CARDIAC CURRENT DENSITY: DETERMINANT OF DEFIBRILLATION

高能量直流电击胸部的应用 患者的目的是将心室 房颤转为血流动力学稳定的室上性 在过去的30年里，节律已经被临床应用。 然而，这些电击可导致MB-肌酸激酶释放 以及明显的心肌坏死。 目前的能量水平用于 除颤是经验性的，并且是高度可变的。 在某种程度上， 是由于量化电剂量的惯例， 除颤的能量单位;然而，电流，而不是 能量使心脏除颤。 在老年人到个人 优化电击的强度，这是必要的 以表征输送到 实际上穿过心脏的胸腔， 使心脏舒张所需的跨心肌电流，以及 改变这些变量的因素。 关于这一点的假设 研究表明：1）跨心肌电流依赖于 经胸结构的相对阻力，2） 胸部和胸内结构可以被建模为3 并联可变电阻，可以预测有效的 从经胸电击传递的跨心肌电流， 和3）除颤依赖于实现最佳的 在心脏的细胞团中的电流密度。 这项建议 将测量跨心肌电流， 量与输送到胸腔的总电流之比。 电解质电流密度将在 闭胸狗的三轴电极系统，将 在4.0 cm 2的空间内测量三维电流密度 12个同时左心室部位的区域。 的 最小心肌电流密度 将确定除颤。 的相关性 电流密度阈值和前瞻性测量受试者 可以预测最佳电气性能的相关参数 将检查每个人的脉搏。 的信息 从这项研究中获得的信息应该进一步阐明 除颤生理学，因此提供了基础 更先进的方法来前瞻性地确定 最小的能量（或电流）， 一个单独的主题。

The practive of delivering high energy DC shocks to the thorax of patients for the purpose of converting ventricular fibrillation to a hemodynamically stable supraventricular rhythm has been clinically employed for the past 30 years. These shocks, however, can result in MB-creatine kinase release and frank myocardial necrosis. Present energy levels used for defibrillation are empiric and highly variable. This, in part, is due to the convention of quantifying the electrical dose for defibrillation in units of energy; however, current rather than energy defibrillates the heart. In older to individually optimize the magnitude of the electrical shock, it is necessary to characterize the percent of total current delivered to the thorax that actually traverses the heart, the requisite transmyocardial current needed to defibrillate the heart, and the factors that alter these variables. The hypotheses of this study are that: 1) transmyocardial current flow is dependent on the relative resistances of the transthoracic structures, 2) the thorax and intrathoracic structures can be modeled as 3 parallel, variable resistors that can predict the effective transmyocardial current delivered from transthoracic shocks, and 3) defibrillation is dependent on achieving on optimal current density in a ceitical mass of the heart. This proposal will measure transmyocardial current flow and compare this quantity to the total current delivered to the thorax. Transmyocardial current density will be determined in closed-chest dogs by a triaxial electrode system that will measure current density in three dimensions over a 4.0 cm2 region from 12 simultaneous left ventricular sites. The minimal myocardial current density necessary to achieve defibrillation will be determined. The correlation between current density thresholds and prospectively measured subject related parameters that may predict the optimal electrical pulse for each individual will be examined. The information obtained from this study should further elucidate the physiology of defibrillation and therefore provide the basis for more sophisticated methods in prospectively determining the minimal amount of energy (or current) required to defibrillate an individual subject.