The pivot is critical to the rotors postulated to maintain AF. We hypothesised that wavefronts circumnavigating the pivot should broaden the distribution of bipolar electrogram amplitude, due to directional information encoded in these signals.This property is measurable by the Shannon entropy (ShEn), a statistical measure of signal amplitude distribution.
Methods
Bipolar recordings were studied in 3 models, and human AF cases. The models were: (i) Induced rotors in isolated rat atria (R) recorded with a multi-electrode array (ii) epicardial plaque recordings of induced AF in sheep (S)(iii) Computer simulations (CS) of rotors in 2D atrial myocytes. Rotor episodes were identified with voltage propagation movies, and verified with LAT maps, with pivot defined as the rotation centre. ShEn was calculated at each bipole. We also studied ShEn distribution near termination sites in 2 permanent AF ablation patients undergoing high-density mapping (500+ points).
Results
We analyzed rotation episodes in animals (R: 12 rotors, duration 80±81 cycles, S: 22 AF episodes, 13 rotors, 4.2±1.5 cycles), and CS (4 cycles). The maximum ShEn bipole (max ShEn) was consistently co-located with the pivot zone (R: 10/12, S: 11/13, CS 1/1). ShEn was consistently inversely correlated with pivot zone distance (Pearson’s r: R -0.54, p<0.001 S -0.49, p<0.001, CS -0.61, p<0.001). In human cases, ShEn was higher at AF termination sites compared to neighbour areas (Z score difference 1.00, p=0.002) and rest of atrium (Z-score difference 0.83, p=0.02).
Conclusions
These data suggest ShEn as a mechanistically-based tool to map stable rotors, implementable by conventional catheter mapping.