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Nursing 519A
1
SS 8/14
Expected Individual Student
Learning Objectives
• Label and discuss the anatomy of the
heart
• Label and describe the purpose of the
conduction system
• Identify the wave forms and
measurements of Normal Sinus Rhythm
• Identify the following rhythms
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Sinus Bradycardia
Sinus Tachycardia
Supraventricular Tachycardia – Atrial Tachycardia
Paroxysmal Atrial Tachycardia
Atrial Flutter
Atrial Fibrillation
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EISLO
Label and discuss the
anatomy of the heart
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Anatomy of the Heart
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•
The adult heart is about the size of a closed fist and sits in front
of the lungs but behind the sternum, in a space called the
mediastinum. The majority of the heart is located to the left of
the sternum.
The atria are located at the anatomical base of the heart, while
the ventricles are located at the anatomical apex of the heart.
The superior and inferior vena cava, right atrium, and part of
the right ventricle are located under the sternum. The apex of
the heart, also the point of maximal intensity, is located at the
fifth intercostal space, mid-clavicular line.
midclavicular line
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http://www.healthline.com/vpvideo/how-the-heart-works
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The heart is a pump that contains four chambers – right atrium (RA), right
ventricle (RV), left atrium (LA), left ventricle (LV).
The right atrium and right ventricle work as one unit to receive deoxygenated blood from the body and pump it to the lungs where it
exchanges carbon dioxide for oxygen. The muscles in the right ventricle are
relatively small because the pressure in the lungs is weak.
The left atrium and left ventricle work as one unit to receive the oxygenated
blood from the lungs and pump it out to the body. The muscles of the left
ventricle are about twice as big as those of the right because it has to
generate enough force for the blood leaving the heart to reach all parts of
the body.
The heart also contains four valves. Two on the right and two on the left.
The valves, under normal conditions, insure that the blood can only flow in
one direction.
The tricuspid valve is located between the right atrium and right ventricle,
the pulmonary valve is located between the right ventricle and pulmonary
artery leading to the lungs.
The mitral valve is located between the left atrium and left ventricle, the
aortic valve is located between the left ventricle and the aorta which leads
to the body.
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Function of the Heart
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The function of the heart is to circulate blood throughout the
body. To do this it receives blood from the body, sends it to
the lungs, then sends it out to the body again full of oxygen
A cardiac cycle consists of the following steps:
– Blood enters the atria (right and left) at the same time;
ventricles are at rest or diastole
– Tricuspid & mitral valves open, 75-80% of blood falls
into ventricles by gravity; ventricles are at rest or
diastole
– Atria contract, pushing the remaining 20-25% of blood
into the ventricle – this is called atrial kick
– Ventricles contract and push the blood volume into the
lungs (from the right side) or into the aorta ( from the left
side); ventricles contracting or systole
Stroke volume = amount of blood ejected by the ventricles
each time they contract
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Electrolytes
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•
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Three major electrolytes responsible for cardiac conduction
and contraction.
– Sodium (Na+)
– Potassium (K+)
– Calcium (Ca+)
Balance is required to maintain electrical conduction through
the myocardium.
When electrolytes get out of balance there is the potential for
serious dysrhythmias.
There must be an electrical impulse for a mechanical
event to occur
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Potassium Imbalance
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EISLO
Label and describe the
purpose of the
conduction system
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L. Bundle Branch
Junction
L. Bundle Branch
CARDIAC CONDUCTION
SYSTEM
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Myocardial Action Potential
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Depolarization
– Phase 1 of the action potential
– Stimulation of the cardiac cell by the pacemaker cell causing an influx of Na and
Ca, outflow of K.
Repolarization
– Phase 2 of the action potential
– No impulse entering the cells can cause it to depolarize
Relative refractory period
– Phase 3 of the action potential
– Impulses entering the cardiac cell now can cause serious, uncontrolled
reactions.
Absolute refractory period
– Phase 4 of the action potential
– The return of the cardiac cells to resting state.
