Properties of spiral waves in a piece of isotropic myocardium

Tachyarrhythmias of the heart can be due to the presence of one or more spi ral waves of electrical activity. Spiral waves were simulated using a previ ously described ionic model of cardiac action potentials in a 75 x 75 netwo rk of compartments. The compartments were connected by means of resistors a nd made isotropic in order to catch basic properties of spiral waves. The c ross-field stimulation technique was used to generate single or double spir al waves. The analysis showed that a spiral wave was created when the secon d excitation front became critically curved, in the wake of the preceding w ave, so that decremental propagation occurred. A spiral wave could also be generated from a wave circulating around an obstacle when the obstacle size was suddenly reduced. The spiral waves steadily circled around an area wit h excitable but unexcited cells. An undisturbed spiral wave in the isotropi c medium circled around in a stable pathway, but drifted along the borders of cells made non-excitable. An excitation within an existing spiral wave c ould generate new spiral naves that interacted with each other and formed c omplex excitation patterns. A sudden prolongation of the refractory period reduced the central area with unexcited cells in the spiral pathway but onl y slightly prolonged the revolution time. A further prolongation of the ref ractory period extinguished the spiral wave when the tip of the spiral wave invaded refractory areas. The described ionic compartment model could accu rately produce spiral waves with properties in line with experimental resul ts reported by others.