1. Ontario Base Hospital Group Education Subcommittee 2008
Chapter 6 for 12 Lead Training -Introduction to 12 Lead Interpretation-
Ontario Base Hospital Group
Education Subcommittee
2008
TIME IS MUSCLE

2. Introduction to 12 Lead Interpretation
REVIEWERS/CONTRIBUTORS
Neil Freckleton, AEMCA, ACP
Hamilton Base Hospital
Jim Scott, AEMCA, PCP
Sault Area Hospital
Ed Ouston, AEMCA, ACP
Ottawa Base Hospital
Laura McCleary, AEMCA, ACP
SOCPC
Tim Dodd, AEMCA, ACP
Dr. Rick Verbeek, Medical Director
AUTHOR
Greg Soto, BEd, BA, ACP
Niagara Base Hospital
2008 Ontario Base Hospital Group

3. Chapter 6 - Objectives
Recognize the usefulness of ECG data provided by computerized 12 Lead ECG
Identify important features of ECG such as Q, R, S, T waves and relate to 12 Lead interpretation
Find J-points and compare to TP segments
Recognize ST-elevation and relate to clinical significance
Become comfortable with recognizing and locating AMI on 12 Lead ECG
Practice a bit of 12 Lead interpretation

4. 12 Lead Interpretation Interpretation vs. STEMI Recognition
It is important to note that upon completion of this training, it is not expected that paramedics will be “interpreting” a 12 Lead but rather recognizing STEMI patients

5. Learning 12 Lead ECG Interpretation
Common Paramedic responses prior to learning 12 Lead ECG Interpretation:
I can’t interpret a 12 Lead ECG like a Cardiologist!
Are you kidding me?
Common Paramedic responses after learning 12 Lead ECG Interpretation:
Hey – that wasn’t as hard as I thought it would be!
Teaching Point:
Paramedics are often intimidated by 12 Lead ECG before learning STEMI interpretation and surprised that it was not more difficult to learn after training.
The important point to emphasize is that paramedics are examining 12 Lead ECGs for very specific findings – ST-elevation. Physicians of all specialities read 12 Lead ECGs for ST-elevation and many other more complex interpretations. Paramedics are looking at the ECG, for the most part, to identify if the patient is a candidate for triage for early AMI reperfusion. Many other features of prehospital 12 Lead ECG may be interesting to learn but ST-elevation is MUST KNOW.
Further, for paramedics with experience in ECG Rhythm Interpretation, explain that ST-elevation on a 12 Lead ECG is easier to learn and much quicker to master than Rhythm Interpretation.
You may wish to retell the following amusing story to highlight the above point:
Tim Phelan, a paramedic from Florida with extensive experience in teaching prehospital 12 Lead ECG, was trying to demonstrate the ease of learning 12 Lead interpretation. One day he and his medic partner spent 30 minutes teaching interpretation to the Janitor in the hospital for which they worked. At the end of this session he seemed to be reasonably comfortable with what STEMI looked like and could locate the AMI. Later Tim and his partner got in trouble for this seemingly innocuous activity. One day, while cleaning floors in the ICU, the Janitor happened upon a conversation between an ICU nurse and physician about the location of an AMI in a newly admitted patient. The Janitor had a look at the ECG himself and noted, “Looks like an Anterior MI to me”. Turns out he was spot on in his interpretation causing some ruffled feathers in the Unit.

6. Essential Interpretation
Goals
Recognize and localize AMI on the ECG
Feel comfortable with 12 Lead interpretation
After a brief review of essential terminology, participants move directly into AMI recognition and localization. In fact, participants will be able to recognize and localize myocardial infarction approximately 30 minutes into this module! A fact that is mentioned in previous slide and re-emphasized here.

