12 Lead ECG interpretation
Ischaemic Changes
Work Shop
Hayley Coxon
Topics covered
• Recap on ECG format and basics
• Normal ECG
• ECG changes in myocardial ischaemia/infarction
• ST segment
• T wave
• Q wave
• Acute MI locations and reciprocal changes
• Other causes of T wave and ST changes
• Practice ECGs
ECG Paper
1 large box = 0.2 seconds
5 large boxes = 1 second
10 mm/1mv
Reference
Time
1 small box = 0.04
seconds
P, QRS & T Wave
Isoelectric line
Normal Intervals
P-R interval:
0.12 - 0.20 sec
(3 to 5 small
squares)
QRS width:
0.08 - 0.12 sec
(2 to 3 small
squares)
PR
interval
QT
interval
QRS
complex
Q-T interval:
0.35 - 0.43 sec
*The PR interval should really be referred to as
the PQ interval, however it is commonly
referred as the PR interval.
Lead Groups
Limb Leads
Chest Leads
(precordial leads)
Lead I
aVR
V1
V4
Lead II
aVL
V2
V5
Lead III
aVF
V3
V6
Bipolar
Unipolar
Unipolar
Standard Bipolar Leads
I
-
II
III
I
+
Einthovens’ Triangle
III
II
+
+
Augmented Unipolar Leads
+
+
Augmented Voltage
Right (aVR)
aVR will always be
negative if the limb
leads are placed
correctly
Augmented Voltage
Left (aVL)
+
Augmented
Voltage Foot (aVF)
Limb leads
Left axis
-90°
-120°
-60°
-30° aV L
-150°
aV R
0° I
+180°
+-30°
+150°
Right axis
+120°
III
+90°
aV F
+60°
II
R Wave Progression
r
R
1
V6
2
2
1
2
S
V1
1
V1
V2
q
V3
V4
V5
V6
12 Lead ECG Check List
“Remember” Always treat the patient - not the ECG.
1.
2.
3.
4
1.
2.
3.
4.
5.
10
The PR interval is between 0.12 & 0.2 sec (3 -5 small squares).
The QRS duration is <0.11 sec (<3 small squares).
The QRS complex should be predominantly upright in leads I & II.
QRS & T waves tend to have the same general direction in the limb
leads.
Confirm that aVR is negative (if not check limb lead placement).
The R wave in the precordial leads must grow from V1 to at least V4.
The ST segment should start isoelectric except in V1 & V2 where it
may be slightly elevated.
The P waves should be upright in I, II & V2 to V6
There should be no Q waves > 0.04 seconds (1 small square) in width
in I, II, V2 to V6.
The T wave must be upright in I, II, V2 to V6.
Chamberlain DA. Personal communication
Normal 12 Lead ECG
ECG patterns of myocardial ischaemia
and infarction
• ST segment depression/elevation
• T waves changes
• Hyperacute
• Inverted T waves
• Biphasic T waves
• Flattened T waves
• Pathological Q waves
• U-wave inversion – less well-known
ST Segment
ST Segment
1
2
3
J Point
J point - starting point when measuring ST segment deviation.
J Point Examples
1
2
3
4
5
6
T Wave
Hyperacute T waves
• Broad, asymmetrically peaked or ‘hyperacute’
T-waves are seen in the early stages of STEMI
Inverted T waves
Biphasic T waves
• Myocardial ischaemia
• Waves go up then down
Flattened T waves
• Dynamic T-wave flattening due to anterior ischaemia
(left)
• T waves return to normal once the ischaemia resolves
(right)
Q Wave
The septum depolarises from left to right
Q waves
• Represents the normal left-to-right depolarisation of the
•
•
•
•
interventricular septum
Small ‘septal’ Q waves are typically seen in the left-sided
leads (I, aVL, V5 and V6)
Small Q waves are normal in most leads
Deeper Q waves (>2 mm) may be seen in leads III and
aVR as a normal variant
Under normal circumstances, Q waves are not seen in the
right-sided leads (V1-3)
Pathological Q Waves
> 1 mm wide
> 2 mm deep
> 25% of depth of QRS complex
Seen in leads V1-3
A normal 12-lead ECG
DOES NOT
rule out an
acute myocardial infarction
Acute Myocardial Infarction
• ST elevation >2mm in V1-V3 and >1mm in all
other leads in >2 contiguous leads1.
