Phase Index Calculation for Anatomical Reentry Using Cross-correlation

We previously showed that reentry in atrial tachycardia (AT) consistently occurs in pairs around two critical boundaries (CBs), which when connected by an ablation line consistently stops the AT.CBs can be identified by calculating the phase index (PI) using local activation times (LATs).However, LATs can be challenging to identify, especially in more complex arrhythmias.To overcome this limitation, we used a novel method using signal crosscorrelation.We compared both methods (LAT versus signal) through 380 spherical simulations of anatomical reentry.1610 evenly placed unipolar electrograms (EGMs) were generated for each simulation.After pre-processing, we derived (1) LATs, and (2) time delays through crosscorrelation.PI was calculated as the sum of (1) LAT differences or (2) correlation-delays, divided by the cycle length.To test robustness, both methods were repeated after adding white Gaussian noise to the original EGMs, with decreasing signal-to-noise ratios (SNR = 10 dB, 5 dB, 0 dB).With no noise, both methods had 100% accuracy.As SNR decreased, the cross-correlation method showed consistently superior accuracy (LAT: 96.1%, 94.1%, and 77.4%, cross-correlation: 100%, 98.6%, and 83.5%).Our results validate the greater robustness of cross-correlation to identify ablation targets thought PI, while avoiding direct LAT annotation.