Characterization of the relationship between systolic shear strain and early diastolic shear strain rates: insights into torsional recoil.

Early diastolic left ventricular (LV) untwisting has been evaluated as a manifestation of LV recoil, reflecting the release of elastic energy stored during systole. The primary goal of this study was to characterize the relationship between systolic strain (e.g., circumferential strain and the shear strains that comprise twist) with the resulting early diastolic shear strain rates, including the rate of untwisting. A further goal was to characterize these relationships regionally from apical to basal locations. Cardiac magnetic resonance imaging tissue tagging was used to measure circumferential strain, global and regional (apex, mid, basal) twist (theta), and circumferential-longitudinal (epsilon(CL)) and circumferential-radial (epsilon(CR)) shear strains along with the corresponding untwisting rates (dtheta/dt) and diastolic shear strain rates (depsilon/dt) in 32 healthy males (33 +/- 7 yr). LV untwisting rates and shear strain rates measured during early diastole varied significantly with the measurement location from apex to base (P < 0.001) but demonstrated significant linear correlation with their corresponding preceding systolic strains (P < 0.001). Untwisting rates and diastolic shear strain rates were not significantly correlated with circumferential systolic strain or end-systolic volume (P > 0.05). Normalization of the untwisting rates to the peak twist (dtheta/dt(Norm) = -13.6 +/- 2.1 s(-1)) or shear strain rates to peak systolic shear strain (depsilon(CL)/dt(Norm) = -15.0 +/- 5.4 s(-1), and depsilon(CR)/dt(Norm) = -14.2 +/- 7.7 s(-1)) yielded a uniform measure of early diastolic function that was similar for all shear strain and twist components and for all locations from apex to base. These findings support a linear model of torsional recoil in the healthy heart, where diastolic shear strain rates (e.g., untwisting rates) are linearly related to the corresponding preceding systolic shear stain component. Furthermore, these findings suggest that torsional recoil is uncoupled from end-systolic volumes or the associated strains, such as circumferential strain.