  Reentry around non-conducting ventricular scar tissue, which often causes
lethal arrhythmias, is typically treated by rapid stimulation from an
implantable defibrillator. However, the mechanisms of termination (success and
failure) are poorly understood. To elucidate such mechanisms, we studied pacing
of anatomical reentry in 1-D and 2-D excitable cardiac media models. Our
results suggest that the existence of inhomogeneity in the reentry circuit is
essential for pacing termination of tachycardia to be successful. Considering
the role of such inhomogeneities may lead to more effective pacing algorithms.
