Essentials of 12 Lead ECG Interpretation

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Essentials of 12 Lead ECG Interpretation

• EMS Professions
• Temple College

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Topics

• Anatomy Revisited
• The 12 Lead ECG Device
• The 12 Lead ECG Format
• Waveform Components
• Lead Views

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Anatomy Revisited

• RCA
• right ventricle
• inferior wall of LV
• posterior wall of LV (75)
• SA Node (60)
• AV Node (gt80)
• LCA
• septal wall of LV
• anterior wall of LV
• lateral wall of LV
• posterior wall of LV (10)

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Anatomy Revisited

• SA node
• Intra-atrial pathways
• AV node
• Bundle of His
• Left and Right bundle branches
• left anterior fascicle
• left posterior fascicle
• Purkinje fibers

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The 12 Lead ECG Device

• Device serves as a voltmeter
• measures the flow of electricity
• Unipolar vs Bipolar Leads

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Bipolar Leads

• 1 positive and 1 negative electrode
• RA always negative
• LL always positive
• Traditional limb leads are examples of these
• Lead I
• Lead II
• Lead III
• View from a vertical plane

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Unipolar Leads

• 1 positive electrode 1 negative reference
  point
• calculated by using summation of 2 negative leads
• Augmented Limb Leads
• aVR, aVF, aVL
• view from a vertical plane
• Precordial or Chest Leads
• V1-V6
• view from a horizontal plane

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The 12-Lead ECG Format
Leads typically produced by devices used
prehospital
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The 12-Lead ECG Format
Fields not typically produced by devices used
prehospital
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The 12-Lead ECG Format
Device prints out 2.5 sec each of Leads I, II,
III then switches to aVR, aVL, aVF then switches
to V1, V2, V3 and then to V4, V5, V6 (varies by
device)
Device computer analyzes all 10 sec of all 12
leads but only prints 2.5 sec of each group
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The 12-Lead ECG Format
The computer diagnosis is not always accurate!!!
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The 12-lead ECG Format
The computer IS very accurate at measuring
intervals durations
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Waveform Components R Wave
First positive deflection R wave includes the
downstroke returning to the baseline
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Waveform Components Q Wave
First negative deflection before R wave Q wave
includes the negative downstroke return to
baseline
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Waveform ComponentsS Wave
Negative deflection following the R wave S wave
includes departure from return to baseline
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Waveform ComponentsQRS

• Q waves
• Can occur normally in several leads
• Normal Q waves called physiologic
• Physiologic Q waves
• lt .04 sec (40ms)
• Pathologic Q
• gt.04 sec (40 ms)

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Waveform ComponentsQRS

• Q wave
• Measure width
• Pathologic if greater than or equal to 0.04
  seconds (1 small box)

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Waveform ComponentsQS Complex
Entire complex is negatively deflected No R wave
present
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Waveform ComponentsJ-Point
Junction between end of QRS and beginning of ST
segment Where QRS stops makes a sudden sharp
change of direction
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Waveform Components ST Segment
Segment between J-point and beginning of T wave
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Waveform Components ST Segment

• Need reference point
• Compare to TP segment
• DO NOT use PR segment as reference!

ST
TP
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Waveform Components Practice

• Find J-points and ST segments

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Waveform Components Practice

• Find J-points and ST segments

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Lead Views
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Lead Groups
I aVR V1 V4 II aVL
V2 V5 III aVF V3 V6
Limb Leads
Chest Leads
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Inferior Wall

• II, III, aVF
• View from Left Leg ?
• inferior wall of left ventricle

I II III
aVR aVL aVF
V1 V2 V3
V4 V5 V6
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Inferior Wall

• Posterior View
• portion resting on diaphragm
• ST elevation ? suspect inferior injury

I II III
aVR aVL aVF
V1 V2 V3
V4 V5 V6
Inferior Wall
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Lateral Wall

• I and aVL
• View from Left Arm ?
• lateral wall of left ventricle

I II III
aVR aVL aVF
V1 V2 V3
V4 V5 V6
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Lateral Wall

• V5 and V6
• Left lateral chest
• lateral wall of left ventricle

I II III
aVR aVL aVF
V1 V2 V3
V4 V5 V6
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Lateral Wall

• I, aVL, V5, V6
• ST elevation ? suspect lateral wall injury

I II III
aVR aVL aVF
V1 V2 V3
V4 V5 V6
Lateral Wall
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Anterior Wall

• V3, V4
• Left anterior chest
• ? electrode on anterior chest

I II III
aVR aVL aVF
V1 V2 V3
V4 V5 V6
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Anterior Wall

• V3, V4
• ST segment elevation ? suspect anterior wall
  injury

I II III
aVR aVL aVF
V1 V2 V3
V4 V5 V6
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Septal Wall

• V1, V2
• Along sternal borders
• Look through right ventricle see septal wall

I II III
aVR aVL aVF
V1 V2 V3
V4 V5 V6
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Septal

• V1, V2
• septum is left ventricular tissue

I II III
aVR aVL aVF
V1 V2 V3
V4 V5 V6
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ST Segment Analysis
For each complex, determine whether the ST
segment is elevated one millimeter or more above
the TP segment
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12-Lead ECG

• AMI recognition
• Two things to know
• What to look for
• Where you are looking

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AMI Recognition

• What to look for
• ST segment elevation
• One millimeter or more (one small box)
• Present in two anatomically contiguous leads