title: Vulnerability in an excitable medium: analytical and numerical studies of initiating unidirectional propagation.
abstract: Cardiac tissue can display unusual responses to certain stimulation protocols. In the wake of a conditioning wave of excitation, spiral waves can be initiated by applying stimuli timed to occur during a period of vulnerability (VP). Although vulnerability is well known in cardiac and chemical media, the determinants of the VP and its boundaries have received little theoretical and analytical study. From numerical and analytical studies of reaction-diffusion equations, we have found that 1) vulnerability is an inherent property of Beeler-Reuter and FitzHugh-Nagumo models of excitable media; 2) the duration of the vulnerable window (VW) the one-dimensional analog of the VP, is sensitive to the medium properties and the size of the stimulus field; and 3) the amplitudes of the excitatory and recovery processes modulate the duration of the VW. The analytical results reveal macroscopic behavior (vulnerability) derived from the diffusion of excitation that is not observable at the level of isolated cells or single reaction units.
authors.affiliation: Department of Medicine (Cardiology), Duke University Medical Center, Durham, North Carolina 27710.
authors.forename: C F
authors.initials: CF
authors.lastname: Starmer
authors.forename: V N
authors.initials: VN
authors.lastname: Biktashev
authors.forename: D N
authors.initials: DN
authors.lastname: Romashko
authors.forename: M R
authors.initials: MR
authors.lastname: Stepanov
authors.forename: O N
authors.initials: ON
authors.lastname: Makarova
authors.forename: V I
authors.initials: VI
authors.lastname: Krinsky
mesh_terms: D000818:Animals; D001145:Arrhythmias, Cardiac / Q000209:etiology* / Q000503:physiopathology; D055592:Biophysical Phenomena; D001703:Biophysics; D003470:Culture Media; D004558:Electric Stimulation; D004594:Electrophysiology; D006321:Heart / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D008955:Models, Cardiovascular
chemical_list: D003470:Culture Media