de Oliveira Pedro Xavier, Bassani Rosana Almada, Bassani José Wilson Magalhães
Departamento de Engenharia Biomédica, Faculdade de Engenharia Elétrica e de Computacão (FEEC), Universidade Estadual de Campinas, 13084-971 Campinas, São Paulo, Brazil.
IEEE Trans Biomed Eng. 2008 Nov;55(11):2635-42. doi: 10.1109/TBME.2008.2001135.
Defibrillator-type shocks may cause electric and contractile dysfunction. In this study, we determined the relationship between probability of lethal injury and electric field intensity (E in isolated rat ventricular myocytes, with emphasis on field orientation and stimulus waveform. This relationship was sigmoidal with irreversible injury for E > 50 V/cm . During both threshold and lethal stimulation, cells were twofold more sensitive to the field when it was applied longitudinally (versus transversally) to the cell major axis. For a given E, the estimated maximum variation of transmembrane potential (Delta V(max)) was greater for longitudinal stimuli, which might account for the greater sensitivity to the field. Cell death, however, occurred at lower maximum Delta V(max) values for transversal shocks. This might be explained by a less steep spatial decay of transmembrane potential predicted for transversal stimulation, which would possibly result in occurrence of electroporation in a larger membrane area. For the same stimulus duration, cells were less sensitive to field-induced injury when shocks were biphasic (versus monophasic). Ours results indicate that, although significant myocyte death may occur in the E range expected during clinical defibrillation, biphasic shocks are less likely to produce irreversible cell injury.
除颤器类型的电击可能会导致电功能和收缩功能障碍。在本研究中，我们确定了在离体大鼠心室肌细胞中致死性损伤概率与电场强度（E）之间的关系，重点关注场的方向和刺激波形。这种关系呈S形，当E>50 V/cm时会出现不可逆损伤。在阈值刺激和致死性刺激期间，当电场沿细胞长轴纵向施加（相对于横向）时，细胞对电场的敏感性要高两倍。对于给定的E，纵向刺激时跨膜电位的估计最大变化（ΔV(max)）更大，这可能解释了对电场更高的敏感性。然而，横向电击时细胞死亡发生在较低的最大ΔV(max)值。这可能是由于横向刺激时预测的跨膜电位空间衰减较平缓，这可能会导致更大膜面积发生电穿孔。对于相同的刺激持续时间，当电击为双相（相对于单相）时，细胞对场致损伤的敏感性较低。我们的结果表明，尽管在临床除颤预期的E范围内可能会发生显著的心肌细胞死亡，但双相电击产生不可逆细胞损伤的可能性较小。
