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Chapter 7 - Acquisition
1. ONTARIO
BASE HOSPITAL GROUP
Chapter 7
for 12 Lead Training
-Acquisition-
Ontario Base Hospital Group
Education Subcommittee
2008
TIME IS
MUSCLE
2. OBHG Education Subcommittee
Acquisition
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
Hamilton Base Hospital
Dr. Rick Verbeek, Medical Director
AUTHOR
Greg Soto, BEd, BA, ACP
Niagara Base Hospital
2008 Ontario Base Hospital Group SOCPC
3. Chapter 7 Objectives
Identify the goals for acquiring 12 Lead ECG
Describe differences between 3-Lead & 12-
Lead ECG
Locate placement of limb & chest leads
Explain causes of artifact and list remedies
Describe dignity issues involved in exposing
chest and list solutions
OBHG Education Subcommittee
4. OBHG Education Subcommittee
Acquisition
Does NOT have to increase
scene time
PHECG studies have found on scene
times to increase minimally (0 - 3
minutes)
Scene time with PHECG improves
with practice and scene organization
12. Lead Placement
Lead placement is critical
If not placed correctly (even by one
interspace) the resulting ECG will
exhibit changes that could be
misconstrued as “abnormal” and
profoundly affect patient care
OBHG Education Subcommittee
13. Limb Lead Placement
Place leads on
limbs
Away from major
muscles or arteries
Have patient
remain still during
12 lead acquisition
(to reduce artifact)
OBHG Education Subcommittee
14. Limb Lead Placement
Place electrodes
on the limbs if
there is a 12 lead
in the patient’s
future – highly
preferable to torso
placement
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15. Limb Lead Placement
Reasons to place
on the torso?
Fracture
Amputation
Artifact
If Limb Leads are
placed on the torso
make sure to
document this
directly on the 12
Lead ECG
OBHG Education Subcommittee
16. OBHG Education Subcommittee
Limb Leads
aVR should be negative
If aVR is upright, check for
reversed limb leads
17. Precordial Chest Leads
For every person, each precordial lead
placed in the same relative position
V1 - 4th intercostal space, R of sternum
V2 - 4th intercostal space, L of sternum
V4 - 5th intercostal space, midclavicular
V3 - between V2 and V4, on 5th rib or in 5th
intercostal space
V5 - 5th intercostal space, anterior axillary line
V6 - 5th intercostal space, mid-axillary
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19. Chest Lead Placement
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V1 is placed in the 4th
intercostal space to the
right of the sternal boarder
To find the 4th intercostal
space feel for the clavicle
Just below the clavicle is the
2nd rib, then 3rd and 4th rib
Between the 4th rib and the 5th
rib is the 4th intercostal space
V2 is placed to the left of
the sternal boarder in the
4th intercostal space
20. Chest Lead Placement
OBHG Education Subcommittee
V4 is placed next in the 5th
intercostal space in the
mid-clavicular line
Find the half way mark on
the left clavicle and move
down one rib so V4 is
between the 5th and 6th ribs
V3 is placed after V4 and
is simply placed in
between V2 and V4 either
on the 5th rib or in the 5th
intercostal space
21. Chest Lead Placement
OBHG Education Subcommittee
V5 is placed in the 5th
intercostal space and the
anterior axillary line
To find the anterior axillary
line lay the patient’s left arm
at their side and follow the
crease line in their armpit
down the front of their chest
V6 is placed in the 5th
intercostal space in the
mid-axillary line
22. Chest Lead Placement
OBHG Education Subcommittee
V1 V2
V3
V4 V5 V6
V1: 4th intercostal space to the right of the sternum
V2: 4th intercostal space to the left of the sternum
V3: directly between V2 and V4
V4: 5th intercostal space at the left mid-clavicular line
V5: level with V4 at the anterior axillary line
V6: level with V5 at the mid-axillary line
23. Exposing the Chest & Pt Dignity
Where required:
Remove clothing only if necessary
Replace with a gown or a sheet
With practice:
Chest leads can be placed on adult women
without exposing breasts
Work around bras where prudent
When placing electrode for V4, use the back of a gloved hand to lift a
women’s left breast AFTER informing her. It is difficult to construe this
action as sexual contact vs. using the front of a cupped hand.
