ECG Lead Placement

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ECG Lead Placement

The system of positioning of leads for performing a 12-

lead ECG is universal. This helps to ensure that, when a

person's ECGs are compared, any changes on the ECG

are due to cardiac injury, not a difference in placement of

leads, this is extremely important with the increasing useof foreign travel. There are universal standards in place

throughout the world.

Interpretation of the findings can vary from doctor to

doctor but methods for obtaining the information are the

same the world over.

These positions may differ slightly when a patient is on

continuous cardiac monitoring. The leads routinely attached to wrists and ankles will be placed on

shoulders and lower abdomen so that movement of limbs has minimal effect on the rhythm trace.

These positions may also differ if a patient is shaking (maybe due to Parkinson's Disease or

hypothermia) or has muscle tremors. In this situation the leads may be moved onto the thighs andforearms.

Seeing an ECG being performed will look something like the scene below. As you can see, the

peripheral leads are correctly placed on wrists and ankles.

Chest Leads

There are 10 wires on an ECG machine that are connected

to specific parts of the body. These wires break down into

2 groups:

1. 6 chest leads

2. 4 limb or peripheral leads (one of these is

"neutral")

The 6 chest leads are positioned as below:

The 6 leads are labelled as "V" leads and numbered V1 to

V6. They are positioned in specific positions on the rib

cage. To position then accurately it is important 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.


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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.

Now look at the picture below showing the position of the

heart in relation to the rib-cage and you get an idea as to

which areas are being looked at by these leads.

Limb Leads

Limb leads are made up of 4 leads placed on theextremities: 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.

Unipolar Leads

But, wait a minute. That gives us nine wires and it is a 12-

lead ECG. Where 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.

Bipolar 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

"Einthovens 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


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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, ofthe 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 V! 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.

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ECG Lead Placement