Abstract
Spiral wave activity and its breakup in excitable media have been considered as possible mechanisms for tachycardia and its transition to fibrillation. However, the mechanism of breakup has not yet been clarified. Here, we have examined the effects of spatial inhomogeneity of heart muscles as one possible factor for the breakup, using computer simulations of two dimensional FHN model with 100×100 cells configuration. Inhomogeneities are introduced as the variances of the refractory period and/or the coupling constant which corresponds to the conduction velocity from cell to cell or from block to block. It is found that, contrary to precedent reports, how large the variance is, cell to cell inhomogeneity does not break up spiral waves. The variance must be from block to block and the minimum size of the block for the breakup depends on the size of spiral waves. The effects of parameter changes in all or in part and those of additional stimulations were also examined. Besides of breakup, we could observe phenomena corresponding to anchoring (pinning) and hot spot. Secondly, we have studied the interactions of spiral waves. It was said that if once several (3-6) spiral waves exist simultaneously, although some of them may disappear by collisions, some may be broken up through their interactions and the resultant number of spiral waves does not change so remarkably. They said this might correspond to and must be sufficient condition for lasting fibrillation. To investigate this possibility, we devised a new method by analysing FHN model properties, which can generates multiple spiral waves with any direction of rotation at any place in the media. Using this method, we embeded six spiral waves in two dimensional media and examined their interactions. Simulation results showed no breakup and we could not approve the above hypothesis.
