Cardiac atrial kick shear wave elastography with ultrafast diverging wave imaging: An in vivo pilot study

Increased myocardial stiffness is characteristic of many diseases, leads to a loss of diastolic function, and is a cause of diastolic heart failure (DHF). Methods to estimate myocardial stiffness include Shear Wave Elastography (SWE). Currently, ultrasound-based cardiac SWE includes acoustic radiation force (ARF)-based methods; however, the in vivo generation and detection of shear waves in myocardium is significantly degraded due to limited ARF penetration and clutter noise. Consistently successful cardiac SWE is limited to low BMI patients. The objective of this research is to develop an ultrafast cardiac SWE technique where the shear wave is generated by the mechanical stimulus of the diastolic atrial kick. The amplitude of this wave is at least one order of magnitude higher than ARF-induced shear waves and thus more easily visualized, having a higher chance of detection and measurement in a broader patient population. Cardiac atrial kick SWE was performed on 14 healthy adults using an ultrafast diverging wave imaging technique. The shear wave speed (SWS) was estimated and correlated to common health measures in the clinic and in echocardiography. For all subjects, the SWS was 1.78 ± 0.34 m/s, similar to other SWE studies for late diastole. The atrial kick SWS was correlated to systemic diastolic pressure (r = -0.75, p = 0.002), E' (r = 0.60, p = 0.02), IVRT' (r = -0.60, p = 0.02), and E'/A' (r = 0.58, p = 0.03). These results suggest this method can be used as a measure of diastolic function and myocardial stiffness, and establish the range of normal values of atrial kick SWS that may be used as reference values when studying myocardial pathologies such as DHF. This research is the first to investigate the in vivo atrial kick SWS in humans using an ultrafast diverging wave imaging technique.