Increased atrial pressure in the isolated rabbit heart resulted in a significant increase in vulnerability to AF that was closely correlated to shortening of the AERP. These changes were completely reversible within 3 minutes after release of the atrial stretch, resulting in prompt termination of AF.

LGE is a powerful predictor of ventricular arrhythmic risk in patients with ventricular dysfunction, irrespective of ICM and NICM etiology. The prognostic power of LGE is particularly strong in patients with severely depressed EF, which suggests its potential to improve patient selection for ICD implantation.

Nollo, Giandomenico, Luca Faes, Alberto Porta, Renzo Antolini, and Flavia Ravelli. Exploring directionality in spontaneous heart period and systolic pressure variability interactions in humans: implications in the evaluation of baroreflex gain. Am J Physiol Heart Circ Physiol 288: H1777-H1785, 2005. First published December 16, 2004; doi:10.1152/ajpheart.00594.2004.-Although in physiological conditions RR interval and systolic arterial pressure (SAP) are likely to interact in a closed loop, the traditional cross-spectral analysis cannot distinguish feedback (FB) from feedforward (FF) influences. In this study, a causal approach was applied for calculating the coherence from SAP to RR (K s-r) and from RR to SAP (Kr-s) and the gain and phase of the baroreflex transfer function. The method was applied, compared with the noncausal one, to RR and SAP series taken from 15 healthy young subjects in the supine position and after passive head-up tilt. For the low frequency (0.04 -0.15 Hz) spectral component, the enhanced FF coupling (K r-s ϭ 0.59 Ϯ 0.21, significant in 14 subjects) and the blunted FB coupling (K s-r ϭ 0.17 Ϯ 0.17, significant in 4 subjects) found at rest indicated the prevalence of nonbaroreflex mechanisms. The tilt maneuver recovered FB influences (K s-r ϭ 0.47 Ϯ 0.16, significant in 14 subjects), which were stronger than FF interactions (K s-r ϭ 0.34 Ϯ 0.19, significant in 9 subjects). At the respiratory frequency, the RR-SAP regulation was balanced at rest (K s-r ϭ 0.30 Ϯ 0.18 and Kr-s ϭ 0.29 Ϯ 0.20, significant in 11 and 8 subjects) and shifted toward FB mechanisms after tilt (K s-r ϭ 0.35 Ϯ 0.19 and Kr-s ϭ 0.19 Ϯ 0.11, significant in 14 and 8 subjects). The causal baroreflex gain estimates were always lower than the corresponding noncausal values and decreased significantly from rest to tilt in both frequency bands. The tilt-induced increase of the phase lag from SAP to RR suggested a shift from vagal to sympathetic modulation. Thus the importance of nonbaroreflex interactions pointed out the necessity of accounting for causality in the cross-spectral analysis of the interactions between cardiovascular variables in healthy humans.cross-spectral analysis; coherence and transfer function; cardiovascular regulation; feedback and feedforward mechanisms; nonbaroreflex interactions SINCE THE INTRODUCTION of the notion that cardiovascular oscillations may be indicative of autonomic nervous system status (3), the analysis of the spontaneous fluctuations in heart rate and blood pressure has been extensively used as a probe for cardiovascular control mechanisms in humans. Particularly, the observation that oscillations in the heart period (RR interval) and the systolic arterial pressure (SAP) are correlated around 0.1 Hz and at the frequency of respiration has prompted many researchers to focus on the interrelationship between these two signals. In this context, the cross-spectral analysis of RR interval and SAP variability series constitutes one of the most widespread tools used to investigate on the coupl...

The analysis of the FF intervals demonstrates a strict correlation with atrial functional refractoriness. The self-termination of atrial fibrillation is related to a prolongation of the functional refractoriness (mean FF), whereas a shortening of both functional and effective refractoriness (fifth percentile) is associated with atrial fibrillation persistence. The provoked shortening of the mean FF at the stimulation site is consistent with the presence of a gap of excitability during atrial fibrillation in the human atria.

A new method for quantifying the organization of single bipolar electrograms recorded in the human atria during atrial fibrillation (AF) is presented. The algorithm relies on the comparison between pairs of local activation waves (LAWs) to estimate their morphological similarity, and returns a regularity index (rho) which measures the extent of repetitiveness over time of the detected activations. The database consisted of endocardial data from a multipolar basket catheter during AF and intraatrial recordings during atrial flutter. The index showed maximum regularity (rho = 1) for all atrial flutter episodes and decreased significantly when increasing AF complexity as defined by Wells (type I: rho = 0.75 +/- 0.23; type II: rho = 0.35 +/- 0.11; type III: rho = 0.15 +/- 0.08; P < 0.01). The ability to distinguish different AF episodes was assessed by designing a classification scheme based on a minimum distance analysis, obtaining an accuracy of 85.5%. The algorithm was able to discriminate among AF types even in presence of few depolarizations as no significant rho changes were observed by reducing the signal length down to include five LAWs. Finally, the capability to detect transient instances of AF complexity and to map the local regularity over the atrial surface was addressed by the dynamic and multisite evaluation of rho, suggesting that our algorithm could improve the understanding of AF mechanisms and become useful for its clinical treatment.