Dipartimento di Matematica, Università degli Studi di Pavia, Via Ferrata 1, 27100 Pavia, Italy.
Europace. 2014 May;16(5):736-42. doi: 10.1093/europace/euu010.
Cardiac unipolar electrode stimulations induce a particular structure of the transmembrane potential distribution (Vm), called virtual electrode polarization (VEP), which plays an important role in the mechanisms of cardiac excitation, reentry induction, and ventricular defibrillation. Recent experimental studies, based on the optical mapping techniques, have shown that premature stimulations also induce significant changes in the intracellular calcium (Cai) spatial distribution. The aim of this work is to investigate and compare by means of numerical simulations the morphology of the Vm and Cai patterns, generated by applying an S1-S2 stimulation protocol with a premature S2 anodal pulse.
We perform parallel finite element simulations of a three-dimensional orthotropic Bidomain model on a block of ventricular tissue by using four membrane models of two species (guinea pig and rabbit), that incorporate the phenomenological or more detailed mechanistic descriptions of the calcium dynamics. During the S2 anodal stimulus, the Cai spatial distribution, computed with all the considered models, presents a configuration similar to the typical VEP pattern of Vm, with a minimum inside the virtual anode and two maxima in the virtual cathodes. After the S2 stimulus turns off, the anode break excitation mechanism yields a Vm pattern exhibiting a clearly propagating wavefront. Differently, the Cai patterns do not show a clear separation between the resting and the activated regions, with the exception of one of the phenomenological models considered, but they show warped dog-bone shaped equi-level lines around an elevation in the virtual anode region.
The VEP pattern of the Cai spatial distribution during the S2 stimulus is in agreement with the previous experimental studies. Moreover, the Cai minimum in the virtual anode can be mainly attributable to the outflow of calcium ions produced by the sodium-calcium (NCX) exchanger, without a significant contribution of the ICaL current.
单极心内膜电极刺激会引起跨膜电位分布（Vm）的特定结构，称为虚拟电极极化（VEP），它在心脏兴奋、折返诱导和心室除颤的机制中起着重要作用。最近的实验研究基于光学映射技术，表明早期刺激也会导致细胞内钙（Cai）空间分布的显著变化。本工作的目的是通过数值模拟研究和比较，在 S1-S2 刺激方案中施加早期 S2 阳极脉冲时，Vm 和 Cai 模式的形态。
我们使用两种物种（豚鼠和兔）的四个膜模型，通过对心室组织块进行三维各向异性双域模型的并行有限元模拟，对钙动力学进行了现象学或更详细的机制描述。在 S2 阳极刺激期间，所有考虑的模型计算的 Cai 空间分布呈现出类似于 Vm 的典型 VEP 模式的配置，在虚拟阳极内有一个最小值和两个在虚拟阴极中的最大值。S2 刺激关闭后，阳极破裂兴奋机制产生了一个 Vm 模式，表现出一个清晰的传播波前。不同的是，Cai 模式在静止和激活区域之间没有明显的分离，除了考虑的一种现象学模型外，但它们在虚拟阳极区域的升高周围显示出扭曲的狗骨状等水平线。
S2 刺激期间 Cai 空间分布的 VEP 模式与以前的实验研究一致。此外，虚拟阳极中的 Cai 最小值主要归因于钠钙（NCX）交换器产生的钙离子外流，而 ICaL 电流的贡献不大。
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