Fiber Orientation in the Canine Left Ventricle during Diastole and Systole

TLDR

Fiber orientation across the left ventricular wall has been investigated in prior studies. The study examined fiber orientation in the canine left ventricle by fixing 18 dog hearts in situ at systole, diastole, and dilated diastole, then measuring fiber angles across the free wall at eight sites using light microscopy on serial paraffin sections. The study found a well‑ordered fiber angle distribution ranging from ~60° at the endocardium to ~–60° at the epicardium, with the greatest thickness‑dependent change at the surfaces; fiber angles remained largely unchanged from diastole to systole (except in the papillary muscle root), a circumferential‑to‑longitudinal fiber ratio of ~10:1 that varies from base to apex, and a ~7°–19° increase in lateral wall angles during systole suggestive of ventricular bending or torsion.

Abstract

Fiber orientation across the left ventricular myocardial wall has been studied. Specimens were obtained from 18 dog hearts rapidly fixed in situ in systole, in diastole, and in dilated diastole. Fiber orientation was determined across the free wall at eight sites from a T-shaped specimen by measurements with light microscopy in serial paraffin sections. Results indicate: (1) The wall has a well-ordered distribution of fiber angles varying from about 60° (from the circumferential direction) at the inner surface to about -60° on the outer surface. The greatest change in angle with respect to wall thickness occurs at the two surfaces (endocardial and epicardial). (2) Fiber angles did not change significantly during the transition from diastole to systole, despite a 28% increase in wall thickness (except in the papillary muscle root region). (3) The proportion of fibers lying in the sector of fiber angles oriented circumferentially (0±22.5°) to those oriented longitudinally (67.5 to 90° and -67.5 to -90°) is approximately 10:1. This ratio increases toward the base and diminishes toward the apex of the left ventricle. (4) All fiber angles in the lateral wall of hearts in systole increased through the wall by approximately 7° near the base and 19° near the apex relative to their counterparts in diastole, indicating bending or torsion of the left ventricle during contraction.