7. 12 Lead ECG
The 12-lead can provide a computer generated interpretation. The computer’s interpretive algorithm is designed to favor “specificity”. In other words, when the machine says “ACUTE MI SUSPECTED” it needs to always be right. The program is almost perfect in that regard, and when you see “ACUTE MI SUSPECTED” the machine is right about 98% of the time.
However, in order to attain that specificity, if the computer isn’t absolutely sure that an AMI is present, it will not say anything about it. Depending on the version of the software in your 12-lead machine, the computer may miss as many as one half of the cases where AMI could be suspected on the ECG.
In other words YOU are the primary interpreter, the computer is your backup.

8. 12 Lead ECG
The computer is very good at measuring intervals and durations. For example, it is actually much better than we are at measuring the PR-interval and the QRS width.
This information is always provided and can be very useful to review in interpreting the 12 Lead ECG.

9. 12 Lead ECG
Some of you may be wondering how anyone can make a sound interpretation with only 2.5 seconds shown in each lead.
Ask the group to look at the highlighted beat in the lead two rhythm strip, ask them to determine the rate, rhythm and interpretation. Of course it cannot be done.
As you well know, when you use an ECG to determine the cardiac rate, rhythm & interpretation, certain sampling time is required. Usually, at least a six second tracing is necessary, and complex rhythms may require even more sampling time.
However, do not be intimidated by the short sampling time in each of the 12-leads. What is different about 12-lead interpretation is this: Only one beat from each lead is needed to make an interpretation. The 2.5 seconds in each lead is usually long enough to capture one good, representative beat. Having said that one ST-segment may be enough to examine, looking at more than one complex may be helpful especially if there is wandering baseline or artifact at any point.
Recognition of AMI involves analyzing the shape of one beat in each lead. With that in mind let’s look at the shape of the waveforms in each lead.

10. R Wave R wave: The first positive deflection.
No matter where it occurs in the complex, the first positive deflection is called the R wave.
The R wave includes not only the upstroke of the positive deflection, but the downstroke returning to the baseline as well.

11. Q Wave Q Wave: A negative deflection preceding the R wave.
If there is any negative deflection in front of the R wave, it is labelled the Q wave.
The Q wave includes the negative down stroke and the return to baseline.

12. S Wave S wave: A negative deflection following the R wave.
Like the Q wave and the R wave, the S wave includes both the departure from and return to the baseline.

13. J-Point
J-Point: The junction between the end of the QRS and the beginning of the ST segment.
The J-point is found by looking for the point where the QRS stops and makes a sudden sharp change of direction.
You may opt to point out to the students that they have already found hundreds of J-points. Every time they have ever measured the width of a QRS, they have found the J-point. While they may not have labeled it as such, the end of the QRS complex is the J-point.

14. ST Segment
ST segment: The ECG segment between the J-point and the beginning of the T wave.
The ST segment is probably the single most important element to identify on the ECG when looking for evidence of AMI.

15. J point - end of QRS complex & beginning of ST segment
The J Point
J point - end of QRS complex & beginning of ST segment

16. Practice Find J-points and ST segments
They are not yet concerned with ST elevation or depression, simply identifying the J-point and ST segment.

17. Practice
Find J-points and ST segments
Review J-points and ST segment.

18. 12-Lead ECG AMI recognition Two things to know What to look for
Where to look
Local medical oversight will determine the criteria used to identify a STEMI patient. All stakeholders must be consulted to determine what criteria should be utilized in a given centre.
The first level of 12-lead interpretation is simply a matter of knowing two facts:
1. What changes an AMI can place on the 12-lead, and
2. Knowing which part of the heart that each lead “sees.”
Lets look at each in more detail.

19. What to look for Example - ST segment elevation
One millimetre or more (one small box) in limb leads
Two millimetres or more (two small boxes) in chest leads
Present in two anatomically contiguous leads
ST segment elevation, measured at the J-point, of 1mm or more is considered an abnormal finding in limb leads (I, II, III, aVF, aVL). Two mm or more is considered an abnormal finding in chest leads (V1 – V6).
Why different definitions of STEMI in limb and chest leads?
The limb leads are a long way away from each other and are not as sensitive as chest (or precordial) leads. It has been found that requiring at least 2mm or more of elevation in chest leads more accurately depicts patterns associated with acute infarct.
When that elevation is found in at least two anatomically contiguous leads, it is considered presumptive evidence of AMI.
NOTE: The concept of anatomically contiguous leads is simple, but may be difficult to explain. Essentially it means two leads looking at adjoining area of tissue. The difficulty comes when trying to determine which leads are contiguous with other leads. Here is one explanation:
If two leads have the same name (i.e., lateral or inferior) they are contiguous. Also, in the chest leads, if they are numerically consecutive, they are also contiguous. For example V2 is called a septal lead, and V3 an anterior lead, but they are anatomically contiguous. Reason:

