Optimizing ventricular fibers: uniform strain or stress, but not ATP consumption, leads to high efficiency

Abstract

The aim of this study was to investigate the influence of fiber orientation in the left ventricular (LV) wall on the ejection fraction, efficiency, and heterogeneity of the distributions of developed fiber stress, strain and ATP consumption. A finite element model of LV mechanics was used with active properties of the cardiac muscle described by the Huxley-type cross-bridge model. The computed variances of sarcomere length (SL(var)), developed stress (DS(var)), and ATP consumption (ATP(var)) have several minima at different transmural courses of helix fiber angle. We identified only one region in the used design space with high ejection fraction, high efficiency of the LV and relatively small SL(var), DS(var), and ATP(var). This region corresponds to the physiological distribution of the helix fiber angle in the LV wall. Transmural fiber angle can be predicted by minimizing SL(var) and DS(var), but not ATP(var). If ATP(var) was minimized, then the transverse fiber angle was considerably underestimated. The results suggest that ATP consumption distribution is not regulating the fiber orientation in the heart.

A Novel Method for Sensitive Determination of Subclinical Left-Ventricular Systolic Dysfunction in Subjects With Obstructive Sleep Apnea

“…Opposite orientation of the myocardial fibers in the subendocardial and subepicardial layers is important for the equal redistribution of stress and strain in the heart. 9 The myocardial wall matures from a single-layered epithelium to a complex, multilayered structure. 23 Successive contraction and relaxation of the ventricular myocardial band produce several fundamental movements of the left ventricle: shortening, lengthening, thickening, thinning, etc.…”

“…Opposite orientation of the myocardial fibers in the subendocardial and subepicardial layer is important for the equal redistribution of stress and strain in the heart. 9 Nonhomogenous deformation of the basal, middle, and apical ventricular segments provides coordinated LV contraction. However, coordination may be disturbed due to the decrease in arterial oxygen saturation and the high negative intrathoracic pressure imposed by OSA.…”

Left Ventricular Form and Function Revisited: Applied Translational Science to Cardiovascular Ultrasound Imaging

“…Indeed, several studies in experimental mechanics and computational modeling have described the LV wall as a chiral structure where right-handed helical myofiber geometry in the subendocardial region transitions gradually into a left-handed geometry in the subepicardial region ( Fig. 1E) (7,(25)(26)(27).…”

“…Indeed, several studies in experimental mechanics and computational modeling have described the LV wall as a chiral structure where right-handed helical myofiber geometry in the subendocardial region transitions gradually into a left-handed geometry in the subepicardial region ( Fig. 1E) (7,(25)(26)(27).Therefore, the long axis of myofibers when viewed from outside the LV rotates clockwise from the endocardium towards the epicardium, with reported net difference in myofiber angulation ranging from +60° to −60° (15). In the short axis views, the myofibers are clustered within layers (myofiber sheets) that are separated by cleft spaces (cleavage planes).…”

“…These counterdirectional movements of a vortex produce suction and expulsion forces that have been exploited for designing energy efficient propellers and turbines (6). Likewise, experimental and mathematical modeling of the clockwise and counterclockwise spiral loops of myofibers in the left ventricle (LV) has shown that counterdirectional geometry provides an efficient distribution of regional stresses and strains (7). Conversely, altered ventricular geometry resulting from cardiac remodeling, regional myocardial dysfunction, or asynchronous conduction distort the efficiency of the loading and expulsion dynamics (8,9).…”