Hsia P W, Mahmud R
Department of Medicine, East Carolina University School of Medicine, Greenville, North Carolina 27858-4354.
Pacing Clin Electrophysiol. 1990 Oct;13(10):1326-42. doi: 10.1111/j.1540-8159.1990.tb02031.x.
The sigmoidal dose-response curve (percent success vs shock energy) suggests a probabilistic nature of defibrillation. The mechanism is still largely unknown, however, random variation in the excitable state during ventricular fibrillation (VF) is suspected. A canine defibrillation study was designed to determine whether random variation in absolute VF voltage (AVFV) (a crude marker of number of excitable cells) was related to success of defibrillation, using a DC shock successful at the 50% level. The results were: (a) transmyocardial resistance (73.4 +/- 1.4 vs 73.6 +/- 1.5 ohms) and delivered energy (6.1 +/- 1.2 vs 6.2 +/- 1.2 joules) were similar; however, (b) AVFV 2 msec prior to DC shock was greater for successful as compared to unsuccessful attempts (0.5 +/- 0.1 vs 0.3 +/- 0.0 mV, P less than 0.01). A mathematical model was subsequently developed based on fluctuation in the number of excitable cells. Variation in the state of excitability resulted in a cyclic window potentially vulnerable to defibrillation. The vulnerable window occurred at a point when the number of excitable cells was low, i.e., a higher state of total depolarization, which was in agreement with the experimental finding. For a given VF pattern, duration of the vulnerable window was regulated by the shock energy. A larger shock energy generated a wider vulnerable window and, in turn, a higher success rate. Finally, the sigmoidal dose-response curve of defibrillation was theoretically constructed by calculating the variable chances of a random DC shock occurring either in a vulnerable window or elsewhere during VF. It is concluded that a vulnerable window susceptible to defibrillation can be demonstrated in the early stages (10 sec) of VF. The mathematical model provides a theoretical basis for the vulnerable window and helps elucidate the probabilistic nature of defibrillation.
S形剂量-反应曲线（成功百分比与电击能量）表明除颤具有概率性本质。然而，其机制仍很大程度上未知，不过怀疑心室颤动（VF）期间可兴奋状态存在随机变化。设计了一项犬类除颤研究，以确定绝对VF电压（AVFV）（可兴奋细胞数量的粗略指标）的随机变化是否与除颤成功相关，使用在50%水平成功的直流电击。结果如下：（a）跨心肌电阻（73.4±1.4对73.6±1.5欧姆）和输送能量（6.1±1.2对6.2±1.2焦耳）相似；然而，（b）与不成功的尝试相比，成功的直流电击前2毫秒的AVFV更大（0.5±0.1对0.3±0.0毫伏，P<0.01）。随后基于可兴奋细胞数量的波动建立了一个数学模型。兴奋性状态的变化导致了一个可能易受除颤影响的循环窗口。易损窗口出现在可兴奋细胞数量较低时，即更高的总去极化状态，这与实验结果一致。对于给定的VF模式，易损窗口的持续时间由电击能量调节。更大的电击能量产生更宽的易损窗口，进而成功率更高。最后，通过计算随机直流电击在VF期间出现在易损窗口或其他地方的可变概率，从理论上构建了除颤的S形剂量-反应曲线。结论是，在VF的早期阶段（10秒）可以证明存在易受除颤影响的易损窗口。该数学模型为易损窗口提供了理论基础，并有助于阐明除颤的概率性本质。
