Which electrogram is described as having signals from a single reference and capturing far-field and local signals?

• A. Bipolar electrogram
• B. Unipolar electrogram
• C. Tripolar electrogram
• D. Intracardiac electrogram

Answer: (B)

The idea being tested is how the recording reference shape affects what the electrogram shows. A unipolar electrogram uses a single sensing electrode at the recording site and a distant reference electrode. Because the reference is far away, the recorded potential includes both the local electrical activity at the tip and additional far-field signals from other parts of the heart. This produces a larger, more global signal that reflects the overall activation pattern, not just the tiny local differences.

In contrast, a bipolar electrogram uses two nearby electrodes and computes the difference between them, which emphasizes the local activation between those two points and tends to cancel distant, or far-field, activity. A tripolar arrangement adds another electrode to improve stability and suppression of noise, still aiming to emphasize local activity. The term intracardiac electrogram is a broad umbrella that can describe recordings in situ but doesn’t specify the single-reference, far-field plus local signal characteristics. Therefore, the description fits the unipolar electrogram.