Development of Comprehensive Electrophysiological Heart Simulator for In-Silico Study

到目前为止，我们的仿真器中的心室形态数据是基于计算机图形学的多边形数据。但为了尽可能准确地估计致命性心律失常，我们必须对患者的个体心室形态进行模拟。因此，我们从MRI图像中手动提取心肌区域，重建一次心跳时的4维（三维空间+时间）心脏形态。首先，我们通过True FISP序列获得了覆盖整个心脏17个阶段的24张横截面短轴图像。其次，我们开发了一个编辑工具，在每张图像的心肌边界上手动放置点，并提取区域。我们还开发了一个三维编辑工具来连接连续切片之间的这些点，并重建了心脏形态多边形数据。为了改进形状并将其作为仿真模型，我们进行了MRI图像之间不同心脏位置的校正、心脏多边形的平滑、到体数据的转换等处理。另一方面，我们建立了二维双域模型来阐明电除颤的机理。模型由均匀型和各向同性双域心肌片组成。膜动力学用改良版的Luo-Rudy-1模型表示，并考虑心肌纤维。在刺激诱导虚电极极化作用下，探讨了电刺激控制螺旋波再入的可能性。因此，在螺旋波再入过程中，一系列局部刺激导致螺旋波移位或捕获，这为螺旋波控制的机制基础提供了见解，从而导致新的电除颤机制。

So far the ventricle morphology data in our simulator were based on the polygon data for the computer graphics. But we have to carry out simulation with a patient's individual ventricle morphology in order to estimate fatal arrhythmia as correct as possible. So we extracted myocardial region manually from MRI images and reconstructed 4-dimensional (3D space + time) heart morphology during one heart-beat. First, we obtained 24 cross-sectional short-axis images that cover the whole heart at each of 17 phases by True FISP sequences. Second, we developed an editor tool to put points manually at the myocardial boundary on each image, and extracted the region. We also developed a 3-dimensional editor tool to link these points between consecutive sections, and reconstructed heart morphological polygon data. To improve the shape and to use it as a simulation model, we performed several processes such as correction of different heart position between MRI images, smoothing of heart polygons, conversion to volume data and so on.On the other hand, we developed the 2-dimensional bidomain model to clarify the electrical defibrillation mechanism. The model was consisted of a homogeneous and an isotropic bidomain myocardial sheet. Membrane kinetics was represented by a modified version of the Luo-Rudy-1 model and myocardial fibers were considered. Possibilities of the electrical stimulation to control spiral wave reentry were investigated under the effects of stimulus induced virtual electrode polarization. As a result, a set of localized stimulations during spiral wave reentry caused spiral wave shift or capture, which provided insight into mechanistic basis of spiral wave control leading to the new electrical defibrillation mechanism.