Wave-train induced unpinning of weakly anchored vortices in excitable media

A free vortex in excitable media can be displaced and removed by a wave-train. However, simple physical arguments suggest that vortices anchored to large inexcitable obstacles cannot be removed similarly. We show that unpinning of vortices attached to obstacles smaller than the core radius of the free vortex is possible through pacing. The wave-train frequency necessary for unpinning increases with the obstacle size and we present a geometric explanation of this dependence. Our model-independent results suggest that decreasing excitability of the medium can facilitate pacing-induced removal of vortices in cardiac tissue.Comment: Published versio

Survival versus collapse: Abrupt drop of excitability kills the traveling pulse, while gradual change results in adaptation

Excitable media show changes in their basic characteristics that reflect temporal changes in the environment. In the photosensitive Belousov-Zhabotinsky (BZ) reaction, excitability is decreased by illumination. We found that a traveling pulse failed to propagate when a certain level of light intensity was switched on abruptly, but the pulse continued propagating when the light intensity reached the same level gradually. We investigated the mechanism of adaptation of pulse propagation to the change in light intensity using two mathematical models, the Oregonator model (a specific model for the photosensitive BZ reaction), and the FitzHugh-Nagumo model (a generic model for excitable media). The appearance of a characteristic such as adaptation is shown to be a general feature for a traveling pulse in excitable media. © 2007 The American Physical Society

Mechanisms of unpinning and termination of ventricular tachycardia

doi:10.1152/ajpheart.01300.2005 You might find this additional information useful... This article cites 40 articles, 12 of which you can access free at

Phase-resolved analysis of the susceptibility of pinned spiral waves to far-field pacing in a two-dimensional model of excitable media

Life-threatening cardiac arrhythmias are associated with the existence of stable and unstable spiral waves. Termination of such complex spatio-temporal patterns by local control is substantially limited by anchoring of spiral waves at natural heterogeneities. Far-field pacing (FFP) is a new local control strategy that has been shown to be capable of unpinning waves from obstacles. In this article, we investigate in detail the FFP unpinning mechanism for a single rotating wave pinned to a heterogeneity. We identify qualitatively different phase regimes of the rotating wave showing that the concept of vulnerability is important but not sufficient to explain the failure of unpinning in all cases. Specifically, we find that a reduced excitation threshold can lead to the failure of unpinning, even inside the vulnerable window. The critical value of the excitation threshold (below which no unpinning is possible) decreases for higher electric field strengths and larger obstacles. In contrast, for a high excitation threshold, the success of unpinning is determined solely by vulnerability, allowing for a convenient estimation of the unpinning success rate. In some cases, we also observe phase resetting in discontinuous phase intervals of the spiral wave. This effect is important for the application of multiple stimuli in experiments

Vortices Termination in the Cardiac Muscle

Methods for termination of three-dimensional electrical vortices in the heart are needed for development of patient-friendly cardiac defibrillation techniques (Nature 475, 235, 2011). The defibrillation technique used today is the delivery of a high-energy electric shock (360 J, 1 kV, 30 A, 12 ms, when applied externally) often associated with severe side effects. Developing low-energy defibrillation methods are hampered by two problems: the unknown locations of the cores of the vortices, and the unpredictable phases of the vortex waves rotating around these cores. The first problem has been resolved through the use of electric field pulses to excite the cores of all pinned vortices simultaneously. Approaches to solve the second problem are being developed. One of them is based on the phase scanning of all pinned vortices in parallel to hit the critical time window (“Vulnerable Window”, VW) of every pinned vortex. We investigate the related physical mechanisms and describe problems created by scanning. We describe also a mechanism by which a 3-dim scroll vortex may be terminated with a VW of the full 2π radians. It makes knowledge of the wave phase no longer required. We describe a mechanism terminating also a free (not pinned) vortex, when the vortex’s core passes not very far from a defect. About 500 experiments with termination of vortices during ventricular fibrillation in pig isolated hearts confirm that pinned vortices, hidden from direct observation, are significant in fibrillation. These results form a physical basis needed for creation of new effective methods for termination vortices underlying fibrillation