20. Contiguous Leads Limb leads that “look” at the same area of the heartOR
Numerically consecutive chest leads

21. Contiguous Leads Inferior wall: II, III, avF
Lateral wall: I, aVL, V5, V6
Septum: V1 and V2
Anterior wall: V3 and V4
Posterior wall: V7, V8, V9
(leads placed on the patient’s back 5th intercostal space creating a 15 lead EKG)

22. Where to look ST segment elevation measurement
0.04 seconds after J point

23. ST Segment Elevation

24. ST Segment Elevation Presumptive evidence of AMI
Indication for acute reperfusion therapy
With an appropriate clinical presentation, ST segment elevation is presumptive evidence of acute myocardial infarction.
These patients benefit from immediate reperfusion, usually in the form of a thrombolytic drug or PCI (Percutaneous Coronary Intervention).
NOTE: In later chapters of this program the participant will be introduced to the full spectrum of Acute Coronary Syndromes (ACS). You may opt to acknowledge that other criteria for reperfusion will be added in later in the program. However, it is appropriate to begin with ST segment elevation.

25. ST Segment Compare to TP segment ST TP
In order to determine if the ST segment is elevated it is necessary to have a reference point.
The TP segment is the best reference to the isoelectric line.
Do not compare the ST segment to the PR segment because the PR can be depressed, giving the illusion of ST segment elevation. ST TP

26. ST Segment Analysis
This time find not only the J-point, but determine if the ST segment is elevated one millimeter or more above the TP segment.
#1 No
#2 Yes
#3 Yes
#4 No (likely BBB)
#5 Yes
#6 No

27. Practice EXERCISE: approximately 2 minutes Instructions:
Review the 12-lead ECG.
Go lead by lead, and pick one good complex in each lead.
Find the J-point and ST segment.
Compare the ST to the TP segment, looking for 1mm (one small box) of elevation (ignore ST depression for now).
Place a checkmark next to any lead with 1mm of ST segment elevation.
Review findings with group, pointing out every J-point and ST segment. Note leads II, III and aVF display elevation.
Remember ST segment elevation is presumptive evidence for AMI. Knowing which part of the heart leads II, III and aVF “sees” would tell you where the infarct is located.

28. Lead “Views”
Each lead has one, and only one, positive electrode. We can think of the positive electrode as a camera or an eye. The view is from the positive electrode toward the negative electrode. The portion of the left ventricle that each leads “sees” is determined by the location of that positive electrode on the patient’s body.
Different placements of the electrodes will yield different viewpoints.
There are six positive electrodes on the chest, yielding six leads.
There are four electrodes on the limbs from which the ECG machine makes another six leads.

29. Lead Groups I aVR V1 V4 II aVL V2 V5 III aVF V3 V6 Limb Leads
Chest Leads

30. Lead “Views”
Here’s what they look like on a patient. You may want to make a humorous remark that this gentleman looks like a younger Saddam Hussein experiencing chest pain.
The ECG machine simultaneously derives the 12-leads from the various positive electrodes.
Let’s discuss which part of the heart each lead “looks” at.

31. Inferior Wall II, III, aVF Left Leg I II III aVR aVL aVF V1 V2 V3 V4
The positive electrode for leads II, III, and aVF is attached to the left leg. The ECG monitor uses this one electrode as the positive electrode for all three leads.
From that perspective, these leads “look up” and “see” the inferior wall of the left ventricle.
NOTE: A heart model is helpful at this juncture, particularly to remind students that the heart does not sit “straight up” in the chest.

