Huang J, KenKnight B H, Walcott G P, Walker R G, Smith W M, Ideker R E
Department of Medicine, University of Alabama at Birmingham, USA.
J Cardiovasc Electrophysiol. 1997 Feb;8(2):161-71. doi: 10.1111/j.1540-8167.1997.tb00778.x.
To test the hypothesis that the effect of shock polarity on defibrillation depends on waveform duration, this study determined strength-duration defibrillation curves of monophasic and biphasic truncated exponential waveforms for both polarities.
Defibrillation thresholds (DFTs) were obtained in 32 pigs for catheter electrodes in the right ventricle (RV) and superior vena cava (SVC) using a modified Purdue technique. Both electrode polarities were tested in five different protocols. In part 1, DFTs were determined with 1- to 14-msec monophasic waveforms. In parts 2, 3, and 4, DFTs were determined with two different sizes of SVC electrodes for biphasic waveforms with a phase 1 of 4 or 6 msec and a phase 2 ranging from 1 to 10 msec. In part 5, DFTs were tested for monophasic waveforms ranging from 2 to 11 msec and for biphasic waveforms with a phase 1 duration corresponding to each monophasic waveform and a phase 2 held constant at 1 msec. Mean DFTs for monophasic waveforms were significantly lower when the RV electrode was an anode than when it was a cathode for waveform durations > or = 3 msec. For biphasic waveforms in which phase 2 was < or = phase 1 in duration, no significant difference in mean DFT was observed when polarity was reversed. Even a phase 2 as short as 1 msec could eliminate the DFT difference between polarities observed with monophasic shocks. When phase 2 was > or = 2 msec longer than phase 1, polarity did affect the DFT of biphasic waveforms; it affected the DFT similarly to a monophasic waveform of the same polarity as phase 2. Phase 1 duration and electrode size also affected the difference in DFT produced by changing the electrode polarity.
For phase durations most commonly used clinically because of their low DFTs, reversing polarity changed defibrillation efficacy for monophasic but not biphasic shocks. For inefficient biphasic waveforms with phase 2 > or = 2 msec longer than phase 1, the DFT was lower when the RV electrode was an anode during phase 2, similar to the polarity difference for monophasic waveforms, suggesting that a long second phase of biphasic waveforms defibrillates in a similar fashion to monophasic waveforms.
为了验证电击极性对除颤的影响取决于波形持续时间这一假设，本研究确定了两种极性的单相和双相截断指数波形的强度-时间除颤曲线。
采用改良的普渡技术，在32头猪身上获取右心室（RV）和上腔静脉（SVC）中导管电极的除颤阈值（DFT）。两种电极极性在五种不同方案中进行测试。在第1部分，用1至14毫秒的单相波形确定DFT。在第2、3和4部分，用两种不同尺寸的SVC电极确定双相波形的DFT，其第1相为4或6毫秒，第2相范围为1至10毫秒。在第5部分，测试2至11毫秒的单相波形以及第1相持续时间与每个单相波形对应且第2相保持在1毫秒不变的双相波形的DFT。当波形持续时间≥3毫秒时，RV电极作为阳极时单相波形的平均DFT显著低于其作为阴极时。对于第2相持续时间≤第1相的双相波形，极性反转时平均DFT无显著差异。即使第2相短至1毫秒也能消除单相电击时观察到的极性之间的DFT差异。当第2相比第1相长≥2毫秒时，极性确实会影响双相波形的DFT；其对DFT的影响类似于与第2相同极性的单相波形。第1相持续时间和电极尺寸也会影响改变电极极性所产生的DFT差异。
对于临床上因DFT低而最常用的相持续时间，极性反转会改变单相电击的除颤效果，但不会改变双相电击的除颤效果。对于第2相比第1相长≥2毫秒的低效双相波形，当第2相期间RV电极作为阳极时DFT较低，这与单相波形的极性差异相似，表明双相波形的长第二相以类似于单相波形的方式进行除颤。
