Abstract Body (Do not enter title and authors here): Background: Cardiac Amyloidosis (CA), particularly transthyretin amyloidosis (ATTR) is characterized by the deposit of amyloid proteins in the extracellular matrix of myocardium leading to increased myocardial stiffness (MS) and impaired diastolic function. Previous studies have shown that 2D ultrasound shear wave elastography (SWE) can quantify non-invasively myocardial shear wave velocity (SWV) characterizing its stiffness. However, myocardium is a tri-dimensional tissue with a helicoidal fiber structure associated to anisotropic mechanical properties that vary over cardiac cycle. Therefore, accurately measuring MS in diastasis phase, under passive stiffness, requires a 3D approach with ECG gating.

Purpose: We aim to demonstrate the feasibility of 3D-SWE for the quantification of diastolic MS in ATTR-CA patients.

Methods: This prospective cohort study included 12 patients with diagnosed ATTR-CA (primary exposure variable) patients that received a standard echocardiographic examination and 3D-SWE. A customized ultrasound device based on a matrix transducer was used to perform 3D-SWE (Fig A) measuring SWV, primary outcome variable, in a myocardial volume of 10x16x16mm³ (Fig C). Positioning was guided by real-time 2D B-mode and acquisitions were trigged during diastasis phase using ECG gating (Fig B). SWV was assessed in 3 myocardial regions: anterior free wall of the right ventricle (RV), basal antero-septal wall (AS) and apex, with 10 acquisitions per segment, totaling 360 transthoracic 3D-SWE acquisitions. Inter-operator variability was evaluated in 3 patients by two sonographers.

Results: 3D-SWE was successfully performed in all patients (82±6 years; 85% men; LVEF: 60±9%; E/E’: 14±7; IVS: 16±3mm and GLS: -11±4%), in the 3 myocardial regions. Median SWV (Q1-Q3) values were 2.85m/s (2.35–3.03) in RV, 5.24 m/s (4.71–5.72) in AS, and 1.24 m/s (1.04–1.56) at the apex. Mean absolute difference over measurements performed by the two sonographers was 0.22m/s (RV), 0.75m/s (AS) and 0.23m/s (apex) and Intra-Correlation Coefficient was 0.96.

Conclusion: Feasibility and good reproducibility of 3D-SWE on ATTR-CA patients was demonstrated. SWV of AS and RV segments were higher than apex segment and MS values reported on healthy volunteer. This distribution of MS among the 3 segments is consistent with apical sparing reported using strain measurement. 3D-SWE has the potential to provide accurate MS assessment for early diagnosis and follow-up of CA patients.