Atrial Fibrillation: A Question of Dominance?

The mechanisms underlying atrial fibrillation (AF) remain poorly understood. In some patients, AF initiation often occurs from arrhythmogenic foci arising at muscular sleeves in a pulmonary vein (PV).Either direct radiofrequency ablation of these foci or, more recently, their disconnection from the left atrium by ablation at venous ostia is the basis for curative AF ablation procedures. However, it is likely that, in most cases, the mechanism of AF maintenance is different from that which initiates it. Isolated animal heart experiments suggest that some cases of AF may be maintained by the uninterrupted periodic activity of a small number of discrete reentrant sites (rotors) located in the posterior left atrial (LA) wall, near the PV/LA junction. During sustained AF, such sources activate at an exceedingly high rotation frequency. Thus rotors near the PV/LA junction dominate over any other slower sources that may form elsewhere and act as the drivers for the entire fibrillatory process. High resolution spectral analysis of the spatial distribution of activation frequencies reveals a hierarchy with appreciable frequency gradients across the atria. Here we briefly review our current understanding of the mechanisms and manifestations of AF and discuss the applicability of spectral analysis tools to the study of AF in patients, with the idea of helping to improve the efficacy of ablation therapies. We focus in part on recent clinical studies that provide justification for the combined use of spectral analysis and electroanatomical mapping to systematically correlate the spatial distribution of excitation frequency with cardiac anatomy, to provide mechanistic insight into different types of AF and to facilitate ablation procedures.