Residual Strain in the Left Ventricular Ex Vivo C57BL/6 Myocardium

Abstract

Residual stress and strain are responsible for maintenance of the optimal left ventricular (LV) modus operandi, implicated in growth, remodeling and mechanical adaptation. This study quantifies LV residual strain (RS) in male C57BL/6 mice hearts (n=5, mean age=10.2 weeks, weight=24 g) using photography, during the no-load to the stress-free transition state. Upon euthanasia the hearts were harvested and immediately perfused with a nifedipine (2x10-4 g/l) and EGTA (10mM/l) solution to delay ischemic contracture. Metallic beads were triangularly placed on the upper surface of an equatorial 2 mm short-axis LV slice in areas spanning lateral, anterior, inferior and septal locations. A radial transmural LV cut was then performed, bisecting the RV insertion point line. Photographs of the slice were captured at baseline and sequentially every 30 s post-sectioning, for a period of 5 min. Segmentation algorithms allowed the identification of the centroids of the bead clusters, followed by calculations of shear residual strains (Exx, Eyy and Exy) and stretch ratios (λ1, λ2). Estimated mean opening angles were 38±2° and 54.1±7.6° after the cut and at 5 min later, respectively. Mean Exx Exy λ1, λ2 values from all quadrants ranged from 0.6–14.5%, -0.5–13%, 0.95–1.39, 0.99–1.49 during the study period. RS quantification is demonstrated with potential usefulness to constitutive stress-strain characterization.