SMALLER CAPACITORS IMPROVE THE BIPHASIC WAVE-FORM

Introduction: Current implantable cardioverter defibrillators (ICDs) u se relatively large capacitance values. Theoretical considerations sug gest, however, that improved defibrillation energy requirements may be obtained with smaller capacitance values. Methods and Results: We com pared the energy requirement for defibrillation in a porcine model usi ng a biphasic waveform generated from two capacitance values of 140 mu F and 85 mu F. Phase 1 reversal of the shock waveform occurred at 65% tilt. Phase 2 pulse width was equal to phase 1. Shocks were delivered through epicardial patch electrodes after 10 seconds of induced ventr icular fibrillation. The defibrillation threshold (I);FT) was determin ed by a ''down-up'' technique requiring three reversals of defibrillat ion success or failure. The DFT was defined as the average of the valu es obtained with all trials starting from the successful Shock prior t o the first failure to defibrillate to the last successful defibrillat ion. In eight experiments, the measured parameters at DFT were as foll ows. The average stored and delivered DFT energies for the 85 mu F cap acitor were 6.1 +/- 2.1 and 6.0 +/- 2.0 J, respectively, compared to 7 .5 +/- 1.3 and 7.4 +/- 1.3 J for the 140 mu F capacitor (P < 0.04). Th e phase 1 pulse widths were significantly shorter for the 85 CIF capac itor (5.1 +/- 0.8 msec vs 9.2 +/- 1.3 msec) and the impedances were lo wer (54.4 +/- 5.8 Omega vs 59.9 +/- 6.3 Omega). The mean leading edge voltage was trending higher for the 85 mu F capacitor, but this differ ence did not reach statistical significance (374 +/- 63 V vs 326 +/- 3 0 V; P = 0.055). Conclusion: Smaller capacitance values do result in l ower energy requirements for the biphasic waveform, at a possibly high er leading edge voltage and a much shorter pulse width. Smaller capaci tance values could represent a significant enhancement of well-establi shed benefits demonstrated with the biphasic waveform.