In standard limb leads, Lead II measures electrical potential between which two electrodes?

• A. RA to LL
• B. RA to LA
• C. LA to LL
• D. RL to LL

Answer: (A)

Lead II records the voltage difference along the frontal-plane axis from the right arm electrode toward the left leg electrode. In this configuration the right arm is the negative terminal and the left leg is the positive terminal, so the lead effectively measures electrical potential between the right arm and the left leg. The right leg electrode is typically used as a ground reference and not part of the measurement for standard limb leads. The other limb leads use different pairs (for example, between the arms or between an arm and the other leg), so they do not describe Lead II.