Huang J, KenKnight B H, Walcott G P, Rollins D L, Smith W M, Ideker R E
Department of Medicine, University of Alabama at Birmingham, USA.
Circulation. 1997 Aug 19;96(4):1351-9. doi: 10.1161/01.cir.96.4.1351.
The upper limit of vulnerability (ULV) hypothesis for defibrillation predicts that maneuvers that alter the ULV will cause a similar alteration in the defibrillation threshold (DFT). The purpose of this study was to test this prediction by evaluating the effects of electrode polarity and waveform duration on the relationship between the DFT and the ULV.
Platinum spring electrodes were placed in the right ventricular (RV) apex and the superior vena cava in 12 pigs. Strength-duration curves were constructed for the DFT and ULV for each electrode polarity with monophasic waveforms (6 pigs) of different durations (2 to 14 ms) and biphasic truncated exponential waveforms (6 pigs) having phase 1 equal to 4 ms and phase 2 of different durations (0 to 10 ms). ULV data were gathered by scanning of the T wave. The ventricular pacing threshold (VPT) and ventricular fibrillation threshold (VFT) were also determined with these same waveforms. For the RV electrode as a cathode for monophasic and the first phase of biphasic stimuli, VPTs for the same waveform duration were significantly lower than for the configuration with the RV electrode as an anode. VFTs were not significantly different for the two electrode polarities with either monophasic or biphasic waveforms. The DFT changed in a fashion similar to the ULV with changes in electrode polarity and phase duration for both monophasic and biphasic waveforms. The ULV and DFT for each waveform duration for each polarity were strongly correlated (r=.83 to .99).
The almost identical changes in ULV and DFT with changes in electrode polarity and waveform duration provide new evidence to support the ULV hypothesis of defibrillation.
除颤的易损性上限（ULV）假说预测，改变ULV的操作将导致除颤阈值（DFT）发生类似改变。本研究的目的是通过评估电极极性和波形持续时间对DFT与ULV之间关系的影响来验证这一预测。
将铂弹簧电极置于12头猪的右心室（RV）心尖和上腔静脉。针对不同持续时间（2至14毫秒）的单相波形（6头猪）以及第一相等于4毫秒且第二相持续时间不同（0至10毫秒）的双相截断指数波形，构建每种电极极性下DFT和ULV的强度-持续时间曲线。通过扫描T波收集ULV数据。还用这些相同波形测定了心室起搏阈值（VPT）和心室颤动阈值（VFT）。对于单相刺激以及双相刺激的第一相，当RV电极作为阴极时，相同波形持续时间下的VPT显著低于RV电极作为阳极的配置。对于单相或双相波形，两种电极极性下的VFT无显著差异。对于单相和双相波形，随着电极极性和相位持续时间的变化，DFT的变化方式与ULV相似。每种极性下每个波形持续时间的ULV和DFT高度相关（r = 0.83至0.99）。
随着电极极性和波形持续时间的变化，ULV和DFT几乎发生相同的变化，这为支持除颤的ULV假说提供了新证据。
