Tachyarrhythmias and electrical instabilities in cardiac tissue

Unstable cardiac rhythm is known to precede dangerous cardiac arrhythmias. Despite a considerable body of experimental data the underlying mechanism of electrical instabilities still remains unclear. This study presents a numerical analysis of the dynamic instabilities in the circulation of a pulse in a ring of excitable tissue that helps to determine physical mechanisms of these instabilities and to understand their potential correlation with complex cardiac rhythms. The authors demonstrate that a pulse width begins to oscillate after an initial perturbation for any length of the ring and the corresponding propagation velocity. The oscillations were found to be either damped or incremental. The incremental oscillations occurred when the ratio of the steady-state circulation period to the period of the pulse width oscillations was of the order of ~0.5. Under the same conditions the external pacing of the ring gives rise to complex rhythms incorporating alternans-like patterns