Lead II records electrical activity from which two electrodes?

• A. Right arm to left leg
• B. RA to LA
• C. Left arm to left leg
• D. RA to RL

Answer: (A)

This question tests how Lead II is defined in the limb-lead system (Einthoven’s triangle). Lead II is the potential difference between the right arm and the left leg, with the right arm electrode serving as the negative terminal and the left leg electrode as the positive terminal. So it records electrical activity along the axis from the right arm toward the left leg, i.e., the right arm to left leg. That’s why the correct pairing is right arm to left leg. The other pairings correspond to different, non-Lead II configurations.