Review Of The Waves
& Intervals Of The EKG
The P Wave
 The
P Wave Is The Signal That
Electrical Potential Has Left
The SA Node, Swept Across
The Atria, & Has Initiated
Atrial Contraction.
What Is A Normal P Wave ?
 Duration
: The Normal
Duration Of A P Wave is 2.0 2.5 mm (.04 - .1 sec)
 If It Is Greater Than 2.75 mm
(.11 sec) It Is Considered To Be
An Abnormal P Wave.
http://www.ovcnet.uoguelph.ca/ClinStudies/Courses/Public/Card
iology/Concepts/ECGConcepts13-16.htm
Amplitude
A Normal Amplitude For A
P Wave Is 2-3 mm.
The P Wave Should Always Be
Gently Rounded - Never
Pointed Or Peaked.
 Abnormal
Amplitude Of The P
Wave Is Often Seen In Cor
Pulmonale, A-V Valve Disease,
Hypertension & In Patients
With Congenital Heart Disease
P
Waves Within The Same
Lead That Are Multiformic
Indicate The Presence Of More
Than One Pacemaker In The
Right Atrium.
 In
The Six Limb Leads, You Will
Generally See P Waves In The
Upright Position Except In aVR &
V1 Where They Are Negatively
Deflected.
http://bioscience.org/images/normalh.gif
 You
Will Frequently See
Biphasic P Waves In Lead III,
Lead V2 & Occasionally In
Lead aVL.
BiPhasic P Wave In V1
The PR Interval
 After
The P Wave There Is A
“Silent Period” Where Nothing
Is Happening In The EKG
Tracing. This Quiescent Period
Is Called The PR Interval.
 The
PR Interval Is A Time Lag
And Represents The Period
During Which There Is AV
Nodal Capture Of The SA
Node Signal.
 The
PR Interval Allows The Atria
To Contract (atrial systole) Which
“Tops Off” The Ventricles With
Blood - An Event Called Atrial
Kick.
 The
PR Interval Is Measured
From The Beginning Of The P
Wave To The Beginning Of
The Q Wave Or The Beginning
Of The R Wave If The Q Wave
Is Absent.
http://doyle.ibme.utoronto.ca/EKG/rhythm/EKGTUTORIAL.htm
 The
PR Interval Represents The
Time Period Encompassing
Atrial Depolarization Up To But
Not Including The Start Of
Ventricular Depolarization.
 “A
major portion of the PR
interval reflects the slow
conduction through the AV node
which is controlled by the
sympathetic-parasympathetic
balance within the autonomic
nervous system”.
Marriott’s Practical Electrocardiography, 9th ed., Galen S. Wagner, pg 39, 1994
 Duration
: The Adult PR
Interval Is Normally Between
3-5 mm Or .12 - .20 Seconds In
Duration. Some Cardiologists
Will Say It Is Normal Out To
.22 Seconds (5 1/2 mm)
 If
The PR Interval Is Longer Than
5 mm, It Is Called A Prolonged
PR Interval & May Indicate The
Presence Of An AV Block.
First Degree AV Block
 The
PR Interval Shortens
During Exercise Because Of
The Sympathetic Tone That
Predominates Over The
Heart.
 If
The PR Interval Could Not
Shorten, Along With Other
Segments In The EKG, Then
Acceleration Of Heart Rate
During Exercise Would Be
Difficult If Not Impossible.
 In
Young Children, The PR
Interval Is Shorter Than In
Adults. The Child’s Heart Rate Is
Also Faster.
 In
A 1 Year Old Child At Rest,
The Normal P-R Interval Is
Typically .11 sec. Or Slightly
Under 3 mm.
 For
Children Who Are 6 Years Of
Age, The P-R Interval At Rest Is .13
Seconds Or Slightly Over 3 mm.
 In
Children 12 Years Of Age,
The P-R Interval At Rest Will Be
.14 Seconds Or About 3.5 mm.
