A systematic investigation of feasible acoustic windows and the impact of myocardial anisotropy for in vivo human cardiac shear wave elastography

Recent advancement in cardiac shear wave elastography (SWE) using pulse-inversion harmonic imaging showed substantial improvement of shear wave motion detection and demonstrated feasibility of transthoracic measurement of human myocardial stiffness. This study aimed at systematically investigating the feasible echocardiographic views for cardiac SWE and the impact of myocardial anisotropy when measuring myocardial stiffness from different scan views transthoracically. Ten healthy volunteers were recruited and scanned three times on three different days. A cardiac SWE sequence with pulse-inversion harmonic imaging and time-aligned sequential tracking was used to measure quantitative myocardial stiffness in late diastole. Seven combinations of echocardiography views and left ventricular (LV) segments were found to be feasible for transthoracic cardiac SWE: basal interventricular septum (IVS) under parasternal short-axis and long-axis views; mid IVS under parasternal short-axis and long-axis views; anterior LV free wall under parasternal short-axis and long-axis views; and posterior LV free wall under parasternal short-axis view. On the same LV segment, the mean diastolic shear wave speed (SWS) measurements from the short-axis view were statistically different from the long-axis view: 1.82 vs. 1.29 m/s for basal IVS; 1.81 vs. 1.45 m/s for mid IVS; and 1.96 vs. 1.77 m/s for anterior LV free wall, indicating that myocardial anisotropy plays a significant role in cardiac SWE measurements. These results establish the preliminary normal range of myocardial SWS under different scan views and provide important guidance for future clinical studies using cardiac SWE.