ECG Leads – Precordial Leads
ECG Leads – Chest Leads:
It is a Unipolar lead having two electrodes, one is positive or exploring electrode applied on the surface of the chest wall and other is indifferent electrode constructed by Wilson central terminal.
Chest lead basically determines electrical activity of the heart transmitted along the horizontal plane (Transverse/Antero –posterior plane)
Vi = Ei – Ie
Vi : – Voltage detected by Chest lead
Ei :- Potential determined by exploring electrode
Ie :- Potential determined by indifferent electrode
All the chest leads determine potential differences between exploring electrode and virtual electrode (indifferent electrode), as we know indifferent electrode has almost zero voltage, so potential difference detected by the chest lead is practically equal to voltage detected by exploring electrode.
Making ECG Leads – Chest leads
To make an ECG Leads – chest lead, negative terminal of the machine is connected via common wire to the negative electrode at left arm, right arm and left leg with high resistance. Exploring electrode connected with positive terminal of the machine is applied on the surface of the chest wall; In this case whatever the electrical activity of the heart transmitted along horizontal plane, the exploring electrode will be able to detect the voltages in relation to the indifferent electrode.
Placement of the ECG Leads – chest leads
There are six standard and three additional chest leads; here we will discuss only six standard chest leads. For all of these, Wilson common terminal will remain same and only the position of exploring electrode will be changed
V1:- Placed in the fourth inter coastal space just to the right of the sternum.
V2:- Placed in the fourth inter coastal space just to the left of the sternum.
V4:- Placed in the mid-clavicular line in the fifth inter coastal space
V5:- Placed in the anterior Axillary line at the same level as lead V4
V6:- Placed in the mid axillary line at the same level as lead V4
For placement of chest leads always follow bonny land marks, never use the nipples to locate the position of any of the chest leads because nipple’s position may vary person to person.
Classification of the ECG Leads – Chest leads
There are two ways to classify the ECG Leads – Chest leads
Anatomical classification of chest leads
V1 and V2 oriented anatomically to the right side of the heart.
V3 and V4 oriented anatomically over the septum.
V5 and V6 oriented anatomically over the left side of the heart.
Functional classification of chest leads
This classification is based on electrical activity from various parts of the ventricles,
V1 and V2:- Septal leads
V3 and V4:- Anterior leads
V5 and V6:- Left leads / Left lateral leads
V1, V2, V3 and V4:- Antero-septal leads
V3, V4, V5 and V6:- Anterolateral leads (Anteroapical leads)
V2, V3, V4 and V5:- Large anterior leads (Main Anterior leads)
Orientation of ECG Leads – Chest leads
The ECG Leads – Chest leads (V1, V2, V3, V4, V5, V6) axis are oriented relative to each other along the horizontal plane almost approximately 30 degrees).
V1:+120degrees
V2:+90 degrees
V3:+60 degrees
V4:+30 degrees
V5:0 degrees
V6:-30 degrees
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