Transcript EKG Basics - Cobb Learning

EKG Basics
• In 1790, the usually
sedate audience of
scientists gasped in
disbelief as Luigi
Galvani, in a flare of
showmanship, made
a dead frog’s leg
dance by electrical
stimulation.
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EKG Basics
• Galvani knew that
the electrical current
would stimulate the
frog’s legs to jump,
and with repeated
stimuli, he could
make them dance.
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EKG Basics
• In the 1790’s,
bringing a dead frog
“back to life” was a
shocking and ghastly
“supernatural” feat.
• Galvani loved
shocking people!
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EKG Basics
• While conducting
research in 1855,
Kollicker and
Mueller found that
when the motor
nerve to a frog’s leg
was laid over it’s
isolated beating
heart, the leg kicked
with each heartbeat.
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EKG Basics
• “Eureka!” they thought, “the
same electrical stimulus that
causes a frog’s leg to kick
must cause the heart to beat.”
• Therefore, the beating of the
heart must be due to a
rhythmic discharge of
electrical stimuli.
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EKG Basics
• In the mid 1880’s, while
using sensor electrodes
placed on a man’s skin,
Ludwig and Waller
discovered that the
heart’s rhythmic electrical
activity could be
monitored from a
person’s skin.
• However, their apparatus
was not sensitive enough
for clinical use.
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EKG Basics
• Enter Willem Einthoven,
a brilliant scientist who
suspended a silvered
wire between the poles
of a magnet.
• Two skin sensors
(electrodes) placed on a
man were then
connected across the
silvered wire, which ran
between the two poles of
the magnet.
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EKG Basics
• The silvered wire
(suspended in the
magnetic field) twitched
to the rhythm of the
subject’s heartbeat.
• This was very
interesting, but
Einthoven wanted a
timed record.
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EKG Basics
• So Einthoven
projected a tiny light
beam through holes
in the magnet’s poles,
across the twitching
silvered wire.
• The wire’s rhythmic
movements were
recorded as waves
(named P, QRS, and
T) on a moving scroll
of photographic
paper.
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EKG Basics
• The rhythmic movements of the wire
(representing the heartbeat) created a
series of distinct waves in repeating
cycles.
• The waves were named P, QRS, and T.
• The clever Einthoven reasoned that he
could record a heart’s abnormal electrical
activity and compare it to the normal.
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EKG Basics
• Thus, a great
diagnostic tool,
Einthoven’s
Electrokardiogram
was created in
1901.
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EKG Basics
• The electrocardiogram
(EKG) records the
electrical activity of the
heart, providing a record
of cardiac electrical
activity, as well as
valuable information
about the heart’s
function and structure.
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EKG Basics
• The EKG is often
recorded on a ruled
piece a paper that gives
a written record of
cardiac activity.
• Cardiac monitors and
cardiac telemetry
provides the same
information on a display
screen.
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EKG Basics
• The EKG records
the electrical
impulses that
stimulate the heart
muscle
(“myocardium”) to
contract.
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EKG Basics
• The heart’s dominant
pacemaker, the SA
Node, begins the
impulse of
depolarization which
spreads outward in
wave fashion,
stimulating the atria
to contract.
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EKG Basics
• The SA Node is the heart’s dominant
pacemaker, and it’s pacing activity is
known as Sinus Rhythm.
• The ability to generate pacemaking stimuli
is known as automaticity.
• Other regions of the heart also have
automaticity, at slower rates than the SA
Node.
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The “P” Wave
• The electrical
impulse, originating
at the SA Node,
spreads as a wave
of depolarization
through both atria,
and this produces
the “P Wave” on
the EKG.
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The “P” Wave
• Thus, the P wave
represents the
electrical activity
(depolarization) of
both atria, and it
also represents the
simultaneous
contraction of the
atria.
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The AV Node
• The atrial
depolarization
stimulus reaches the
AV Node, where
depolarization
slows, producing a
brief pause, thus
allowing the blood in
the atria to enter the
ventricles.
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The AV Node
• Remember, the
AV Node is the
only electrical
conduction
pathway between
the atria and the
ventricles.
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“HIS” Bundle and
Left and Right Bundle Branches
• Depolarization
passes through the
AV Node slowly, but
upon reaching the
ventricular
conduction system,
depolarization
conducts very
rapidly through the
HIS Bundle, and
the Left and Right
Bundle Branches.
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Purkinje Fibers
• The left and right
Bundle Branches
transmits the wave of
electrical activity to the
Purkinje Fibers.
