Spiral waves in a computer model of cardiac excitation.

Spiral excitation fronts have been demonstrated in association with reentry in a computer model of propagated excitation. Fronts were initiated by the reentrant circuits but the spiral configurations themselves occurred outside the circuits. Excitation initiated near the initial portion of reentrant circuits propagated greater distances during a particular time period than excitation initiated from later portions of the circuit. This resulted in spiral configuration of excitation fronts in which the front was located at increasing distance from the latest initiating event. Excitation fronts that did not themselves have spiral configurations in certain matrices were identifiable as parts of spiral configurations that occurred when the same reentrant events were present in other matrices. Spiral waves were initiated by either leading circle reentry associated with functional block to propagation or reentry associated with structural obstacles. They also occurred in the presence of initially uniform refractory periods and resulted in self-sustained reentrant excitation. This however, required particular conditions of excitation such that recovery times constituted a functional block permitting leading circle reentry.