Effects Of Endocardium And Epicardium On Left Atrial Mechanics-A Finite Element Study

The heart is an important human organ.Heart-related diseases,such as atrial fibrillation and heart failure,have affected people's lives.They have become a public health problem in society.Although there are many diagnostic and therapeutic methods,the relevant pathological mechanism of the disease has not yet been clarified.At present,the use of finite element methods in conjunction with medical cardiac imaging techniques allows for a more in-depth study of the pathological mechanisms and physiology of heart-related diseases.However,the walls of the atria are relatively thin and multi-layered,irregular in geometry,and the anisotropic materials properties.Thus,the current phase of the finite element modeling of the atrium has yet to be improved.Features such as the human atrium of the mechanical material parameters and the wall of the hierarchical structure have not been taken into account.This study constructed a three-dimensional finite element model of the left atrium using the realistic geometric shape of human,the multi-layered atrial wall structure containing the inner and outer membranes,the recently measured human left atrial tissue parameters,and the transverse isotropy,hyper-elastic constitutive equations.The atrial filling status was simulated by applying pressure inside the atrial chamber,and the stress and strain of each layer of the atrial wall in each region were calculated.Finally,the effect of endocardium and epicardium and their thickness changes on the mechanical properties of the myocardium was analyzed by comparing it with two other models: one is single-layer atrial model(myocardium model)and the other is the model with different membrane thickness.The results showed that endocardial stress was highest,epicardial stress was second high,and myocardium stress was minimal;and as the thickness of the membrane increased,the stress of the endocardium and epicardium gradually decreased.The stress of the myocardium was not substantially change as membrane increased.In the myocardium model,the Myo-Endo layer near the endocardium is more stressed than the Myo-Epi layer near the epicardium.The stress and strain in longitudinally distributed myocardial bundle are greater than in the circumferential distribution.In all models,the degree of strain showed a trend from large to small from the inside to the outside.The degree of endocardial strain was the largest,the degree of strain in the myocardium was middle,and the degree of epicardial strain was the smallest.The endocardium and the epicardium are located on the inner and outer sides of the atrium,which can reduce the effect of internal and external atrial chambers on the myocardium.It can also play a role in restraining and buffering the myocardium,effectively preventing myocardial deformation and excessive expansion.Changes in membrane thickness have an effect on the stress and strain of each layer of the atrium wall.The effect of endocardial and epicardial membranes is that as the thickness increases,its stress and strain tend to become smaller.The main reason is to reduce the degree of strain,and have less effect on its stress.This study clarified that the atrial and epicardial membranes play an important role in atrial mechanics.It is necessary to include the information of the endocardium and the epicardium in the modeling studies to more accurately understand the pathological mechanism of atrial-related diseases in the future.