• The Purkinje Fibers
distribute the
depolarization stimulus
to the ventricular
myocardial cells,
producing a QRS
complex on the EKG.
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Ventricular Conduction System
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The “Q” Wave
• The Q Wave is the
first downward
stroke of the QRS
Complex, and it is
followed by an
upward R Wave.
• The Q Wave is
often not present.
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QRS Complex
• The upward R Wave
is followed by a
downward S Wave.
This total QRS
Complex represents
the electrical activity
of ventricular
depolarization.
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ST Segment
• Following the QRS
complex, there is a
segment of horizontal
baseline known as the
ST Segment, and then
a broad T Wave
appears.
• The ST Segment
represents the initial
phase of Ventricular
Repolarization.
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ST Segment
• The ST Segment
should be flat and
level with the baseline.
• If the ST Segment is
elevated or depressed
beyond the baseline, it
is a sign of serious
problems.
ST Normal
ST Elevation
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T Wave
• The T Wave
represents the final
“rapid” phase of
ventricular
repolarization.
• At this time, the
ventricular myocardial
cells recover their
resting negative
charge, so they will be
ready to depolarize
again.
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QT Interval
• The QT Interval
represents the
duration of ventricular
systole (contraction of
the ventricles) and is
measured from the
beginning of the QRS
until the end of the T
Wave.
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The Cardiac Cycle
• The Cardiac Cycle
is represented by the
P Wave, QRS
Complex, the T
Wave, and the
baseline that follows
until another P Wave
appears. This cycle
is repeated
continuously.
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The Cardiac Cycle
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The Cardiac Cycle
The P Wave represents atrial depolarization
(contraction).
The PR Segment represents the pause at the AV
Node.
The QRS Complex represents ventricular
depolarization (contraction).
The ST Segment represents the initial phase of
ventricular repolarization.
The T Wave represents the final, rapid phase of
ventricular repolarization.
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EKG Paper
• The EKG is recorded
on ruled (graph
paper).
• The smallest divisions
are 1 millimeter (mm)
squares.
• The large black
square has sides that
are 5 mm long.
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EKG Paper
• The horizontal axis
represents time.
• Each small box
represents .04
seconds.
• Each large black
box represents .2
seconds.
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EKG Paper
• By measuring
along the
horizontal axis,
we can
determine the
duration of any
part of the
cardiac cycle.
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EKG Leads
• The standard EKG is composed of 12
separate leads (or wires) that are
attached to electrodes (sensors).
• There are 6 limb leads recorded by using
arm and leg electrodes.
• There are 6 chest leads obtained by
placing electrodes at different positions on
the chest.
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EKG Leads
Limb Leads
Chest Leads
I
V1
II
V2
III
V3
AVR
V4
AVL
V5
AVF
V6
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EKG Lead Location
Leads
What they are looking at:
V1, V2
Right side of heart
-Anterior Descending Artery
V3, V4
Septum between ventricles
-Anterior Descending Artery
V5, V6, I, AVL
Left (lateral) side of heart
-Circumflex Artery
II, III, AVF
Inferior part of heart
-Right or Left Coronary Artery
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Heart Rate
• When examining an
EKG, you should
first consider the
rate.
• The rate is read as
cycles per minute.
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Heart Rate
• The SA Node is the
heart’s dominant
pacemaker,
generating a sinus
rhythm.
• The SA Node paces
at a resting rate
range of 60 to 100
per minute.
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Heart Rate
• When the SA Node
paces the heart rate
slower than 60 per
minute, it is called
Sinus Bradycardia.
• When the SA Node
paces the heart rate
faster than 100 per
minute, it is called
Sinus Tachycardia.
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Heart Rate
• Other potential pacemakers, known as ectopic
foci have the ability to pace the heart (at a
slower rate), if the normal SA Node pacemaking
fails.
• These foci are located in the :
-Atrial Foci – rate of 60-80 per minute
-Junctional Foci – rate of 40-60 per minute
-Ventricular Foci – rate of 20-40 per minute
*Rapid pacemaking activity suppresses slower
activity
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Determining the Heart Rate from an
EKG
• Step 1:
-Find a specific R
Wave that peaks
on a heavy black
line (this will be the
start line)
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Determining the Heart Rate from an
EKG
• Step 2:
-Count off “300,
150, 100” for every
thick black line that
follows the start
line, naming each
line as shown…
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Determining the Heart Rate from an
EKG
• Step 3:
-Count off the
next three lines
after “300, 150,
100” as “75, 60,
50.”
