(Circulation. 1995;91:91-95.)
© 1995 American Heart Association, Inc.
A Prospective Randomized Comparison in Humans of Biphasic Waveform 60-µF and 120-µF Capacitance Pulses Using A Unipolar Defibrillation System
From the Department of Medicine, University of Washington (Seattle).
Correspondence to Gust H. Bardy, MD, Mail Stop RG-22, University Hospital, Seattle, WA 98195.
Background Improving unipolar implantable cardioverter-defibrillator (ICD) effectiveness has favorable implications for ICD safety, efficacy, and size. Advances in defibrillation efficacy would accelerate ICD ease of use by decreasing device size and by minimizing morbidity and mortality related to an improved defibrillation safety margin. The specific purpose of the present study was to determine whether unipolar defibrillation efficacy could be improved further in humans by lowering biphasic waveform capacitance.
Methods and Results We prospectively and randomly compared the
defibrillation efficacy of a 60-µF and a 120-µF capacitance
asymmetrical 65% tilt biphasic waveform using a unipolar
defibrillation system in 38 consecutive cardiac arrest survivors before
implantation of a presently available standard transvenous
defibrillation system. The right ventricular defibrillation electrode
had a 5-cm coil located on a 10.5F lead and was used as the anode. The
system cathode was the electrically active 108-cm2 surface
area shell (or "can") of a prototype titanium alloy pulse
generator placed in a left infraclavicular pocket. The defibrillation
pulse was derived from either a 60-µF or a 120-µF capacitance and
was delivered from RV 
CAN. Defibrillation threshold (DFT) stored
energy, delivered energy, leading-edge voltage and current, pulse
resistance, and pulse width were measured for both capacitances
examined. The 60-µF capacitance biphasic pulse resulted in a
stored-energy DFT of 8.5±4.1 J and a delivered-energy DFT of
8.4±4.0
J. In 34 of 38 patients (89%), the stored-energy DFT was <15 J.
Leading-edge voltage at the DFT was 517±128 V. Mean pulse impedance
for the 60-µF waveform was 60.6±7.1 
. The 120-µF
capacitance
biphasic pulse resulted in a stored-energy DFT of 10.1±7.4 J and a
delivered-energy DFT of 10.0±7.2 J (P=.13 and .13,
respectively). In 28 of 38 patients (74%), the stored-energy DFT was
<15 J (P=.052). Leading-edge voltage at the DFT with the
120-µF capacitance pulse was 386±142 (P<.00001). Mean
pulse impedance for the 120-µF waveform was 60.7±7.0
(P=.80).
Conclusions The results of the present study suggest that a relatively small capacitance, 60 µF, can be used for unipolar defibrillation systems without compromising defibrillation energy requirements compared with more typical ICD capacitance values, but this will require a higher circuit voltage. The use of lower capacitance also provides a modest increase in the percent of patients who have very low energy defibrillation requirements, an important issue should maximum ICD energy be decreased from the present level of 34 J. Such a move to smaller output devices could allow significant decreases in device size, a necessary feature of making cardioverter-defibrillator implantation comparable to that of standard pacemaker surgery.
Key Words: death, sudden • fibrillation • tachycardia • defibrillation
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