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Background: Anisotropy of conduction facilitates re-entry and is, therefore, a key determinant of the stability of atrial fibrillation (AF). Little is known about the effect of AF on atrial bundle architecture and consequent changes in anisotropy of conduction and maintenance of AF.Methods and Results: Direct contact mapping was performed in left atria of goats with acute AF (n=6) or persistent AF (n=5). The degree and direction of anisotropic conduction were analyzed. Mapped tissue regions were imaged by high-resolution MRI for identification of endocardial and epicardial bundle directions. Correlation between endocardial and epicardial bundle directions and between bundle directions and anisotropic conduction was quantified. In persistent AF, epicardial bundles were oriented more perpendicularly to endocardial bundles than in acute AF (% angles<20° between epicardial and endocardial bundle directions were 7.63% and 21.25%, respectively; P<0.01). In acute AF, the direction of epicardially mapped anisotropic conduction correlated with endocardial but not with epicardial bundles. In persistent AF, the direction of anisotropic conduction correlated better with epicardial than with endocardial bundles (% angles<20° between direction of anisotropic conduction and bundle direction were 28.77% and 18.45%, respectively; P<0.01).Conclusions: During AF, atrial bundle rearrangement manifests itself in more perpendicular orientation of epicardial to endocardial bundles. Propagation of fibrillation waves is dominated by endocardial bundles in acute AF and by epicardial bundles in persistent AF. Together with the loss of endo-epicardial electrical connections, rearrangement of atrial bundles underlies endo-epicardial dissociation of electrical activity and the development of a 3-dimensional AF substrate. [ABSTRACT FROM AUTHOR]

Background: Several recent studies suggest rotors detected by phase mapping may act as main drivers of persistent atrial fibrillation. However, the electrophysiological nature of detected rotors remains unclear. We performed a direct, 1:1 comparison between phase and activation time mapping in high-density, epicardial, direct-contact mapping files of human atrial fibrillation.Methods: Thirty-eight unipolar electrogram files of 10 s duration were recorded in patients with atrial fibrillation (n=20 patients) using a 16×16 electrode array placed on the epicardial surface of the left atrial posterior wall or the right atrial free wall. Phase maps and isochrone wave maps were constructed for all recordings. For each detected phase singularity (PS) with a lifespan of >1 cycle length, the corresponding conduction pattern was investigated in the isochrone wave maps.Results: When using sinusoidal recomposition and Hilbert Transform, 138 PSs were detected. One hundred and four out of 138 PSs were detected within 1 electrode distance (1.5 mm) from a line of conduction block between nonrotating wavefronts detected by activation mapping. Far fewer rotating wavefronts were detected when rotating activity was identified based on wave mapping (18 out of 8219 detected waves). Fourteen out of these 18 cases were detected as PSs in phase mapping. Phase analysis of filtered electrograms produced by simulated wavefronts separated by conduction block also identified PSs on the line of conduction block.Conclusions: PSs identified by phase analysis of filtered epicardial electrograms colocalize with conduction block lines identified by activation mapping. Detection of PSs using phase analysis has a low specificity for identifying rotating wavefronts during human atrial fibrillation using activation mapping. [ABSTRACT FROM AUTHOR]