Page 20 - Twist: definitions and anatomic restrictions
There is a difference between rotation and twist. "Rotation" of an object affects all of it equally. It can only be caused when the object has some purchase against an external frame of reference or it is rotated by an external force. "Twist" is when different parts of an object rotate by differing degrees: this needs no frame of reference and can be achieved by forces within the object. "Torsion" usually means a force that resists the twisting force, particularly if it persists to provide a restoring force. "Wringing" is a particular form of twist, caused by an external force. It has come to infer that the ends of the structure being wrung are twisted in opposite directions with the middle remaining stationary. An object cannot wring itself, and I think it is misleading to apply the term to cardiac motion.
When the LV rotates or twists about its long axis, it termed clockwise or anticlockwise as viewed from the apex.
There are some anatomical considerations that I think have been neglected in the debate over the mechanisms of twist. The ventricular mass can to rotate or twist within the pericardial cavity, but any movement at the base of the ventricles has to be quite limited as its walls are firmly attached to the atria. The posterior walls of the atria are firmly fixed to the immobile tissues of the mediastinum, but as they are fluid filled bags, a small degree of movement is possible at the atrioventricular ring. I do not think that the atria have any mechanism of their own for rotation, but I do think that the atrioventricular ring can be rotated by the right ventricular outflow tract (next page).
As the ventricular mass has no purchase against the pericardium, it cannot rotate by virtue of its own musculature, but it can be carried round by rotation at the atrioventricular ring. It can twist itself by oblique forces generated by the myocardium.
To return to our image of the dissected heart above, if the atrioventricular ring is stationary and the outer oblique muscles (upper arrow) contract, the result would be a strong counter-clockwise twist of the ventricular mass of increasing amplitude towards the apex, as below.
However, the inner oblique muscles are pulling in the other direction (lower arrow, top image), balancing the external muscle. If speckle tracking truly shows that there is a net anti-clockwise twist at the apex, then the external muscles probably have a degree of dominance.