Abstract Background Cardiac Amyloidosis (CA) is characterized by the deposit of amyloid proteins in the extracellular matrix of myocardium. Transthyretin amyloidosis (ATTR) is the most common type of CA associated with increased myocardial stiffness (MS). Previous studies have shown that 2D ultrasound-based acoustic radiation force shear wave elastography (SWE) can quantify the myocardial shear velocity and characterize MS alterations 1. However, the myocardium is a tri-dimensional soft material composed of a complex helicoidal distribution of fibers which is associated to anisotropic mechanical properties that vary over the cardiac cycle. Therefore, quantitative assessment of MS in diastasis phase requires a 3D approach with ECG gating. Purpose We aim to demonstrate the feasibility of 3D-SWE for the quantitative assessment of diastolic MS in ATTR-CA patients. Methods We have designed a new ultrasound device dedicated to 3D-SWE for the quantitative assessment of MS. It is based on a matrix transducer that remotely generates a shear wave in the myocardium using acoustic radiation force and track its propagation using ultrafast imaging at a framerate of 3000 volumes/s (Fig A). The shear wave velocity (SWV) is measured in a myocardial volume of 16 x 16 x 16 mm³. Positioning was performed using a real-time 2D B-mode and 3D-SWE acquisitions were performed in diastasis phase using ECG synchronization (Fig B). This study included 390 transthoracic 3D-SWE acquisitions on 13 diagnosed ATTR-CA patients (75±12 years of age). Measurements were conducted on three myocardial segments: the anterior free wall of the right ventricle (RV) and the basal antero-septal wall (AS) in parasternal long axis view and the apex in apical four chamber view, with 10 acquisitions per segment. Inter-operator variability was also evaluated in a subset of three patients by two sonographers. Results We were able to observe the shear wave propagation for all patients (Fig C). In the RV segment the median SWV was, 2.96m/s; interquartile range, 2.21-3.22m/s. In the AS segment: median SWV, 5.26m/s; interquartile range, 4.58-5.82m/s. In the Apex: median SWV, 1.43m/s; interquartile range, 1.09-1.74m/s. Mean Absolute Difference (MAD) over measurements performed by the two sonographers was 0.22m/s, 0.75m/s and 0.23m/s respectively for RV, AS and Apex and Intra-Correlation Coefficient (ICC) was 0.96. Conclusion The feasibility and good reproducibility of 3D-SWE on ATTR CA patients was demonstrated. The SWV of AS and RV segments were higher than normal MS values reported in the literature on healthy volunteer of the same age 1. In contrast, the velocity of apex segment was much lower. This distribution of MS among the three segments is consistent with other observations such as apical sparing reported using strain measurement in CA patient. 3D-SWE has the potential to provide accurate MS assessment for early diagnosis and follow-up of CA patients.
Meki et al. (Thu,) studied this question.