Brillouin microspectroscopy for myocardial stiffness assessment in pathological mouse models

Cardiovascular diseases (CVDs) are the major cause of mortality worldwide. Biomechanical changes in the myocardium, particularly variations in myocardial stiffness, have shown links to common CVDs. However, there is currently no device in the clinics that is able to assess in vivo and directly the stiffness of the myocardium. Such a tool would provide new insights into the underlying mechanism of pathology.

Brillouin spectroscopy is an emerging tool in biology for the characterization of the elastic and viscoelastic behavior of samples in a non-destructive, all-optical and label free manner. This study proposes that Brillouin microspectroscopy can be applied to distinguish between healthy and diseased myocardium following myocardial infarction (MI) and pressure overload compensatory hypertrophy, both known to result in significant ventricular wall remodeling.

Ligation of the left descending artery (LAD) and transverse aortic constriction (TAC) were performed to generate MI and cardiac hypertrophy models respectively. Highresolution echocardiography speckle tracking imaging was performed on mice before sacrifice for correlation purposes and stiffness of heart samples was measured through means of Brillouin microspectroscopy using a tandem Fabry-Pérot spectrometer. Sets of points were obtained for the left ventricle (LV), interventricular septum (IVS) and right ventricle (RV) from short axis sections of diseased and healthy hearts.

Results showed that the values for Brillouin frequency shift (νB) remained homogeneous in control samples while infarcted and healthy regions showed significant differences, with the values for the fibrotic area being markedly higher. Values from the LV and IVS were on average higher than those from the RV in hypertrophic samples as well but a more in depth study in needed. We conclude that Brillouin microspectroscopy can detect variations in the myocardium caused by disease with great resolution and therefore, may be used for further research of cardiac tissue biomechanics, monitoring and evaluation of diseases and development of therapeutic approaches.