Structural and Functional Bases of Cardiac Fibrillation : Differences and Similarities Between Atria and Ventricles

Evidence accumulated over the last 25 years suggests that, whether in atria or ventricles, fibrillation may be explained by the self-organization of the cardiac electrical activity into rapidly spinning rotors that give way to spiral waves that break intermittently and result in fibrillatory conduction. The dynamics and frequency of such rotors depend on ion channel composition, excitability, and refractory properties of the tissues involved, as well as on the thickness and respective 3-dimensional fiber structure of the atrial and ventricular chambers. Therefore, improving understanding of fibrillation has required the use of multidisciplinary research approaches, including optical mapping, patch clamping, and molecular biology, and the application of concepts derived from the theory of wave propagation in excitable media. Moreover, translation of such concepts to the clinic has recently opened new opportunities to apply novel mechanistic approaches to therapy, particularly during atrial fibrillation ablation. Here we review the current understanding of the manner in which the underlying myocardial structure and function influence rotor initiation and maintenance during cardiac fibrillation. We also examine relevant underlying differences and similarities between atrial fibrillation and ventricular fibrillation and evaluate the latest clinical mapping technologies used to identify rotors in either arrhythmia. Altogether, the data being discussed have significantly improved our understanding of the cellular and structural bases of cardiac fibrillation and pointed toward potentially exciting new avenues for more efficient and effective identification and therapy of the most complex cardiac arrhythmias.