Transmural myocardial deformation in the ischemic canine left ventricle.

The myocardium is a complex three-dimensional structure consisting of myocytes interconnected by a dense collagen weave that courses in different directions. Regional ischemia can be expected to produce complex changes in ventricular deformation. In the present study, we examined the effects of ischemia on two- and three-dimensional finite strains during acute transmural myocardial ischemia in 13 open-chest anesthetized dogs. In contrast to systolic deformation observed during the control period in which circumferential shortening exceeded longitudinal shortening, our results indicate that after 5 minutes of acute ischemia, end-systolic in-plane lengthening across the left ventricular wall occurs in approximately equal amounts in the circumferential and longitudinal directions. Along with these changes in extensional strains, there were significant negative transverse shearing deformations during ischemia. Myocardial ischemia also resulted in a loss of the normal end-systolic transmural gradients of shortening and thickening. Three-dimensional end-diastolic strains indicate that the left ventricular wall undergoes a significant passive reconfiguration that varies transmurally with lengthening in the epicardial tangent plane and wall thinning increasing from the epicardium toward the endocardium. The large systolic changes in shearing deformations with ischemia could potentially influence collateral blood flow and certainly indicate that uniaxial measurements of deformation in the ischemic myocardium, which do not account for shearing deformation, are incomplete and must be interpreted with caution. Moreover, normal transmural systolic gradients in deformation, which would be anticipated on geometric grounds, are lost during ischemia, implying that the material properties of ischemic tissue or the loading conditions imposed on the ischemic region by partially impaired adjacent myocardium vary transmurally.