Abstract 3074: Torsional Modulus: A Simple, Novel Index of Ventricular Stiffness
Background: Left ventricular (LV) torsion results from the helical arrangement of epicardial and endocardial myocyte fiber layers, which have opposing pitch. Torsion is viewed as a marker of LV function, and although torsional analysis models exist, they are difficult to use and complex in nature.
Hypothesis: A simple stress-strain relation describes torsion angle equilibrium in terms of wall thickness (WT) and end-diastolic diameter (EDD). A linear relationship can be demonstrated between torsion/unit length (T) and (EDD +WT)−1 the slope of which is theoretically proportional to the ratio of the circumferential component of fiber force (F) to intrinsic tissue stiffness. We hypothesized this slope would be higher than normal in mitral regurgitation (MR) due to the known increase in intrinsic tissue compliance.
Methods: Control subjects (NRM; n=39) and MR patients (n=36) underwent tagged MRI. Torsional modulus was defined as the ratio of maximal net torque from the counter-aligned helical layers (torque=F*WT) to T. From materials theory, this modulus is proportional to the mass/unit length in a cylindrical shell of radius EDD/2 and thickness WT, and to intrinsic tissue stiffness to rotation (Int).
Results: MR had increased EDD and LV mass (p<0.05 vs. NRM) with similar WT, T, and EF. T had no relation to WT (which is directly proportional to the torque; upper figure⇓ panels) but had a linear relationship with (EDD+WT)−1, with higher slope in MR indicative of greater F/Int (lower panels).
Conclusion: Stress-strain analysis of LV torque equilibrium demonstrates higher F/Int in MR, compared to NRM. This simple linear relation may provide a useful marker of intrinsic LV tissue stiffness.