  Reentrant waves propagating in a ring or annulus of excitable media model is
the basic mechanism underlying a major class of irregular cardiac rhythms known
as anatomical reentry. Such reentrant waves are terminated by rapid electrical
stimulation (pacing) from an implantable device. Because the mechanisms of such
termination are poorly understood, we study pacing of anatomical reentry in a
one-dimensional ring of model cardiac cells. For realistic off-circuit pacing,
our model-independent results suggest that circuit inhomogeneities, and the
electrophysiological dynamical changes they introduce, may be essential for
terminating reentry in some cases.
