Ventricular Electrical - Mechanical Composite Model Preliminary Modeling And Simulation Studies

The computer heart model is the one combining transmission procedure of heart electric stimulus, myocardial contraction, valve vibration, blood flow and other physiological properties of the in vivo heart. Using the powerful computational ability and image processing ability of computer, the model should reproduce the shape, motion and function of human heart, so as to make it possible to better evaluate mechanical, electrical, and physio-pathological properties of the heart. At present, the important things in modeling heart are bioelectrical activity, myocardial mechanical property and their coupling problems.Leaded by professor Lu Weixue, the researchers in Biomedical Institute of Zhejiang University have developed an electrical model, LFX. Using this model, we can get the excitation series and other bioelectrical properties of the in vivo heart. Based on the model LFX, Dr. Liu has constructed a three-dimensional finite element mechanical model of left ventricle, which included the electrical properties of the heart. Liu made an attempt to combine the electrical model and mechanical model of the heart. Based on the previous work, in this article the author has established a biventricular model including the displacements of cardiac dipoles during the period of the systole of heart, which made the previous static heart get energy and can beat. Finally the 12-lead ECG was calculated and the motion and deformation of the ventricular wall were analyzed.Firstly, on the basis of considering the fiber orientation of ventricles fully, the two ventricles were segmented into a number of finite elements by using of FEM. Secondly, normal cardioelectrical excitation series was read from LFX model simulation. Thirdly, the active forces per finite element at different time during the period of systole of the heart were calculated by means of isoparametric theory and composite theory, and also the displacements of cardiac dipoles during the period of systole was calculated. Finally, we simulated the 12-lead ECG and some parametersto describe the motion and deformation of ventricular wall, such as displacement, strain, torsion angle and so on.The simulation results show that: (1) The ST-T of the 12-lead ECG has a reasonable improvement than the previous LFX model; (2) During the period of systole, the right ventricular free wall moves towards septum, and at the same time, the base and middle of the free wall move towards apex, which make the volume of right ventricle smaller; the minimum principle strain E3 is biggest at the apex, then at the middle of free wall, and its direction is in the approximate direction of the epicardial muscle fibers. (3) During the period of systole, left ventricular wall has different degrees of thickness at different material point; the base and middle of the left ventricular free wall move towards the apex and the apex remains almost static; torsion angle, which describe the torsion of wall along the long axis of left ventricle, is biggest at the apex; the minimum principle strain E3 is biggest at apex and its direction on the surface of middle wall of left ventricle is in the approximate direction of fiber orientation. The results were compared with solutions obtained from MR tagging images and those from other models, and it proved that the model and its precision had attained the expected ,goal.In a word, the model established by the work of this article mainly investigated the motion and deformation caused by the cardioelectrical excitation and the influence to cardioelectrical excitation transmission caused by the displacements of ventricular wall. In the international cardiac research area, many researchers are throwing themselves into the work that combine the electrical and mechanical properties of biventricle. But at present, there are no literature reported the ECG and motion analysis of ventricles at the same time. It proved that our virtual biventricular model has provided an effective and noninvasive method to investigate the physio-pathological properties of the hear...