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ECG Leads : Precordial /Chest Leads Placement

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  • Revised on: 2020-08-06

Upon understanding the physiology of the heart and electrical activity that leads to the formation of ECG waves, there is a need to apply it in the clinical setting.  

The knowledge on correct placement of electrocardiogram leads is key to getting correct readings and eventual diagnosis.

An ECG is a series of waves and deflections recording the heart’s electrical activity from a certain “view.” Many views, each called a ECG lead, monitor voltage changes between electrodes placed in different positions on the body.

An ECG electrode is a conductive pad attached to the skin to enable the recording of the cardiac electrical activity. An ECG lead is an electrical picture of the heart created after analyzing the electrical currents detected by the electrodes. Each lead gives a different view of the electrical activity of the heart, and so a different ECG pattern.

A standard ECG is the 12-Lead ECG with 12 leads obtained from 10 electrodes.

For easier understanding and interpretation of an electrocardiogram its important that you know each the direction from which the leads look at the heart.

Precordial ECG Leads

Chest leads V1 to V6 are unipolar leads and consist of a single positive electrode (exploring electrode) with a reference point found at the electrical center of the heart known as Wilson central terminal (WCT).

The Wilson central terminal is a virtual point located approximately at the center of the chest or the center of Einthoven's triangle. WCT is an average of the three limb leads computed by connecting all these leads to one terminal vial electrical resistance.

Ideally, the sum of these potentials is zero as per Kirchhoff's law. But since the triangle formed isn't a perfect equilateral triangle these potential is at almost zero potential. This point is, therefore, a reference electrode at the center of the heart.

As a result of the "location" of the ground lead (WCT) being in the center of the chest, the precordial leads have exploring electrodes located anteriorly on the chest wall. This enables them to measure electrical activity that is moving in a horizontal (axial) plane of the heart i.e front-back direction and a right-left direction.

axial plane ecg

Placement of chest leads

Remember they are chest leads and not breast leads. Therefore when placing then don't place them over the breast tissue. You should avoid using the nipple to locate the intercostal spaces instead use the chest bony landmarks to avoid errors.

  • V1 is placed in the 4th Intercostal space to the right of sternum (right sternal border)
  • V2 is placed in the 4th Intercostal space to the left of the sternum (left sternal border)
  • V3 is placed directly between V2 and V4 ( therefore you should place V4 first before V3).
  • V4 is placed on the 5th Intercostal space at the left midclavicular line.
  • V5 is placed at the level with V4 at the left anterior axillary line and lastly
  • V6 is placed at the level with V5 at the left mid-axillary line.

You might have noticed that lead V4 to V6 is on the same level laterally (5th intercostal space).

What are the relations of the chest leads to the heart?

Anatomically the ECG leads V1 and V2 to look at the right ventricle, V3 and V4 look at the septum between the ventricles and the anterior wall of the left ventricle, and V5 and V6 look at the anterior and lateral walls of the left ventricle.

relationship between chest leads to the heart

Functionally these ECG leads are classified as per the electrical activity that they are most sensitive with.

V1 and V2 are known as septal leads. These leads primarily to observe the electrical activity of the ventricular septum.

V3 and V4 are known as anterior leads because they observe the electrical activity of the anterior part of the left ventricular wall.

V5 and V6 are anterolateral leads. This is because they observe or detect the electrical activity of the anterolateral walls of the left ventricle.

You can remind yourself on the basic physiology of an electrocardiogram and formation of the waves in this video here