Block M, Hammel D, Böcker D, Borggrefe M, Seifert T, Fastenrath C, Scheld H H, Breithardt G
Department of Cardiology/Angiology, Hospital of the Westfälishce Wilhelms-University of Münster, Germany.
J Cardiovasc Electrophysiol. 1995 May;6(5):333-42. doi: 10.1111/j.1540-8167.1995.tb00405.x.
The size of current implantable cardioverter defibrillators (ICD) is still large in comparison to pacemakers and thus not convenient for pectoral implantation. One way to reduce ICD size is to defibrillate with smaller capacitors. A trade-off exists, however, since smaller capacitors may generate a lower maximum energy output.
In a prospective randomized cross-over study, the step-down defibrillation threshold (DFT) of an experimental 90-microF biphasic waveform was compared to a standard 125-microF biphasic waveform. The 90-microF capacitor delivered the same energy faster and with a higher peak voltage but provided only a maximum energy output of 20 instead of 34 J. DFTs were determined intraoperatively in 30 patients randomized to receive either an endocardial (n = 15) or an endocardial-subcutaneous array (n = 15) defibrillation lead system. Independent of the lead system used, energy requirements did not differ at DFT for the experimental and the standard waveforms (10.3 +/- 4.1 and 9.5 +/- 4.9 J, respectively), but peak voltages were higher for the experimental waveform than for the standard waveform (411 +/- 80 and 325 +/- 81 V, respectively). For the experimental waveform the DFT w as 10 J or less using an endocardial lead-alone system in 10 (67%) of 15 patients and in 12 (80%) of 15 patients using an endocardial-subcutaneous array lead system.
A shorter duration waveform delivered by smaller capacitors does not increase defibrillation energy requirements and might reduce device size. However, the smaller capacitance reduces the maximum energy output. If a 10-J safety margin between DFT and maximum energy output of the ICD is required, only a subgroup of patients will benefit from 90-microF ICDs with DFTs feasible using current defibrillation lead systems.
与起搏器相比，目前植入式心脏复律除颤器（ICD）的体积仍然较大，因此对于胸壁植入来说不太方便。减小ICD体积的一种方法是使用更小的电容器进行除颤。然而，这存在一个权衡，因为较小的电容器可能产生较低的最大能量输出。
在一项前瞻性随机交叉研究中，将实验性90微法双相波形的降阶除颤阈值（DFT）与标准的125微法双相波形进行比较。90微法的电容器能更快地释放相同能量，且峰值电压更高，但最大能量输出仅为20焦耳，而非34焦耳。对30例随机接受心内膜（n = 15）或心内膜 - 皮下阵列（n = 15）除颤导线系统的患者进行术中DFT测定。无论使用何种导线系统，实验波形和标准波形在DFT时的能量需求无差异（分别为10.3±4.1焦耳和9.5±4.9焦耳），但实验波形的峰值电压高于标准波形（分别为411±80伏和325±81伏）。对于实验波形，使用单纯心内膜导线系统时，15例患者中有10例（67%）的DFT为10焦耳或更低；使用心内膜 - 皮下阵列导线系统时，15例患者中有12例（80%）的DFT为10焦耳或更低。
较小电容器提供的持续时间较短的波形不会增加除颤能量需求，并且可能减小设备体积。然而，较小的电容会降低最大能量输出。如果ICD的DFT与最大能量输出之间需要10焦耳的安全裕度，那么只有一部分患者将受益于使用当前除颤导线系统DFT可行的90微法ICD。
