Cardiac shear wave elastography can detect myocardial remodelling in LBBB patients undergoing CRT
Authors: Wouters L , Papangelopoulou K , Bezy S , Duchenne J , Puvrez A , Voros G , D'hooge J , Voigt J U 
Published: June 2023

Abstract

Funding Acknowledgements
Type of funding sources: None.

Background
Cardiac shear wave elastography (SWE) allows for the non-invasive assessment of myocardial stiffness via the detection of shear waves travelling through the heart after e.g. mitral valve closure (MVC). The propagation speed of these waves is directly related to myocardial stiffness. Myocardial stiffness depends on the intrinsic properties of the myocardium. Therefore, processes that alter these intrinsic properties, such as cardiac remodelling, could influence shear wave speed. In this way, SWE could be an interesting tool to directly and non-invasively monitor cardiac remodelling over time.

Purpose
To evaluate the effect of reverse remodelling on myocardial stiffness in left bundle branch block (LBBB) patients undergoing cardiac resynchronization therapy (CRT).

Methods
Fourteen non-ischemic patients with LBBB undergoing CRT were included. SWE was performed 1 day after CRT implantation and repeated after 6 and 12 months. Eleven age-matched healthy volunteers served as controls. Volumetric response was defined as ≥15% decrease in end-systolic volume after 1 year of CRT. Echocardiographic images were taken during biventricular (BiV) pacing ON (resynchronized) and BiV pacing OFF (native LBBB conduction), both with a conventional ultrasound machine and an experimental high frame rate ultrasound scanner (999 ± 134 frames/s). For SWE, LV parasternal long-axis views were acquired. Shear waves were visualized in M-modes of the septum, colour coded for tissue acceleration. The slope of the shear waves in the M-mode represents their propagation speed (Figure 1A).

Results
All included patients were volumetric responders. LV ejection fraction and global longitudinal strain improved significantly over time. LV volumes decreased significantly in all patients during one year of CRT (Table 1), reflecting reverse remodelling. Shear wave speed was significantly higher immediately after implantation compared to healthy controls during BiV ON (5.9±1.5 vs 4.6±1.1 m/s; p = 0.02; Figure 1B), but not at 6 months (5.3±1.5 vs 4.6±1.1 m/s; p = 0.19) and 12 months (5.1±1.1 vs 4.6±1.1 m/s; p = 0.39) after implantation (Figure 1B), indicating that myocardial stiffness normalized over time due to reverse remodelling. Moreover, shear wave speed was significantly higher during BiV OFF compared to BiV ON immediately after implantation (5.9±1.5 vs 6.7±1.4 m/s; p = 0.022) and at 6 months (5.3±1.5 vs 6.1±1.4 m/s; p = 0.048), indicating that the reintroduction of dyssynchrony increases shear wave speed after MVC (Figure 1B). One year after implantation shear wave speed was not significantly different between BiV ON and OFF (5.1±1.1 vs 5.2±0.4 m/s; p = 0.78; Figure 1B). This could imply that dyssynchrony decreases over time as a result of reverse remodelling.

Conclusion
SWE can non-invasively detect changes in myocardial properties during reverse remodelling under CRT. Myocardial stiffness gradually decreases towards the range of age-matched healthy hearts after CRT.