 In
Grown Adults 18 Years Of
Age And Older, The P-R
Interval At Rest Will Be 3-5 mm
In Length.
 Prolonged
P-R Intervals Are
Symptomatic Of : AV Blocks Due
To Coronary Disease &
Rheumatic Fever.
 Sometimes,
Prolonged P-R
Intervals Not Related To Heart
Disease, Can Be Seen In Healthy
Athletes - An Aberration Called A
Normal Variant. This Can Be
Seen In About ~ 1% - 2% Of The
Healthy, Young Population.
Pathologies Resulting In PR
Interval Shortening
 Shortened
P-R Intervals Are
Seen In Patients With
Pheochromocytoma And
Wolfe-Parkinson-White
Syndrome
 Pheochromocytoma
is a tumor in
the adrenal medulla that results in
a greater-than-normal release of
catecholamines. The high blood
concentration of catecholamines
causes the heart rate to accelerate.
 Wolff-Parkinson-White
Syndrome
is a medical condition in which
atrioventricular myocardial
accessory pathways electrically
pre-excite the ventricles to
contract producing an extremely
short PR interval.
 These
accessory electrical
pathways are remnants of
fetal pathways that did not
disappear after birth. The
Bundle Of Kent has been
implicated as a common
aberrant pathway in W-P-W.
 W-P-W
occurs in ~ .15% - .20%
of the population or 2:1,000
people. Patients with W-P-W
are otherwise healthy.
 W-P-W
effects men more than
women and can evolve into atrial
and ventricular dysrhythmias
with a general mortality up to 4%
of the effected population.
 Patients
with W-P-W often
complain of episodic symptoms
that include chest discomfort,
dizziness, and palpitations.
http://homepages.enterprise.net/djenkins/ecghome.html
http://www.heartinfo.org/physician/ecg/wpw.htm
The Q Wave
 Definition
: The Q Wave Is The
First Downward Deflection After
The P Wave & Before The R Wave.
 Sometimes
Q Waves Are
Present & Sometimes They
Are Absent Depending On
The Lead.
 It
is common to normally see
Q waves in leads I, II, aVL and
in V4-6.
A
Normal Q Wave Is Not Wider In
Duration Than 0.5 mm Or About
.02 Seconds. Its Normal Amplitude
Is < 1 mm.
Q
Waves Are An Indication
Of Ventricular Septal Wall
Depolarization.
 They
Appear Before The QRS
Complex Because The Fascicle
That Conducts The Signal Is
Higher Than The Right And
Left Bundle Branch That Give
You The QRS Complex.
Q
Waves Of Normal Size Have
No Diagnostic Meaning In
Normal Hearts Except That
The Septum Has Depolarized.
Significant Q Waves
Q
waves In Leads I, II, aVF, &
aVL Can Mean Something If ...
1. They Are Between 25% - 33%
Of The Amplitude Of The R
Wave.
2. They Are Greater Than 0.04
Seconds (1 mm) In Duration.
Q
waves of any size are
normal in leads aVR.
 If
They Are 25%-33% Of The
Total Amplitude Of The R Wave,
Then They Are Significant For
The Presence Of An MI In The
Lead Where The Q Wave
Appears.
 In
Other Words, If The
Significant Q Wave Appears In
Leads II, III Or aVF, Then The
MI Must Have Occurred In The
Inferior Portion Of The Heart The Right Coronary Is Blocked.
 If
The Significant Q Wave
Appeared In Lead I Or aVL,
Then The MI Must Have
Occurred In The Antero-Lateral
Or Lateral Portions Of The Left
Ventricle.
 Since
Lead I & aVL Cover The
Lateral Wall Of The Left
Ventricle, Then The Occlusion
Likely Occurred In The
Circumflex Or The Marginal
Branches Of The Left Coronary.
