Fig. 1.
Four evenly spaced short-axis grid-tagging slices between the base and apex are used to measure the global twist and rate of untwisting and the regional equivalents at basal (■), mid (●), and apical (▵) locations. All strains were measured using the change in length, ΔL, per unit length, L, as shown in the inset. For circumferential strain, ΔL and L were measured in the circumferential direction. For circumferential-longitudinal shear strain (ϵCL), ΔL was the difference in circumferential displacement for slices separated by a longitudinal distance, L. For circumferential-radial shear strain (ϵCR), ΔL was the difference in circumferential displacement for epicardium and endocardium separated by a radial distance, L.