Mechanisms for discordant alternans

Discordant Altelrnans Mechanism. Introduction: Discordant alternans has the potential to produce larger alternans of the ECG T wave than concordant al ternans, but its mechanism is unknown. Methods and Results: We demonstrate by one- and two-dimensional simulation of action potential propagation models that discordant alternans can form s pontaneously in spatially homogeneous tissue through one of two mechanisms, due to the interaction of conduction velocity and action potential duratio n restitution at high pacing frequencies or through the dispersion of diast olic interval produced by ectopic foci. In discordant alternans due to the first mechanism, the boundaries marking regions of alternans with opposite phase arise far from the stimulus site, move toward the stimulus site, and stabilize. Dynamic splitting of action potential duration restitution curve s due to electrotonic coupling plays a crucial role in this stability. Larg er tissues and faster pacing rates are conducive to multiple boundaries, an d inhomogeneities of tissue properties facilitate or inhibit formation of b oundaries. Conclusion: Spatial inhomogeneities of electrical restitution properties ar e not required to produce discordant alternans.