Role of virtual electrodes in arrhythmogenesis: Pinwheel experiment revisited

Virtual Electrodes in Arrhythmogenesis. Introduction: Recent experimental e vidence demonstrates that a point stimulus generates a nonuniform distribut ion of transmembrane potential (virtual electrode pattern) consisting of la rge adjacent areas of depolarization and hyperpolarization, This simulation study focuses on the role of virtual electrodes in reentry induction. Methods and Results: We simulated the electrical behavior of a sheet of myo cardium using a two-dimensional bidomain model with straight fibers. Membra ne kinetics were represented by the Beeler-Reuter Drouhard-Roberge model. S imulations were conducted for equal and unequal anisotropy ratios. S1 wavef ront was planar and propagated parallel or perpendicular to the fibers, S2 unipolar stimulus was cathodal or anodal. With regard to unequal anisotropy , for both cathodal and anodal stimuli, the S2 stimulus negatively polarize s some portion of membrane, deexciting it and opening an excitable pathway in a region of otherwise unexcitable tissue, Reentry is generated by break excitation of this tissue and subsequent propagation through deexcited and recovered areas of myocardium. Figure-of-eight and quatrefoil reentry are o bserved, with figure-of-eight most common. Figure-of-eight rotation is seen in the direction predicted by the critical paint hypothesis. With regard t o equal anisotropy, reentry was observed for cathodal stimuli only at stren gths > -95 A/m. Conclusion: The key to reentry induction is the close proximity of S2-induc ed excited and deexcited areas, with adjacent nonexcited areas available fo r propagation.