The Pinwheel Experiment Revisited

The critical point hypothesis explains the origin of some cardiac arrhythmias, and the bidomain model describes electrical stimulation of the heart. In this paper, the critical point hypothesis is combined with the bidomain model. The result is four new predictions about the pinwheel experiment, a fundamental experiment in cardiac electrophysiology. These are: (1) The duration of the vulnerable period during cathodalS2stimulation is longer for anS1wavefront propagating perpendicular to the fibers than for anS1wavefront propagating parallel to the fibers. (2) For anodalS2stimulation with theS1wavefront propagating parallel to the fibers, the vulnerable period splits into two periods with an “invulnerable period” between them. (3) For anodalS2stimulation with theS1wavefront propagating perpendicular to the fibers, the vulnerable period consists of only one period. (4) A previously suggested mechanism for the upper limit of vulnerability (S2is so strong that the entire tissue is depolarized by an amount greater thanS*) is no longer applicable.