Definition
- ECG is the graphic record of the heart's electrical activity, recorded from body-surface electrodes; it represents the algebraic sum of action potentials of all cardiac muscle fibers.
- Recorded at a paper speed of 25 mm/s:
- 1 small square (1 mm)0.04 s
- 1 large square (5 mm)0.20 s
ECG Leads
Classification of ECG leads
Category
Bipolar limb
- Leads
- I, II, III
- Principle
- Potential difference between two limb electrodes (Einthoven triangle)
Augmented unipolar limb
- Leads
- aVR, aVL, aVF
- Principle
- Exploring electrode vs indifferent electrode of the other two limbs
Unipolar chest (precordial)
- Leads
- V1 to V6
- Principle
- Exploring chest electrode vs Wilson's terminal