Which leads are the standard limb leads?

• A. Bipolar leads
• B. Augmented leads
• C. Unipolar leads
• D. Baseline

Answer: (A)

The standard limb leads are the bipolar ones, because they measure the heart’s electrical potential between two limb electrodes rather than from one electrode to a central reference. In practice, these three leads correspond to measuring RA to LA, RA to LL, and LA to LL, forming Einthoven’s triangle. Because each lead uses two poles (two electrodes), it’s described as bipolar.

Augmented limb leads, by contrast, are unipolar—they use a single limb electrode with a reference and their signals are augmented for visibility. The baseline is not a lead at all; it’s simply the zero reference line on the tracing.