Spatial and Temporal Organization in Ventricular Fibrillation

Abstract

Ventricular fibrillation (VF) is the leading heart rhythm alteration that results in sudden cardiac death, yet the detailed mechanisms of the arrhythmia remain elusive. Fibrillation has been defined as “turbulent” cardiac electrical activity, which conjures up the idea of totally random and disorganized activation of the ventricles. I review theoretical concepts and recently published results based on a newly developed algorithm, “two-dimensional phase mapping,” which demonstrates that VF is not random and may be analyzed quantitatively. The approach is based on video imaging of voltage-sensitive dye fluorescence to record transmembrane potential simultaneously from 20,000 sites on the epicardial surface of rabbit and sheep ventricles. During VF, activity shows a strong periodic component centered near ∼500 beats/min. Phase maps reveal that VF depends on the organization of electrical waves around a small number of “phase singularities” that have relatively short lifespans and form as a result of interactions of wavefronts with obstacles in their paths. Overall, the evidence demonstrates that there is a high degree of temporal and spatial organization in cardiac fibrillation. The results may pave the way for a better understanding of the mechanisms of VF in normal, as well as in diseased, hearts.