Jones J L, Jones R E
Crit Care Med. 1980 Mar;8(3):167-71. doi: 10.1097/00003246-198003000-00016.
Clinical and experimental information exists in the literature which suggests that defibrillation with higher energies than are required results in a decreased percentage of success. Previous work in this laboratory which showed the occurrence of postshock arrhythmias caused by a prolonged depolarization of the cell membrane in myocardial cells in vitro, led to the hypothesis that the decreased percent success at high energies in vivo might be due to the development of similar shock-induced arrhythmias which could immediately refibrillate the heart. The purpose of these experiments was to test this hypothesis. Myocardial cells grown in vitro were subjected to rectangular wave electric field stimulation of varying intensity and duration. Postshock arrhythmias were evaluated using a photovoltaic cell mounted on a closed-circuit television monitor. The photocell converted the change in light intensity produced as the cell contracted to an electrical signal which was read out on a strip chart. Strength-duration curves were formed both for excitation (production of a single extrasystole) and for specific degrees of arrhythmia. These were compared with strength-duration curves obtained for a specific percent success defibrillation in vivo by other investigators. These experiments showed a close similarity between the in vivo and in vitro data, thus, strengthening the hypothesis that decreasing percentage of success of defibrillation with increasing intensity at high energies is due to secondary arrhythmias produced by the shock. The experiments further suggest that in vitro myocardial cells are a valuable screening system for determining waveforms which maximize the ratio between the voltages producing postshock arrhythmias and those producing excitation (defibrillation). This ratio, defined as the "safety factor" of the waveform, varies with the duration of the rectangular wave. Durations having high safety factors can produce defibrillation with a high percentage of success; however, waveforms having low safety factors make it impossible to achieve a high percentage of success defibrillation with any applied voltage. This information suggests that the minimum voltage required for successful defibrillation always be used and that defibrillators be produced with waveforms which maximize the safety factor.
文献中存在临床和实验信息，表明使用高于所需能量进行除颤会导致成功百分比降低。本实验室先前的工作表明，体外心肌细胞中细胞膜长时间去极化会导致电击后心律失常的发生，由此提出假说：体内高能量下成功百分比降低可能是由于类似的电击诱发心律失常的发展，这种心律失常可立即使心脏再次发生纤颤。这些实验的目的是检验这一假说。体外培养的心肌细胞受到不同强度和持续时间的矩形波电场刺激。使用安装在闭路电视监视器上的光电管评估电击后心律失常。光电管将细胞收缩时产生的光强度变化转换为电信号，该信号在带状图表上读出。形成了激发（产生单个期外收缩）和特定程度心律失常的强度-持续时间曲线。将这些曲线与其他研究者在体内特定除颤成功百分比下获得的强度-持续时间曲线进行比较。这些实验表明体内和体外数据非常相似，因此，强化了以下假说：高能量下随着强度增加除颤成功百分比降低是由于电击产生的继发性心律失常。实验进一步表明，体外心肌细胞是一种有价值的筛选系统，用于确定能使产生电击后心律失常的电压与产生激发（除颤）的电压之比最大化的波形。这个比率被定义为波形的“安全系数”，它随矩形波的持续时间而变化。具有高安全系数的持续时间可产生高百分比成功的除颤；然而，具有低安全系数的波形使得在任何施加电压下都不可能实现高百分比成功除颤。这些信息表明应始终使用成功除颤所需的最小电压，并生产具有能使安全系数最大化波形的除颤器。
