Properties of cardiac alternans: the effect of supernormal conduction velocity
B. Echebarria*
Departament de Física Aplicada, Universitat Politècnica de Catalunya, Barcelona, Spain.
Among the known precursors of life-threatening ventricular arrhythmias and sudden cardiac death are T wave alternans, defined as a periodic beat to beat change in the amplitude or shape of the ECG T wave. Although T wave alternans provide a global measure of the propagation at the whole heart level, they have been related to alternations in the duration of the excited phase (or action potential duration APD) at the single cell level, thereby establishing a causal link between electrical alternans and the initiation of ventricular fibrillation. We investigate the appearance of alternans by numerical simulations and stability analysis of one-dimensional reaction-diffusion models. The effects of conduction velocity (CV) restitution, ectopic beats, and the role of spatial gradients of electrical restitution properties are investigated. We also study the effect of supernormal CV, that crucially affects the phenomenology of alternans in simulated tissue as well as the related bifurcation diagram. In particular, it allows for stable concordant alternans in one-dimensional paced cables and related stable period-2 traveling waves in one-dimensional rings, in contrast to analogous situations with normal CV restitution where alternans leads to temporally modulated waves and discordant alternans.