Electrogram recording: Unipolar, bipolar, omnipolar and multipolar electrograms

The intracardiac electrogram is the basis of cardiac electrophysiology, but the signal displayed on the review screen is not the raw signal from the heart. Rather, it passes through a series of steps: acquisition, amplification, conversion, and filtering. Each of these can alter signal morphology with clinical consequences for the electrophysiologist. This review follows the signal from its acquisition to its display, examining how it changes at each step and what those changes mean clinically. We explain how noise enters the recording and how to remove it. We then review unipolar and bipolar electrograms, covering the strengths, limits, and pitfalls of each. We examine newer vendor-specific electrogram constructions, including omnipolar electrograms and near-field discrimination through spatial and frequency-based techniques. For each, we explain how it works and where it fails. Throughout, we draw on real clinical examples from our laboratory to illustrate these concepts.