Souza J J, Malkin R A, Ideker R E
Department of Medicine, University of North Carolina Hospitals, Chapel Hill.
Circulation. 1995 Feb 15;91(4):1247-52. doi: 10.1161/01.cir.91.4.1247.
An upper limit to the strength of shocks that induce fibrillation during the vulnerable period, the upper limit of vulnerability (ULV), has been shown to exist in both humans and animals. The purpose of this study was to compare ULV and defibrillation (DF) probability of success curves for a clinically useful nonthoracotomy lead system.
Sixteen pentobarbital-anesthetized pigs were studied. Single-capacitor biphasic waveforms with both phases 5.5 ms in duration were used for ULV and DF testing. A right ventricular catheter electrode served as first-phase cathode and a superior vena cava catheter electrode coupled with a cutaneous R2 patch electrode served as common first-phase anodes. A pacing catheter was placed in the right ventricle to deliver a train of 15 S1 stimuli at a pacing interval of 250 to 300 ms. A ULV shock was delivered on the peak of the T wave as measured from the surface ECG; if ventricular fibrillation was induced, a DF shock was delivered after 10 seconds of fibrillation. Shock voltages were determined by an up-down protocol. Ventricular fibrillation was induced an average of 53 times in each animal. The composite data indicate that below V97, that is, the voltage that leaves the animal in normal sinus rhythm 97% of the time when delivered on the peak of the T wave or the voltage that defibrillates 97% of the time, ULV is lower than DF. ULV and DF became significantly correlated at V80 and maximally correlated at V97. Even at V97, however, ULV and DF differed by more than 100 V in 2 of the 16 animals.
ULV approximately equaled DF at V97. This is fortunate because it is clinically important to set the device voltage at the uppermost portion of the probability of success curve. Estimating DF V97 from ULV V97 would reduce the number of fibrillation inductions needed to establish defibrillation shock strength requirements. However, the large difference between ULV V97 and DF in a few animals indicates that further improvement and testing of algorithms for determining ULV V97 must be developed before the technique is used clinically.
在易损期诱发纤颤的电击强度存在上限，即易损性上限（ULV），这在人类和动物中均已得到证实。本研究的目的是比较临床上有用的非开胸导联系统的ULV和除颤（DF）成功概率曲线。
对16只戊巴比妥麻醉的猪进行了研究。ULV和DF测试均使用单相持续时间为5.5毫秒的双相波形。右心室导管电极作为第一相阴极，上腔静脉导管电极与皮肤R2贴片电极作为共同的第一相阳极。将起搏导管置于右心室，以250至300毫秒的起搏间期发放一串15次的S1刺激。在体表心电图测量的T波峰值处发放ULV电击；如果诱发了心室纤颤，则在纤颤10秒后发放DF电击。电击电压通过上下法确定。每只动物平均诱发心室纤颤53次。综合数据表明，在V97以下，即在T波峰值发放时使动物97%的时间处于正常窦性心律的电压或97%的时间能除颤的电压，ULV低于DF。ULV和DF在V80时显著相关，在V97时相关性最大。然而，即使在V97时，16只动物中有2只的ULV和DF相差超过100伏。
在V97时ULV约等于DF。这很幸运，因为将设备电压设置在成功概率曲线的最上部在临床上很重要。从ULV V97估计DF V97将减少确定除颤电击强度要求所需的纤颤诱发次数。然而，少数动物的ULV V97和DF之间的巨大差异表明，在该技术临床应用之前，必须进一步改进和测试用于确定ULV V97的算法。
