Impact of bipolar vector orientation and inter-electrode spacing on electrograms during human atrial fibrillation

Abstract Background In patients with atrial fibrillation (AF), local atrial bipolar electrograms (EGM) are clinically used to determine peak-to-peak voltage (Vpp), dominant frequency (DF) and Shannon Entropy (ShEn) for electroanatomical substrate characterization and substrate-based ablation. The effect of bipolar vector orientation and inter-electrode spacing on these EGM-derived measures during AF is unclear. Methods To quantify the impact of bipolar vector orientation and inter-electrode spacing, bipolar EGM (10,496 and 20,968 atrial sites, respectively) were reconstructed from unipolar EGM recorded with an array of 18 electrodes in 14 patients with persistent AF. We compared Vpp, DF and ShEn between any two adjacent bipolar vectors with a difference of 45 degree. Vpp, DF and ShEn values were ranked into different classes from highest to lowest value. To quantify the effect of inter-electrode spacing, bipolar EGM were constructed from electrodes spaced 4mm, 8mm, and 12mm apart, respectively. Results First, bipolar vector orientation significantly impacts Vpp (maximal difference: 1.341±2.169 mV vs. 0.595±0.652 mV; p<0.01) and the percentage of atrial low voltage areas (Vpp<0.05mV) (maximal difference: 62.31% vs. 32.54%). Bipolar vector orientation also influences DF (maximal difference: 8.547±2.971 Hz vs. 6.360±1.077 Hz; p<0.01) and ShEn (maximal difference: 4.898±0.488 vs. 4.120±0.650; p<0.01) measurements. Second, inter-electrode spacing affects Vppincreasing from 0.854±1.299 mV to 1.013±1.302 mV for 4mm, and 12mm, respectively (p<0.01). The percentage of atrial low voltage areas differed between 53.77% and 42.03% for 4mm and 12mm, respectively. Furthermore, inter-electrode spacing alters DF (maximal difference: 7.316±2.239 Hz vs. 7.234±2.124 Hz; p<0.01) and ShEn (maximal difference: 4.364±0.714 vs. 4.514±0.624; p<0.01) measurements. Conclusions Bipolar vector orientation and inter-electrode spacing both significantly affect bipolar EGM-derived measures that may result in significant uncertainty around the electroanatomical substrate characterization in AF patients, which should be considered in the development of future mapping catheter tools and algorithms.