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Determining the Heart Rate from an
EKG
• Step 4:
-Where the next
R Wave falls,
determines the
heart rate.
-It’s that simple!
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Determining the Heart Rate from an
EKG
What is this patient’s Heart Rate?
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Determining the Heart Rate from an
EKG
In the previous EKG,
the heart rate was
60, and P Waves
were absent.
Which ectopic foci
acted as the
pacemaker for this
case of
bradycardia?
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Determining the following Heart Rates
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Determining the rhythm on an
EKG
The EKG provides
the most
accurate means
of identifying
cardiac
arrhythmias
(abnormal
rhythms).
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Determining the rhythm on an
EKG
On an EKG, there is a
consistent distance
(duration) between
similar waves during
a normal , regular
cardiac rhythm.
This is due to the
automaticity of the
SA Node, which
maintains a constant
cycle of pacing
impulses.
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Determining the rhythm on an
EKG
An EKG is scanned for
the repetitive continuity
of a regular rhythm.
Breaks in the
continuity, such as a
pause, presence of an
early (premature) beat,
or sudden rate change
warn us of a rhythm
disturbance.
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Irregular Rhythms
Wandering Pacemaker
An irregular rhythm produced by the
pacemaker activity wandering from the SA
Node to nearby atrial foci.
This produces cycle length variation as well
as variation in the shape of the P Wave
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Wandering Pacemaker
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Multifocal Atrial Tachycardia
Multifocal Atrial Tachycardia (MAT) is a
rhythm of patients with Chronic Obstructive
Pulmonary Disease (COPD).
The heart rate is over 100 bpm with P waves
of various shapes, since three or more atrial
foci are involved.
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Multifocal Atrial Tachycardia
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Atrial Fibrillation
Atrial Fibrillation is caused by the
continuous, rapid firing of multiple atrial
foci. Since no single impulse depolarizes
the atria completely, and only one
occasional atrial depolarization gets
through the AV Node to stimulate the
ventricles, an irregular ventricular rhythm
is produced.
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Atrial Fibrillation
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A
B
C
What is pacing the rhythm of EKG C?
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Premature Beats
Premature beats occur when an irritable
foci fires a single stimulus
Premature Atrial Contraction (PAC)
Premature Ventricular Contraction
(PVC)
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Premature Atrial Contraction
A Premature Atrial Contraction (PAC)
originates suddenly in an irritable atrial
foci, and it produces an abnormal P Wave
earlier than expected.
The abnormal P Wave leads to a QRS
Complex that occurs “out of its normal
rhythm.”
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Premature Atrial Contraction
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Premature Ventricular Contraction
A Premature Ventricular Contraction
(PVC) originates suddenly in an irritable
ventricular foci.
It produces a giant ventricular complex (big
and wide QRS)on the EKG.
There is no P Wave before the abnormal
QRS Complex, because the atria have not
depolarized (contracted).
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Premature Ventricular Contraction
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Tachyarrhythmias
A Tachyarrhythmia originates in a very
irritable foci that paces rapidly.
Sometimes more than one active foci is
generating the pacing stimuli.
Paroxysmal Tachycardia: 150-250 bpm
Flutter: 250-350 bpm
Fibrillation: 350-450 bpm
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First Degree AV Heart Block
Normally, there is a pause at the AV Node, which allows blood
to enter the ventricles.
In First Degree AV Block, there is a longer than normal pause
before ventricular stimulation.
This is seen on an EKG as a PR Interval longer than one large
square (.2 Seconds).
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Myocardial Infarction
Myocardial Infarction
(MI) results from the
complete occlusion of a
coronary artery.
The area of the
myocardium supplied
by the occluded
coronary artery
becomes non-viable
and neither depolarizes
or contracts.
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Myocardial Infarction
The classic triad of
myocardial infarction
is:
Ischemia
Injury
Infarction
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Myocardial Infarction
Ischemia: a decrease
in blood supply from
the coronary arteries
to the myocardium of
the heart.
Characterized by
inverted T Waves on
the EKG
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Myocardial Infarction
Injury: indicates the
acuteness of an
infarct.
ST Elevation denotes
myocardial injury.
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Myocardial Infarction
Infarction: permanent damage
to the myocardium is called
an infarction.
A Significant Q Wave is one
that is at least 1 small square
wide (.04 sec), or 1/3 the
height (or greater) of the
QRS amplitude (Height).
Significant Q Waves indicate
permanent damage to the
myocardium from a heart
attack.
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Myocardial Infarction
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Myocardial Infarction
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Myocardial Infarction
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