Resetting and termination of reentry in a loop-and-tail cardiac model

Ventricular tachycardia is a type of cardiac arrhythmia that can be associated with a wave circulating around in a loop. Because this rhythm is potentially fatal, its termination is highly desirable. Theoretical approaches have suggested that discontinuity in the phase resetting response to electrical stimuli is indicative of the ability for such termination. We investigate the usefulness of such theoretical predictions when the stimulus site is located at some distance away from the reentrant loop, as would typically be the case during antitachycardia pacing in the heart. We show that there exists a critical tail length below which termination of reentry occurs over a range of stimulus timing values as predicted theoretically by a discontinuous window in the phase resetting curve. Above this critical length, however, a paradoxical situation exists: termination of reentry appears impossible, yet there is a point discontinuity in the phase resetting curve. These findings offer insight into termination using a single stimulus in a loop-and-tail model, an important step toward understanding the mechanism of antitachycardia pacing.