Yuniarti Ana Rahma, Lim Ki Moo
Department of IT Convergence Engineering, Kumoh National Institute of Technology, 61 Daehak-ro, Gumi, 39177, South Korea.
Biomed Eng Online. 2017 Jan 10;16(1):11. doi: 10.1186/s12938-016-0295-6.
The existence of non-excitable cells in the myocardium leads to the increasing conduction non-uniformity and decreasing myocardial electrical conductivity. Slowed myocardial conduction velocity (MCV) believed to enhance the probability of cardiac arryhthmia and alter the cardiac mechanical pumping efficacy, even in sinus rhythm. Though several studies on the correlation between MCV and cardiac electrical instabilities exist, there has been no study concerning correlation or causality between MCV and cardiac mechanical pumping efficacy, due to the limitation in clinical methods to document and evaluate cardiac mechanical responses directly. The goal of this study was to examine quantitatively the cardiac pumping efficacy under various MCV conditions using three-dimensional (3D) electromechanical model of canine's failing ventricle.
The electromechanical model used in this study composed of the electrical model coupled with the mechanical contraction model along with a lumped model of the circulatory system. The electrical model consisted of 241,725 nodes and 1,298,751 elements of tetrahedral mesh, whereas the mechanical model consisted of 356 nodes and 172 elements of hexahedral mesh with Hermite basis. First, we performed the electrical simulation for five different MCV conditions, from 30 to 70 cm/s with 10 cm/s interval during sinus pacing. Then, we compared the cardiac electrical and mechanical responses of each MCV condition, such as the electrical activation time (EAT), pressure, volume, and energy consumption of the myocardium. The energy consumption of the myocardium was calculated by integrating ATP consumption rate of each node in myofilament model.
The result showed that under higher MCV conditions, the EAT, energy consumption, end diastolic and systolic volume are gradually decreased. Meanwhile, the systolic pressure, stroke volume, stroke work, and stroke work to ATP are increased as the MCV values increased. The cardiac functions and performances are more efficient under higher MCV conditions by consuming smaller energy (ATP) while carrying more works.
In conclusion, this study reveals that MCV has strong correlation with the cardiac pumping efficacy. The obtained results provide useful information to estimate the effect of MCV on the electro-physiology and hemodynamic responses of the ventricle and can be used for further study about arrhythmogeneis and heart failure.
心肌中存在非兴奋性细胞会导致传导不均匀性增加和心肌电导率降低。心肌传导速度（MCV）减慢被认为会增加心律失常的可能性，并改变心脏的机械泵血效能，即使在窦性心律时也是如此。尽管已有多项关于MCV与心脏电不稳定之间相关性的研究，但由于直接记录和评估心脏机械反应的临床方法存在局限性，尚无关于MCV与心脏机械泵血效能之间相关性或因果关系的研究。本研究的目的是使用犬类衰竭心室的三维（3D）机电模型，定量研究在各种MCV条件下的心脏泵血效能。
本研究中使用的机电模型由电模型、机械收缩模型以及循环系统的集总模型组成。电模型由241,725个节点和1,298,751个四面体网格单元组成，而机械模型由356个节点和172个具有Hermite基的六面体网格单元组成。首先，我们在窦性起搏期间对五种不同的MCV条件进行了电模拟，范围从30至70 cm/s，间隔为10 cm/s。然后，我们比较了每种MCV条件下的心脏电和机械反应，如心肌的电激活时间（EAT）、压力、容积和能量消耗。心肌的能量消耗通过对肌丝模型中每个节点的ATP消耗率进行积分来计算。
结果表明，在较高的MCV条件下，EAT、能量消耗、舒张末期和收缩末期容积逐渐降低。同时，随着MCV值的增加，收缩压、每搏量、每搏功和每搏功与ATP的比值增加。在较高的MCV条件下，心脏功能和性能通过消耗较少的能量（ATP）而承担更多的功，从而更有效。
总之，本研究表明MCV与心脏泵血效能密切相关。所得结果为评估MCV对心室电生理和血流动力学反应的影响提供了有用信息，可用于心律失常发生机制和心力衰竭的进一步研究。
