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Figure 3 Sequence of Twist Mechanics Explained in an Experimental Animal Model
Electric and mechanical activation are initiated in the apical subendocardial region. During isovolumic contraction (IVC) (A), the subendocardial myofibers (right-handed helix) shorten with stretching of the subepicardial myofibers (left-handed helix), producing a brief clockwise rotation of the apex and a counterclockwise rotation of the left ventricular base. During ejection (B), the subendocardial and subepicardial layers shorten simultaneously, with shortening strains near the apex exceeding those of the base. The larger arm of moment of the subepicardial fibers dominates the direction of twist, causing rotation of the apex and base in counterclockwise and clockwise directions, respectively. During isovolumic relaxation (IVR) (C), subepicardium lengthens from the base toward the apex and the subendocardium from the apex toward the base. The subsequent period of diastole is characterized by relaxation in both layers with minimum untwisting (D). This figure refers to the experimental model that was used in Sengupta et al. (22). Figure illustration done by Rob Flewell.
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