Transmural Wave Speed Gradient May Distinguish Intrinsic Myocardial Stiffening From Preload-Induced Changes in Operational Stiffness in Shear Wave Elastography.

Abstract

Shear wave elastography (SWE) is a promising technique to non-invasively assess myocardial stiffness based on the propagation speed of mechanical waves. However, a high wave propagation speed can either be attributed to an elevated intrinsic myocardial stiffness or to a preload-induced increase in operational stiffness. Our objective was to find a way to discriminate intrinsic myocardial stiffening from stiffening caused by an increased pressure in SWE. We used the finite element method to study the shear wave propagation patterns when stiffness and/or pressure is elevated, compared to normal stiffness and pressure. Numerical findings were verified in a few human subjects. The transmural wave speed gradient was able to distinguish changes in intrinsic stiffness from those induced by differing hemodynamic load (a speed of ±3.2 m/s in parasternal short-axis (PSAX) view was associated with a wave speed gradient of -0.17 ± 0.15 m/s/mm when pressure was elevated compared to 0.04 ± 0.05 m/s/mm when stiffness was elevated). The gradient however decreased when stiffness increased (decrease with a factor 3 in PSAX when stiffness doubled at 20 mmHg). The human data analysis confirmed the presence of a wave speed gradient in a patient with elevated ventricular pressure. Cardiac SWE modeling is a useful tool to gain additional insights into the complex wave physics and to guide post-processing. The transmural differences in wave speed may help to distinguish loading-induced stiffening from intrinsic stiffness changes. The transmural wave speed gradient has potential as a new diagnostic parameter for future clinical studies.