Myofiber Architecture of the Human Atria as Revealed by Submillimeter Diffusion Tensor Imaging

Abstract

Background-Accurate knowledge of the human atrial fibrous structure is paramount in understanding the mechanisms of atrial electric function in health and disease. Thus far, such knowledge has been acquired from destructive sectioning, and there is a paucity of data about atrial fiber architecture variability in the human population. Methods and Results-In this study, we have developed a customized 3-dimensional diffusion tensor magnetic resonance imaging sequence on a clinical scanner that makes it possible to image an entire intact human heart specimen ex vivo at submillimeter resolution. The data from 8 human atrial specimens obtained with this technique present complete maps of the fibrous organization of the human atria. The findings demonstrate that the main features of atrial anatomy are mostly preserved across subjects although the exact location and orientation of atrial bundles vary. Using the full tractography data, we were able to cluster, visualize, and characterize the distinct major bundles in the human atria. Furthermore, quantitative characterization of the fiber angles across the atrial wall revealed that the transmural fiber angle distribution is heterogeneous throughout different regions of the atria. Conclusions-The application of submillimeter diffusion tensor magnetic resonance imaging provides an unprecedented level of information on both human atrial structure, as well as its intersubject variability. The high resolution and fidelity of this data could enhance our understanding of structural contributions to atrial rhythm and pump disorders and lead to improvements in their targeted treatment. (Circ Arrhythm Electrophysiol. 2016;9:e004133.

Mechanisms of arrhythmogenesis related to calcium-driven alternans in a model of human atrial fibrillation

“…Thus, CDA may reflect some of the progressive changes that occur in the underlying substrate during long-standing AF which make standard therapies ineffective. However, in the present study, we modeled fibrotic changes due to AF as a global decrease in tissue conductivity, without taking into account specific patterns of structural heterogeneity that can influence arrhythmia organization272829. Further work is needed to determine how interaction of structural and functional mechanisms affect arrhythmia organization in AF273031, particularly in patients that do not respond to ablation therapy.…”

Influence of atrial contraction dynamics on cardiac function

“…However, recent advances in atrial electrophysiological modelling and DTMRI measurements of the atria are likely to improve this aspect [35]. The impact of the choice of atrial fibre on atrioventricular function is as of yet unknown, and this would be a particularly interesting avenue of future research.…”

MRI use for atrial tissue characterization in arrhythmias and for EP procedure guidance

“…Disruption of this ordered structure, such as due to the presence of regions of fibrotic tissue, can cause AF 23, 24 . A recent study using MRI diffusion-tensor imaging (DTI) 25 of ex-vivo human atria provides excellent visualization of this complex anatomy (Figure 2). While In-vivo cardiac DTI is currently difficult to perform, there are multiple groups working on making it possible.…”

“…Color code on right measures the similarity to the fiber tract direction on the epicardial surface. (After Pashakhanloo F et al, Circulation Arrhythmia & Electrophysiology 2016 25 , with permission )…”