Why are unipolar limb leads referred to as such?

Why are unipolar limb leads referred to as such?

• A. They have only one electrode
• B. They represent only positive potentials
• C. They are based on male subjects
• D. They measure only lateral movements

Answer: (B)

Unipolar limb leads are referred to as such because they measure the electrical potentials in relation to a "virtual" reference point, which is derived from the average of the potentials of the other two limbs. Each unipolar lead has one active electrode that picks up the electrical signals and a reference that is not actually recorded by a physical electrode.

In the context of option B, saying they represent only positive potentials highlights that unipolar leads specifically focus on positive deflections, as the output is based solely on one electrode's input compared to a calculated average of the others, leading to the depiction of positive voltage changes. This means the unipolar leads record potential differences in a manner that emphasizes positive voltage fluctuations relative to this reference point, providing essential information on the heart's electrical activity.

All of this illustrates why the designation of unipolar limbs emphasizes their unique measurement approach compared to bipolar leads, which use two electrodes to capture the potential difference between them directly.