Application of Hurst exponents to assess atrial reverse remodeling in paroxysmal atrial fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia in clinical practice. Although its termination mechanisms are not still completely known, previous works have reported significant electrocardiographic differences between immediately and non-immediately terminating episodes of paroxysmal AF (PAF). However, none studied how long these differences still hold as we move backward in time. The present work studies a time interval long enough to identify earlier signs forecasting atrial reverse remodeling that will provoke spontaneous AF termination. Reverse remodeling was estimated by measuring AF organisation with the second-order generalised Hurst exponent, H(2), which provided the highest accuracy. Organisation is associated with the number of simultaneous reentries in the atria, which plays a key role in reverse remodeling, thus causing arrhythmia termination. The computation of H(2) depended on two critical parameters: the analysed interval length (L) and the maximum search window for self-similarities (tau(max)). A study with 660 combinations on these two parameters was performed together with the sampling frequency (f(s)) of the recording. The results reported that optimal computational parameters are L = 15 s, tau(max) = 20 milliseconds and f(s) = 1024 Hz. A statistically significant organisation increase was observed during the last 2 min before AF termination, thus suggesting that reverse remodeling only occurs very close to the termination event.