OBHG Education Subcommittee
24. Video - Acquisition
Play 12 Lead ECG Acquisition
OBHG Education Subcommittee
video here
25. Reduce Artifact:
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Skin Prep
Dry moist skin
Clip or shave excess hair
Abrade dead skin with skin prep tape,
plastic backing of 12 lead stickers or dry
4x4 gauze
26. Other Causes of Artifact
Patient movement
Cable movement
Vehicle movement
Electro-Magnetic Interference
OBHG Education Subcommittee
27. Patient Movement
Make patient as
comfortable as possible:
Supine preferred
Sitting most common with
chest pain/SOB patients
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28. Patient Movement
Check for subtle movement:
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Toe tapping, shivering
Look for muscle tension:
Hand grasping rail, head raised to
“watch”
Coach the patient:
Lie still, stop talking, breath slow and
quiet
29. Cable Movement
Some “slack” between monitor
and patient is needed
Not too much “slack” (leads can
come off electrodes)
OBHG Education Subcommittee
30. OBHG Education Subcommittee
EMI
Electro-Magnetic Interference
EMI can interfere with electronic
equipment:
Airlines prohibit use of electronic
equipment during take-off
31. OBHG Education Subcommittee
EMI
Maintain awareness of possible
EMI interference:
Cell phones
Radios
Most electrical devices
Fluorescent lights
32. OBHG Education Subcommittee
Clear ECG
Things to look for…
Little or no artifact
Steady baseline
Which is worse for
reading 12 Lead ECG?
34. Ahhh! Much Better
Note: the baseline straightened out by
simply repositioning the patient cables
and clipping them onto the sheet.
OBHG Education Subcommittee
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Hands-on experience obtaining 12-leads builds proficiency.
Generally EMS providers must obtain 20-30 ECGs before they feel confident and comfortable with acquisition techniques.
Once EMS providers have gained proficiency in this technique, on-scene time need not be significantly increased.
Anecdotal note: Some systems have reported a decrease in scene time on cardiac calls since the introduction of 12-leads. The explanation lies in heightened awareness of time to treatment secondary to recognizing acute MI.
More on scene organization later.
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Before clarity of the 12-lead can be discussed it is important to look at the differences between a 3-lead ECG rhythm strip and a 12-lead ECG.
A 12 Lead ECG capable monitor-defibrillator provides all of the functions of previous 3-lead monitors. It would be easy to assume that the difference lies in its ability to obtain extra leads.
However, one of the biggest differences between the two machines is that the 12-lead is designed to obtain a DIAGNOSTIC ECG.
Literally, the 12-lead is designed to record more accurate waveforms than the typical 3-lead ECG.
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The typical “3-lead” ECG was never designed to capture QRS-ST-T waveforms with complete accuracy. The 3-lead was designed to provide enough information for the user to determine cardiac rate, rhythm and ultimately ECG Interpretation.
Because artifact makes interpretation difficult, the 3-lead is set to “filter out” artifact by reducing the spectrum of cardiac electrical activity that it “sees”. This strategy significantly reduces artifact and still renders waveforms of sufficient quality for rate and rhythm determination.
However, in doing so, the QRS-ST-T may not always be accurately represented.
Therefore, you cannot rely on monitor quality (3 or 4 lead ECG) for ST analysis. It is not uncommon for paramedics with monitor quality 3 or 4 lead ECG to find ST-elevation in leads 2 & 3 and assume Inferior STEMI only to discover in ED that the 12 Lead did not confirm STEMI. If you want to examine STEMI you must acquire a 12 Lead ECG.
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The 12-lead is designed to accurately reproduce the QRS-ST-T waveforms.
In order to do so the 12-lead must “look” at a broader spectrum of cardiac electrical activity. This spectrum is referred to as “frequency response”
This broader spectrum is referred to as “diagnostic quality”.
A diagnostic quality ECG is necessary for accurate ST segment analysis.
Unfortunately, when in diagnostic quality, all 12-lead ECGs are more susceptible to more artifact than are 3-lead ECGs.
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As previously mentioned, the cost of the more accurate waveforms is paid for by the presence of artifact. Also consider the fact that 12-lead analysis may require careful scrutiny of small, 1mm changes in waveforms.
Putting these facts together describes the reality we face:
Just when we need the ECG to be its very clearest, is exactly when it is most likely to have artifact.
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Because of the increased “window” to electrical signals, additional steps must be taken to reduce the amount of artifact produced.
Removing excess hair and prepping the skin allows the electrode gel to better penetrate the skin, thus receiving a stronger signal with less artifact.
