Properties of spiral waves in a piece of isotropic myocardium.

Tachyarrhythmias of the heart can be due to the presence of one or more spiral waves of electrical activity. Spiral waves were simulated using a previously described ionic model of cardiac action potentials in a 75 x 75 network of compartments. The compartments were connected by means of resistors and made isotropic in order to catch basic properties of spiral waves. The cross-field stimulation technique was used to generate single or double spiral waves. The analysis showed that a spiral wave was created when the second excitation front became critically curved, in the wake of the preceding wave, 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 with excitable but unexcited cells. An undisturbed spiral wave in the isotropic medium circled around in a stable pathway, but drifted along the borders of cells made non-excitable. An excitation within an existing spiral wave could generate new spiral waves that interacted with each other and formed complex excitation patterns. A sudden prolongation of the refractory period reduced the central area with unexcited cells in the spiral pathway but only slightly prolonged the revolution time. A further prolongation of the refractory period extinguished the spiral wave when the tip of the spiral wave invaded refractory areas. The described ionic compartment model could accurately produce spiral waves with properties in line with experimental results reported by others.