Ultrasound shear wave elastography for detection of myocardial fibrosis

Abstract

Aims: Diffuse interstitial or replacement fibrosis is a common feature of a large variety of cardiomyopathies. These alterations contribute to increased myocardial stiffness (MS). 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 valve closure, and their propagation velocity is directly related to MS. The objective of this study was to investigate whether SW velocities (SWVs) can distinguish between interstitial and replacement fibrosis.

Methods and results: Fifty-two patients [30 heart transplanted patients (52.6 ± 16.0 years, 80% male) and 22 hypertrophic cardiomyopathy patients (54.4 ± 15.6 years, 85% male)] and 37 healthy volunteers (47.2 ± 16.6 years, 76% male) were included. SW elastography was performed using an experimental scanner at 1172 ± 302 frames per second. Patients were classified according to T1 mapping, extracellular volume (ECV) mapping, and late gadolinium enhancement measured by cardiac magnetic resonance into three groups: no fibrosis, interstitial fibrosis (MIF), and replacement fibrosis (MRF). SWVs differed among groups (P < 0.001), with a significant post hoc test between MIF and MRF and subjects without fibrosis (6.5 ± 1.1 m/s and 8.7 ± 1.2 m/s, respectively). Significant correlations were noted between SWVs and ECV values (r = 0.70, P < 0.0001) and native T1 values (r = 0.48, P = 0.0004). SWVs below 6.0 m/s showed the highest accuracy to identify patients without fibrosis [sensitivity 90%, specificity 90%, area under the curve (AUC) = 0.95]. A cut-off of 8.1 m/s could distinguish MRF from MIF (sensitivity 69%, specificity 100%, AUC = 0.92).

Conclusion: Natural SWVs can distinguish between normal and pathological myocardium and depend on the fibrosis burden of the myocardium.

Keywords: high-frame-rate echocardiography; myocardial fibrosis; myocardial stiffness; shear wave.