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Basic EKG interpretation
Janie McCloskey,
RN, MSN
Objectives
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Explain the relationship between mechanical
and electrical events in the heart
Interpret basic dysrhythmias generated from
the SA and AV nodes as well as the atria and
ventricles
Describe appropriate interventions for common
dysrhythmias
Explain the basics of cardiac pacing
Basic Cardiac Review
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Heart is a muscular organ behind the sternum
between the 2nd and 6th rib
Bottom tip points the left and is called the apex
The atria lie to right
Major function is to circulate blood
4 chambers
atrial septum
ventricular septum
Basic Cardiac Review
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Septa divide the heart into 2 pumping systems,
the right and left heart
Right heart pumps blood to the pulmonary
circulation.
Left heart pumps to the body.
The heart contracts and relaxes in an
organized rhythm by mechanical and electrical
factors.
Mechanical Activity of the Heart
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Mechanical power comes from muscular
contractions: diastole and systole
Diastole occurs when the ventricles receive
blood from the atria
Systole is the contraction of the ventricles to
send blood to the PA and the aorta.
Systole and Diastole occur simultaneously
between the right and left sides of the heart.
Electrical Activity of the Heart
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Automaticity is the ability of cardiac cells and
muscle to generate its own electrical activity
Cardiac Conduction System
transmitselectrical impulses to cause the heart
to contract.
Electrical Activity of the Heart
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Electrical activity is divided into 2 phases:
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Depolarization-a stimulated state (contraction)
Repolarization-a recovery state
Depolarization and Repolarization occur
because of a cellular shift of – and + charged
ions in and around myocardial cells.
Electrical Activity of the Heart
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At rest, K+ in greater amounts intracellularly
and Ca+ and Na+ are in greater amounts
extracellularly
When the cells are electrically stimulated, they
change their permeability.
Sodium and calcium enter the cell quickly
Potassium moves out of the cell
Depolarization/Repolarization
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Depolarization is the active electrical phase
associated with systole
Toward the end of depolarization, Na stops
shifting, Na and K are returned to their proper
places to allow the heart to repolarize and wait
for the next depolarization
Repolarization is a resting state of the muscle
when the ventricles fill known mechanically as
diastole
Refractory Periods
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Absolute Refractory Period is when cells
have depolarized and are starting to repolarize.
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No impulse can be conducted to cause a
contraction
Relative Refractory Period is a vulnerable
time for the heart
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Cells are repolarized to the point that a strong
electrical impulse would result in contraction
Electrical Conduction Components
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Sinoatrial Node (SA Node)
Atrio-Ventricular Node (AV Node)
Ventricular System (His Purkinje System)
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Bundle of His
R and L Bundle Branches
Purkinje fibers
Electrical Conduction Components
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SA Node
 Located in RA where the superior vena cava
joins the atrial tissue mass
 The heart’s pacemaker
 Initiates 60-100 bpm
 Depolarization and simultaneous contraction
of the atria cause a P Wave.
Electrical Conduction Components
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AV Node
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located in lower R atrium
 Only “normal” conduction pathway between
atria and ventricles
 Delays transmission of impulse from atria to
ventricles to allow ventricles to fill
 Acts as a back up pacemaker 40-60bpm
Electrical Conduction Components
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Bundle of His: Thick cord of nerve fibers in
the first 1/3 of the ventricular septum
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Divides into 2 bundles
R bundle branch has 1 fascicle
L bundle branch has 2 fascicles:
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anterior/superior
posterior/inferior
Electrical Conduction Component
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Purkinje Fibers
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Network that carries electrical impulses deep into
ventricular muscle
Can also provide an intrinsic rhythm of 20-40 bpm if
the nodes fail to conduct and impulse.
