Regional localisation of left ventricular sheet structure: integration with current models of cardiac fibre, sheet and band structure

Abstract

The architecture of the heart remains controversial despite extensive effort and recent advances in imaging techniques. Several opposing and non-mutually compatible models have been proposed to explain cardiac structure, and these models, although limited, have advanced the study and understanding of heart structure, function and development. We describe key areas of similarity and difference, highlight areas of contention and point to the important limitations of these models. Recent research in animal models on the nature, geometry and interaction of cardiac sheet structure allows unification of some seemingly conflicting features of the structural models. Intriguingly, evidence points to significant inter-individual structural variability (within constrained limits) in the canine, leading to the concept of a continuum (or distribution) of cardiac structures. This variability in heart structure partly explains the ongoing debate on myocardial architecture. These developments are used to construct an integrated description of cardiac structure unifying features of fibre, sheet and band architecture that provides a basis for (i) explaining cardiac electromechanics, (ii) computational simulations of cardiac physiology and (iii) designing interventions.

Constitutive modelling of passive myocardium: a structurally based framework for material characterization

“…For a detailed description of the individual functionalities of these four chambers, see Katz (1977). There is still an ongoing debate concerning the structure of the heart (Gilbert et al 2007), and, in particular, the anisotropic cardiac microstructure. One approach describes the heart as a single muscle coiled in a helical pattern, whereas the other approach considers the heart to be a continuum composed of laminar sheets, an approach we are adopting in the present work.…”

Construction and validation of anisotropic and orthotropic ventricular geometries for quantitative predictive cardiac electrophysiology

“…The smooth transmural change of the helix angle is clearest in the left ventricular wall and septum, and there is a similar, but more irregular in long-axis sections, change through the right ventricular wall. The 'sheet' structure is more complex and irregular (see [32] for a review). The FA throughout the ventricular walls, septum and papillary muscle is generally between 0.1 and 0.2, with lower values at the boundaries.…”

“…There is still controversy about the organization of myocytes within the myocardium, in sheets, and about the large-scale organization of the ventricular wall, into bands [32]. Ventricular muscle cells (myocytes) are elongated cells, from 50 to150 mm in length and 10 to 20 mm in diameter, and have more end-to-end than transverse connections with neighbouring cells via intercalated discs [33,34].…”

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

“…However, recent studies suggest that sheet structure is highly variable between individual canines, and is variable between species [24]. As such, a single structural model may not be appropriate for simulating propagation in an anatomically detailed ventricular wedge, or in the complete ventricles.…”

“…The cleavage planes ran radially from the endocardium to the epicardium and, when viewed in a long axis transmural plane, could be seen to shift from a base-apex direction near the apex through to an apex-base direction in basal regions. This architecture, however, has been disputed by several groups for numerous reasons -see [24] for a review. Furthermore, histological techniques, even if the tissue does not require fixing as for polarised light microscopy, require reconstruction of fibre and sheet orientations from sections, and introduce problems of distortion and alignment.…”