Final answer:
Lead aVL records electrical activity from a midpoint between the right arm and left leg to the left arm on an ECG, which measures the heart's electrical activity.
Step-by-step explanation:
The lead that records electrical activity from a midpoint between RA (right arm)/LL (left leg) to the LA (left arm) is lead aVL. An electrocardiogram (ECG) is a test that measures the electrical activity of the heart, which is represented as vectors of depolarization and repolarization on the ECG. These vectors are measured between pairs of electrodes placed on the body. The standard ECG includes 12 leads, which give a complete picture of the heart's electrical activity. The lead in question, aVL, gives insight into the electrical activity of the heart muscles as they depolarize and contract (atrial depolarization) and then repolarize after the contraction is completed (ventricular repolarization).