What does Lead III measure?

Lead III measures the voltage difference between the right arm and the left leg. This lead is part of the standard 12-lead ECG system and reflects electrical activity as it travels through the heart. In the context of the ECG, electrodes are placed on the right arm, left arm, and left leg to form the leads.

In Lead III, the left leg acts as the positive electrode while the right arm is the negative electrode. This configuration allows Lead III to capture the electrical impulses that travel between these two points, providing vital information about the heart’s electrical activity, specifically during depolarization and repolarization phases. The angle of Lead III is typically positioned to encompass the inferior aspect of the heart, making it particularly useful for assessing electrical activity originating from that region.

The other choices mistakenly identify combinations of electrodes or concepts that do not accurately represent the purpose of Lead III.