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12-Lead EKG
MEPN Level IV
1
OBJECTIVES
• Discuss the changes in T wave and
ST segment morphology with an MI
• List the criteria for identification of
right or left bundle branch blocks.
• List the anatomically congruent
leads associated with an inferior,
lateral and anterior wall MI
• Describe morphology of Q wave
presence
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3
ECG Leads
• 6 limb leads (frontal plane)
– 3 bipolar leads
– 3 unipolar leads
• 6 precordial leads (horizontal plane)
– V1 – V6
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Einthoven’s Triangle
Limb Leads
BIPOLAR
Lead I
RA (-) to LA (+)
Lead II
RA (-) to LL (+)
Lead III
LA (-) to LL (+)
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AUGMENTED (UNIPOLAR) LEADS
Augmented leads
combine 2 leads
together (the null
point) from the
center point of the
triangle with one
positive pole.
aVR (Augmented
Voltage Right Arm
positive) is a
combination of
bipolar Leads I
and II
aVL (Augmented
Voltage Left Arm
Positive) is a
combination of I
and III
aVF (Augmented
Voltage Left Foot
positive) is a
combination of
Bipolar Leads II
and III
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WHAT ARE THE
LEADS
LOOKING AT?
I & AVL
II, III & AVF
LIMB and AUGMENTED
LEADS
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Precordial Lead Placement
V1 – 4th
intercostal
space right of
sternum
V2 - 4th
intercostal
space left of
sternum
V4 – 5th
intercostal
space
midclavicular
line
V3 – midway
between V2
and V4
V6 – 5th
intercostal
space
midaxillary
line
V5 – same
level as V4 at
anterior
axillary line
between V4
and V6
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RIGHT SIDED EKG
Same lead position as left side –
looks directly at the
Right ventricle
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Posterior leads:
Posterior View
V7 – lateral to V6 at
posterior axillary line
V8 – level of V7 at the
mid-scapular line
V9 – level of V8 at the
paravertebral line
(left posterior thorax
midway from spine to V8)
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PRECORDIAL LEADS
V1 & V2
V3 & V4
V5 & V6
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calibration marker
LIMB LEADS
AUGUMENTED
LEADS
PRECORDIAL LEADS
Bottom line is continuous strip
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R – Wave Progression
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R – Wave Progression
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• Myocardial ischemia
– Various definitions are used. The term
commonly refers to diffuse ST
segment depression, usually with
associated T wave inversion
• Myocardial injury
– Injury always points outward from the
surface that is injured with ST
segment elevation
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Ischemia, Injury, Infarction
Waveforms
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ST
Segments
ST segment should be electrically
neutral
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• Visual aid in
determining:
– Ischemia or
injury to
myocardium
– Normal should
be at baseline
– Depressed ST
segment - >2
mm below
baseline
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EKG 1
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ST Segment Elevation
• ST segment elevation is attributed
to impending infarction
– but can also be due to pericarditis or
vasospastic (variant) angina.
• The height of the ST segment is
measured at a point 2 boxes after
the end of the QRS complex
– significant if it exceeds 1 mm in a limb
lead or 2 mm in a precordial lead.
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EKG 2
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T Waves
• T waves are normally positive in
leads with a positive QRS
• T waves are normally asymmetrical
• T waves are normally not more
than 5 mm high in limb leads or 10
mm high in precordial leads or 2/3
the height of the R wave
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T wave
Ischemia
Hyperkalemia
Ischemia
Ischemia
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Hyperkalemia
EKG 3
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ST-T Wave
• Combination of infarction and often
hyperkalemia
• Called Tombstone ‘T’ because of
the shape.
• Usually a sign of impending cardiac
death.
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EKG 4
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Pathology of an MI
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Localization of ECG Pathology
• Inferior: Abnormalities that appear
in leads II, III, and aVF (called the
inferior leads) indicate pathology on
the inferior or diaphragmatic
surface of the heart.
• Lateral: Leads I, aVF, and V5-V6
are called lateral leads. Abnormality
in these leads indicates pathology
on the lateral, upper surface of the
heart.
• Anterior: Anterior pathology is
seen in leads V1-V4, and often in
lead I.
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Overview of Infarcts
Location of
Infarct
Arterial
Supply
Indicative
Changes
Reciprocal
Changes
Anterior
LAD
V1-V4
II, III, aVF
Inferior
RCA
II, III, aVF
I, aVL
Lateral
Circumflex
I, aVL, V5,
V6
V1
Posterior
Posterior
Descending
(RCA)
None
V1, V2
Septal
Septal
Perforating
(LAD)
Posterior
Descending
(RCA
Loss of R
wave in V1,
V2, or V3
None
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T Wave
Elevation
T
ST
Segment
Elevation
ST
ST
Q
T
Pathological
Q Wave
Q
Q
T
T Wave
Inversion
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EKG Changes from Infarction
First Detectable
Change in EKG
•Tall T-waves
•increase in height
•more symmetric
•may occur in the
first few minutes
Hyper-acute Phase
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Acute Phase
•ST Segment Elevation
•Primary indication of injury
•Occurs in first hour to hours
ST Segment Elevation in Leads
•1mm or greater in limb leads
•2 mm or greater in chest leads
•Hallmark indication of AMI
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View of Inferior Heart
Wall
Leads II, III, aVF
- Looks at inferior
heart wall
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Inferior
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EKG 5
Inferior
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EKG 6
View of Lateral Heart Wall
Leads I and aVL
– Looks at lateral heart
wall
– Looks from the left
arm toward heart
*Sometimes referred
to as High Lateral or
High Apical view*
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View of Lateral Heart Wall
Leads V5 & V6
– Looks at lateral heart
wall
– Looks from the left
lateral chest toward
heart
*Sometimes
referred to as Low
Lateral or Low
Apical view*
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View of Entire Lateral Heart Wall
Leads I, aVL, V5, V6
- Looks at the lateral wall of
the heart from two different
perspectives
Lateral
Wall
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Lateral
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EKG 7
Lateral
EKG 8
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View of Anterior Heart Wall
• Leads V3, V4
– Looks at anterior
heart wall
– Looks from the left
anterior chest
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Anterior
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EKG 9
Anterior
4610
EKG
View of Septal Heart Wall
Leads V1, V2
- Looks at septal
heart wall
- Looks along sternal
borders
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Putting it ALL together
ANTERIOR
LATERAL
S
E
P
T
A
L
LATERAL
LATERAL
INFERIOR
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Q Waves
• Definition
– Septal depolarization
– Normally present in I, aVL, V6
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Two types of Q
waves
– Non-pathologic
• Narrow, shallow Q
waves
• Not visible in all leads
– Pathologic
• > 0.04 in duration; at
least 1/4 to 1/3 height of
R wave
• Represent an infarcted
area of myocardium
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PATHOLOGICAL Q WAVES
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Bundle Branch Blocks
If the QRS duration is > .12
there is usually an abnormality of
conduction of the ventricular
impulse
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RBB Block
Most common ventricular
conduction defect
Can be acute or chronic
Acute RBBB is associated
with an acute anterior MI
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EKG 11
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RBBB
LBB Block
Always indicates a
diseased heart
More common in
older adults
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EKG 12
LBBB
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