The His Purkinje System
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Activates ventricular depolarization - contraction of
the ventricles seen as QRS complex
Rate of Pacemakers
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SA node 60-100 BPM
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AV node 40-60 BPM
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Ventricles
20-40 BPM
EKG’s
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Monitor electrical activity of the heart on graph
paper
12 lead EKG (diagnostic)
Continuous cardiac monitoring
 5 lead monitoring (most critical care units)
 3 lead monitoring (ER’s and Telemetry)
Leads
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Lead refers to the electrodes placed on the
patient’s skin to record the electrical activity
Each waveform is representative of an
electrical event in the heart
Leads have conductive adhesive to ensure a
good tracing of electrical activity
Lead position will determine whether the
waveforms are positive or negative
Telemetry Monitoring
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5-lead or 3-lead system
Most common positions are Lead II or MCL1
upright P and clear QRS views
Modified Chest lead simulates V1
6 second strips are run at the start of each
shift, specific hourly intervals, and prn
EKG Paper
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EKG paper is a collection of small squares
inside large boxes.
Time is measured horizontally
1 small square = 0.04 seconds
There are 5 small squares to each large box
5 squares x 0.04 seconds = 0.20 seconds
1 large box which is dark line to dark line is
equal to 0.20 seconds
Measuring Time
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Slashes on the top of the graph paper mark the
time
There are 15 boxes between each slash mark
(15 x 0.20 seconds = 3 seconds)
Space between 1st and 2nd slash = 3 seconds
Space between 1st and 3rd slash = 6 seconds
Measuring Voltage
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Voltage is measured vertically
There is an imaginary baseline called the
isoelectric line where the voltage is at zero
1 small vertical square = 0.1millivolt(mV) and
1mm2
1 large square = 0.5 millivolt (mV) 5mm2
EKG paper: how to measure
•Each small box = 0.04 sec
•Each large box = 0.20 sec
•Each small box = 0.1 mV
•Each large box = 0.5 mV
0.1 mV
0.5 mV
The Cardiac Cycle - ECG
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Electrical activity can be graphed and
measured on paper.
Each waveform is related to an electrical event
in the heart.
Changes in the waves and measured
segments indicate alteration in normal
electrical conduction system
P Waves
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SA Node fires an impulse to depolarize the atria
P waves indicate Atrial Depolarization
Rounded in shape, usually upright
Usually no more than 0.3 mV high
Changes can mean the impulse came from
somewhere other than SA node.
Absence can mean SA failure
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See page 7 in graphics booklet
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PR Interval
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PR interval = total time of atrial depolarization
From the SA to the AV Node impulse is delayed
before reaching the bundle of His
It is a pause after the P, tracing returns to the
isoelectric line
Normal PR interval is 0.12 – 0.20 seconds
Measured from beginning of P to start of QRS
QRS Complex
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QRS complex is caused by ventricular
depolarization
Q is the first negative deflection (if present)
R is the first upward stroke usually tall
S is the negative stroke after the R
Normal length of QRS is 0.04 – 0.12 seconds *
< 0.12
(Sole 0.06 - 0.10)
Wide QRS indicates conduction problems in the
ventricles
QT Interval
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QT Interval measures the time for ventricular
depolarization and repolarization
QT Interval is from the beginning of the QRS
complex to the end of the T wave
The slower the HR, the longer the QT (usually
0.32-0.44)
Not used in Rhythm determination
ST Segment
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Connects the QRS complex with the T wave
Segment not a wave
Should be isoelectric
ST depression is ischemia medication
Not measured by itself, but incorporated into
the QT interval
T Wave
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Represents ventricular repolarization
Ventricles recover rapidly causes a T Wave
Occurs after the QRS complex
Usually positive, broad, and rounded waveform
T waves are not directly measured
Relative refractory period
Interpreting Rhythms 6 Easy Steps
(Any order)
Step 1
 Look for P and QRS sequence
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There should be a P before each QRS
Are the P’s consistent?
Should be a QRS after each P
QRS should be followed by T’s
Interpreting Rhythms
Step 2
♥ Check PR interval
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Should be 0.12 –0.20
Are PR intervals consistent
Interpreting Rhythms
Step 3
 QRS duration and configuration
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Normal length of QRS is 0.04 – 0.12 seconds
* (Sole 0.06 - 0.10)
Q if present is the first negative deflection
R is the first positive
S is the negative deflection after the R
Are the QRS complexes consistent?
Interpreting Rhythms
Step 4
 What is the rate?
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The rate tells you how fast the heart is depolarizing
HR = 300 / # of boxes between R to R interval
HR = 1500 / # of small squares between an R to R
interval. This only works on regular rhythms!
