What lead placement is referred to as the ground in a three lead system?

In a three-lead ECG system, the lead that serves as the ground is commonly referred to as the reference or neutral lead. In this setup, the black lead is associated with the left arm (LA), which is used for measuring electrical activity from the heart. However, in standard convention, the right leg (RL) lead, typically colored blue, is utilized as a ground or reference point. This lead captures any stray electrical activity and minimizes interference, allowing for a more accurate representation of the heart’s electrical signals from the left arm and right arm leads.

The placement of the reference or ground lead is crucial because it helps stabilize the ECG readings. With the right lead acting as a ground, it ensures that the measurements from the left arm and right arm are more reflective of the heart's activity without significant noise from external electrical influences. Therefore, the correct identification of a ground lead in this context is indeed blue (RL).