Biomechanical Properties and Microstructure of Heart Chambers: A Paired Comparison Study in an Ovine Model

Abstract

Mechanical properties of the cardiac tissue play an important role in normal heart function. The goal of this study was to determine the passive mechanical properties of all heart chambers through a paired comparison study in an ovine model. Ovine heart was used due its physiological and anatomical similarities to human heart. A total of 189 specimens from anterior and posterior portions of the left and right ventricles, atria, and appendages underwent biaxial mechanical testing. A Fung-type strain energy function was used to fit the experimental data. Tissue behavior was quantified based on the magnitude of strain energy, as indicator of tissue stiffness, at equibiaxial strains of 0.10, 0.15, and 0.20. Statistical analysis revealed no significant difference in strain energy storage between anterior and posterior portions of each chamber, except for the right ventricle where strain energy storage in the posterior specimens were higher than the anterior specimens. Additionally, all chambers from the left side of the heart had significantly higher strain energy storage than the corresponding chambers on the right side. Furthermore, the highest to lowest stored strain energy were associated with ventricles, appendages, and atria, respectively. Microstructure of tissue specimens from different chambers was also compared using histology.

Biomechanical properties and microstructure of neonatal porcine ventricles

“…This is surprising given that the LVFW has a greater proportion of collagen. Our observation, of a greater ratio of collagen to myocyte fibres in the LVFW, is consistent with previous reports of higher collagen content preserving wall thickness during diastole and systole [51,[72][73][74] ( Table 2). Since a higher collagen content would typically be associated with greater stiffness in mature tissues, the less stiff behaviour observed here might be related to the collagen state in a 1-day neonatal heart.…”

“…This peak was then fitted with a Gaussian function, reporting the preferred fibre orientation [49,50]. A custom MATLAB code was also adopted to quantify the surface area ratio of collagen to myocyte fibres, using image thresholding based on RGB (red, green and blue) values [51].…”

Current Understanding of the Biomechanics of Ventricular Tissues in Heart Failure

“…While the uniaxial mechanical test offers a quicker and easier examination of the material mechanical property, the biaxial mechanical test better mimics the in vivo loading conditions and provides more comprehensive measurements of the anisotropic mechanical behavior [17,19,20,22,[39][40][41]. Both methods have been used in prior studies of LV and RV mechanical properties [17,20,[22][23][24][25][26][27][28][29][30][39][40][41][42][43][44][45][46] (please see Table 1 for a summary of these studies).…”

“…The characterization of the anisotropic behavior of ventricles is highly dependent on the definition of the biaxial coordinate system. To date, there are two main types of coordinate systems: the main fiber and cross-fiber coordinate system [17,30,44], and the outflow tract and cross-outflow tract coordinate system [20,29,40]. Using the former coordinate system, it is consistently observed that the tissue behaves stiffer in the fiber direction compared with the cross-fiber direction [22].…”

“…Similarly, Ahmad et al found that the neonatal porcine RV had significantly greater anisotropy than the LV in different anatomic regions [89]. However, Javani et al reported that the ovine LV was more anisotropic than the RV [44]. Ghaemi et al reported that both LV and RV were anisotropic, but there was no comparison between these chambers [22].…”