Introduction. Atrial cardiomyopathy is a complex pathology that includes both structural and electrical changes in atrial tissue. This concept has been difficult to apply to preventative clinical practice, as metrics to assess the health of atrial tissues need to be defined, before the onset of symptoms such as atrial fibrillation. To achieve this goal, a thorough understanding of atrial biomechanics is required, capturing its complex passive mechanical behavior and its macro- and microstructure. Working with human right and left atrial appendage tissue, right after it is surgically excised at the University Hospital of Saint-Etienne, we have developed a framework for the characterization of passive biomechanics of the atrium.
Methods. A biaxial tensile testing machine for the characterization of small samples (7mm x 7mm) was designed and built in house. Biaxial multi-step stress relaxation tests were performed on the appendage tissue samples, considering the longitudinal direction as the main direction of the trabeculae. To derive stresses, the thickness of the sample was first measured with a caliper. After mechanical testing, samples were fixed in ethanol in their "zero strain" configuration. Using Lugol solution to enhance contrast, microCT imaging was then performed to investigate the microstructural organization of the tissue. Orientation of the cardiomyocytes were extracted with Cardiotensor.
Results & Discussion. Preliminary results show a strong hyperelastic and viscoelastic response of the tissue as well as significant intra-sample variability. The microCT imaging revealed both the macrostructure (i.e. the geometry of the sample) and information about the cardiomyocyte bundles orientation. This approach will allow us to link microstructural features to the mechanical response of the tissue and help design numerical model of atrial appendages. Future work will include in vivo MR imaging to understand how the mechanical behavior of the atrium (during the reservoir phase) is impacted by its local mechanical properties.