1KU Leuven Cardiovascular Sciences Leuven, Belgien; 2University Hospital Gasthuisberg Dept. of Cardiology Leuven, Belgien
Background: Cardiac shear wave elastography (SWE) allows for the non-invasive assessment of myocardial stiffness via the detection of shear waves propagating through the myocardium, e.g. after mitral valve closure (MVC). The propagation speed of these waves is directly related to myocardial stiffness. Myocardial stiffness is an intrinsic property of the myocardium that may be altered e.g. by remodelling or fibrosis. In this way, SWE could be an interesting tool to directly and non-invasively monitor myocardial properties 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: Nineteen 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 (Figure 1B). LV volumes decreased in all patients during one year of CRT, reflecting reverse remodelling (Figure 1B). Shear wave speed was significantly higher immediately after implantation compared to healthy controls during BiV ON (5.8±1.3 vs 4.6±1.1 m/s; p=0.014; Figure 1C), but not at 6 months (5.5±1.3 vs 4.6±1.1 m/s; p=0.067) and at 12 months (5.3±1.4 vs 4.6±1.1 m/s; p=0.18) after implantation (Figure 1C), 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 (5.8±1.3 vs 6.3±1.1 m/s; p=0.017), indicating that the reintroduction of dyssynchrony increases shear wave speed after MVC (Figure 1C). However, 6 months and 1 year after implantation shear wave speed was not significantly different between BiV ON and OFF (5.5±1.3 vs 6.1±1.3 m/s; p=0.14; 5.3±1.4 vs 5.6±1.0 m/s; p=0.49; Figure 1C). We hypothesize that these findings could be related to decreasing dyssynchrony and changing wall stress in the septum due to reverse remodelling after CRT.
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.