Laminar fiber architecture and three-dimensional systolic mechanics in canine ventricular myocardium

Previous studies suggest that the laminar architecture of left ventricular myocardium may be critical for normal ventricular mechanics. However, systo lic three-dimensional deformation of the laminae has never been measured. T herefore, end-systolic finite strains relative to end diastole, from biplan e radiography of transmural markers near the apex and base of the anestheti zed open-chest canine anterior left ventricular free wall (n = 6), were ref erred to three-dimensional laminar microstructural axes reconstructed from histology. Whereas fiber shortening was uniform [-0.07 +/- 0.04 (SD)], radi al wall thickening increased from base (0.10 +/- 0.09) to apex (0.14 +/- 0. 13). Extension of the laminae transverse to the muscle fibers also increase d from base (0.08 +/- 0.07) to apex (0.11 +/- 0.08), and interlaminar shear changed sign [0.05 +/- 0.07 (base) and -0.07 +/- 0.09 (apex)], reflecting variations in laminar architecture. Nevertheless, the apex and base were si milar in that at each site laminar extension and shear contributed similar to 60 and 40%, respectively, of mean transmural thickening. Kinematic consi derations suggest that these dual wall-thickening mechanisms may have disti nct ultrastructural origins.