Letter by Ganesan et al Regarding Article, "Wavefront Field Mapping Reveals a Physiologic Network Between Drivers Where Ablation Terminates Atrial Fibrillation".

November 2019 1 Anand N. Ganesan, MBBS, PhD Dhani Dharmaprani, BEng Andrew D. McGavigan, MD To the Editor: Leef et al1 present an important study using wavefront field mapping to reveal a physiological network between drivers in cases where atrial fibrillation terminates. The directed vector approach utilized to demonstrate the connection of counterchiral spiral waves recalls the topological restrictions on phase singularities (PSs), outlined by Gray et al2: (1) phase lines cannot intersect; (2) PSs are joined by other isophasic lines to PS of opposite chirality or nonconducting boundaries; (3) PSs form and terminate as oppositely rotating pairs. Given the intrinsic topological connectedness of counter-chiral spiral waves via isophasic lines, it would be interesting to study these phenomena in cases where termination did not occur because these may also be present in the absence of AF termination. This is certainly a feature observable in the phase maps presented by Child et al.3 A further point addressed during the study is fluctuating nature of PS, which the authors postulated occurs via undefined mechanisms.1 In fact, the fluctuation of PS may potentially be an intrinsic topological property. Because each PS creates zones where all phases of the cycle are simultaneously present, the timing of incoming waves is likely to stochastically encounter tissue in the critical phase for new wavebreak and thus cause a new PS to form.4 This creates an endless cycle of PS regeneration that is a feature of the perpetuation of AF and VF.5 A final point made by Winfree4 and Gray et al2 is on the nature of PS termination. For topological reasons, PS termination can only occur via fusion with a wave emanating from a migrating spiral or migration to a boundary. The ability to terminate the arrhythmia at a distance from the PS observed by Leef et al could equally be consistent with the notion that AF termination is a form of stochastic ergodicity breaking, rather than via a direct effect on individual PS. The interesting approach presented by Leef et al points to the need for further studies of the mechanisms of AF and VF termination.