Characterization of the normal cardiac myofiber field in goat measured with MR-diffusion tensor imaging

Abstract

Cardiac myofiber orientation is a crucial determinant of the distribution of myocardial wall stress. Myofiber orientation is commonly quantified by helix and transverse angles. Accuracy of reported helix angles is limited. Reported transverse angle data are incomplete. We measured cardiac myofiber orientation postmortem in five healthy goat hearts using magnetic resonance-diffusion tensor imaging. A novel local wall-bound coordinate system was derived from the characteristics of the fiber field. The transmural course of the helix angle corresponded to data reported in literature. The mean midwall transverse angle ranged from −12 ± 4° near the apex to +9.0 ± 4° near the base of the left ventricle, which is in agreement with the course predicted by Rijcken et al. (18) using a uniform load hypothesis. The divergence of the myofiber field was computed, which is a measure for the extent to which wall stress is transmitted through the myofiber alone. It appeared to be <0.07 mm−1 throughout the myocardial walls except for the fusion sites between the left and right ventricles and the insertion sites of the papillary muscles.

Reconstruction and Quantification of Diffusion Tensor Imaging-Derived Cardiac Fibre and Sheet Structure in Ventricular Regions used in Studies of Excitation Propagation

“…Our mean value for the three combined hearts of FA = 0.25 ± 0.09 is similar to measurements from other studies, with values of 0.36 in canine [29], 0.35 in goat [23], 0.27 in mouse [41], and 0.36, 0.32 and 0.3 in diastolic, early and late systolic rat respectively [11] having been reported. Thus, fibre direction in the three hearts was well determined.…”

“…Thus, data from different hearts were aligned at the midwall where h = 0, and the centroid for each slice is at h = −1. This normalisation method removes errors associated with identifying the locations of the endocardial and epicardial surfaces and has been validated by Geerts et al [23], who showed that the standard deviation of the inclination angle data was much reduced when compared to the usual endocardial-to-epicardial normalisation method.…”

“…A normalised transmural position was assigned to each voxel in each sector using the method described by Geerts et al [23]. The location of the midwall was first defined as the position where a fit to the transmural course of the inclination angles (see definition below) changed sign.…”

Variability of the Human Cardiac Laminar Structure

“…The fibrous nature of the heart has been known for centuries, tracing back to as early as 1694 [28], but has been limited to tedious histological studies [20]. The cardiac fiber structure can now be imaged with diffusion tensor magnetic resonance imaging (DT-MRI) [2,15], however the variability of the fiber structure in humans is still not well known (due to the very limited number and the value of post-mortem healthy human hearts) and is largely speculated from studies on other species (dogs [12,13,11,26,22,21,9], goats [8], and rats [3]). Recently, Lombaert et al [17,18] constructed a statistical atlas of the human cardiac fiber architecture and assessed its variability.…”

Passive Ventricular Mechanics Modelling Using MRI of Structure and Function

“…The primary eigenvector, therefore can be used for mapping the 3D orientation of the myocardial fibres throughout the heart muscle [4]. Myocardial fibre orientation is an important determinant of myocardial wall stress [5] and exhibits a large regional and transmural variation.…”