Download 12 Lead Interpretation - Sunnybrook Centre For Prehospital Medicine

12 Lead Interpretation
Objectives
•
•
•
•
•
Ischemia, injury and infarction
ECG complex review
J point
ST segment
STEMI recognition
Ischemia to Infarct
•
•
•
•
•
Infarction is an evolving process
As the infarct evolves ECG changes may occur quickly or more
gradually
These changes may be seen on the 12 lead as they evolve
Acquiring more then one 12 lead may be necessary
A normal 12 lead does not rule out acute myocardial infarction
The ECG Complex
•
•
•
•
The J point is the point where the S wave ends and the ST segment
begins
ST elevation is measured after the J point
The ST segment is compared to the base line
The base line or isoelectric line is found at the bottom of the
calibration bar
J point
ST Segment
•
•
•
Starts with the J point
Ends with the beginning of the T wave
Elevation or depression of the ST segment is measured 0.08
seconds (2 small squares) to the right of the J point
ST segment
PR Interval
•
•
•
Begins at the end of the P wave
Ends at the beginning of the QRS
When determining the isoelectric or baseline find the PR interval of 2
consecutive complexes, draw a line using a straight edge and
measure ST elevation from this line; this is the most accurate way to
determine if the ST segment is elevated
PR Interval
Isoelectric line
TP Segment
•
•
•
•
Begins at the end of the T wave
Ends at the beginning of the P wave
Can be used as a back up to the PR interval to determine the
baseline when assessing ST elevation
Not as accurate as the PR interval
TP segment
Hyperacute T-wave
•
As an acute myocardial infarction
develops various 12 lead ECG changes
occur
•
Initially the 12 lead ECG may show tall or
hyperacute T-waves signifying cardiac
ischemia – may only be present for a short
time after ischemia has begun (5 to 30
minutes)
•
Paramedics may not see this change as
many patients wait for at least 30 minutes
to call EMS
T-wave
ST segment elevation
•
•
•
•
•
•
Usually seen with in the first few
hours after the onset of symptoms
Changes may be very subtle or
pronounced
Any elevation in 2 contiguous
leads is significant
ST segment elevation greater than
1mm or 2mm in precordial leads
(V1 through V6)
1mm = 1 small square on the ECG
paper
For more information on ST
segment abnormality click on this
link:
http://www.madsci.com/manu/ekg_st-t.htm
Measure ST elevation
from this point
J point
PR Interval
2mm or 2 small
squares
Tombstones
• Pronounced ST
segment elevation
may appear as
tombstones
• Tombstones are a
result of the fusing of
the ST segment and
T wave
tombstone
Pathological Q wave
•
•
•
•
Indicate a loss of viable
myocardium
May develop 1 to 2 hours
after the onset of symptoms
but can take anywhere from
12 to 24 hours to develop
Abnormal Q waves are at
greater then one third of the
R wave height deep and
greater then 1mm (or 1
small square) wide
Q waves may be visible in
a patient without infarct but
will not meet the
parameters to be
considered abnormal
Greater than
1mm wide
Reciprocal Changes
•
•
•
Are seen as ST depression in the opposite leads from where the ST
elevation is seen
Leads II, III and aVF are opposite to Leads I, aVL, and all of the V
leads
Therefore, if there is ST elevation in leads II, III and aVF any ST
depression (if present) would be seen in leads I, aVL and any of the
V leads
Reciprocal Changes
•
•
•
ST segment depression seen in the opposite leads from ST segment
elevation
Highly sensitive as an indicator of acute MI
Frequently seen in larger infarctions
ST elevation
Reciprocal ST depression
The 12 Lead Printout
Calibration bar (the isoelectric line is indicated by the bottom of the calibration bar)
25mm/sec
Paper speed indicates
how fast the paper
moves (5 larger
squares = 1 second)
On the Zoll 12 lead printout there is a break in the ECG to
indicate where the tracing changes to the next lead
Practice
Locate the J point in each of the above complexes
Click the mouse to check your location
The J point is at the end of the S. This is located where the
upstroke of the S changes to become horizontal.
