Abstract 17601: Quantitative Assessment of Systolic and Diastolic Myocardial Stiffness Using Shear Wave Imaging: In vivo Validation in a Large Animal Model

Abstract

Background: Quantitative imaging of myocardial viscoelastic properties can be useful for the evaluation of systolic and diastolic cardiac functions. We have demonstrated previously in Langendorff perfused rat hearts that Shear Wave Imaging (SWI) can assess quantitatively the time-varying myocardial stiffness. In this study, we validate SWI in vivo in an ovine model of normal and ischemic/reperfused myocardium.

Methods: SWI was performed in vivo in 10 open-chest sheep. Shear waves were generated remotely in the myocardium using the acoustic radiation force induced by a linear ultrasonic probe (8MHz). The shear wave propagation was imaged in real-time using an ultrafast scanner (12000 frames/s, Supersonic imagine, France). Local stiffness was derived from shear wave speed. Simultaneously, end-systolic as well as end-diastolic pressure volume and segment length relationships (ESPLR and EDPLR) were measured with a pressure catheter and sonomicrometers during transient caval occlusions at rest and increasing rates of infused dobutamine (N=5). Finally, the ligation of a diagonal of the LAD coronary artery was achieved during 2 hours (N=5) and 15 min (N=5), followed by 30 min of reperfusion.

Results: SWI end-systolic stiffness was strongly correlated with the slope of the ESPLR (r=0.84, p<0.0001) whereas no dependence was found with ES pressure (r=0.1, p=0.73). In contrast, diastolic stiffness was unchanged during dobutamine infusion. In the 15 min ischemic/reperfused myocardium no stiffness change was observed. However, SWI diastolic stiffness increased after 2 hours of ischemia from 5.4±1.1 to 18.7±6.9kPa and even more after reperfusion (36.6±14.7kPa). The stiffening was confirmed by the exponential stiffness coefficient of EDPLR which increased from 6.6±1.8 to 23.3±10.2. TTC staining on the explanted myocardium confirmed the presence of a large infarcted zone.

Conclusion: SWI was able to quantify systolic myocardial stiffness that correlated strongly to the regional myocardial contractility during different inotropic conditions. Secondly, the strong passive stiffness increase of infarcted myocardium was quantified successfully by SWI. This validation is a major step towards a novel non invasive myocardial stiffness imaging technique.