Circ Arrhythm Electrophysiol Rearrangement of Atrial Bundle Architecture and Consequent Changes in Anisotropy of Conduction Constitute the 3-Dimensional Substrate for Atrial FibrillationClinical Perspective by Bart Maesen, Stef Zeemering, Carlos Afonso, Jens Eckstein, Rebecca A.B. Burton, Arne van Hunnik, Daniel J. Stuckey, Damian Tyler, Jos Maessen, Vicente Grau, Sander Verheule, Peter Kohl, and Ulrich Schotten Circ Arrhythm Electrophysiol Volume 6(5):967-975 October 15, 2013 Copyright © American Heart Association, Inc. All rights reserved.

A, Endocardial aspect of the recording location of the mapping array. A, Endocardial aspect of the recording location of the mapping array. Atrial tissue is mechanically fixed between transparent frame and counter-frame via sutures (blue). Note the endocardial bundle network. B, Processing of MRI images. Original MRI images are converted to a stack of images, allowing reconstruction of an epicardial to endocardial view. C and D, Identification of endocardial and epicardial bundle direction. Grid (red) represents the mapping array, and each square within the grid represents 1 electrode. In each square, a green marker line indicates endocardial or epicardial bundle direction. Black lines indicate that no direction can be determined or no structure is defined for that square. Large in-plane image sections through the MRI data are used for determination of endocardial (C) and epicardial (D) bundle direction. Small images indicate the plane through the endocardial and epicardial region used for analysis. ENDO indicates endocardium; and EPI, epicardium. Bart Maesen et al. Circ Arrhythm Electrophysiol. 2013;6:967-975 Copyright © American Heart Association, Inc. All rights reserved.

Atrial refractory period measurements (AERP) at different pacing cycle lengths for acute atrial fibrillation (aAF) and persistent AF (persAF). *P<0.05 between aAF and persAF. Atrial refractory period measurements (AERP) at different pacing cycle lengths for acute atrial fibrillation (aAF) and persistent AF (persAF). *P<0.05 between aAF and persAF. Bart Maesen et al. Circ Arrhythm Electrophysiol. 2013;6:967-975 Copyright © American Heart Association, Inc. All rights reserved.

Representative maps and corresponding electrograms of acute atrial fibrillation (aAF; A, B) and persistent AF (persAF; C, D). Representative maps and corresponding electrograms of acute atrial fibrillation (aAF; A, B) and persistent AF (persAF; C, D). Representative isochrone maps of 1 beat of aAF (A) and 1 beat of persAF (C). The area is activated by 5 waves in aAF (A) and 13 waves in persAF (C), identified using shades of gray. Dotted lines indicate underlying endocardial bundles; arrows indicate direction of propagation. Peripheral waves are indicated by arrows. Black asterisks indicate epicardial breakthroughs. Corresponding electrograms and their location on the map (red asterisk) are depicted for aAF (*1–*4) and persAF (*5–*8). As more waves are simultaneously present in persAF compared with aAF, electrograms in persAF (eg, *8) show more fractionation (fractionation representing activation of surrounding waves picked up by the electrode) than electrograms in aAF (eg,*1). B and D, Same maps as in A and C with only endocardial bundles (black) and direction of wave propagation (white arrows). In aAF, direction of propagation is mainly dominated by endocardial bundles (B). In persAF, this anatomic agreement between direction of propagation and endocardial bundle pattern is lost (D). Bart Maesen et al. Circ Arrhythm Electrophysiol. 2013;6:967-975 Copyright © American Heart Association, Inc. All rights reserved.

Spread of absolute angle differences (range 0° to 90°) between direction of epicardial and endocardial bundles during acute atrial fibrillation (aAF; A) and persistent AF (persAF; B). Spread of absolute angle differences (range 0° to 90°) between direction of epicardial and endocardial bundles during acute atrial fibrillation (aAF; A) and persistent AF (persAF; B). Schematic representation of endocardial and epicardial bundles in aAF (C) and persAF (D). Endo indicates endocardium; Epi, epicardium; mean, the mean angle difference; N, number of observations; Puniform, test for uniform distribution; and ratio, the ratio of small angle differences/(small+large angle differences). Bart Maesen et al. Circ Arrhythm Electrophysiol. 2013;6:967-975 Copyright © American Heart Association, Inc. All rights reserved.

Spread of absolute angle differences (range 0° to 90°) between anisotropy of conduction velocity (CV; A–D) or anisotropy of conduction likelihood (E–H) and endocardial or epicardial bundle orientation. Spread of absolute angle differences (range 0° to 90°) between anisotropy of conduction velocity (CV; A–D) or anisotropy of conduction likelihood (E–H) and endocardial or epicardial bundle orientation. Data for acute atrial fibrillation (AF; A, B, E, F) and persistent AF (C, D, G, H). Mean indicates the mean angle difference; N, number of observations; Puniform, test for uniform distribution; and ratio, the ratio of small angle differences/(small+large angle differences). See text for further explanation. Bart Maesen et al. Circ Arrhythm Electrophysiol. 2013;6:967-975 Copyright © American Heart Association, Inc. All rights reserved.