NONSUSTAINED REENTRY FOLLOWING SUCCESSIVE STIMULATION OF CARDIAC TISSUE THROUGH A UNIPOLAR ELECTRODE

Reentry Following Unipolar Stimulation. Introduction: Using numerical simulations, we predict that nonsustained reentry occurs following a s trong, premature stimulus through a unipolar electrode. Methods and Re sults: Our simulations were based on the bidomain model of cardiac tis sue, and the active membrane properties were represented by the Beeler -Reuter model, An outwardly propagating wavefront was excited by all i nitial stimulus (S1), A second stimulus (S2) was then applied through the same electrode: Nonsustained reentry or reentrant-like behavior fo llowed the S2 stimulus for both cathodal and anodal stimulation, and w ere associated with ''break'' stimulation but not with ''make'' stimul ation, The direction of spiral-wave rotation was reversed when the pol arity of the stimulus mas reversed, These complex dynamics occur only for a narrow: window of S1-S2 intervals. During anodal S2 stimulation, two different modes of reentry exist, Our simulations also explain th e ''no response'' phenomenon. Conclusion: Our mathematical model predi cts that both anodal and cathodal unipolar S2 stimulation results in r eentry, This behavior arises from an interaction of virtual anodes and cathodes surrounding the stimulating electrode.