Swerdlow C D, Kass R M, O'Connor M E, Chen P S
Division of Cardiology, Cedars-Sinai Medical Center, Los Angeles, California, USA.
J Cardiovasc Electrophysiol. 1998 Apr;9(4):339-49. doi: 10.1111/j.1540-8167.1998.tb00922.x.
The upper limit of vulnerability (ULV) correlates with the defibrillation threshold (DFT). The ULV can be determined with a single episode of ventricular fibrillation and is more reproducible than the single-point DFT. The critical-point hypothesis of defibrillation predicts that the relation between the ULV and the DFT is independent of shock waveform. The principal goal of this study was to test this prediction.
We studied 45 patients at implants of pectoral cardioverter defibrillators. In the monophasic-biphasic group (n = 15), DFT and ULV were determined for monophasic and biphasic pulses from a 120-microF capacitor. In the 60- to 110-microF group (n = 30), DFT and ULV were compared for a clinically used 110-microF waveform and a novel 60-microF waveform with 70% phase 1 tilt and 7-msec phase 2 duration. In the monophasic-biphasic group, all measures of ULV and DFT were greater for monophasic than biphasic waveforms (P < 0.0001). In the 60- to 110-microF group, the current and voltage at the ULV and DFT were higher for the 60-microF waveform (P < 0.0001), but stored energy was lower (ULV 17%, P < 0.0001; DFT 19%, P = 0.03). There was a close correlation between ULV and DFT for both the monophasic-biphasic group (monophasic r2 = 0.75, P < 0.001; biphasic r2 = 0.82, P < 0.001) and the 60- to 110-microF group (60 microF r2 = 0.81 P < 0.001; 110 microF r2 = 0.75, P < 0.001). The ratio of ULV to DFT was not significantly different for monophasic versus biphasic pulses (1.17 +/- 0.12 vs 1.14 +/- 0.19, P = 0.19) or 60-microF versus 110-microF pulses (1.15 +/- 0.16 vs 1.11 +/- 0.14, P = 0.82). The slopes of the ULV versus DFT regression lines also were not significantly different (monophasic vs biphasic pulses, P = 0.46; 60-microF vs 110-microF pulses, P = 0.99). The sample sizes required to detect the observed differences between experimental conditions (P < 0.05) were 4 for ULV versus 6 for DFT in the monophasic-biphasic group (95% power) and 11 for ULV versus 31 for DFT in the 60- to 110-microF group (75% power).
The relation between ULV and DFT is independent of shock waveform. Fewer patients are required to detect a moderate difference in efficacy of defibrillation waveforms by ULV than by DFT. A small-capacitor biphasic waveform with a long second phase defibrillates with lower stored energy than a clinically used waveform.
易损性上限（ULV）与除颤阈值（DFT）相关。ULV可通过单次室颤发作来确定，且比单点DFT更具可重复性。除颤的临界点假说预测，ULV与DFT之间的关系与电击波形无关。本研究的主要目的是验证这一预测。
我们对45例植入胸内心脏转复除颤器的患者进行了研究。在单相-双相组（n = 15）中，测定了来自120微法电容器的单相和双相脉冲的DFT和ULV。在60至110微法组（n = 30）中，比较了临床使用的110微法波形和新型60微法波形（第1相倾斜70%，第2相持续时间7毫秒）的DFT和ULV。在单相-双相组中，单相波形的所有ULV和DFT测量值均高于双相波形（P < 0.0001）。在60至110微法组中，60微法波形在ULV和DFT时的电流和电压更高（P < 0.0001），但存储能量更低（ULV时低17%，P < 0.0001；DFT时低19%，P = 0.03）。单相-双相组（单相r2 = 0.75，P < 0.001；双相r2 = 0.82，P < 0.001）和60至110微法组（60微法r2 = 0.81，P < 0.001；110微法r2 = 0.75，P < 0.001）中，ULV与DFT之间均存在密切相关性。单相与双相脉冲（1.17±0.12对1.14±0.19，P = 0.19）或60微法与110微法脉冲（1.15±0.16对1.11±0.14，P = 0.82）的ULV与DFT之比无显著差异。ULV与DFT回归线的斜率也无显著差异（单相与双相脉冲，P = 0.46；60微法与110微法脉冲，P = 0.99）。在单相-双相组中，检测实验条件之间观察到的差异（P < 0.05）所需的样本量，ULV为4例，DFT为6例（95%检验效能）；在60至110微法组中，ULV为11例，DFT为31例（75%检验效能）。
ULV与DFT之间的关系与电击波形无关。与DFT相比，通过ULV检测除颤波形疗效的适度差异所需的患者更少。具有长第二相的小电容器双相波形以低于临床使用波形的存储能量进行除颤。
