Deale O C, Lerman B B
Department of Medicine, New York Hospital-Cornell University Medical College, NY 10021.
Circ Res. 1990 Dec;67(6):1405-19. doi: 10.1161/01.res.67.6.1405.
To achieve transcardiac threshold current during transthoracic defibrillation, a considerably larger current must be delivered to the thorax to compensate for the shunting effect of the lungs, the thoracic cage, and other elements of the torso. This shunting effect is thus an important determinant of transthoracic defibrillation threshold and can be quantified by the transcardiac current fraction (FC, the ratio of transcardiac to transthoracic threshold currents). Previous estimates of FC have ranged from as low as 3% to as high as 45%. The purpose of of this study was to quantify both FC and the major intrathoracic current pathways. Transthoracic and intrathoracic voltages and currents were simultaneously measured during high-voltage transthoracic shocks in 20 dogs. With correction factors determined from another set of 12 dogs, these raw data were corrected to compensate for field distortion caused by the presence of the intrathoracic electrodes, and the adjusted data were fit to a resistive network model. The results showed that 82% of the transthoracic current was shunted by the thoracic cage, while 14% was shunted by the lungs. The remaining 4% (FC) is the portion that passed through the heart. There was good agreement between the two independent methods used to calculate FC. Analysis based on the model indicated that FC was 3.7%, whereas FC determined by direct measurement with calibrated electrodes was 4.2%. Therefore, the results of this study, in contrast to earlier estimates of FC, show that defibrillation in dogs is achieved by only 4% of the total transthoracic current.
在进行经胸除颤时，为了达到经心内的阈值电流，必须向胸部输送大得多的电流，以补偿肺、胸廓和躯干其他部分的分流效应。因此，这种分流效应是经胸除颤阈值的一个重要决定因素，并且可以通过经心内电流分数（FC，即经心内阈值电流与经胸阈值电流之比）来量化。先前对FC的估计范围低至3% 高至45%。本研究的目的是量化FC以及主要的胸内电流通路。在20只犬进行高压经胸电击期间，同时测量经胸和胸内的电压及电流。利用从另外12只犬获得的校正因子，对这些原始数据进行校正，以补偿胸内电极存在所导致的场畸变，并且将校正后的数据拟合到一个电阻网络模型。结果显示，82% 的经胸电流被胸廓分流，而14% 被肺分流。其余4%（FC）是通过心脏的部分。用于计算FC的两种独立方法之间具有良好的一致性。基于模型的分析表明，FC为3.7%，而通过校准电极直接测量确定的FC为4.2%。因此，与早期对FC的估计不同，本研究结果表明，犬只的除颤仅通过4% 的总经胸电流即可实现。
