Comparison of Biomechanical Properties and Microstructure of Trabeculae Carneae, Papillary Muscles, and Myocardium in the Human Heart

Abstract

Trabeculae carneae account for a significant portion of human ventricular mass, despite being considered embryologic remnants. Recent studies have found trabeculae hypertrophy and fibrosis in hypertrophied left ventricles with various pathological conditions. The objective of this study was to investigate the passive mechanical properties and microstructural characteristics of trabeculae carneae and papillary muscles compared to the myocardium in human hearts. Uniaxial tensile tests were performed on samples of trabeculae carneae and myocardium strips, while biaxial tensile tests were performed on samples of papillary muscles and myocardium sheets. The experimental data were fitted with a Fung-type strain energy function and material coefficients were determined. The secant moduli at given diastolic stress and strain levels were determined and compared among the tissues. Following the mechanical testing, histology examinations were performed to investigate the microstructural characteristics of the tissues. Our results demonstrated that the trabeculae carneae were significantly stiffer (Secant modulus SM2 = 80.06 ± 10.04 KPa) and had higher collagen content (16.10 ± 3.80%) than the myocardium (SM2 = 55.14 ± 20.49 KPa, collagen content = 10.06 ± 4.15%) in the left ventricle. The results of this study improve our understanding of the contribution of trabeculae carneae to left ventricular compliance and will be useful for building accurate computational models of the human heart.

Current Understanding of the Biomechanics of Ventricular Tissues in Heart Failure

“…This procedure has been described in the mechanical tests of cardiac tissues [17,[22][23][24][25][26][27][28][29]. The number of preconditioning cycles in the biaxial/uniaxial tests varied among 5-10 cycles for the animal (canine, bovine, and murine) myocardium [17,22,[24][25][26][27][28][29], whereas Sommer et al and Fatemifar et al showed that, after 3-5 cycles, the human heart tissue reached stable biaxial behavior [23,30]. Owing to the viscoelastic nature of the tissue, a sufficient resting period should be given between the tests.…”

“…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].…”

Continuous Heart Volume Monitoring by Fully Implantable Soft Strain Sensor

“…The dimensions and composition of the strain sensors were chosen such as to match the Young modulus ( E ) of the myocardium up to 600 kPa. [ 28 ] Figure S9c,d, Supporting Information show the mechanical properties of Sensor 1 and Sensor 2, each one with E = 666 kPa and E = 647 kPa, respectively. In addition, a similar procedure is currently used for the attachment of temporary defibrillators without showing any severe adverse effects.…”

Ex vivo Methods for Measuring Cardiac Muscle Mechanical Properties

“…Trabeculae and papillary muscles are typically employed as proxies for the myocardium in the investigation of cardiac ventricular mechanics as they are linearly arranged, present throughout both ventricles of the heart, and are thought to be roughly homologous with the ventricular free walls and septum ( Goo et al, 2009 ), however, small ventricular wall strips have also been used ( Fatemifar et al, 2018 ). It is important to describe the origin of the muscle tissue (papillary, trabecular or free wall) as it has recently been shown that trabeculae are stiffer than either papillary muscles or myocardial strips from the same heart ( Fatemifar et al, 2018 ), and can contain more collagen. Additionally, RV tissues have been shown to be stiffer than LV tissues ( Sacks and Chuong, 1993 ; Fatemifar et al, 2018 ).…”