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ABSOLUTE-RELATIVE
REFRACTORY PERIODS
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ABSOLUTE
The muscle is drained and needs a
moment to recharge
An impulse sent to a muscle during
this phase would not cause it to
contract
From the beginning of the Q to the
middle of the T wave
RELATIVE
The cell is not fully charged but will
still attempt to contract if stimulated
An impulse during this period can
cause premature contractions
leading to compromised filling and
poor ejection of blood from the heart
It can also lead to life-threatening
arrhythmias that severely
compromise the hearts ability to
pump and death can occur quickly
Absolute
Relative
Think of this as flushing a toilet…..when
the tank is emptied you can push the
handle down but it will not flush again
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Autonomic Nervous System
Sympathetic Nervous System
Originates from thoracic vertebrae
Responsible for “fight or flight” response
Causes blood pressure to rise; pulse to go faster; pupils to dilate; respiratory rate
to deepen and get faster; blood is shunted from “non-essential functions”
Triggered by:
•Fear
•Stress
•Pain
•Exercise
•Drugs (prescription/non-prescription)
•Caffeine
•Nicotine
Parasympathetic Nervous System
Originates from carotid arteries called vagal nerve
Responsible for “rest & digest” response
Causes blood pressure to decrease; heart rate slows; respiratory rate slows;
blood is moved to bowels, bladder to enhance digestion; an overall energy
conservation occurs
Triggered by:
•Carotid massage
•Valsalva maneuver
•Abnormal or sudden rise in blood pressure
•Pain
•Nausea/vomiting
•Medications
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EISLO
Identify the wave forms
and measurements of
Normal Sinus Rhythm
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Putting it all together
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The SA Node fires,
stimulates the atria to
contract
This creates the P wave
and tells us the atria
have depolarized
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When the impulse reaches the AV node it is held for a
fraction of a second
This creates the P-R interval which represents atrial
depolarization and repolarization- the time it takes for the
impulse to travel from the SA node to the AV node
Bundle of His
•The impulse leaves the AV node and travels through the Bundle of
His, Bundle Branches and Purkinje Fibers
•This stimulates the ventricles to contract creating the QRS complex
representing ventricular depolarization
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Components of the EKG
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P wave
– Depolarization of the atria
QRS
– Depolarization of the ventricle
T wave
– Repolarization or resting phase of the ventricle
PR Interval
– Delay in the AV node to allow the atria to contract
ST Segment
– represents early phase of ventricular muscle recovery
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QT Interval
– Represents the total time for ventricular depolarization and
repolarization. It should be no longer than ½ of the R-R interval
Isoelectric Line
– Baseline or starting point for each component
Isoelectric
line
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Other Important Components
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T Wave
– T wave corresponds to ventricular repolarization
– Usually rounded and upright
– T waves that are inverted, peaked, or flattened may be
due to electrolyte imbalance, hyperventilation, CNS
disease, ischemia or MI
– Occasionally a U wave is visible following the T wave, it
is smaller and represents repolarization of the Purkinje
Fibers
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EKG Paper
• EKG paper runs at 25 mm/sec
• EKGs are read left to right and are
measured in seconds
V
O
L
T
A
G
E
TIME
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Telemetry
• Electrodes – disc shaped patches with conduction
gel in the middle of the disc
– Electrodes allow conduction of the electrical
impulses from the patient into the machine for
visualization
• Leads – carry the electrical impulses to the
monitoring equipment
• Skin Preparation
• Artifact – occurs when an electrode gel has dried up
or with patient movement
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White
Lead
Black
Lead
RA
Brown
Lead
LA
V1
RL
Red
Lead
LL
Green
Lead
White lead – right upper chest wall
Black lead – left upper chest wall
Green lead – right lower chest
Red lead – left lower chest
Brown lead – right side of sternum 4th intercostal space
White clouds above the green grass, black smoke
over the red fire, brown is the trunk of the tree
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5 Lead Set-up
Lead V1
Leads II, III
Lead I
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Positive and Negative Deflections
QRS complexes can be above or below
the isoelectric line depending on the flow of
electricity across the heart
P, T and U wave inversion (negative
deflection) is not normal
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Rhythm
“Marching Out”
R waves are the same distance apart
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Rate
•
If the rhythm is irregular the most accurate method to
determine the rate is auscultation of the apical pulse
This is a Nursing “standard of care”
Apical pulse is located at the point of maximal intensity
(PMI); 5th intercostal space, mid-clavicular line.
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6-SECOND STRIP METHOD
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This is the least accurate method
Identify (2) 3 second markers (total of 6 seconds)
Count the number of R wave complexes
Multiply this by 10 = the approximate number of
beats per minute
3 seconds
6 seconds
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Memorization Method
Division Method
This is the most accurate method
Count the number of small boxes between 2 R
waves Divide 1500 by the number of boxes
# of small boxes
1500
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Division Method
This is the most accurate method
Count the number of small boxes between 2 R waves
Divide 1500 by the number of boxes
# of small boxes
1500 = 55
OR
# of .20 boxes
300 = 60
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P Waves
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Are P waves present?
