ECG Grid Paper
The ECG paper recording speed is typically 25 mm/s.
They are 10 in number and placed externally on the skin at various designated positions, as outlined in the following table.
|12 lead ECG Electrodes||Placement|
|RA||On the Rt arm, avoiding thick muscle|
|LA||In the same location where RA was placed, but on lt arm|
|RL||On the Rt leg, lateral calf muscle.|
|LL||In the same location where RL was placed, but on the left leg.|
|V1||In the 4th ICS to the right of the sternum|
|V2||In the 4th ICS to the left of the sternum|
|V3||Between leads V2 and V4|
|V4||In the 5th ICS on the Lt midclavicular line|
|V5||Horizontally even with V4 on the left anterior axillary line|
|V6||Horizontally even with V4 and V5 on the Lt midaxillary line|
|Rt-sided Electrodes – To detect Rt Ventricular MI|
|V1R||4th Lt ICS, sternal edge|
|V2R||4th Rt ICS, sternal edge|
|V3R-V6R||Positioned as mirror images to the standard precordial leads on the Rt side|
|Posterior Electrodes – To detect Posterior wall MI|
|V7||Horizontal plane of V4-V6; posterior axillary line|
|V8||Horizontal plane of V4-V6; below the scapula|
|V9||Horizontal plane of V4-V6; at the paravertebral border|
The term “lead” in ECG refers to the 12 different vectors along which the heart’s depolarization is measured and recorded. ECG leads are of two types: frontal and horizontal.
Frontal leads are also known as “limb leads.” They view the heart in vertical plane.
Frontal leads are of two types:
- Standard leads (Bipolar limb leads): I, II, & III
- Augmented leads (Unipolar limb leads): aVR, aVL, & aVF
Einthovens’s triangle is an imaginary formation of an inverted equilateral triangle, comprising three limb leads, at two shoulders & pubis with the heart at center.
Einthoven’s law states that when potential difference between the bipolar leads is measured simultaneously at any given moment, the potential in lead II is equal to the sum of potentials in leads I and III.
Orientation of augmented leads
Unipolar limb leads are of low electrical potential and are instrumentally augmented. They are oriented in the following way:
- Lead aVR – Augmented unipolar right arm lead, oriented to face the heart from right shoulder.
- Lead aVL – Augmented unipolar left arm lead, oriented to face the heart from left shoulder.
- Lead aVF – Augmented unipolar left leg lead.
Horizontal (Precordial) Leads
Horizontal (precordial) leads view the heart in the horizontal plane.
They include leads V1-V6.
Lead Grouping in ECG
Multiple leads that examine the same area are called contiguous leads. They are grouped in the following way:
- I, aVL, V5, V6 – Lateral leads
- II, III, aVF – Inferior Leads
- V1, V2 – Anteroseptal leads
- V3, V4 – Anterior leads