Zlochiver Sharon
Department of Biomedical Engineering, Faculty of Engineering, Tel-Aviv University, 69978 Ramat-Aviv, Tel-Aviv, Israel.
Cardiovasc Eng. 2010 Dec;10(4):190-200. doi: 10.1007/s10558-010-9104-1.
Current density threshold and liminal area are subthreshold parameters of the cardiac tissue that indicate its susceptibility to external and internal stimulations. Extensive experimental and theoretical research has been conducted to quantify these two parameters in normal conditions for both animal and human models. Here we employed a 2D numerical model of human cardiac tissue to assess these subthreshold parameters under the pathological conditions of heart failure and fibrosis. Stimuli were applied over an area ranging from 0.04 to 1 mm² using various pulse durations. The current density threshold decreased with increasing stimulation area or pulse duration. No significant changes were found in both parameters between control conditions and heart failure in the atrial tissue, while in the ventricular tissue, heart failure resulted in significantly reduced excitability with higher stimulation current magnitudes needed for excitation and larger liminal areas. This results from the specific ionic remodeling in ventricular heart failure that affects both subthreshold active currents such as I(K₁) and connexin 43 conductance. In fibrosis, increased fibroblast to myocyte coupling coefficient had a non-linear influence on current density thresholds, with an initial increase of current magnitude followed by a relaxation phase down to the current magnitude threshold for the control condition with no fibrosis. The results show that subthreshold excitation properties of the myocardium are influenced in a complex, non-linear manner by cardiac pathologies. Such observations may contribute to our understanding of impulse capturing properties, relevant, for example, for the generation of ectopic foci-originated arrhythmias and for the efficient design of cardiac stimulating electrodes.
电流密度阈值和阈下面积是心脏组织的阈下参数，表明其对外部和内部刺激的敏感性。已经进行了广泛的实验和理论研究，以量化动物和人类模型在正常条件下的这两个参数。在这里，我们采用了人类心脏组织的二维数值模型，以评估心力衰竭和纤维化等病理条件下的这些阈下参数。使用各种脉冲持续时间在0.04至1平方毫米的区域上施加刺激。电流密度阈值随着刺激面积或脉冲持续时间的增加而降低。在心房组织中，对照条件和心力衰竭之间的这两个参数均未发现显著变化，而在心室组织中，心力衰竭导致兴奋性显著降低，兴奋所需的刺激电流幅度更高，阈下面积更大。这是由于心室心力衰竭中特定的离子重塑，它影响了诸如I(K₁)和连接蛋白43电导等阈下活性电流。在纤维化中，成纤维细胞与心肌细胞耦合系数的增加对电流密度阈值有非线性影响，最初电流幅度增加，随后是一个弛豫阶段，直至降至无纤维化对照条件下的电流幅度阈值。结果表明，心肌的阈下兴奋特性受到心脏病理的复杂非线性影响。这些观察结果可能有助于我们理解冲动捕获特性，例如，对于异位灶起源的心律失常的发生以及心脏刺激电极的有效设计。
