Sinusoidal stimulation of myocardial tissue: Effects on single cells

Sinusoidal Stimulation of Cardiac Cells. Introduction: Cardiac tissue subje cted to sinusoidal stimulus is characterized by action potentials (APs) tha t have extended plateau phases, sustained for the duration of the stimulus. Extended action potential durations (APDs) are beneficial because they dis rupt wandering wavelets in the fibrillating heart. To investigate the mecha nisms by which periodic stimulus affects cardiac tissue, particularly the d evelopment of sustained depolarization, computer simulations of single card iac cells exposed to alternating current (AC) are performed. Methods and Results: Two modes of stimulation of the cell are examined: ext ernal field stimulation and transmembrane current injection. Several membra ne models, including Luo-Rudy I and II, are used in the simulations. Extern al AC field stimuli increase the APD of the single cell. The extended plate au of the cellular AP is characterized by periodic oscillations that are 1: 2 phase locked with the applied stimulus, This specific behavior is due to the variations in stimulus magnitude and polarity along the cell border, wh ich elicit opposite electrical responses from the cell sides. These pointwi se responses are averaged in the macroscopic cellular response and result i n sustained oscillatory depolarization that lasts for the duration of the s timulus. In contrast, the cell undergoing current injection does not develo p an extended APD, Conclusion: The simulations demonstrate that variation of membrane potentia l within a cell is of paramount importance to the formation of an extended AP plateau in response to AC stimulation.