 Use
The Precordial Chest Leads To
Look For Significant Q Waves For
The Presence Of An MI In The
Anterior Portion Of The Heart V1 - V6 - The LAD Is Occluded.
The R Wave
 Definition
: The R Wave Is The
First Upward Deflection After
The P Wave.
 In
the precordial chest leads,
there should be an R wave
progression - i.e. - an ever
increasing amplitude of the R
wave from V1 through V6
http://www.heartinfo.org/physician/ecg/norm.htm
R
wave progression occurs
because the precordial chest
leads sweep across the thoracic
cage looking from the thinner
right ventricle across to the
thicker left ventricle.
 Loss
of the R wave progression is
abnormal and signals the possible
presence of bundle branch blocks
or the occurrence of a myocardial
infarction.
The S Wave
 Definition
: The S Wave Is
Defined As The First Downward
Deflection After The R Wave.
 There
is a normal progressive
decrease in the size of the S
wave in the precordial leads.
 V1
through V2 should have
large S waves with a
decreasing appearance of S
through V5 and V6.
http://www.heartinfo.org/physician/ecg/norm.htm
QRS Complex Generalities
 Mostly
Upward Deflected
QRS Complexes Are Found In
Leads I, II, III, aVF, aVL, V4,
V5, and V6.
 Mostly
Downward Deflected
QRS Complexes Will Be Seen In
Leads aVR And V1,V2, And
Sometimes V3.
 The
QRS Complex Signals The
Depolarization Of The
Ventricles.
A
Normal QRS Complex Has
A Duration of ~ .06 - .12 Sec.
Or About 1.5 - 3.0 mm.
 If
The QRS Is >3mm, The
Medical Staff Will Construe It
To Mean There Is An Abnormal
Intraventricular Conduction
Pathway.
The ST Segment
 The
ST Segment Is The Pause
After The QRS Complex - The
Interval Between The End Of
The QRS Complex & The
Beginning Of The T Wave.
 It
Symbolizes The End Of
Ventricular Depolarization To
The Start Of Ventricular
Repolarization.
 It
Is During This Phase Of The
EKG When The Heart Is Being
Passively Perfused - The
Windkessel Effect.
 The
ST Segment Slopes
Gently Up Toward The
Isoelectric Line From The J
Point And Ends At The
Beginning Of The T Wave.
The ST Segment
Normal EKG w/ J Point In aVL
 Normal
Up Sloping Of The ST
Segment May Be 1-2 mm In IndoEuropeans And As Much As 4 mm
In African-Americans
 The
Normal Duration Of The
ST Segment Is About 2-3 mm.
ST Segment Elevation
 When
The ST Segment Is
Elevated In A Patient With
Known Disease, It Is Usually
A Sign Of An Evolving
Transmural Infarction - An MI
In Progress.
ST Segment Elevation
ST Segment Elevation
 So....,
The Classic Signs Of An
Acute MI In Progress Are :
–Elevated ST Segment
–Inverted T Wave
–Presence Of A Q Wave
Signs Of An
Anterior Wall Infarction
Anterior Wall Infarction
 An
anterior wall MI is usually
caused by an occlusion of the LAD
 EKG
changes are seen in any of
the precordial chest leads - V1 - V6
ST Segment Changes
With An Acute Anterior MI
 ST
segment elevation in V1-V6
and in Leads I and aVL (the
lateral wall leads).
 Reciprocal ST segment
depression in Leads II, III &
aVF (the inferior leads)
Acute Anterior Myocardial Infarction
http://homepages.enterprise.net/djenkins/ami.html
 In
An Uncomplicated MI,
These EKG Changes Will
Largely Disappear Once The
Infarction Has Frankly
Resolved - Usually In About 3
Or More Days.
Mature Anterior Wall MI
Signs Of An
Inferior Wall Infarction
Inferior Wall Infarction
 This
infarction occurs on the
diaphragmatic surface of the
heart.
