556 Shear wave imaging using ultra-high frame rate echocardiography for the assessment of structural changes in cardiac transplant recipients
Authors: Petrescu A M , Bezy S , Cvijic M , Santos P , Orlowska M , Pedrosa J , Van Keer J , Duchenne J , Bogaert J , Van Cleemput J , Von Bardeleben S , D"hooge J , Voigt J U 
Published: January 2020

Abstract

Background
Cardiac allografts undergo characteristic alterations of the extracellular matrix, including myocardial fibrosis, that contribute to functional changes, particularly diastolic dysfunction due to increased myocardial stiffness(MS). Histological examination is the gold standard for myocardial fibrosis quantification, however, it requires endomyocardial biopsies which are invasive and not without risk. Increased native T1 and extracellular volume(ECV) using CMR T1 mapping have shown good correlation with biopsy evidence of myocardial interstitial fibrosis in heart transplant(HTx) recipients. Echocardiographic shear wave(SW) elastography is an emerging approach for measuring MS in vivo. SWs occur after mechanical excitation of the myocardium, e.g. after mitral(MVC) and aortic valve closure(AVC), and their propagation velocity is directly related to MS, thus providing an opportunity to assess stiffness at end-diastole(ED) and end-systole(ES).

Purpose
The aim was to investigate if natural shear wave velocities increase with the degree of diffuse myocardial fibrosis in HTx recipients.

Methods
We prospectively enrolled 22 HTx patients (8.8 ± 5.9 years post-HTx) that underwent CMR during their annual check-up. We performed SW elastography in parasternal long axis views of the left ventricle(LV) using an experimental scanner (HD-PULSE) equipped with a clinical phased array transducer (Samsung Medison P2-5AC) at 1100 ± 250 frames per second. Tissue acceleration maps were extracted from an anatomical M-mode line along the midline of the LV septum. The SW propagation velocity at MVC and AVC was measured as the slope on the M-mode acceleration map(FigureA). All patients underwent right heart catheterization on the same day for the measurement of pulmonary capillary wedge pressure(PCWP), as surrogate for LV filling pressure. The CMR protocol consisted of standard sequences including native and post-contrast T1 mapping. To evaluate diffuse myocardial fibrosis, native T1 and ECV were measured in the anteroseptal wall over all available short-axis slices.

Results
We found good correlations between SW velocities at ED and both myocardial T1 (r = 0.8,p &lt; 0.001,FigureB) and ECV (r = 0.6,p &lt; 0.05,FigureC) measured with CMR. Similarly, we found significant correlations between SW velocities at ES and T1 (r = 0.7,p &lt; 0.005) and ECV (r = 0.5,p &lt; 0.05), respectively. Furthermore, we observed a significant correlation between SW velocities at ED and PCWP (r = 0.6,p &lt; 0.05).

Conclusions
Both end-diastolic and end-systolic shear wave velocities showed a good correlation with CMR defined myocardial fibrosis in cardiac transplant patients. Shear wave velocities at end-diastole correlated with invasively-determined left ventricular filling pressure, reflecting the impact of the fibrous changes on the left ventricular diastolic function. These results suggest the potential of cardiac shear wave elastography for the assessment of structural changes in cardiac transplant recipients.
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