electrograms

An electrogram is a recording of the electrical potentials generated by biological tissue in response to electrical activity, captured with electrodes placed on or inside the tissue. In cardiology, electrograms are used to record electrical signals from within the heart (intracardiac electrograms) or from the body surface, and they are often distinguished from the standard electrocardiogram, which summarizes whole-heart activity from external leads. Electrograms reflect local activation and conduction properties of the heart rather than global activity.

Electrograms can be unipolar or bipolar. A unipolar electrogram uses a single distal electrode and a distant reference, providing a broader view of electrical potential at the recording site. A bipolar electrogram uses two closely spaced electrodes and emphasizes local differences, reducing far-field signals. Intracardiac electrograms are obtained with catheters during electrophysiology studies and can record signals from atrial, ventricular, or specialized conduction tissues such as the His-Purkinje system. Key features include local activation time, amplitude, and waveform morphology; fractionated or delayed electrograms indicate slow conduction or scar tissue, while “double potentials” can reveal boundaries between healthy and diseased tissue.

Clinically, electrograms are central to arrhythmia mapping and ablation. Mapping systems correlate electrogram timing with anatomy to identify earliest activation sites, reentry circuits, and areas of slow conduction or scar that sustain arrhythmias. Abnormal electrograms guide ablation targets to interrupt arrhythmogenic pathways. In noninvasive contexts, surface electrograms (the traditional electrocardiogram) monitor global cardiac activity, while invasive electrograms provide spatially resolved local information essential for precise diagnosis and treatment planning.

Safety considerations include the risks of invasive recording procedures, such as infection or vascular injury, and interpretation requires expertise to distinguish true pathological signals from noise, artifact, or contact issues.