BASIC 12 LEAD ECG
INTERPRETATION
Dr. Jeffrey Elliot Field, HBSc. DDS,
Fellow, American Dental Society of Anesthesia
Diploma, the National Dental Board of Anesthesia.
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Objectives
 To gain a cursory understanding of 12 lead ECG’s
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Basic 12 Lead
Interpretation
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 12 lead ECG’s give you the opportunity to look for all
the arythmias we have studied in a 360 degree view of
the heart with the added bonus of being able to
diagnose and localize myocardial infarctions ( i.e.
areas of muscle damage)
 Remember to look at all leads to rule out all of the
arrhythmias and abnormalities we have studies thus
far.
 In particular look first at Leads I , II, and III as these
will be the most familiar to you .
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In a 12 lead ECG 10 electrodes/leads attached to the patient.
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Myocardial Infarction
 Myocardial infarctions can be categorized as follows:
 -Q-wave MI
 -Non Q-wave MI
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Q-Wave Myocardial Infarction
 This is the classic presentation for MI’s.
 The developing MI is seen as ST segment elevation
followed by deepening Q-waves in the leads where ST
segment elevation was 1st seen.
 The ECG changes are accompanied by elevated cardiac
enzymes and markers and of course physical signs and
symptoms of an MI ( chest pain ,nausea ,vomiting ,
etc)
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Non Q-Wave Myocardial Infarction
 In this case you get classic signs and symptoms
symptoms of an MI(i.e. elevated cardiac enzymes and
markers and of course physical signs of an MI ( chest
pain ,nausea ,vomiting , etc)
But non of the usual ECG changes ( i.e. ST segment
elevation and deepening Q-waves). In fact sometimes
the only clue on the ECG are inverted T-waves.
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Cardiac Enzyme changes and
Markers for MI
 There are 4 markers for cardiac enzymes as follows:
 CK-MB isoenzyme
 CK-MB isoforms
 Myoglobin
 Troponin T or Troponin I
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Relative Advantages and
Disadvantages of the Various
cardiac Markers
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CK-MB
Isoenzyme
Myoglobin
CK-MB
Isoforms
Troponin (
Tor I)
Specific for
cardiac muscle
Damage
No
No
No
Yes
Sensitivity=
early rise ( 1-6
hours after
damage
Yes
YES
Yes
Yes
Sensitivity=
sustained
elevation after
damage
No
No
No
Yes
Sensitivity=
will detect
reinfarction
soon after the
initial episode
Yes
No
Yes
No
Diagnostic use
verified by
clinical studies
Yes
Yes
Yes
Yes
Prognostic Use
verified by
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clinical
studies
No
No
No
Yes
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Score
CK-MB
Isoenzyme
Myoglobin
CK-MB
Isoforms
Troponin
( Tor I)
3 yes
3 No
2 Yes
4 No
3 Yes
3 No
5 yes
1 No
Therefore the best test overall is Troponin T or I. But these will not
detect reinfarction and therefore more than one test is required.
The current recommendation is to combine one of the CK-MB tests
with one of the Troponin tests.
It should be noted that high troponin levels post MI correlate with poor
outcomes.
Finally please note CK-MB also rises in unstable angina ( damaged cells
that will recover ) as well as MI ( damaged cells that won’t recover) so it
won’t differentiate between unstable angina and an MI
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Localizing Myocardial infarctions
 Anterior( blockage of left anterior descending artery) –
look for ECG changes in leads V1-V4
 Inferior ( blockage of right coronary artery or less
commonly right circumflex)- look for ECG changes in
leads II, III, and AVF
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Anterior MI
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Inferior MI
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Localizing Myocardial infarctions continued
 Lateral Infarction ( blockage of circumflex or diagonal
branch of the LAD)-look in leads V5, V6 and AVL
 Posterior (blockage of right coronary artery or
circumflex) –look for mirror image changes to anterior
in V1-V4 (i.e. ST depression and dominant R-wave).
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Posterior MI
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Lateral MI
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