Phase Singularities in Cardiac Patch Model with Non-conductive Fibrotic Area during Atrial Fibrillation

Tiago Paggi de Almeida1, Mark Nothstein2, Xin Li1, Michela Masè3, Flavia Ravelli3, Diogo C. Soriano4, Arthur S. Bezerra5, Fernando S. Schlindwein1, Takashi Yoneyama5, Olaf Dössel2, G. André Ng1, Axel Loewe2
1University of Leicester, 2Karlsruhe Institute of Technology (KIT), 3Università degli Studi di Trento, 4Universidade Federal do ABC, 5Instituto Tecnológico de Aeronáutica


Aims: Fibrosis creates heterogeneities in the cardiac tissue, favouring re-entrant activity driving atrial fibrillation (AF). Their relationship, however, remains controversial, and rotor detection related to fibrosis poses challenges. In the present work, in-silico cardiac patches with non-conductive fibrotic area were used to investigate the occurrence and characteristics of rotors described by phase singularities (PSs). Methods: A stable rotational source was generated by cross-field stimula-tion in an isotropic virtual tissue patch. Membrane kinetics were represented by a Courtemanche model adapted to mimic AF conditions (conduction velocity: 0.22 m/s). Uniformly distributed fibrotic elements were incorporated around the centre of the patch (zero conductivity; fibrotic densities of 20%, 30% and 40%; Fig 1A). Electrograms (EGMs) were calculated in direct con-tact with the endocardial surface (8 s; 1 kHz). The phase of the EGMs was determined using Hilbert transform. PSs were detected using the topological charge method and PS density maps (PSDMs) were generated (Fig 1B). Bipo-lar EGMs (bip-EGMs) were obtained from the original signals (filter 30-300 Hz). The bip-EGMs were investigated using six markers: sample entropy (SampEn), determinism (DET), peak-to-peak (PP), wave similarity (WS), organization index (OI) and cycle length (CL). Results: 77.1% of the PSs occurred inside the fibrotic region with a higher density in the border zone for 20% density; 99.8% for 30%; 99.7% for 40%. SampEn was significantly higher for bip-EGMs collected in regions with PSDM≥5, while DET, PP and WS were significantly lower (P<0.0001; Fig 1C). OI was significantly lower in PS regions for 30% and 40% densities (P<0.0001). Conclusions: PSs tended to meander outside the fibrotic area for lower fi-brotic density. The presence of PSs induced significant changes in the ampli-tude, dynamics and morphology of bip-EGMs. Markers for bip-EGMs offer a complementary way for rotor detection in the presence of non-conductive fibrosis.