Effect of electrode size and distance to tissue on unipolar and bipolar voltage electrograms and their implications for a near-field cutoff

Characteristics of electrograms depend on the electrode design and distance to the electric source. Our aim was to assess the impact of electrode design and distance from the myocardial electric source on the unipolar and bipolar electrograms to deduce a far-field cut-off. We retrospectively analyzed left atrial electroanatomical maps of 25 patients acquired using an ablation catheter with a 4.5 mm tip-, mini- and 2 mm ring electrodes. The unipolar and bipolar electrograms were characterized based on peak-to-peak amplitude, signal duration, maximal slope, and relative power of the high frequency spectrum above 50 Hz (HF_rel). The unipolar electrograms of ring electrodes showed an increased amplitude (140%), slope (150%) and HF_rel (16% vs. 11%) compared to the tip- and mini-electrodes. The median amplitude, slope, and HF_rel for the ring electrodes followed a power-law decay with distance with a steep decline up to 4 mm. This near-field cut-off can be identified based on a HF_rel above 10% in unipolar electrograms. In conclusion, we observed a higher unipolar amplitude for small ring-electrodes compared to larger tip-electrodes. The rapid decay of the amplitude, slope, and HF_rel up to a distance of 4 mm is suggestive for near-field cut-off identified based on HF_rel above 50 Hz.Clinical Trial Registration: NCT04095559.