Behrens S, Li C, Franz M R
Cardiology Division, Veteran Administration Medical Center, Washington, DC 20422, USA.
Pacing Clin Electrophysiol. 1997 Sep;20(9 Pt 1):2179-87. doi: 10.1111/j.1540-8159.1997.tb04234.x.
The upper limit of vulnerability (ULV) has been used in clinical studies to predict the DFT in patients with ICDs. Despite the ULV-DFT correlation, uncertainties about the optimal timing of the ULV determination remain. Previous studies using monophasic or biphasic shock waveforms reported differences in the ULV timing with respect to the electrocardiographic T wave. The purpose of this study was to directly compare the ULV timing for mono- versus biphasic T wave shocks. In ten isolated rabbit hearts, mono- and biphasic shocks were delivered randomly during the vulnerable window and at varying shock strengths to determine the ULV. The ULV timing was expressed as the coupling interval at the ULV, the myocardial repolarization state at the ULV measured by monophasic action potential recordings, and the relation between the ULV and the peak of the simultaneously recorded volume conducted T wave. The ULV for biphasic shocks occurred at longer coupling intervals than for monophasic shocks (188.0 +/- 9.5 ms vs 173.5 +/- 8.8 ms, P < 0.001). This resulted in a more repolarized myocardial state at the ULV for biphasic than for monophasic shocks (81.1% +/- 7.5% vs 66.9% +/- 9.0%, P = 0.002). The ULV for monophasic shocks occurred predominantly during the upslope of the T wave (8.0 +/- 9.7 ms before the peak of the T wave) whereas the ULV for biphasic shocks occurred at or after the peak of the T wave (5.9 +/- 9.3 ms after the peak of the T wave) (P < 0.001). Biphasic shocks delay the timing of the ULV as compared to monophasic shocks. This is important for the prediction of the DFT by ULV measurements.
易损性上限（ULV）已在临床研究中用于预测植入式心律转复除颤器（ICD）患者的除颤阈值（DFT）。尽管存在ULV与DFT的相关性，但关于确定ULV的最佳时机仍存在不确定性。先前使用单相或双相电击波形的研究报告了ULV时机在心电图T波方面的差异。本研究的目的是直接比较单相与双相T波电击的ULV时机。在10个离体兔心脏中，在易损窗口期间随机施加单相和双相电击，并改变电击强度以确定ULV。ULV时机表示为ULV时的耦合间期、通过单相动作电位记录测量的ULV时的心肌复极状态，以及ULV与同时记录的容积传导T波峰值之间的关系。双相电击的ULV发生在比单相电击更长的耦合间期（188.0±9.5毫秒对173.5±8.8毫秒，P<0.001）。这导致双相电击在ULV时的心肌复极状态比单相电击更复极（81.1%±7.5%对66.9%±9.0%，P = 0.002）。单相电击的ULV主要发生在T波的上升支（在T波峰值前8.0±9.7毫秒），而双相电击的ULV发生在T波峰值处或之后（在T波峰值后5.9±9.3毫秒）（P<0.001）。与单相电击相比，双相电击延迟了ULV的时机。这对于通过ULV测量预测DFT很重要。
