2相折返是触发于心肌动作电位时程2相吗？
Does phase 2 reentry really be triggered in phase 2 of action potential duration in myocardium?

2相折返被认为是在特定的条件下，心室肌动作电位时程差异过大，毗邻细胞分别处于高电位2相和可 兴奋间期，显著的电压梯度引起较强的电紧张性扩布，导致折返发生。但心脏异质性本身是相对宏观的概念，相 邻细胞间心肌异质性并不明显，其动作电位时程的差异也不可能过大，邻近细胞间能否激动既取决于细胞跨壁电 压差，也取决于心肌细胞离子通道即时功能状态。而心室肌动作电位时程3相变化幅度大，且存在超常期，易于 激动，相邻细胞间较短的动作电位时程差异即为心律失常的发生提供了可能。因此，2相折返触发高电位可能更 多在于心室肌动作电位3相，而非2相。
Phase 2 reentry is considered to happen in phase 2 of action potential duration in myocardium when the adjacent ventricular cells are respectively in a high potential state and excitable period so that the high voltage gradient leads to stronger electrotonic spread. However, the heterogeneity of the heart is a relative concept macroscopically. Microscopically, the heterogeneity between the adjacent cells is not obvious, and the difference in the action potential duration is not remarkable. Whether the myocardial cells can be excited or not depends on both the voltage difference among the cytomembranes and the real-time function state of ion channels. As for the phase 3 of action potential duration in myocardium, large varied amplitude of voltage gradient happens in this period, and it includes supernormal phase, which makes myocardial cells excited easily. In the phase 3, the minor differences in the action potential duration between adjacent cells can offer the conditions for arrhythmia development. Therefore, the phase 2 reentry is triggered by high potential in phase 3 of action potential duration in myocardium rather than in phase 2