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Limb leads should be placed on the limbs. The traditional placement is near the ankles and wrists. Wrist placement can be complicated by some watches that create EMI. It may be acceptable to use lateral deltoid position for upper limb leads.
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A more proximal placement on the extremities is acceptable and, in fact, usually reduces movement artifact. Just be sure to keep the electrodes off the trunk. Never place the lower limb electrodes above the pelvis.
The following note is included in the student manual. Please determine local policies and preferences in order to address any related questions.
“The proper position for the limb electrodes is on the limbs, and that should be your technique. However, standard operating procedure in some receiving facilities is to place the electrodes on the trunk, near the limb. If this is to be done, at least make certain that the upper electrodes are near the deltoid, and the lower electrodes are below the umbilicus.”
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AVR provides the ECG Interpreter the “Square root of Squat” (to use slang). However, even then it gives you something: Because the positive electrode for aVR is located on the right arm, normal ventricular activation moves away from aVR. Thus, aVR is typically negative.
If aVR is upright, it may be the result of altered conduction or it could be due to misplaced limb leads.
When aVR is positive always confirm proper lead placement.
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V1fourth intercostal space to the right of the sternum
V2fourth intercostal space to the left of the sternum
V3directly between leads V2 and V4
V4fifth intercostal space at left midclavicular line. The above picture shows V4 placed almost on the nipple. This is not accurate in terms of general approach to lead placement. It is now standard & acceptable to place V4 under the Left breast in line with the midclavicular line.
V5level with lead V4 at left anterior axillary line
V6level with lead V5 at left midaxillary line
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Exposing the chest before obtaining the 12-lead may be required to obtain proper positioning of chest leads. If a gown is not available a sheet may be used, however, the gown is preferable.
Many paramedics experienced in 12 Lead ECG acquisition have found that working around a patients clothing is easy and fast and may save patient embarrassment.
Exposing breast tissue and discrete handling of patient’s modesty is NOT just an issue for considering in women. Some large male patients may be embarrassed by display of breast tissue.
POINT OF EMPHASIS:
When placing electrode for V4, use the back of a gloved hand to lift a women’s left breast AFTER informing her. It is difficult to construe this action as sexual contact vs. using the front of a cupped hand.
An easy alternative is to ask the female patient (or male with large breasts) to lift their left breast to permit the paramedic to place the electrode and wire.
Bras: In diaphoretic women with bras, positioning Lead V4 chest electrode under bra strap below the left breast can actually help prevent the electrode from falling off.
As paramedics have commonly experienced, patients experiencing ischemic chest pain often present with acute diaphoresis. The extremely sweaty patient can present a challenge to paramedics attempting to acquire a 12 Lead ECG as the electrodes often fail to adhere and fall off the chest before an ECG can be acquired.
The above picture demonstrates a problem solving approach that paramedics can use to acquire a 12 Lead ECG with even the most diaphoretic of patients. As the picture shows, one paramedic places then presses on each of the CHEST Leads holding them in place. This manoeuvre does not interfere with acquisition of a valid 12 Lead.
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Once the electrodes are applied to the skin (and the has been prepped as needed), there are still other sources of artifact to consider.
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It is important to place the patient in a position of comfort. The reduction in muscle tension will help to prevent artifact. When possible, the patient should be in the supine position for a 12-lead ECG.
Sometimes this is not feasible, practical or desirable.
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Even small movements can produce artifact. Take a moment to look for even minor patient movements.
In the ambulance the patient may have a firm grasp on the stretcher rail or strain to look at the 12-lead monitor. Both of these activities can result in increased artifact.
Helpful technique: Keep the patient’s arms resting on a steady surface.
In colder temperatures ensure the patient is warm and free from shivering.
When the time comes to press the 12 Lead button to acquire the 12 Lead it is important to stress to the patient not to talk or move during acquisition.
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The cables should have enough “slack” to avoid tugging on the electrodes.
Helpful technique: the clip should be attached to the patient’s clothing or the sheet to keep the cables in place.
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60 cycle interference is one type of EMI.
Interference from other electrical devices is another.
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Any electrical device has the potential to produce artifact on the ECG. Be sure to have all responders turn down (or off) pagers, cell phones and portable radios during ECG acquisition. May need to turn the lights outs or move the patient.
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Answer: Wandering baseline as reading ST segments relies on lateral reference that can not be obtained if the baseline wanders up and down.
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Note how the baseline straightened out by simply repositioning the patient cables and clipping them onto the sheet.
What technique(s) would you consider in order to resolve the muscle artifact?
