Natural shear wave elastography to assess diastolic function in univentricular hearts: a prospective cohort study
Authors: Cattapan I , Youssef A , Caenen A , Cools B , Budts W , Gewillig M , Van De Bruaene A , D'hooge J , Voigt J U 
Published: June 2023

Abstract

Funding Acknowledgements
Type of funding sources: None.

Background
Ventricular compliance is known to have a direct impact on ventricular filling and therefore on diastolic function. Chamber compliance, in turn, is directly related to myocardial stiffness. The operational stiffness of the myocardium can be non-invasively assessed using shear wave elastography (SWE). SWE thus offers a novel tool to study diastolic function.
To date, non-invasive evaluation of diastolic function remains challenging, particularly in Fontan patients in which conventional approaches have not been validated.
Aim of the study: i) to assess feasibility of shear waves elastography on univentricular hearts; ii) to document the observed natural shear wave speed after mitral valve closure (MVC) in both paediatric and adult Fontan patients; iii) to consider whether SWE can provide additional information on diastolic function in these hearts.

Materials and methods
We enrolled 26 consecutive Fontan patients: 18 paediatric and 8 adult patients (mean age 18 ± 12,8 years, range 3–43y). High frame rate parasternal long-axis views were acquired using an experimental scanner (1375±270 frame/s). Images were processed offline by extracting tissue Doppler acceleration coded M-modes drawn in the middle of the interventricular septum as well as the free walls using in-house developed software. Conventional echocardiographic parameters of systolic and diastolic function were collected using a high-end clinical scanner.

Results
54% of the patients enrolled had left-dominant ventricles, while the remaining 46% was right-dominant. Feasibility of shear waves and average velocities are reported in Table I. Average shear waves velocities were significatively higher than previously collected data from healthy volunteers in our laboratory (6,8 ± 2,3 m/s after mitral valve closure versus 3,54 ± 0,93 m/s; p&lt; 0,001). There was no correlation between shear waves velocities and age (r=0.38, p = 0.85 after MVC, septal) and no significant difference between children and adults (p = 0.85). Ventricular dominance did not significantly influence shear waves velocities. For 6 patients a recent measurement of end-diastolic pressure was available (average value 12,8 ± 3,37 mmHg). Shear waves velocities after MVC on the anterior wall showed a strong correlation with invasive end diastolic pressure (r=0,96, p = 0,003; graph 1). No other conventional echo parameters showed a significative correlation with invasively measured filling pressures.

Conclusions
Our findings show for the first time that measurements of natural shear waves are feasible in univentricular hearts with Fontan circulation. Their myocardium appears stiffer than normal. Whether this depends on an alteration of intrinsic myocardial properties (fibrosis) and/or on preload conditions, remains to be understood. Our data indicate that shear wave elastography may have the potential to facilitate the non-invasive assessment of diastolic function in univentricular hearts.