12 lead ekg interpretation · pdf file9/30/2016 4 section i normal ecg laying the ground work...
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12 Lead EKG Interpretation
Louann B. Bailey, DNP, APRN, FAANP
Cleveland Clinic Akron General
Disclosures
• I have no disclosures
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Objectives
• At the conclusion of this presentation the participant will be able to– Outline a systematic approach to 12 lead ECG
interpretation
– Demonstrate the process for determining axis
– List criteria for LVH, RVH, LBBB, RBBB, Bifasicular and trifasicular block, acute and chronic MI changes
– Define QTc significance
– Contrast features of VT vs SVT with aberrancy
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Objectives
• At the conclusion of this presentation the participant will be able to– Outline a systematic approach to 12 lead ECG
interpretation
– Demonstrate the process for determining axis
– List criteria for LVH, RVH, LBBB, RBBB, Bifasicular and trifasicular block, acute and chronic MI changes
– Define QTc significance
– Contrast features of VT vs SVT with aberrancy
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Introduction
• Section I
– Normal ECG, laying the ground work
• Section II
– Axis
• Section III
– Hypertrophy
• Section IV
– BBB, Bi-trifasicular blocks
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Introduction
• Section V
– Landscape of an MI
• Section VI
– QT abnormalities
• Section VII
– Other Cardiac conditions
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Section I
Normal ECG
Laying the ground work
Laying the ground work for
12 lead interpretation
• A tool, a sign, an extension of the history
and physical examination
• Must take a sensible approach to analyze
an ECG
• The ECG reflects the heart and all its
functions
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Systematic approach
• Compare with old ECG
• Look at Rate
• Look at Rhythm
• Look at Axis
• Look at Hypertrophy
• Look at I’s
Intervals, ischemia, injury, infarct
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Laying the ground work cont.
• The ECG language is not difficult, just
different
• Practice, Practice, Practice
• Obtain good, easy to understand
resources
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12 lead ECG
• A Normal ECG is dependent on intact
plumbing, electrical, and structural
components of the heart
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ECG
Dependent Factors
• Plumbing
• Electrical
• Structural
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ECG
Plumbing
• Coronary Arteries– Right coronary
– Left Main Coronary
• Left anterior descending
• Circumflex artery
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ECG
Electrical
• SA node: major electrical pacemaker
Blood supply: Right coronary artery
• AV node: initiates ventricular contraction
Blood supply: Right coronary artery and or circumflex
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ECG
Electrical
• Bundle of HIS: ventricular contraction
Blood supply: Left anterior descending
• Purkinje fibers: ventricular contraction
Blood supply: Left anterior descending
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Electrical
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ECG
Structural
• Chambers
• Muscle
• Valves
• Nervous system
• Vascular
• Position of the heart
and great vessels
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Heart Valves and positions
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Layers of the Heart
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12 lead ECG
• A Normal ECG is dependent on intact
plumbing, electrical, and structural
components of the heart
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Limb Leads
• View the frontal plane
• Include leads I, II, III, aVR, aVL and aVF
• Provide inferior, superior, and lateral views of heart
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Precordial Leads
• View horizontal plane and include leads V1, V2, V3, V4, V5, and V6
• Provide inferior, superior, and lateral views of heart
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Frontal/Limb leads Precordial leads
Rhythm strip
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Frontal leadsLimb leadsVertical leads
Precordial leadsHorizontal leads
Rhythm strip
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12 lead ECG
• An Abnormal ECG may result from
disrupted plumbing, electrical, structure or
a combination of all the above.
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Frontal/Limb Leads Precordial Leads
Rhythm Strip
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ECG
Sensible Approach
• Rate
• Rhythm
• Axis
• Hypertrophy
• 4 I’s
Intervals, Ischemia, Injury, Infarction
If possible, always have an old ECG for comparison
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ECG
Electrical
• There can be electrical activity and no
mechanical response, but there can never
be mechanical response without electrical
activation
• Electrical activity precedes mechanical
activity (contraction)
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ECG
Electrical
• There can be electrical activity and no mechanical response, but there can never be mechanical response without electrical activation
• Except in severe scleroderma
• Electrical activity precedes mechanical activity (contraction)
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Electrophysiology of the Heart
Properties of cardiac Muscle
• Myocardial cells: Make up bulk of heart
muscle, actual contractile units.
• Specialized cells: Four specific
properties that govern automaticity,
excitability, conductivity and contractility.