HR = # of QRS complex in a 6 second strip x10
OR…find an R on a black line and count each black
line 300, 150, 100, 75, 60, 50 to the next R.
Interpreting Rhythms
Step 5
 Is the rhythm regular or irregular?
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If P waves are present, its an atrial rhythm
Check regularity with calipers or paper and pen
Measure P to P and R to R intervals
If the marks are off by more than one small box it is
irregular
Interpreting Rhythms
Step 6
 Interpret the rhythm
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Use systematic analysis by applying the rules
Each rhythm is a DEFINITION!!!!
Let’s learn some rhythms so you can apply
what you have learned!
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Each rhythm has unique characteristics
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Hence why they each have their own name!
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Dysrhythmia interpretation is developed
through practice
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First you need to learn Normal,
then you will recognize Abnormal!
Normal Sinus Rhythm
(Sinus Rhythm)
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The benchmark of all rhythms. Understanding
this normal rhythm will help you see abnormal
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P before each QRS
Upright small rounded P waves
Atrial and ventricular rate are the same (60-100)
Rhythm is essentially regular
PR interval is 0.12 – 0.20
QRS is 0.04 to 0.12 seconds * (Sole 0.06 - 0.10)
Normal Sinus Rhythm
HR = 300 / # of boxes between R to R interval
HR = 1500 / # of small squares between an R to R interval.
This only works on regular rhythms!
HR = # of QRS complex in a 6 second strip x10
OR…find an R on a black line and count each black line 300,
150, 100, 75, 60, 50 to the next R.
Learning Dysrhythmias
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Dysrhythmia and Arrhythmia are sometimes
used interchangeably.
Dysrhymthia is a better term because it refers
to irregularities in Rhythm where as arrhythmia
literally means without a rhythm.
You have learned the only normal rhythm, now
let’s learn some Dysrhythmias!!!!
Sinus Dysrhythmias
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Sinus dysrhythmias involve problems with the
SA node or its conduction. They are usually
caused by medications, vagal stimulation,
ischemia, or hypoxia.
Sinus Dysrhythmias include:
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Sinus Bradycardia
Sinus Tachycardia
Sinus Dysrhythmia
Sinus Arrest/Sinus Exit Block
Sinus Bradycardia
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It’s first name is Sinus so expect:
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Upright rounded P waves
Regular rhythm
PR interval 0.12 – 0.20
Normal QRS 0.04 – 0.12 (Sole 0.06 – 0.10)
Its last name is Bradycardia so the key is that
its rate is less than 60 bpm
Sinus Bradycardia
Causes and Treatment
Causes
 Increased vagal stimulation
 Effects of medication
 SA node ischemia, hypoxia, IICP
 Normal in some athletes
Treatment
 Pts usually asymptomatic (sleeping) need no Tx
 If symptomatic, Atropine, Epinephrine, Dopamine or
temporary pacemaker
Sinus Tachycardia
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First name is sinus so expect:
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Upright rounded P waves
Regular rhythm
PR interval 0.12 – 0.20
Normal QRS 0.04 – 0.12 (Sole 0.06 – 0.10)
Its last name is Tachycardia so the key is that
its rate is greater than 100 bpm (but less than
150)
Sinus Tachycardia
Causes and Treatments
Causes:
 Exercise
 Stimulants
 Increased body temperature
 Hypo and Hypervolemia
Treatments:
 Assess reason for tachycardia, if asymptomatic, no tx.
 If symptomatic, remove stimulus, and give Ca Channel
blockers, Beta blockers, vagal stimulation
Atrial Dysrhythmias
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Atrial Dysrhythmias are most often caused by
increased automaticity in the R and L atria or
both:
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PAC’s
SVT/PAT
Atrial Flutter
Atrial Fibrillation
Premature Atrial Contractions
Its name defines it!
♥ Underlying rhythm is regular, usually NSR, PAC
causes irregularity
♥ Rate variable, dependent on underlying rhythm
and frequency of PACs.
♥ P wave
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premature
different shape from beat generated from SA node,
may be pointed, inverted, missing or a shortened PR
interval
May impose on the preceding T wave
QRS normal
PAC
Cause and Treatment
Cause:
 Impulses come from various foci in the atria
 Usually benign
 Can indicate atrial irritability
Treatment
 PAC’s are usually benign – no treatment
 If patient is symptomatic withdraw stimuli and if
necessary tx with Beta blockers
Paroxysmal Atrial Tachycardia
Supraventricular Tachycardia
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PAT and SVT are just that!
