title: Virtual electrode effects in defibrillation.
abstract: This modeling study demonstrates that a re-entrant activity in a sheet of myocardium can be extinguished by a defibrillation shock delivered via extracellular point-source electrodes which establish spatially non-uniform applied field. The tissue is represented as a homogeneous bidomain with unequal anisotropy ratios in the cardiac conductivities. Spiral wave re-entry is initiated in the bidomain sheet following an S1-S2 stimulation protocol. The results indicate that the point-source defibrillation shock establishes large-scale changes in transmembrane potential in the tissue (virtual electrodes) that are 'superimposed' over regions of various degrees of membrane refractoriness in the myocardium. The close proximity of large-scale shock-induced regions of alternating membrane polarity is central to the ability of the shock to terminate the spiral wave. The new wavefronts generated following anode/cathode break phenomena restrict the spiral wave and render the tissue too refractory to further maintain the re-entry. In contrast, shocks delivered via line electrodes establish, in close proximity to the electrode, changes in transmembrane potential that are of same-sign polarity. These shocks are incapable of terminating the re-entrant activation.
authors.affiliation: Department of Biomedical Engineering, Tulane University, New Orleans, LA 70118, USA.
authors.forename: N
authors.initials: N
authors.lastname: Trayanova
authors.forename: K
authors.initials: K
authors.lastname: Skouibine
authors.forename: P
authors.initials: P
authors.lastname: Moore
mesh_terms: D016880:Anisotropy; D001145:Arrhythmias, Cardiac / Q000503:physiopathology / Q000628:therapy*; D019295:Computational Biology / Q000379:methods; D004554:Electric Countershock / Q000295:instrumentation / Q000379:methods*; D004566:Electrodes; D004867:Equipment Design; D006321:Heart / Q000033:anatomy & histology / Q000502:physiology / Q000503:physiopathology*; D006801:Humans; D008564:Membrane Potentials; D008955:Models, Cardiovascular