Left ventricular fibre architecture in man.

Abstract

SUMMARY In order to investigate the possibility of regional variation of ventricular structure, 25 normal postmortem human hearts were studied by inspection of cavity shape and subepicardial fibre orientation, by dissection, and by the histology of sections in two orthogonal planes. Ventricular architecture was complex. Inlet and outlet long axes were separated by 30 degrees in the left ventricle. In the right the corresponding figure was 90 degrees. The thickest part of the left ventricular wall was at the base. At the apex there was potential endo-and epicardial continuity. Left ventricular cavity shape departed significantly from any simple geometric figure, there being, consistently, regions of both positive and negativecurvature on the diaphragmatic aspect. The presence of trabeculae caused considerable variation in wall thickness. Striking variation was found in the arrangement of subepicardial muscle fibres. Most pronounced was the contrast between the longitudinal arrangement of fibres observed on the oblique margin and the circumferential arrangement of those on the acute. On the diaphragmatic surface of the left ventricle, fibres near the crux and apex ran circumferentially while those between ran obliquely; those on the diaphragmatic surface of the right ventricle also ran circumferentially. Deeper in the myocardium the arrangement was simpler. In the mid-wall of the left ventricle fibres were circumferential, best developed towards the base and in the upper part of the septum. Near the apex of the left ventricle and in the mid-wall of the right ventricle such fibres were sparse. The subendocardial region consisted of longitudinally directed fibres forming the trabeculae and papillary muscles, while fibres deep to and between the trabculae coursed more obliquely. These findings were confirmed by histology. Models based on uniform myocardial fibre structure cannot explain wall movement in normal subjects, and are likely to have significant limitations if used to investigate left ventricular function in disease.Although there is a wealth of anatomical work devoted to the study of fibre orientation in the human heart, this topic has received little detailed attention over the past 20 years, apart from the studies of Streeter' and Torrent-Guasp.2 This is surprising since much attention has been focused on measurements of cavity volume, pressure, and their derivatives with time, with calculation of systolic and diastolic wall stress. Though such studies imply anatomical knowledge, little recourse has been made to actual morphology, but instead geometrical assumptions have been made concerning left ventricular architecture. With the development of improved methods of investigating the left ventricle, the need for precise anatomical information has become pressing. In this paper therefore a de-

Strain‐encoded (SENC) magnetic resonance imaging to evaluate regional heterogeneity of myocardial strain in healthy volunteers: Comparison with conventional tagging

“…However, there are groups who observed, contrary to our findings, that the highest strain values can be obtained by MR tagging in the posterior region of the LV (2,22). The functional differences may be explained by the architecture of the heart with different fiber structure and probably the different regional afterload (28,29). Longitudinal strain was also slightly heterogeneous, with the highest longitudinal peak strain values at the inferior and inferolateral basal regions.…”

Influence of endocardial-epicardial crossover of muscle fibers on left ventricular wall mechanics

“…Reported circumferential direction, causing a more compliant values of zhe1jX range from -80 to -50" in the behavior along the circumferential direction. subepicardial layers and from +20 to +80" in the Within the wall, the applied variations ,of the helix subendocardial layers (Greenbaum et al, 1981; Ross and transverse fiber angle modified the distributions and Streeter, 1975;Streeter, 1979;Streeter et al, 1969). of sarcomere length and active muscle fiber stress to The transverse angle atrans is positive in the basal half a similar amount (top panels of Figs 7 and 8).…”

The impact of endurance exercise training on left ventricular systolic mechanics

“…Two distinct layers of myocardium, a subepicardial layer with circumferentially oriented fibers and a subendocardial layer with longitudinally coursing fibers, comprise the RV (17). "Cross-over" fibers from both RV layers, predominantly those with circumferential orientation, traverse into the interventricular septum where they constitute a significant portion of this structure (12). Structural or functional changes in the RV myocardium such as those reported in this cohort may therefore impact interventricular septal function.…”