Impulses originate above the ventricles (atria)
Rate greater than 150 bpm
P waves are present although can be difficult to
detect because of rate.
PR is not measurable
QRS is usually normal, but fast
Paroxysmal means starts and ends suddenly
PAT and SVT
Causes and Treatments
Cause:
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Usually caused by emotional stress, overexertion,
caffeine, tobacco, deep inspiration
Also common in Rheumatic heart disease, CAD, or
digitalis toxicity
Treatment:
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Vagal Stimulation
Medication: Adenosine, Cardizem, or Beta blockers
Paroxysmal Atrial Tachycardia
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- Starts and stops suddenly
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- Rate greater than 150
Atrial Flutter
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First name is Atrial – focus is from the atria
Last name is Flutter because of characteristic
biphasic flutter waves (sawtooth)
Irritable foci in the atria fire constantly
Atrial rates are 250-350, usually regular
Ventricular rate are slower, regular
PR interval not measurable
QRS is usually normal
Qualified as 2:1, 3:1, 4:1
Atrial Flutter
Cause and Treatment
Cause:
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Rarely occurs in normal hearts
Associated with CAD, HTN, MVP, CHF, PE
Treatments:
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If rapid ventricular response (2:1) medication to control
ventricular rate: diltiazem, digoxin, beta blockers
Anti-arrhythmic drugs: Pronestyl, Cordarone, Corvert
Patients are sometimes Heparinized to prevent stroke
Cardioversion, Radiofrequency catheter ablation
Atrial Fibrillation
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First name is Atrial – focus is from the atria
Last name is Fibrillation so the atria are quivering not
contracting purposefully.
Wavy baseline with no discernable P wave
Atrial rate is greater than 350, but not measurable
Atrial and ventricular rhythms are irregular
Ventricular response is usually less than 100 bpm
No measurable PR interval
QRS is normal
Atrial Fibrillation
Causes and Treatments
Causes:
 Underlying heart disease, CAD, HTN, cardiomyopathy,
ETOH, cardiac surgery
 Can be chronic or intermittent
 Most common arrhythmia in US and Canada
 Incidence increases with age
Treatment:
 Beta blockers, Ca channel blockers and cardioversion
 Patients are sometimes Heparinized to prevent stroke
First Degree AV Block
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This is a block caused by the AV Node
Every SA impulse is conducted but the length
of AV conduction is prolonged
Conduction is normal through the ventricles
What you will see is:
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Normal rate and rhythm
P wave is normal
Prolonged PR – greater than 0.20
QRS is normal
First Degree AV Block
Causes:
 MI, angina, hyperthyroidism, vagal stimulation
 Medication like Digitalis, Beta blockers, IV
Verapamil
Treatment:
 Usually none
 Patient is watched if it occurs after a cardiac
event because it can be a precursor to more
serious blocks
Second Degree AV Block
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Second degree is not a prolonged atrial
impulse, it is an interruption of conduction
On EKG you will see impulses initiated but no
conduction to the ventricles so you have some
P waves without QRS following them
There are 2 types:
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Mobitz Type I (Wenckebach)
Mobitz Type II
Second Degree AV Block
Mobitz Type I
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Occurs within the AV node
Less serious of the 2 types
Each impulse produces a longer and longer
delay until 3rd or 4th beat does not make it
through to the ventricles and the beat is dropped
P’s normal, PR’s gradually longer
Atrial rate is normal (60-100) vent is slower
QRS is normal but complex is dropped
Second Degree AV Block
Mobitz Type I
Causes:
 Usually associated with ischemia in an Inferior
wall MI, Digitalis toxicity, medications
 Usually temporary and tolerated well
Treatment:
 If asymptomatic, observation
 If symptomatic, medication or temp pacer
Second Degree AV Block
Mobitz Type II
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More serious of the 2nd degree AV Blocks
Block occurs at or below the AV Node, at
Bundle of His, or the bundle branch area
2 or 3 P waves for each QRS
P’s are normal, PR remains fixed on conducted
beats
QRS is widened
Often leads to complete block
Second Degree AV Block
Mobitz Type II
Causes:
 Acute anterior MI
 Rheumatic Heart Disease
 Digitalis toxicity
 CAD
Treatment:
 Pacemaker
 Atropine, Epi, Isuprel, Dopamine until
placement
Third Degree Heart Block
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Called complete heart block
No P waves are conducted to the ventricles
Conduction is blocked through the AV Node to
the Bundle of His, and bundle branches
The atria and ventricles beat independently of
each other (AV dissociation)
Atrial rate is 60-100 Ventricular rate 20-60
Third Degree Heart Block
Causes:
 Fibrosis or calcification of the conduction
system, CAD, MI, Myocarditis, cardiomyopathy,
open heart surgery
Treatment:
 Pacemaker insertion
Dysrhythmias of the Ventricles
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Ventricular Dysrhythmias occur when
depolarization occurs incorrectly
We will learn:
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PVC’s
Ventricular Tachycardia
Ventricular Fibrillation
Idioventricular Rhythm
Ventricular Standstill (Asystole)
Premature Ventricular Contractions
PVC’s
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Generated anywhere in the ventricles.
