Delgado C, Steinhaus B, Delmar M, Chialvo D R, Jalife J
Department of Pharmacology, State University of New York Health Science Center, Syracuse 13210.
Circ Res. 1990 Jul;67(1):97-110. doi: 10.1161/01.res.67.1.97.
Computer simulations and isolated tissue experiments were used to characterize the relation between excitability and margin of safety for propagation in anisotropic ventricular myocardium. Longitudinal, uniform transverse, and nonuniform transverse tissue directions were modeled in a one-dimensional Beeler-Reuter based cable. Stimulation threshold was smallest in the nonuniform transverse direction. The safety factor for propagation was determined in the model as the total axial charge that was available for depolarizing downstream tissue divided by the threshold charge that was just sufficient for continued propagation and was largest in the longitudinal direction. The strength-interval plot for the junction between simulated longitudinal and nonuniform transverse directions identified a range of stimulus strengths and intervals that resulted in nonuniform transverse but not longitudinal propagation. When high values of transverse resistance were used, higher stimulus strengths during premature stimulation resulted in longitudinal but not nonuniform transverse propagation. The experimental strength interval plots from 17 L-shaped preparations of isolated sheep epicardial muscles had similar characteristics. In nine additional L-shaped tissue experiments, changing extracellular K+ concentrations from 4 to 20 mM resulted in progressive membrane depolarization and conduction impairment in both directions. However, in eight of nine experiments, complete block occurred first in the transverse direction. In one experiment, block was simultaneous in both directions. We conclude that, under normal conditions, threshold requirements for active propagation are lower for transverse than for longitudinal propagation. In addition, when active membrane properties are impaired, the safety factor for propagation is larger in the direction along the longitudinal axis of the cells.
利用计算机模拟和离体组织实验来表征各向异性心室心肌中兴奋性与传播安全边际之间的关系。在基于一维Beeler-Reuter的电缆模型中模拟了纵向、均匀横向和非均匀横向的组织方向。非均匀横向方向的刺激阈值最小。在该模型中，传播安全因子被确定为可用于使下游组织去极化的总轴向电荷除以刚好足以维持传播的阈值电荷，且在纵向方向上最大。模拟的纵向和非均匀横向方向之间连接处的强度-间期图确定了一系列刺激强度和间期，其导致非均匀横向而非纵向传播。当使用高横向电阻值时，过早刺激期间较高的刺激强度导致纵向而非非均匀横向传播。来自17个分离的绵羊心外膜肌肉L形标本的实验强度-间期图具有相似的特征。在另外9个L形组织实验中，将细胞外钾离子浓度从4 mM改变为20 mM导致两个方向上的渐进性膜去极化和传导障碍。然而，在9个实验中的8个中，完全传导阻滞首先发生在横向方向。在1个实验中，两个方向同时发生阻滞。我们得出结论，在正常条件下，主动传播的阈值要求横向低于纵向。此外，当主动膜特性受损时，沿细胞纵轴方向的传播安全因子更大。