Do they have a positive or negative deflection
Is there one in front of each QRS (1:1)
Remember that the P wave represents Atrial depolarization
PR Interval
The SA node fires, atria contract, impulse travels to the AV node where
it is held for a fraction of a second, this creates the P-R interval – atrial
depolarization and repolarization
Prolonged P-R interval can be indicative of impaired AV node
conduction
Measure from the beginning of the P-wave to the beginning of the QRS
Normal range is .12 – .20
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QRS Complex
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Represents ventricular depolarization
Impulse leaves AV node, travels through the Bundle of His, Bundle
Branches and Purkinje Fibers stimulating the ventricles to contract
Measure from the negative deflection of the Q to where the S meets
the isoelectric line. If no Q wave is present measure to the R wave.
Normal range is ≤ .12 seconds
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Q-T INTERVAL
• Average Range .34 - .44 this measurement
varies with heart rate
– A measurement of >.47 indicates possible
myocardial problems
– >.50 is in the danger zone
• Begins at the Q wave and ends at the end
of the T wave.
• The most accurate measurement of the QT
is the QTc (c means corrected) interval.
QT(c) =
QT interval
√RR interval
• Or said another way: The QT interval divided by
the square root of the R to R interval
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EKG Interpretation-Criteria
• General rules
– Read each strip left to right
– Be consistent look at each wave form and measurement
across the strip
– Learn normal parameters
• Rhythm
– Regular or irregular
• Rate
– Calculate the rate
• P waves
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Present?
Upright?
1 in front of each QRS?
PR Interval .12-.20
• QRS complex
– Narrow, look the same
– Measurement < .12
• QT Interval
– .34 - .44
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Sinus Rhythms
Normal Sinus Rhythm
• Rhythm – Regular
• Rate – 60 – 100 bpm
• P waves – upright and matched 1:1
(each QRS is preceded by a P wave)
• PR Interval – .12 – .20
• QRS Duration - ≤.12
• QT Interval - .34 - .44
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EISLO
Identify the following
rhythms
– Sinus Bradycardia
– Sinus Tachycardia
– Supraventricular Tachycardia
(Atrial Tachycardia)
– Paroxysmal Atrial Tachycardia
– Atrial Flutter
– Atrial Fibrillation
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Sinus Bradycardia
• Same criteria as Sinus Rhythm except
– The rate is < 60 (40-59)
Sinus Tachycardia
• Same criteria as Sinus Rhythm except
– The rate is > 100 (101-140)
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Sinus Arrhythmia
• Rhythm – slightly Irregular, varies with respirations
due to vagal stimulation
• Rate – variable
• P waves – A P wave precedes each QRS complex.
All P waves look alike an all are upright
• PR Interval – .12 – .20
• QRS Complex - ≤.12
• QT interval - .34 - .44
inspiration
speeds up
expiration
slows down
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Supraventricular Tachycardia (SVT)
Atrial Tachycardia
• Rhythm – Regular
• Rate – >150 bpm
• P Waves
– Due to fast rate the T and P are
together in one waveform
• PR and QT interval not measurable
• QRS Complex - ≤.12
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Paroxysmal Atrial Tachycardia
PAT has a sudden onset, the heart resolves the
problem without intervention
• Rhythm – Regular with an underlying rhythm
• Rate – >150 bpm – the heart resets the rate by
itself
• P Waves
– Due to fast rate the T and P are together in one
waveform
• PR and QT interval - not measurable in the SVT state
but the parameters can be measured in the underlying
rhythm
• QRS Complex - ≤.12
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Atrial Flutter
• Rhythm – regular or irregular
• Rate – variable
• P waves
– Sawtooth in shape
• PR interval and QT interval not
measurable
• QRS Complex - ≤.12
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Atrial Fibrillation
• Atrial fibrillation is the chaotic
depolarization of the atria. The result
is a very disorganized EKG rhythm
• Rhythm – always irregular
• Rate – variable
• P Waves – isoelectric line appears to be
undulating, chaotic, no organized or
identifiable wave forms
• PR and QT interval – not measurable
• QRS Complex - ≤.12
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Lethal Rhythms you need to
recognize
Ventricular Tachycardia
Ventricular Fibrillation
Asystole
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