Unifocal - they look the same
Multifocal - they look different
Patterns:
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Bigeminy
Trigeminy
Quadrigeminy
Couplets
More on PVC’s
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P waves usually absent before QRS
No PR intervals associated with PVC’s
QRS is > than 0.12 seconds and distorted with
a pause
ST segment is in the opposite direction of QRS
Rhythm is made irregular by PVC’s
Severity depends on frequency and underlying
condition
PVC’s
Cause and Treatment
Cause:
 Stimulants, stress, MI, MVP, CHF, CAD
Treatment:
 Depends on frequency and symptoms
 Remove contributing factors
 Anti-arrhythmic drugs like Lidocaine, Pronestyl,
or Amiodorone
Ventricular Tachycardia
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3 or more PVC’s
Rate 100-250, no P, QRS wide and distorted
Sustained = more than 30 sec
Unsustained = less than 30 sec
Can be monomorphic or polymorphic
Life threatening dysrhythmia because it
reduces Cardiac Output and often progresses
to V fib
V-Tach
Causes:
 Acute MI, CAD, electrolyte imbalances, MVP,
cardiomyopathy, reperfusion, Digitalis toxicity,
CNS disorders, Swan insertions, Caths
Treatment:
 Anti-arrhythmic drugs like Procanimide,
Lidocaine, Amiodorone
Ventricular Fibrillation
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Quivering of the ventricles caused by multiple
foci in the ventricles
Total loss of cardiac output – no heart rate
Amplitude varies due to electrical activity
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Coarse vs. fine
Course responds better
No P,Q,R,S,or T are visible
V-Fib
Cause:
 Primary has no obvious cause or heart disease
 Most are secondary to another illness: MI, CAD
cardiomyopathy, reperfusion, Swan insertions
Cardiac Catheterization, pacemaker insertions,
electrocution
Treatment:
 Defibrillation and drug therapy
Idioventricular Rhythm
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IVR is an escape rhythm generated from the
Purkinje fibers when dominant pacers fail
Rate is about 20 – 40 bpm usually regular
No P or PR
QRS is wide usually more than 0.12
Treated by cause
Idioventricular Rhythm
Cause and Treatment
Cause:
 Escape rhythm, AV blocks, reperfusion,
catheterizations, Acute MI, Digitalis toxicity
Treatment:
 Specific to cause
Ventricular Standstill (Asystole)
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Complete cessation of all heart electrical and
mechanical activity (flat line)
Multiple causes
Lethal dysrhythmia that requires immediate
medical intervention (ACLS, intubation,
defibrillation, IV meds and possible pacing
Pacemakers
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Electronic devices used in place of the SA or
AV Nodes when they fail or are damaged
Battery provides the electrical impulse that
stimulates the myocardial conduction system
Temporary or permanent
Can be internal or external
Permanent demand pacer is the most common
kicks in when rate drops below a certain rate
Pacing Rhythms
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Pacers are easily recognized on EKG strips.
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Atrial
Ventricular
Both
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The impulses cause a “spike” on the EKG
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Pacer malfunction includes:
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Failure to capture