Page 22 - Overall twist is a summation event?
I would like to suggest that the twisting motion of the left ventricle, demonstrated originally by fluoroscopy by McDonald in 1970 and more lately by MRI tagging and by echo speckle tracking, can be explained by combining counter clockwise twist generated by the dominant outer oblique layer with overall clockwise rotation. The image above has the first in black arrows and the second in green.
This model assumes that the twist seen in the basal third of the ventricle is a small but significant distance from the mitral ring. Here the oblique layer induces a small degree of twist, which appears early as it can occur in the isovolumic phase. Later in systole, as the ventricles empty, clockwise rotation sets in. The amplitude of rotation is greater than the twist, so the net result is that an initial counter-clockwise movement changes to a net clockwise movement.
At the apex, the twisting movement is maximal and exceeds the rotational movement at all times, so the apex shows net counterclockwise rotation. Hence the impression that the ventricle is being wrung
These opposing patterns at the extremes of the ventricle become more balanced in the middle third, and at some point they will cancel and net rotation will be will be zero.
In this way, the usual representation of the rotational movements, typified by the graph below, is satisfied without having to invoke a reversal of twist at the base.
I suspect that the ventricle grows and adapts with the objective to minimise cardiac motion in all directions except the beneficial long axis motion of the atrioventricular ring, and that it is no coincidence that in the middle of the left ventricle, at its maximal diameter and greatest power, rotation relative to the framework of the chest is nil.