Hwang C, Swerdlow C D, Kass R M, Gang E S, Mandel W J, Peter C T, Chen P S
Division of Cardiology, Cedars-Sinai Medical Center, Los Angeles, CA 90048.
Circulation. 1994 Nov;90(5):2308-14. doi: 10.1161/01.cir.90.5.2308.
The upper limit of vulnerability is the stimulus strength above which electrical stimulation cannot induce ventricular fibrillation even when the stimulus occurs during the vulnerable period of the cardiac cycle. The purpose of this study was to test the hypothesis that the upper limit of vulnerability can accurately predict the defibrillation threshold in patients undergoing implantable cardioverter-defibrillator (ICD) implantation using nonthoracotomy lead systems.
We studied 77 patients at the time of ICD implantation. Multiple endocardial-endocardial and endocardial-subcutaneous shock pathways were used. Two different protocols were used to test the upper limit of vulnerability. In protocol 1 (n = 17), the upper limit of vulnerability was tested with two shocks on the peak or the up-slope of the T wave of paced rhythm. The shocks were given randomly either at the peak and 20 milliseconds before the peak of T wave (n = 7) or at 20 and 40 milliseconds before the peak of T wave (n = 10). In protocol 2 (n = 60), the upper limit of vulnerability was tested with three shocks delivered at 0, 20, and 40 milliseconds before the peak of the T wave. The weakest shock that failed to induce ventricular fibrillation by a 5-J step-down or step-up method was defined as the upper limit of vulnerability. The defibrillation threshold was also determined by a 5-J step-down or step-up method. In protocol 1, the upper limit of vulnerability (9 +/- 6 J) was significantly lower than the defibrillation threshold (13 +/- 7 J) with a correlation coefficient of .87 and P < .001. In protocol 2, the upper limit of vulnerability (13 +/- 6 J) was not significantly different from the defibrillation threshold (13 +/- 6 J) with a correlation coefficient of .85 and P < .001. In 45 of the 60 patients, the upper limit of vulnerability was < or = 15 J; all had a defibrillation threshold of < or = 20 J. In 51 of the 60 patients, the upper limit of vulnerability was within 5 J of the defibrillation threshold. The upper limit of vulnerability overestimated the defibrillation threshold by > 10 J in 8 patients and underestimated the defibrillation threshold by > 10 J in only 1 patient. The overestimation and underestimation occurred only in patients with the upper limit of vulnerability > 15 J.
When tested with three shocks on and before the peak of the T wave, the upper limit of vulnerability accurately predicted the defibrillation threshold in patients undergoing ICD implantation using nonthoracotomy lead systems. This method required either one or no episodes of ventricular fibrillation in most patients.
易损性上限是指即使刺激发生在心动周期的易损期，高于该强度的电刺激也不能诱发心室颤动。本研究的目的是验证以下假设：使用非开胸导联系统进行植入式心律转复除颤器（ICD）植入的患者，易损性上限能够准确预测除颤阈值。
我们在77例患者进行ICD植入时对其进行了研究。采用了多条心内膜-心内膜和心内膜-皮下电击通路。使用两种不同方案测试易损性上限。在方案1（n = 17）中，在起搏心律的T波峰值或上升支上给予两次电击来测试易损性上限。电击随机在T波峰值以及T波峰值前20毫秒（n = 7）或T波峰值前20和40毫秒（n = 10）给予。在方案2（n = 60）中，在T波峰值前0、20和40毫秒给予三次电击来测试易损性上限。通过5焦耳递减或递增方法未能诱发心室颤动的最弱电击被定义为易损性上限。除颤阈值也通过5焦耳递减或递增方法确定。在方案1中，易损性上限（9±6焦耳）显著低于除颤阈值（13±7焦耳），相关系数为0.87，P<0.001。在方案2中，易损性上限（13±6焦耳）与除颤阈值（13±6焦耳）无显著差异，相关系数为0.85，P<0.001。在60例患者中的45例中，易损性上限≤15焦耳；所有患者的除颤阈值均≤20焦耳。在60例患者中的51例中，易损性上限与除颤阈值相差在5焦耳以内。8例患者的易损性上限高估除颤阈值超过10焦耳，仅1例患者的易损性上限低估除颤阈值超过10焦耳。高估和低估仅发生在易损性上限>15焦耳的患者中。
当在T波峰值及其之前给予三次电击进行测试时，易损性上限能够准确预测使用非开胸导联系统进行ICD植入患者的除颤阈值。该方法在大多数患者中只需一次或无需诱发心室颤动发作。