32. Inferior Wall I II III aVR aVL aVF V1 V2 V3 V4 V5 V6 Inferior Wall
NOTE: This is a posterior view of the heart.
The portion of the heart that rests on the diaphragm is called the “inferior wall”.
Leads II, III, and aVF, “look” up and see the inferior wall.
When ST segment elevation is noted in II, III and aVF, suspect an inferior infarction.
Inferior Wall

33. Lateral Wall I and aVL Left Arm I II III aVR aVL aVF V1 V2 V3 V4 V5 V6
Leads I and aVL share the positive electrode on the left arm.
From the perspective of the left arm, these leads “see” the lateral wall of the left ventricle.

34. Lateral Wall V5 and V6 Left lateral chest I II III aVR aVL aVF V1 V2
V5 and V6 are positioned on the lateral wall of the left chest which is why these two leads also “see” the lateral wall of the left ventricle.

35. Lateral I, aVL, V5, V6 I II III aVR aVL aVF V1 V2 V3 V4 V5 V6
Lateral Wall I II
III
aVR
aVL
aVF V1 V2 V3 V4 V5 V6
Portions of the lateral wall are shown here from both the anterior and posterior perspective.
Leads I, aVL, V5 and V6 “see” the lateral wall. When ST segment elevation is seen in these leads, consider a lateral wall infarction.

36. Anterior Wall V3, V4 Left anterior chest I II III aVR aVL aVF V1 V2 V3
The positive electrode for these two leads is placed on the anterior wall of the left chest. This correlates to their designation as anterior leads.

37. Anterior Wall V3, V4 I II III aVR aVL aVF V1 V2 V3 V4 V5 V6
Of course, ST segment elevation in V3 and V4 implies an anterior wall infarction.

38. Septal Wall V1, V2 Along sternal borders I II III aVR aVL aVF V1 V2 V3
These leads are positioned one on each side of the sternum. From that placement they “look through” the right ventricle and “see” the septal wall.
NOTE: The septum is left ventricular tissue.

39. Septal V1,V2 I II III aVR aVL aVF V1 V2 V3 V4 V5 V6
V1 and V2 “look through” the right ventricle to “see” the septum.

40. AMI Localization I II III aVR aVL aVF V1 V2 V3 V4 V5 V6
Anterior: V3, V4
Septal: V1, V2
Inferior: II, III, AVF
Lateral: I, AVL, V5, V6 I II
III
aVR
aVL
aVF V1 V2 V3 V4 V5 V6
This represents the 3x4 format of the 12-lead ECG.
Each box represents one lead, and the viewpoint of that lead is indicated.

41. AMI Recognition I Lateral aVR II Inferior aVL Lateral III Inferior
V1 Septal
V4 Anterior
II Inferior
aVL Lateral
V2 Septal
V5 Lateral
III Inferior
aVF Inferior
Each box represents one lead, and the viewpoint of that lead is indicated.
NOTE: Refer participants to their pocket card where this information is summarized as well.
V3 Anterior
V6 Lateral

42. AMI Recognition Know what to look for Know where you are looking
ST elevation
> 1mm in limb leads
> 2mm chest leads
Two contiguous leads
Know where you are looking
You will soon have this memorized

43. Mnemonic for Location S = V1 (Septal) L = I (Lateral) S = V2 (Septal)
Rhyme, phrase or device for remembering something
“LII – LI – ASS (backwards) – ALL”
S = V1 (Septal)
S = V2 (Septal)
A = V3 (Anterior)
A = V4 (Anterior)
L = V5 (Lateral)
L = V6 (Lateral)
L = I (Lateral)
I = II (Inferior)
I = III (Inferior)
L = aVL (Lateral)
I = aVF (Inferior)
This mnemonic device may work for some learners to remember the locations of the walls of the heart in relation to the 12 Lead ECG. However, emphasize to the learners that commitment to memorizing the locations of leads is essential for fast and consistent recognition.

