Understanding Electrocardiography lesson -2

Lead: It is the electrical picture of the heart.

The 12-lead ECG is generated from ten physical electrodes that are attached to the skin.

  (the right leg electrode acts as an earthing electrode).

They comprise three groups:

Three dipole limb leads, three augmented voltage limb leads and six unipole chest leads.

         Bipolar Lead:- I, II, III.

         Unipolar lead:-Chest lead (V1-V6) + aVL , aVR, aVF.

 Lead-I: left Chest wall,

Lead –II: left hip,

Lead-III: Right hip.

Lead-aVR: Right shoulder.

Lead-aVL: left shoulder.

Lead-AVF: Perineum.

The six chest leads are unipolar recordings obtained by electrodes in the following positions: lead V₁, fourth intercostal space, just to the right of the sternum; lead V₂, fourth intercostal space, just to the left of the sternum; lead V₃, midway between V₂ and V₄; lead V₄, midclavicular line, fifth intercostal space; lead V₅, anterior axillary line, same level as V₄; and lead V₆, midaxillary line, same level as V₄ and V₅.

Leads- I,II, and aVL  indicates the  changes in left lateral surface of the heart.

Lead- III and aVF   indicates the inferior wall changes in the heart.

Lead : V1-V6 indicates the extensive anterolateral changes.

Lead: V1-V2  indicates the septal changes.

Lead:V3-V4  indicates the anterior changes.