Cardiomyocytes - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 251

Dog cardiomyocytes form myofibers with a given orientation that varies from the
endocardium to the epicardium with an angle from 70 degrees with respect

to the horizontal (equatorial) plane, the major axis of the truncated ellipsoid-like left
ventricle being vertical [ 429 ].
The wall circumferential sheet thickness is given by the cross size of four to
six cardiomyocytes. Subepicardial and subendocardial myofibers follow helical
paths, whereas midmyocardial myofibers are roughly circumferential. The myofiber
orientation can be quantified by helix 78 and transverse 79 angles.
Cardiac myofiber postmortem orientation has been measured in 5 healthy goat
hearts using diffusion tensor imaging (DTI; Vol. 6 - Chap. 6. Images, Signals,
and Measurements) [ 430 ]. The helix angle is evaluated at several sectors 80 in the
equatorial LV slice. 81 From the endocardium to the epicardium, the helix angle
varies from nearly 90 to

+ 70 to −

− 60 degrees in the anterior sector, from nearly 90 to − 30

degrees in the posterior sector, and from nearly 50 to 80 degrees in the septal

sector. The transverse angle was determined in the midmyocardial free wall for all
slices from apex to base and averaged over the circumference. The mean transverse
angle varied from 12

−

4 degrees near the heart base.
In fetal and neonatal human heart, the direction of muscular fibers has been
provided for each studied slice parallel to the equatorial plane by elevation and
azimuthal angles with respect to a given horizontal axis [ 431 ]. The technique is
based on polarized light transmission and resulting image processing. In slices near
the heart base, myocardial fibers cross the myocardium from the endocardium to
the epicardium in a counterclockwise manner, whereas the reverse is observed in
slices near the apex. Near the equatorial plane, the elevation angle continuously
ranges from

± 4 degrees near the apex to 9 ±

70 degrees near the endocardium.
Near the heart base and near the apex, a discontinuity in elevation angle variation is
observed at mid-thickness, the angle varying from

− 50 degrees near the epicardium to +

+ 40 to + 70 degrees near the

endocardium for both base and apex, and from 65 degrees

near the epicardium in apex and base slices, respectively. Myocardial fibers are

− 40 to − 50 or to −

78 The helix angle is the angle between the myofiber direction and the plane perpendicular to the
local major axis.
79 The transverse angle is the angle between the local circumferential direction and the projection
of the fiber direction on the plane normal to the local major-axis direction.
80 The helix angle is determined in anterior, interpapillary muscle, posterior, and septal angular
wall sectors of 20 degrees.
81 The equatorial slice is defined as the slice positioned at one-third of the major-axis length from
the heart base; the base corresponds to the slice nearest to the outflow tract, but outside it; the apex
is the first slice showing the cardiac wall from the chest wall.