• Myocardial injury presents as raised ST1.
• Infarction can present as Q wave1.
aVR
V1 Septal
V4 Anterior
II Inferior
aVL Lateral
V2 Septal
V5 Lateral
III Inferior
aVF Inferior
V3 Anterior
V6 Lateral
I
Lateral
1. The Task Force on the management of acute myocardial infarction of the
European Society of Cardiology. Eur Heart J 2003;24:28-66
Evolution of an acute myocardial infarction
A.
Onset
D.
> 24 Hours
B.
15 Minutes
C.
> 1 Hour
E.
F.
Days
Later
Months
later
Location of infarctions
Septal AMI
V1, V2
Anterior AMI
V3, V4
Lateral AMI
Inferior AMI
II, III, AVF
V5, V6 - (I, AVL)
Inferior AMI
I aVR V1
II aVL V2
III aVF V3
II
V4
V5
V6
III
II
aVF
Right Sided Chest Lead Placement
Move the standard left chest leads
to the right side in the same
position
V3R Directly between V1 & V4R.
V4R Fifth intercostal space,
midclavicular line.
V5R Level with V4R at left
anterior axillary line
V6R Level with V5R at midaxillary
line (midpoint of the armpit).
V4R is the most sensitive indicator
of a right ventricular infarction
RV Infarction (standard Leads)
RV Infarction (Right Sided Leads)
V4R
V5R
V6R
Antero-septal AMI
V1 V2
V3
V4
I aVR V1
II aVL V2
III aVF V3
V4
V5
V6
Antero-lateral AMI
aVL
V6
V5
V4
V3
V1 V2
I
II
I
III
aVR V1 V4
aVL V2
V1 V5
V4
aVF V3 V6
V2 V5
V3
V6
I
Lateral AMI
aVL
I
I
aVR
V1
V4
II
aVL
V2
V5
III
aVF
V3
V6
Reciprocal Changes
• If a lead is looking directly at the infarct site it will produce
ST segment elevation
• When a lead sees the infarct from the opposite perspective,
the ST segment may become depressed in that lead
II, III aVF
I, aVL, V leads
Infarction Overview
Site
Indicative Leads Reciprocal Leads
Inferior
II, III & aVF
I & aVL
Septal
V1 – V2
None
Anterior
V3 – V4
None
Anteroseptal
V1 – V4
None
Lateral
I, aVL & V5 - V6
II, III & aVF
Anterolateral I, aVL & V3 –V6
II, III & aVF
Posterior
None
V1 – V4
? Posterior AMI V1-V4 Depression
Posterior - Lead Placement
V1 - V3 are moved round to
become V7 - V9.
They are placed on the same
horizontal plane as V4
V7 Posterior axillary line
V8 Midscapular line in between
V7 & V9
V4
V4
V9 To the left of the spine
V7 V8 V9
Posterior ECG
Dynamic Changes in AMI
Pre-hospital ECG showing possible hyperacute
S-T changes in anterior leads
Dynamic Changes in AMI
2nd ECG taken 20mins later, showing established
antero-lateral S-T elevation
Identify the following 6 ECG
infarction sites
ECG 1
ECG 2
ECG 3
ECG 4
ECG 5
ECG 6
ECG 7
Other causes of ST Segment Elevation
• Pericarditis
• Benign early repolarization
• Left bundle branch block
• Left ventricular hypertrophy
• Ventricular aneurysm
• Brugada syndrome
• Ventricular paced rhythm
• Raised intracranial pressure
Pericarditis
Benign early repolarisation
LV Aneurysm
Brugarda
LBBB
Pericarditis
Benign early repolarisation
Raised Intracranial Pressure
Other reasons for inverted T waves
• Normal finding in children
• Persistent juvenile T wave pattern
• Bundle branch block
• Ventricular hypertrophy (‘strain’ patterns)
• Pulmonary embolism
• Hypertrophic cardiomyopathy
• Raised intracranial pressure
LVH
Hypokalaemia
Waves go down then up
Raised Intracranial Pressure
Thank you
More practice ECGs?