These cells make up the heart’s electrical
conduction system
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Key Properties of Myocardial Cells
• Automaticity– Can produce electrical activity without outside nerve
stimulation
• Excitability– Ability to respond to an electrical stimulus
• Conductivity– Ability to transmit an electrical stimulus from cell to cell
throughout myocardium
• Contractility– Ability of myocardial cell to contract when stimulated by
an electrical impulse
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Autonomic Nervous System
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Electrophysiology of the HeartAutonomic Nervous System control
Sympathetic nerves: supply primarily ventricles, chemical mediators are hormones norepinephrine and epinephrine
(Tachy arrhythmias)
Parasympathetic: supply primarily atria, stimulation of vagus nerve causes the release of the hormone acetylcholine
(Brady arrhythmias)
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• Cardiac cycle begins with RA and LA receiving blood from systemic and pulmonary circulations
– Rising pressure within atria forces tricuspid and mitral valves open
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• Heartbeat initiated by an electrical impulse that arises from SA node
• Impulse travels through atria
– generates a positive waveform on ECG and contraction of atria
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• Impulse slows as it passes through AV node from atria to ventricles
– Allows atria time to finish filling ventricles
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• Impulse then rapidly travels through His-Purkinje system
– Seen as a flat line following P wave
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• Depolarization of septum and ventricular walls generates QRS complex and contraction of ventricles
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• Repolarization of ventricles is represented on ECG by ST segment and T wave
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The Electrocardiogram
What is important to know
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William Einthoven
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Normal ECG
• ECG Paper
Usually moves at a rate of 25mm/second
There are horizontal lines, indicating time, five
large boxes of 5mm each equal 25mm or 1
second of time
There are vertical lines, indicating voltage,
calibrated so that a 1mV standardization
signal produces a deflection of exactly 10mm,
(full standardization).
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How things are measured
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Limb Leads Precordial Leads
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Limb Leads Precordial Leads
VerticalVoltage
HorizontalTime
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Standardization
Horizontal lines indicating time
Vertical lines indicating mV
Normal EKG
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ECG Analysis
• Five Step Process is a logical and systematic
process for analyzing ECG tracings
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Relationship of conduction to ECG
measurement
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Normal Sinus Rhythm
Characteristics• Rate: 60 - 100 BPM
• Rhythm: Regular
• P waves: Upright and round, one preceding each QRS complex
• QRS complexes: Narrow, 0.06 - 0.12 seconds in duration
• PR Interval: 0.12 - 0.20 seconds in duration
• T waves: Upright and slightly asymmetrical
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Calculating Heart Rate
• Several methods can be used including:
– 6-Second Interval x 10 Method
– 300, 150, 100, 75, 60, 50 Method
– 1500 Method
– Rate Calculator
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3 seconds 6 Seconds
3 second = 15 blocks 6 seconds = 30 blocks
1 block
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6-Second Interval x 10 Method
• Quick and easy and does not require tools or devices
• Not as accurate as other methods
• Multiply by 10 the number of QRS complexes found in a
six second portion of ECG tracing
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300, 150, 100, 75, 60, 50 Method
• If the second R wave does not fall on a bold line
the heart rate is approximated
– Example: if it falls between the 4th and 5th bold line
the heart rate is between 60 and 75 BPM
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300, 150, 100, 75, 60, 50 Method
• If the second R wave falls in between two bold
lines the heart rate can be more precisely
determined using the identified values for each
thin line
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Rate rulers
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1500 Method
• Most accurate and requires no special tools but math calculation must be done to determine heart rate
• Cannot be used with irregular rhythms
• Count the number of small squares between two consecutive R waves and divide 1500 by that number
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300
150100
75
1500÷20= 75
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1500 ÷ 8 = 187
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1500 ÷ 13 = 115
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75
1500 ÷ 23 = 53
3 seconds
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3 seconds
4 X 20 = 80Only 2 out of the 4 is generating a pulse
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ECG Paper
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ECG Leads
• Direction an ECG waveform takes depends on whether electrical currents are traveling toward or away from a positive electrode
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ECG Leads
• Planes provide a cross-sectional view of heart
– Frontal plane
– Horizontal plane
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Bipolar Leads
• Record difference in electrical potential between a positive and negative electrode
• Uses a third electrode called a ground
• Include leads I, II and III
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Limb Leads - Lead I
• Positive electrode - left arm (or under left clavicle)
• Negative electrode - right arm (or below right clavicle)
• Ground electrode - left leg (or left side of chest in midclavicular line just beneath last rib)
• Waveforms are positive
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Limb Leads - Lead II
• Positive electrode - left leg (or on left side of chest in midclavicular line just beneath last rib)
• Negative electrode - right arm (or below right clavicle)
• Ground electrode - left arm (or below left clavicle)
• Waveforms are positive
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Limb Leads - Lead III
• Positive electrode - left leg (or left side of the chest in midclavicular line just beneath last rib)
• Negative electrode - left arm (or below left clavicle)
• Ground electrode - right arm (or below right clavicle)
• Waveforms are positive or biphasic
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Limb Leads - Augmented Leads
• Includes aVR, aVL and aVF
• Unipolar
• Enhanced by ECG machine because waveforms produced by these leads are normally small
I
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Limb Leads - Lead aVR
• Positive electrode placed on right arm
• Waveforms have negative deflection
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Limb Leads - Lead aVL
• Positive electrode placed on left arm
• Waveforms have positive deflection
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Limb Leads - Lead aVF
• Positive electrode located on left leg
• Waveforms have a positive deflection
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Precordial Leads
• Includes leads V1, V2, V3, V4, V5 and V6
• Positioned in order across the chest
• Unipolar
– Opposing pole is center of heart as calculated by
ECG
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Bipolar leads Augmented leads Unipolar leads
Essential parts of the ECGFrontal leads Precordial leads
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Normal EKG
Leads II, III, aVFInferior leads
Leads I, aVLLateral leads Leads V1, V2
Septal leadsLeads V3, V4Anterior leads
Leads V5, V6Lateral leads
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