Nonsustained Reentry Following Successive Stimulation of Cardiac Tissue Through a Unipolar Electrode

INTRODUCTION: Using numerical simulations, we predict that nonsustained reentry occurs following a strong, premature stimulus through a unipolar electrode. METHODS AND RESULTS: Our simulations were based on the bidomain model of cardiac tissue, and the active membrane properties were represented by the Beeler-Reuter model. An outwardly propagating wavefront was excited by an initial stimulus (S1). A second stimulus (S2) was then applied through the same electrode. Nonsustained reentry or reentrant-like behavior followed the S2 stimulus for both cathodal and anodal stimulation, and were associated with "break" stimulation but not with "make" stimulation. The direction of spiral-wave rotation was reversed when the polarity of the stimulus was 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 the "no response" phenomenon. CONCLUSION: Our mathematical model predicts that both anodal and cathodal unipolar S2 stimulation results in reentry. This behavior arises from an interaction of virtual anodes and cathodes surrounding the stimulating electrode.