Practice
Isoelectric Line
Isoelectric Line
Isoelectric
Isoelectric Line
Elevated
Depressed
• Locate the J point in each of the above complexes
• Identify ST segment abnormalities
• Click the mouse to check your answers
• The red dot shows the J point
• The red line shows the ST segment 0.08 seconds (2
small squares) from the J point
Normal 12 Lead
•
•
•
Notice where the J point is for one complex in each lead
Also look at the ST segment for one complex in each lead
This an example of a 12 lead that the Zoll E series will generate
Practice ECG # 1
•
•
•
•
•
Look for the J point and ST elevation in the above 12 lead
Look for reciprocal changes
Which lead groups are involved?
What area of the heart is involved?
Which coronary artery feeds this area of the heart?
Answer ECG # 1
•
•
•
•
Leads II, III, aVF all have ST elevation, these are contiguous inferior
leads
Leads I, aVL, V2, V3 and V4 all have ST depression signifying
reciprocal changes
These changes are consistent with an acute inferior MI
In 90% of the population the inferior aspect of the heart blood supply is
via the right coronary artery
Practice ECG # 2
•
•
•
•
•
Look for the J point and ST elevation in the above 12 lead
Look for reciprocal changes
Which lead groups are involved?
What area of the heart is involved?
Which coronary artery feeds this area of the heart?
Answer ECG # 2
•
•
•
•
•
ST elevation in Leads I, aVL, V2, V3, V4, V5
Lead II and III show reciprocal changes as well as evidence of an old
MI (in the form of a pathological Q wave)
Lateral leads (I, aVL and V5) as well as Anterior and septal lead
groups (V2, V3 and V4)
Anterior and Lateral are the main areas of the heart involved
Left anterior descending and the left circumflex arteries supply this
area of the heart
Practice ECG # 3
•
•
•
•
•
Look for the J point and ST elevation in the above 12 lead
Look for reciprocal changes
Which lead groups are involved?
What area of the heart is involved?
Which coronary artery feeds this area of the heart?
Answer ECG # 3
•
•
•
•
•
ST elevation in leads II, III and aVF
Reciprocal changes in leads I, aVL, V2 and V3
Leads II, III and aVF are contiguous inferior leads
This is an acute inferior MI
This area of the heart is supplied by the right coronary artery in 90%
of the population
Practice ECG # 4
•
•
•
•
•
Look for the J point and ST elevation in the above 12 lead
Look for reciprocal changes
Which lead groups are involved?
What area of the heart is involved?
Which coronary artery feeds this area of the heart?
Answer ECG # 4
•
•
•
•
•
ST elevation in leads I, V2, V3, V4, V5, V6 and aVL
Reciprocal changes shown in leads III and aVF
V3 and V4 are anterior leads, I, aVL, V5 and V6 are lateral leads
This is an acute anteriolateral MI
Left anterior descending and left circumflex arteries supply these
areas of the heart
Practice ECG # 5
•
•
•
•
•
Look for the J point and ST elevation in the above 12 lead
Look for reciprocal changes
Which lead groups are involved?
What area of the heart is involved?
Which coronary artery feeds this area of the heart?
Answer ECG # 5
•
•
•
•
•
ST elevation in leads II, III, aVF and V6
Reciprocal changes in leads V2, V3 and V4
II, III and aVF are inferior leads, V6 is a lateral lead and ST elevation
must be present in at least 2 leads that view the same area of the heart
This is an acute inferior MI
The inferior area of the heart is supplied by the right coronary artery in
90% of the population
Practice ECG # 6
•
•
•
•
•
Look for the J point and ST elevation in the above 12 lead
Look for reciprocal changes
Which lead groups are involved?
What area of the heart is involved?
Which coronary artery feeds this area of the heart?
Answer ECG # 6
•
•
•
•
•
ST elevation in leads V1, V2, V3 and V4
There are no obvious reciprocal changes
V1 and V2 are septal leads, V3 and V4 are anterior leads
This is an acute anterioseptal MI
The left anterior descending artery supplies this area of the heart
Thank You for participating in
Sunnybrook – Osler Centre for
Prehospital Care online education!
If you have any questions please
bring them with you to class!