3-DIMENSIONAL RESIDUAL STRAIN IN MIDANTERIOR CANINE LEFT-VENTRICLE

All previous studies of residual strain in the ventricular wall have b een based on one-or two-dimensional measurements. Transmural distribut ions of three-dimensional (3-D) residual strains were measured by bipl ane radiography of columns of lead beads implanted in the midanterior free wall of the canine left ventricle (LV). 3-D bead coordinates were reconstructed with the isolated arrested LV in the zero-pressure stat e and again after local residual stress had been relieved by excising a transmural block of tissue. Nonhomogeneous 3-D residual strains were computed by finite element analysis. Mean +/- SD (n = 8) circumferent ial residual strain indicated that the intact unloaded myocardium was prestretched at the epicardium (0.07 +/- 0.06) and compressed in the s ubendocardium (-0.04 +/- 0.05). Small but significant longitudinal sho rtening and torsional shear residual strains were also measured. Resid ual fiber strain was tensile at the epicardium (0.05 +/- 0.06) and com pressive in the subendocardium (-0.01 +/- 0.04), with residual extensi on and shortening, respectively, along structural axes parallel and pe rpendicular to the laminar myocardial sheets. Relatively small residua l shear strains with respect to the myofiber sheets suggest that prest retching in the plane of the myocardial laminae may be a primary mecha nism of residual stress in the LV.