44. Using mnemonic on ECG
You may want to write the Letters in the corner of each Lead when interpreting L S A I L S L I I A L

45. Antero Septal Greg Soto Note:
I have found the best way to teach interpretation is to begin, at this point, to have each participant interpret the 12 Leads while going around the room. If they miss anything or are incorrect be sure to point out proper interpretation while supporting participants. Encourage each participant to use the same following consistent approach:
Review the 12-lead ECG.
Go lead by lead, and pick one good complex in each lead.
Find the J-point and ST segment.
Compare the ST to the TP segment, looking for (ignore ST depression for now).
Place a check mark next to any lead with ST segment elevation.
Localize the area of infarction.
Acute antero-septal wall infarction
After reviewing this ECG, check in with the group. Press to see if everyone feels comfortable with the information presented to this point. If so, proceed to the next topic. The broader pattern of ECG changes are produced by infarction.

46. Extensive Anterior Instructions: Review the 12-lead ECG.
Go lead by lead, and pick one good complex in each lead.
Find the J-point and ST segment.
Compare the ST to the TP segment, looking for 1mm (one small box) of elevation (ignore ST depression for now).
Place a check mark next to any lead with 1mm of ST segment elevation.
Localize the area of infarction.
ST↑: Leads I, aVL, V1-V6 = Extensive Anterior STEMI

47. Inferior Instructions: Review the 12-lead ECG.
Go lead by lead, and pick one good complex in each lead.
Find the J-point and ST segment.
Compare the ST to the TP segment, looking for 1mm (one small box) of elevation (ignore ST depression for now).
Place a check mark next to any lead with 1mm of ST segment elevation.
Localize the area of infarction.
Inferior wall infarction
Note ST depression in I, AVL and V1-V3. The ask the participants to compare the elevation in aVF to the depression in aVL. Ask them if aVF elevation pattern looks similar to aVL if it were flipped upside down? Tell them there is a reason for this – it is called reciprocal changes.
Lets talk about one cause of ST depression, known as reciprocal ST depression.

48. Extensive Anterior Instructions: Review the 12-lead ECG.
Go lead by lead, and pick one good complex in each lead.
Find the J-point and ST segment.
Compare the ST to the TP segment, looking for 1mm (one small box) of elevation (ignore ST depression for now).
Place a check mark next to any lead with 1mm of ST segment elevation.
Localize the area of infarction.
Extensive anterior (septal + anterior + lateral)

49. Inferior Instructions: Determine which leads show ST elevation.
Which leads show ST depression.
Localize the area of infarction.
Determine if a reciprocal pattern exists.
ST elevation exists in II, III and aVF. ST depression in I and aVL
Does it fit the reciprocal pattern? Yes.
NOTE: Not every lead on each side of the seesaw must be elevated or depressed in order to assume reciprocal changes. Rather it is more a matter of at least some leads on one end of the seesaw being elevated and some being depressed.

50. Extensive Anterior Instructions:
Determine which leads show ST elevation.
Which show ST depression.
Localize the area of infarction.
Determine if a reciprocal pattern exists.
Here the elevation is in leads I, aVL, V1-V5
And the depression is in leads II, III and aVF
Extensive anterior infarction, with reciprocal depression

51. Normal ECG
ST segments are iso-electric.

52. Inferior Ask group to look for ST elevation.
The ST elevation implied epicardia ischemia (injury pattern).

53. Infero-lateral
Inferolateral STEMI with RCs and Q-waves in II, III, aVF & V5.

54. Inferior Instructions for presenter:
Review the 12-lead ECG slowly with the participants .
Go lead by lead, and pick one good complex in each lead.
Find the J-point and ST segment.
Compare the ST to the TP segment, looking for 1mm (one small box) of elevation in limb leads and 2 mm in chest leads (ignore ST depression for now).
Place a check mark next to any lead with ST segment elevation.
Localize the area of infarction.
Acute inferior wall infarction

55. Inverted T-waves = ischemia
Inverted T-waves in aVL, V1 – V3
Leads us into next discussion.

56. QUESTIONS?

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