An ECG is made by measuring the electrical activity that goes through the heart. This activity measured using external electrodes:
- six chest electrodes: V1 – V6
- four extremity electrodes: left arm, right arm, left foot, and a neutral electrode
With these electrodes it is possible to derive twelve different leads: six precordial leads and six extremity leads. In this animation, we focus on the leads I to III of the extremity leads.
- Lead I measures the electrical activity between the right arm and left arm.
- Lead II measures the electrical activity between the right arm and the left foot
- Lead III measures the electrical activity between the left arm and left foot.
When the electrical activity moves towards the leads, it will create a positive deflection of the QRS-complex of that lead. Electrical activity that moves away from the lead will create a negative deflection of the QRS-complex of that lead.