Shear wave speed after mitral valve closure increases with increased preload after a passive leg raise

Background Cardiac shear wave elastography (SWE) allows for the non-invasive assessment of myocardial stiffness via the detection of natural shear waves (SW) travelling through the heart after e.g. mitral valve closure (MVC). The propagation speed of these waves is directly related to myocardial stiffness. Given the non-linear end-diastolic stress strain relation of the myocardium, myocardial stiffness depends on both intrinsic tissue properties and loading conditions. Therefore, changing loading conditions, for example during a passive leg lift, could influence SW speed. Purpose To evaluate the effect of preload increase during a passive leg lift on shear wave speed and LV diastolic properties in heart failure patients. Methods Ten heart failure patients that presented to the hospital for a routine check-up were included. SWE was performed before and immediately after lifting the legs of the patient by placing them on a triangular-shaped pillow at an angle of 37° (fig 1A). For SWE, tissue doppler imaging of the LV parasternal long axis view was acquired at a high frame rate (1048±97 fps) using a research ultrasound scanner. SWs after MVC were visualized in M-modes of the septum, colour coded for tissue acceleration (fig 1B). The slope of the shear waves in the M-mode represents their propagation speed. SW speeds were measured in a semi-automatic manner. Results Patient characteristics are presented in table 1. Eight patients had diastolic dysfunction grade 1, the other 2 patients had diastolic grade 2. There was a significant increase in E/A ratio during passive leg lift and a significant shortening of E-wave deceleration time, indicating that preload increased. SW speed increased significantly during the passive leg lift (3.4±0.7 vs 4.3±1.2 m/s; p=0.017; fig 1C), indicating that SW speed increases with increasing preload. There was a significant correlation between SW speed and E/A (r=0.56; p=0.015; fig 1D) and SW speed and E/e’ (r=0.54; p=0.013; fig 1E), showing that SW speed reflects LV filling pressures. Additionally, there was a significant correlation between the difference in E deceleration time and the difference in SW speed (r=0.81; p=0.005; fig 1F) between baseline and leg lift. Furthermore, a significant correlation was observed between changes in E deceleration time and SW speed at baseline (r=-0.74; p=0.014; fig 1G). Both observations indicate a dependence of shear wave speed on changing loading conditions. Conclusion SW speed significantly increases during increased preload evoked by a passive leg lift. Therefore, SW speed seems to reflect the filling state of the heart and could become an interesting non-invasive tool to evaluate diastolic properties of the LV.