Modulation of ventricular fibrillation in isolated perfused heart by dofetilide

Ventricular fibrillation: dynamics and ion channel determinants

Ventricular fibrillation (VF) is the leading cause of sudden cardiac death. This brief review addresses issues relevant to the dynamics of the rotors responsible for functional reentry and VF. It also makes an attempt to summarize present-day knowledge of the manner in which the dynamic interplay between inward and outward transmembrane currents and the heterogeneous cardiac structure establish a substrate for the initiation and maintenance of rotors and VF. The fragmentary nature of our current understanding of ionic VF mechanisms does not even allow an approach toward a "Theory of VF". Yet some hope is provided by recently obtained insight into the roles played in VF by some of the sarcolemmal ion channels that control the excitation-recovery process. For example, strong evidence supports the idea that the interplay between the rapid-inward sodium current and the inward-rectifier potassium current controls rotor formation, as well as rotor stability and frequency. Solid evidence also exists for an involvement of L-type calcium current in the control of rotor frequency and in determining VF-to-ventricular tachycardia conversion. Less clear, however, is whether or not time dependent outward currents through voltage-gated potassium channels affect the fibrillatory process. Hopefully, taking advantage of currently available approaches of structural, molecular and cellular biology, together with computational and imaging techniques, will afford us the opportunity to further advance knowledge on VF mechanisms.

Arrhythmogenesis in the heart: Multiscale modeling of the effects of defibrillation shocks and the role of electrophysiological heterogeneity

The mechanisms of initiation of ventricular arrhythmias as well as those behind the complex spatiotemporal wave dynamics and its filament organization during ventricular fibrillation (VF) are the topic of intense research and debate. Mechanistic inquiry into the various mechanisms that lead to arrhythmia initiation and VF maintenance is hampered by the inability of current experimental techniques to resolve, with sufficient accuracy, electrical behavior confined to the depth of the ventricles. The objective of this article is to demonstrate that realistic 3D simulations of electrical activity in the heart are capable of bringing a new level of understanding of the mechanisms that underlie arrhythmia initiation and subsequent organization. The article does this by presenting the results of two multiscale simulation studies of ventricular electrical behavior. The first study aims to uncover the mechanisms responsible for rendering the ventricles vulnerable to electric shocks during a specific interval of time, the vulnerable window. The second study focuses on elucidating the role of electrophysiological heterogeneity, and specifically, differences in action potential duration in various ventricular structures, in VF organization. Both studies share common multiscale modeling approaches and analysis, including characterization of scroll-wave filament dynamics.