The Effect of Electrode-Tissue Distance on Unipolar and Bipolar Voltage Electrograms for large-Tip, Ring-, and Mini-Electrodes

Background The characteristics of intracardiac unipolar and bipolar voltage electrograms (EGM) acquired by electrophysiological catheters depend on the electrode design and configuration.The aim of the study was to assess the impact of electrode design and distance from the myocardial electric source on the unipolar and bipolar intracardiac electrograms recorded with a multi-electrode ablation catheter do deduce a cut-off for far-field versus near-field discrimination. Methods We retrospectively analyzed left atrial electroanatomical maps of 25 patients performed using an ablation catheter with a 4.5 mm tip-, mini- and 2 mm ring electrodes. The unipolar and bipolar EGMs were characterized based on peak-to-peak amplitude, signal duration (width), maximal slope, and relative power of the high frequency spectrum (HF_rel). Distances of the electrode from the tissue were calculated from the electroanatomic reconstruction. Results We analyzed EGMs of 5183 catheter positions. The unipolar EGM of ring electrodes showed an increased amplitude (140%), slope (150%) and HF_rel (16% vs 11%) compared to the tip- and mini-electrodes. In contrast, for bipolar EGM, the tip-ring pair showed the largest amplitude, width, and slope. The median amplitude, slope, and HF_rel for the ring electrodes followed a power-law decay function with distance. A cut-off of 4 mm was determined for far-field versus near-field discrimination. Conclusions We showed a higher unipolar amplitude for small ring-electrodes compared to larger tip electrodes. Furthermore, a rapid decay of the amplitude, slope, and HF_rel with distance could be observed. The decay functions are suggestive for a near-field cut-off distance below 4mm from the tissue.