Linear and nonlinear coupling between atrial signals

In this article, three methods for the analysis of the relationships among atrial electrical activities in different sites recorded during sinus rhythms (SR) and atrial fibrillation (AF) will be presented and discussed. The properties of pairs of atrial signals (ASs) will be characterized through a linear parameter obtained from the estimation of the cross-correlation (CC) function, using a nonlinear association (NLA) estimator and through a synchronization index based on the corrected cross-conditional entropy (CCE). These parameters will be employed to assess possible changes in the determinism and dynamics of AS induced by adrenergic stimulation, which is supposed, but not yet demonstrated, to promote both spiral wave maintenance and wave break-up thus fragmenting atrial conduction. The sympathetic stimulation is mimicked by isoproterenol infusion, and the effects of this drug are evaluated in a group of patients in four experimental conditions: 1) SR, 2) SR during isoproterenol (SRISO) administration, 3) AF, and 4) AF during isoproterenol administration (AFISO)