One of my SUPER Pet Peeves…. Get the Leads in the Right Position!!!
- Up to 50 percent of cases have V1 and V2 EKG electrode placement in too high of a location which can mimic an anterior MI and cause T wave inversion.
- Up to 33 percent of the cases have the precordial electrodes (V1-V6) lower or laterally misplaced which also leads to misdiagnosis.
Note: It is impossible to place the chest leads by “sight”! You need to palpate the first intercostal rib space and down to the forth intercostal space.
Artifact: Latin term for your tracing looks like crap…
The heart’s electrical signal has very little output, so it can easily be combined with other signals of identical frequency to create artifact. It is not very uncommon to have some form of artifact for a 12 lead EKG electrode placement but it’s important to attempt to lessen any interference in order to ensure an accurate ECG. The following are a few guidelines that are very helpful to reduce artifact while performing EKG’s.
- Place patient in a supine position if the patient will tolerate.
- Place the patient’s arms down by their side to relax their shoulders.
- Patient’s legs should be uncrossed.
- Electrical devices such as mobile phones should be away from the patient as these devices may interfere with the machine.
- Dry the skin if it is diaphoretic or moist.
- Shave any hair that can interfere with electrode placement.
- Use new electrodes tabs if prior tabs are not in place. Do not mix and match electrodes types.
- If you are using adhesive electrode dots, gel should be moist.
- Electrodes should not be placed over bones and over areas where there is a lot of muscle movement. For chest leads, electrode sensor should be over the intercostal space and not the rib.
- Sometimes an abrasive material such as a wash cloth may need to be used to remove dead skin cells.
- Alcohol prep pads and a little scrubbing can be used to remove oils and dirt from the skin.
|V1||4th Intercostal space to the right of the sternum|
|V2||4th Intercostal space to the left of the sternum|
|V3||Midway between V2 and V4|
|V4||5th Intercostal space at the midclavicular line|
|V5||Anterior axillary line at the same level as V4|
|V6||Midaxillary line at the same level as V4 and V5|
|RL||Anywhere above the ankle and below the lower hip|
|RA||Anywhere between the shoulder and the lower forearm|
|LL||Anywhere above the ankle and below the lower hip|
|LA||Anywhere between the shoulder and the lower forearm|
There are 10 wires on an ECG machine that are connected to specific parts of the body. These wires break down into 2 groups:
- 6 chest leads
- 4 limb or peripheral leads (one of these is “neutral”)
The anatomy landmarks of the torso
The 6 leads are labelled as “V” leads and numbered V1 to V6. They are positioned in specific positions on the rib cage.
An easy way to locate landmarks is to palpate the clavicle and trace it back to the sternal border. The space that you palpate is the 1st intercostal space. Walk your fingers down the intercostal spaces until you reach the 4th intercostal space.
Another way to locate lead placement is to be able to identify the “angle of Louis”, or “sternal angle”.
To find it on yourself, place your fingers gently at the base of your throat in a central position and move your fingers downward until you can feel the top of the sternum, or rib cage. From this position, continue to move your fingers downward until you feel a boney lump. This is the “angle of Louis”.
The angle of Louis is most easily found when the patient is lying down as the surrounding tissue is tighter against the rib cage.
From the angle of Louis, move your fingers to the right and you will feel a gap between the ribs. This gap is the 2nd Intercostal space. From this position, run your fingers downward across the next rib, and the next one. The space you are in is the 4th intercostal space. Where this space meets the sternum is the position for V1.
Go back to the “angle of Louis” and move into the 2nd intercostal space on the left. Move down over the next 2 ribs and you have found the 4th intercostal space. Where this space meets the sternum is the position for V2.
From this position, slide your fingers downward over the next rib and you are in the 5th intercostal space . Now look at the chest and identify the left clavicle, a bone that runs from the left shoulder to the top of the sternum. The position for V4 is in the 5th intercostal space , in line with the middle of the clavicle (mid-clavicular). V3 sits midway between V2 and V4.
Follow the 5th intercostal space to the left until your fingers are immediately below the beginning of the axilla, or under-arm area. This is the position for V5.
Follow this line of the 5th intercostal space a little further until you are immediately below the centre point of the axilla, (mid-axilla). This is the position for V6.
Mark your lead locations with surgical marker if you need to remove stickers. The goal is to have repeatability and consistency in your tracings. Location really does matter.
Speaking of location, if you need to elevate the head of the bed to do tracing (i.e. patient having respiratory distress and can’t lie flat, etc.), note on the tracing the elevation of the head of bed in degrees.
One other item to note on tracing is was the patient having chest pain/pressure at the time the tracing was captured. Sometime the absence of pain/pressure is as important as one taken during symptoms.
Limb leads are made up of 4 leads placed on the extremities: left and right wrist; left and right ankle.
The lead connected to the right ankle is a neutral lead, like you would find in an electric plug. It is there to complete an electrical circuit and plays no role in the ECG itself.
That gives us nine wires and it is a 12-lead ECG. Here are the other 3…
Well, so far we have nine wires. They all look directly at the heart with tunnel vision. They only give information based on what is immediately in front of them. These nine wires are known as “unipolar leads”.
The three active peripheral leads are AVr, AVL, and AVf.
The “AV” stands for “Augmented Vector”. The last letter refers to position, which are as follows:
|Label||Meaning of label||Position of lead on body|
|AVr||Augmented vector right||Right wrist|
|AVL||Augmented vector left||Left wrist|
|AVf||Augmented vector foot||Left foot|
These 3 leads create a triangle with the heart in the middle, as below. The lines into the centre indicate the line of sight of these leads.
Well, the 2 leads situated on the right and left wrist (or shoulders), AVr and AVL respectively, and the lead situated on the left ankle (or left lower abdomen) AVf, make up a triangle, known as “Einthoven’s Triangle”. Information gathered between these leads is known as “bipolar”. It is represented on the ECG as 3 “bipolar” leads. So,
- information between AVr and AVl is known as lead l.
- Information between AVr and AVf is known as lead ll
- Information between AVl and AVf is known as lead lll
Now we have 12 leads, we need to know which regions of the heart each lead is looking at and what groups they make up.
Regions of the Heart
- AVL is on the left wrist or shoulder and looks at the upper left side of the heart.
- Lead l travels towards AVL creating a second high lateral lead.
- AVf is on the left ankle or left lower abdomen and looks at the bottom, or inferior wall, of the heart.
- Lead ll travels from AVr towards AVf to become a 2nd inferior lead
- Lead lll travels from AVL towards AVf to become a 3rd inferior lead.
- V2 V3 and V4 look at the front of the heart and are the anterior leads.
- V1 is often ignored but if changes occur in V1 and V2 only, these leads are referred to as Septal leads.
- V5 and V6 look at the left side of the heart and are the lateral leads.
The ECG below shows where these leads are when printed.