In ovine hearts, subepicardial radial wall thickening increased significantly from week 1 to week 8 after marker implantation, driven by subepicardial sheet extension and sheet-normal shear.
The study proposes a mechanistic model suggesting that a selective decrease in subepicardial intercellular matrix stiffness is responsible for the elimination of the transmural wall thickening gradient 1-8 weeks after marker implantation surgery in ovine hearts.
In an attempt to provide a better understanding of our finding that regions with contracting left ventricular myofibers need not develop a significant transmural systolic wall thickening gradient, the analytic approach of Costa et al. was applied to the four-dimensional dynamic data obtained 1 and 8 wk after surgical implantation of transmural radiopaque beads in the lateral equatorial left ventricular wall in seven ovine hearts. Quantitative histology of tissue blocks demonstrated that fiber angles varied linearly across the wall in this region from -37 degrees in the subepicardium to +18 degrees in the subendocardium. Sheet angles exhibited a pleated-sheet behavior, alternating sign from subepicardium to subendocardium. From end diastole (reference configuration) to end systole (deformed configuration), fiber strain was uniformly negative, sheet extension and sheet thickening were uniformly positive, and sheet-normal shear contributed to wall thickening at all wall depths. Subepicardial radial wall thickening increased significantly from week 1 to week 8, with significant increases in the contributions from subepicardial sheet extension and sheet-normal shear. At 1 and 8 wk, the contribution of sheet-normal shear to wall thickening was substantial at all transmural depths; the contribution of sheet extension to wall thickening was greatest in the subepicardium and least in the subendocardium, and the contribution of sheet thickening to wall thickening was greatest in the subendocardium and least in the subepicardium. A mechanistic model is proposed that provides a working hypothesis that a selective decrease in subepicardial intercellular matrix stiffness is responsible for elimination of the transmural wall thickening gradient 1-8 wk after marker implantation surgery.
Cheng et al. (Sat,) conducted a other in Left ventricular mechanics (n=7). Surgical implantation of transmural radiopaque beads was evaluated on Transmural sheet strains and wall thickening. In ovine hearts, subepicardial radial wall thickening increased significantly from week 1 to week 8 after marker implantation, driven by subepicardial sheet extension and sheet-normal shear.