The Impact of Valve Stenosis and Replacement on Wave Characteristics in Cardiac Shear Wave Elastography

Abstract

Cardiac shear wave elastography (SWE) is a non-invasive technique to assess myocardial stiffness, based on the speed of waves that travel through the heart after valve closure. The wave physics underlying natural SWE remains incompletely understood. Therefore, we investigated the impact of wave excitation sources on 3 wave propagation aspects – wave amplitude (determined as wave acceleration magnitude), temporal wave width and speed. SWE was applied to 17 patients with aortic stenosis (AS), 13 AS patients that underwent transcatheter aortic valve implantation (TAVI), 10 AS patients that underwent surgical aortic valve replacement (AVR) and 18 age-matched healthy volunteers (HV). Absolute wave acceleration was lower in AS, TAVI and AVR patients compared to HV (1.5±0.60 vs 2.8±1.1 m/s2; p=0.001; 1.6±0.78 vs 2.8±1.1 m/s2; p=0.010; 1.7±0.66 vs 2.8±1.1 m/s2; p=0.015). Wave acceleration amplitude (measured as negative peak acceleration of the tissue) correlated with wave speed (r=0.388; p=0.003), implying that absolute wave acceleration is smaller in a stiffer heart. Subgroup analysis showed that the correlation between wave peak acceleration and speed is less steep in AS patients vs. HV (slopes: 0.23 vs 0.47 s). This implies that stenotic valves generate a wave with a lower acceleration magnitude compared to native valves. Further, temporal wave width was lower in TAVI patients vs. HV (8.7±2.3 vs 12.5±3.0 ms; p=0.002) and there was no difference in wave speed after aortic valve closure (AVC) between the groups. To conclude, wave acceleration magnitude and width offer additional insights into SWE physics next to wave speed and should be verified in a larger cohort.