Sobie E A, Tung L
Department of Biomedical Engineering, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
J Cardiovasc Electrophysiol. 1998 Jul;9(7):743-56. doi: 10.1111/j.1540-8167.1998.tb00961.x.
Even though the clinical advantage of biphasic defibrillation waveforms is well documented, the mechanisms that underlie this greater efficacy remain incompletely understood. It is established, though, that the response of relatively refractory cells to the shock is important in determining defibrillation success or failure. We used two computer models of an isolated ventricular cell to test the hypothesis that biphasic stimuli cause a more uniform response than the equivalent monophasic shocks, decreasing the likelihood that fibrillation will be reinduced.
Models of reciprocally polarized and uniformly polarized cells were used. Rapid pacing and elevated [K]o were simulated, and either 10-msec rectangular monophasic or 5-msec/5-msec symmetric biphasic stimuli were delivered in the relative refractory period. The effects of stimulus intensity and coupling interval on response duration and postshock transmembrane potential (Vm) were quantified for each waveform. With reciprocal polarization, biphasic stimuli caused a more uniform response than monophasic stimuli, resulting in fewer large gradients of Vm (only for shock strengths < or = 1.25x threshold vs < or = 2.125x threshold) and a smaller dispersion of repolarization (1611 msec2 vs 1835 msec2). The reverse was observed with uniform polarization: monophasic pulses caused a more uniform response than did biphasic stimuli.
These results show that the response of relatively refractory cardiac cells to biphasic stimuli is less dependent on the coupling interval and stimulus strength than the response to monophasic stimuli under conditions of reciprocal polarization. Because this may lead to fewer and smaller spatial gradients in Vm, these data support the hypothesis that biphasic defibrillation waveforms will be less likely to reinduce fibrillation. Further, published experimental results correlate to a greater degree with conditions of reciprocal polarization than of uniform polarization, providing indirect evidence that interactions between depolarized and hyperpolarized regions play a role in determining the effects of defibrillation shocks on cardiac tissue.
尽管双相除颤波形的临床优势已有充分记录，但这种更高疗效背后的机制仍未完全明了。不过，已确定相对不应期细胞对电击的反应在决定除颤成败方面很重要。我们使用两个孤立心室细胞的计算机模型来检验这一假设，即双相刺激比等效的单相电击能引起更均匀的反应，从而降低颤动再次诱发的可能性。
使用了相互极化和均匀极化细胞的模型。模拟快速起搏和升高的细胞外钾浓度([K]o)，并在相对不应期施加10毫秒的矩形单相或5毫秒/5毫秒的对称双相刺激。对每种波形量化刺激强度和耦合间期对反应持续时间和电击后跨膜电位(Vm)的影响。在相互极化情况下，双相刺激比单相刺激引起更均匀的反应，导致Vm的大梯度更少(仅对于电击强度≤1.25倍阈值与≤2.125倍阈值相比)以及复极化离散度更小(1611毫秒²对1835毫秒²)。在均匀极化情况下观察到相反结果：单相脉冲比双相刺激引起更均匀的反应。
这些结果表明，在相互极化条件下，相对不应期心脏细胞对双相刺激的反应比单相刺激的反应对耦合间期和刺激强度的依赖性更小。因为这可能导致Vm中的空间梯度更少、更小，这些数据支持双相除颤波形不太可能再次诱发颤动的假设。此外，已发表的实验结果与相互极化条件的相关性比均匀极化条件更大，间接证明去极化和超极化区域之间的相互作用在决定除颤电击对心脏组织的影响中起作用。
