AJP - Heart and Circulatory Physiology, Vol 243, Issue 1 1-12, Copyright © 1982 by American Physiological Society
Helical fibers in myocardium of dogs change their pitch as they contract
G. D. Meier, M. C. Ziskin and A. A. Bove
We have investigated the dynamic relationship between fiber structure and
deformation of the epicardium in the canine right ventricle. We have
reconstructed this deformation as the motion undergone by groups of three
radiopaque markers implanted close together in small epicardial regions. As
reported earlier, this motion has a stretch and a rotation component. The
stretch relates to shortening in the epicardial segment, whereas the
rotation describes how this segment changes orientation during the heart
cycle. If one postulates this segment as attached to a myocardial spiral,
then one can interpret the systolic shortening of the ventricular axis as a
compression of the spiral with decrease in pitch and the diastolic
lengthening as an extension with increase in pitch. If one further
postulates that the epicardial segment is attached to a right-hand spiral,
then decreases in pitch imply local clockwise segment rotations, and
increases, local counterclockwise rotations. From the motion of the
implanted markers, we have found that a small segment ion the midfree wall
of the right ventricle twists first locally clockwise as the ventricular
axis shortens and later counterclockwise as the axis lengthens. We conclude
that deformation of the epicardium is the result of a helical fiber
arrangement that is characteristic of the endocardial half of the wall.
Near the apex we observed the segment rotation to be reversed:
counterclockwise during systole and clockwise during diastole. This
observation implies a left-hand helix, which is the path of the apical
epicardial fibers, suggesting that the endocardial half of the wall is no
longer predominant here.
