Quantitative Assessment of the Spatial Organization of Atrial Fibrillation in the Intact Human Heart

Abstract

Background Atrial activation during atrial fibrillation (AF) is frequently described as random or chaotic. We propose that activation during AF is constrained by the principles of reentrant excitation; that these constraints impart a measurable spatial organization to activation during AF; and that the distance over which activation sequences remain well correlated can be readily measured and related both to the propensity of AF to sustain itself as well as to atrial tissue wavelength. Methods and Results We describe a novel signal-processing technique that quantifies the correlation in activation sequences recorded from five equally spaced sites in the right atrium in patients undergoing electrophysiology studies. In 20 patients in AF (12 with paroxysmal AF, 5 with chronic AF, and 3 with no clinical history of AF), the average correlation was 0.54±0.12 at 11 mm and 0.32±0.11 at 44 mm, compared with 0.95±.023 and 0.91±.023 in sinus rhythm. In AF, the correlation versus distance relation was monotonically decreasing, well fit by a decaying exponential function. The space constant of this exponential function, termed the activation space constant, provides a single objective metric of the spatial organization of activation during AF. The mean activation space constant for the group was 2.6±1.15 cm. Chronic AF had the lowest mean activation space constant (1.84±0.36 cm) and AF in patients with no prior history of AF had the highest (3.06±0.40 cm) (P<.05), with paroxysmal AF characterized by intermediate values (2.80±1.4 cm). Conclusions Using a novel method to measure the spatial organization of atrial activation during AF, we have demonstrated that AF in the intact human heart is organized over a length scale consistent with reentrant excitation. Preliminary results suggest a relationship between measured spatial organization and the clinical course of the arrhythmia. Further work is needed to determine whether measurement of spatial organization may be useful in prospective patient-specific selection of therapeutic options.