Spatial characterization of electrogram morphology from transmural recordings in the intact normal heart

Area of Science:

• Cardiac electrophysiology
• Arrhythmogenic substrate mapping

Background:

• Unipolar (UE) and bipolar electrograms (BE) are crucial for identifying arrhythmogenic substrate.
• Understanding how electrogram amplitude changes with distance and depth is vital for accurate mapping.

Purpose of the Study:

• Quantify the effect of propagation distance on local electrogram amplitude.
• Determine the existence and nature of transmural electrophysiological gradients.

Main Methods:

• Mapping was conducted on 5 sheep using >50 transmural needles in the left ventricle (LV).
• Electrograms were recorded during multisite bipolar pacing from epicardial and endocardial electrodes.
• Analysis included stimulus distance, activation time, and amplitude (V-P, VP-P) for unfiltered UE and BE (unfiltered and filtered).

Main Results:

• UE amplitude significantly attenuated with increasing distance (V-P: 7.0±0.5%, VP-P: 5.4±0.3% per cm).
• BE amplitude attenuation with distance was insignificant (VP-P unfiltered: 2.2±0.5%, filtered: 1.7±1.4% per cm).
• Significant transmural gradients were observed: highest amplitude at epicardial layers for UE and endocardial for BE. Epicardial propagation was consistently earlier than endocardial.

Conclusions:

• Electrogram amplitude is inversely proportional to propagation distance for UEs, but not BEs.
• Conduction preferentially propagates via the epicardium, contributing to transmural amplitude gradients.