 It
is frequently caused by an
occlusion to blood flow through
the right coronary
ST Segment Changes
With An Acute Inferior MI
 ST
segment elevations in Leads
II, III and aVF
 Reciprocal ST segment changes
in Leads I, aVL, V1-V6.
Acute Inferior Myocardial Infarction
http://homepages.enterprise.net/djenkins/ami.html
 In
An Uncomplicated MI,
These EKG Changes Will
Largely Disappear Once The
Infarction Has Frankly
Resolved - Usually In About 3
Days.
A Mature Inferior Wall MI
Old Inferior Wall MI
Signs Of A
Lateral Wall Infarction
Lateral Wall Infarction
 This
type of MI involves the
lateral wall of the heart - the left
ventricle.
 It
is often caused by an occlusion
to blood flow through the
circumflex artery.
 ST
segment elevations will be
seen in the lateral chest leads Leads I, aVL and V5 and V6.
Acute Lateral Wall MI
 In
An Uncomplicated MI,
These EKG Changes Will
Largely Disappear Once The
Infarction Has Frankly
Resolved - Usually In About 3
Days.
Mature Lateral Wall Infarct
 For
All Types Of MI’s, The Q
Wave Often Remains As The
Only Residual Sign That An
Infarction Has Occurred. Also,
The ST Segment May Be
Permanently Depressed.
ST Segment Depression
 When
The ST Segment Is
Depressed, Then It Is Usually
A Sign Of Cardiac Ischemia.
ST Segment Depression
Types Of
ST Segment Depression
 ST
Segment Depression May
Be A Permanent Part Of The
EKG Tracing.
 At
Rest The Patient May Have A
Normal ST Segment. However,
It May Become Depressed As
The Person’s Exercise Level Is
Increased Above The Heart’s
Ability To Receive Adequate
Perfusion.
 The
ST segment depression
will begin to appear as the
heart becomes ischemic
 It will continue to be more
depressed the more ischemic
the heart becomes.
 The
ST segment will normalize
once the exercise intensity is
reduced to a level in which the
heart receives enough perfusion
to support the work that is being
demanded.
The T Wave
 The
T Wave Represents
Repolarization Of The
Ventricles.
 Repolarization Proceeds From
The Apex Of The Heart To The
Base Of The Heart.
 In
Normal Hearts, The T Wave
Is Usually Upright In Leads I,
II, III, aVF, aVL, & V2-V6.
 In
Normal Hearts, The T Wave
Will Usually Be Upside Down
In aVR And V1.
 The
Normal Duration Of The
T Wave Is About 1-2 mm.
 Normal
Amplitude For The T
Wave Is Highly Variable.
T
Waves Get Taller During
GXT’s And Exercise.
T Waves During Infarction
 With
infarction, the T wave
usually becomes tall and narrow referred to as “peaking”.
 With
time and the onset of
ischemia, the T wave will invert.
The QT Interval
 The
QT Interval Encompasses
The Time From The Beginning
Of The Q Or R Wave Through
The End Of The T Wave.
 The
QT Interval Represents
40% Of The Normal Cardiac
Cycle Whether At Rest Or
During Exercise.
 The
QT Interval Becomes
Shorter As The Heart Rate
Increases.
Summary Of Durations &
Amplitudes Of The P-QRS-T
P
Waves
Normal
Duration : 2.5 mm
Normal Amplitude : 2-3 mm
 PR
Intervals
Normal
Duration : 3-5 mm
Q
Waves
Normal
Duration : < .5 mm
Normal Amplitude : <25% of R
amplitude or ~ 1.0 mm
 QRS
Complex
Normal
Duration : < 3.0 mm
Normal Amplitude : Variable
 ST
Segment
Normal
Amplitude : 1-2 mm
Normal Duration : 2-3 mm
T
Wave
Normal
Duration : 2 mm
Normal Amplitude : < 5 mm in
Limb Leads & < 10 mm in
Precordial Leads