Swerdlow C D, Kass R M, Chen P S, Hwang C, Raissi S
Division of Cardiology, Cedars-Sinai Medical Center, Los Angeles, Calif.
Circulation. 1994 Oct;90(4):1840-6. doi: 10.1161/01.cir.90.4.1840.
The time constant of truncated exponential pulses used with implantable defibrillators is determined by the output capacitor size and defibrillation pathway resistance. The optimal capacitor size is unknown.
This study compared defibrillation threshold (DFT) for standard 120-microF capacitors (DFT120) and smaller 60-microF capacitors (DFT60) at implantation of cardioverter-defibrillators in 67 patients using epicardial electrodes (15 patients) or one of four transvenous electrode configurations (52 patients). Paired comparisons of DFT60 and DFT120 were made for 44 defibrillation pathways using monophasic pulses and for 53 pathways using biphasic pulses. Truncated exponential pulses with 65% tilt were used. Pooled data from all electrode configurations showed a significant inverse correlation between pathway resistance and the ratio of stored energy DFT60 to DFT120 (monophasic pulses: r = .75, P = .0001; biphasic pulses: r = .68, P = .0001). Data from all electrode configurations formed a continuum with 120-microF capacitors superior for low-resistance pathways and 60-microF capacitors superior for high-resistance pathways. For pathways with resistance < or = 40 omega, the modest advantage of 120-microF capacitors applied primarily to pathways with low DFTs: 8.2 +/- 6.1 versus 9.6 +/- 5.4 J (P = .001) for monophasic pulses and 4.1 +/- 2.8 versus 5.1 +/- 3.1 J (P < .02) for biphasic pulses. The greater advantage of 60-microF capacitors for pathways with resistance > or = 61 omega applied to pathways with higher DFTs: 12.4 +/- 4.3 versus 23.1 +/- 6.4 J (P = .0001) for monophasic pulses and 8.5 +/- 4.9 versus 12.5 +/- 6.4 J (P = .0001) for biphasic pulses. For pathways using monophasic 120-microF pulses versus 95% for 60-microF pulses. Similarly, the DFT was < or = 10 J for 48% of pathways using biphasic 120-microF capacitors versus 83% for 60-microF pulses.
In comparison with conventional 120-microF capacitors, 60-microF capacitors had clinically insignificant higher DFTs for low-resistance pathways and clinically important lower DFTs for high-resistance pathways. Optimal capacitance is inversely related to pathway resistance for clinical defibrillation pathways and waveforms.
植入式除颤器使用的截断指数脉冲的时间常数由输出电容大小和除颤路径电阻决定。最佳电容大小尚不清楚。
本研究比较了67例使用心外膜电极（15例患者）或四种经静脉电极配置之一（52例患者）植入心脏转复除颤器时，标准120微法电容（DFT120）和较小的60微法电容（DFT60）的除颤阈值（DFT）。对44条使用单相脉冲的除颤路径和53条使用双相脉冲的路径进行了DFT60和DFT120的配对比较。使用了倾斜度为65%的截断指数脉冲。来自所有电极配置的汇总数据显示，路径电阻与存储能量DFT60与DFT120的比值之间存在显著的负相关（单相脉冲：r = 0.75，P = 0.0001；双相脉冲：r = 0.68，P = 0.0001）。来自所有电极配置的数据形成了一个连续体，120微法电容在低电阻路径上更优，60微法电容在高电阻路径上更优。对于电阻≤40Ω的路径，120微法电容的适度优势主要适用于DFT较低的路径：单相脉冲时为8.2±6.1 J对9.6±5.4 J（P = 0.001），双相脉冲时为4.1±2.8 J对5.1±3.1 J（P < 0.02）。60微法电容对于电阻≥61Ω的路径具有更大优势，适用于DFT较高的路径：单相脉冲时为12.4±4.3 J对23.1±6.4 J（P = 0.0001），双相脉冲时为8.5±4.9 J对12.5±6.4 J（P = 0.0001）。对于使用单相120微法脉冲的路径，DFT≤10 J的比例为95%，而60微法脉冲为86%。同样，使用双相120微法电容的路径中，48%的DFT≤10 J，而60微法脉冲为83%。
与传统的120微法电容相比，60微法电容在低电阻路径上的DFT略高，在临床上无显著意义，而在高电阻路径上的DFT较低，具有临床重要性。对于临床除颤路径和波形，最佳电容与路径电阻呈负相关。
