Functional reentrant waves propagate outwardly in cardiac tissue

The dynamical nature of cardiac arrhythmias has been investigated for decades by researchers from a wide range of disciplines. One long-standing unsettled issue involves whether the mechanism of functional re-entry should be described by the "leading-circle" hypothesis or the "spiral-wave" hypothesis, which rely on inward and outward wave propagation, respectively. To address this issue, we investigated two-dimensional FitzHugh-Nagumo type models and found that inwardly propagating waves could occur in the spontaneous oscillatory mode, but not the excitable mode. However, such spontaneous oscillatory behavior is characterized by small-amplitude, sinusoidal oscillations that are fundamentally different from the stimulus-driven, excitable behavior of cardiac myocytes. This finding suggests that inward wave propagation, which is posited by the leading circle hypothesis for the purpose of maintaining functional re-entry, is unlikely to occur in cardiac tissue. (C) 2004 Published by Elsevier B.V.