Effects of the intracellular Ca2+ dynamics on restitution properties and stability of reentry in rabbit atrial tissue model

Atrial fibrillation (AF) is commonly associated with rapid excitation of the atria, but mechanisms of its initiation are unknown. Intracellular Ca²⁺ dynamics has been shown to affect cell restitution properties and, as a result, patterns of rapid reentrant excitation in ventricles at early stages of ventricular fibrillation. We study effects of the intracellular Ca²⁺ concentration changes on restitution properties and stability of reentry in atrial cell and tissue models. Our simulations show that Ca²⁺ and action potential alternans caused by such effects are transient, and resultant break-ups of reentrant waves are reversible - but subsequent accumulation of intracellular Ca²⁺ can lead to self-termination of reentry. Hence, other factors (such as tissue anisotropy) may play more prominent role in break-up of atrial reentry into AF.